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1.  The CRKL gene encoding an adaptor protein is amplified, overexpressed, and a possible therapeutic target in gastric cancer 
Background
Genomic DNA amplification is a genetic factor involved in cancer, and some oncogenes, such as ERBB2, are highly amplified in gastric cancer. We searched for the possible amplification of other genes in gastric cancer.
Methods and Results
A genome-wide single nucleotide polymorphism microarray analysis was performed using three cell lines of differentiated gastric cancers, and 22 genes (including ERBB2) in five highly amplified chromosome regions (with a copy number of more than 6) were identified. Particular attention was paid to the CRKL gene, the product of which is an adaptor protein containing Src homology 2 and 3 (SH2/SH3) domains. An extremely high CRKL copy number was confirmed in the MKN74 gastric cancer cell line using fluorescence in situ hybridization (FISH), and a high level of CRKL expression was also observed in the cells. The RNA-interference-mediated knockdown of CRKL in MKN74 disclosed the ability of CRKL to upregulate gastric cell proliferation. An immunohistochemical analysis revealed that CRKL protein was overexpressed in 24.4% (88/360) of the primary gastric cancers that were analyzed. The CRKL copy number was also examined in 360 primary gastric cancers using a FISH analysis, and CRKL amplification was found to be associated with CRKL overexpression. Finally, we showed that MKN74 cells with CRKL amplification were responsive to the dual Src/BCR-ABL kinase inhibitor BMS354825, likely via the inhibition of CRKL phosphorylation, and that the proliferation of MKN74 cells was suppressed by treatment with a CRKL-targeting peptide.
Conclusion
These results suggested that CRKL protein is overexpressed in a subset of gastric cancers and is associated with CRKL amplification in gastric cancer. Furthermore, our results suggested that CRKL protein has the ability to regulate gastric cell proliferation and has the potential to serve as a molecular therapy target for gastric cancer.
doi:10.1186/1479-5876-10-97
PMCID: PMC3388458  PMID: 22591714
CRKL; Gastric cancer; Cell proliferation; Overexpression; Copy number amplification
2.  Amplification of CRKL induces transformation and EGFR inhibitor resistance in human non small cell lung cancers 
Cancer discovery  2011;1(7):608-625.
We previously identified a region of recurrent amplification on chromosome 22q11.21 in a subset of primary lung adenocarcinomas. Here we show that CRKL, encoding for an adaptor protein, is amplified and overexpressed in non-small cell lung cancer (NSCLC) cells that harbor 22q11.21 amplifications. Overexpression of CRKL in immortalized human airway epithelial cells promoted anchorage independent growth and tumorigenicity. Oncogenic CRKL activates SOS1-RAS-RAF-ERK and SRC-C3G-RAP1 pathways. Suppression of CRKL in NSCLC cells that harbor CRKL amplifications induced cell death. Overexpression of CRKL in EGFR mutant cells induces resistance to gefitinib by activating ERK and AKT signaling. We identified CRKL amplification in an EGFR inhibitor treated lung adenocarcinoma that was not present prior to treatment. These observations show that CRKL overexpression induces cell transformation, credential CRKL as a therapeutic target for a subset of NSCLC that harbor CRKL amplifications and implicate CRKL as an additional mechanism of resistance to EGFR-directed therapy.
doi:10.1158/2159-8290.CD-11-0046
PMCID: PMC3353720  PMID: 22586683
non small cell lung cancer; CRKL; cell transformation; RAP1; oncogene
3.  High CC chemokine receptor 7 expression improves postoperative prognosis of lung adenocarcinoma patients 
British Journal of Cancer  2013;109(5):1100-1108.
Background:
Chemokines and chemokine receptors not only have significant roles in cancer metastasis and tumorigenesis but also act as antitumour agents. The interaction between the Crk-like adaptor protein (CrkL), which is encoded by the CRKL gene, and non-receptor tyrosine kinase c-ABL is reported to transform many cells into malignant cells. We examined the effects of CC chemokine receptor 7 (CCR7), CCR7 ligands and CrkL and c-ABL in lung adenocarcinoma.
Methods:
One hundred and twenty patients with lung adenocarcinoma were included in this historical cohort analysis. We examined CCR7 and CCR7 ligands and CrkL and c-ABL mRNA expressions in surgically resected lung adenocarcinoma specimens and evaluated their contribution to prognosis, and the relationship with epidermal growth factor receptor (EGFR) and TP53 mutations.
Results:
High CCR7 mRNA expressions indicated better prognoses than those of the groups with low CCR7 mRNA expressions (P=0.007, HR=2.00, 95% CI of ratio: 1.22 –3.31). In lung adenocarcinoma, CrkL and c-ABL mRNAs were related to CCR7 mRNA expression (P<0.0001). CrkL and c-ABL mRNA expressions were influenced by EGFR mutations. A high expression of CCL19 was a good prognostic factor of lung adenocarcinoma.
Conclusion:
We propose that CCR7 and CCL19 are clinically good prognostic factors and that CCR7 is strongly related to CrkL and c-ABL kinase mRNA expression in lung adenocarcinoma.
doi:10.1038/bjc.2013.440
PMCID: PMC3778295  PMID: 23922113
CCR7; CrkL; c-ABL; chemokine; lung adenocarcinoma; CCL19
4.  Oncogenic Signaling Adaptor Proteins 
Signal transduction pathways activated by receptor tyrosine kinases (RTK) play a critical role in many aspects of cell function. Adaptor proteins serve an important scaffolding function that facilitates key signaling transduction events downstream of RTKs. Recent work integrating both structural and functional genomic approaches has identified several adaptor proteins as new oncogenes. In this review, we focus on the discovery, structure and function, and therapeutic implication of three of these adaptor oncogenes, CRKL, GAB2, and FRS2. Each of the three genes is recurrently amplified in lung adenocarcinoma or ovarian cancer, and is essential to cancer cell lines that harbor such amplification. Overexpression of each gene is able to transform immortalized human cell lines in in vitro or in vivo models. These observations identify adaptor protein as a distinct class of oncogenes and potential therapeutic targets.
doi:10.1016/j.jgg.2015.09.001
PMCID: PMC4643408  PMID: 26554907
5.  Crk-like adapter protein is overexpressed in cervical carcinoma, facilitates proliferation, invasion and chemoresistance, and regulates Src and Akt signaling 
Oncology Letters  2016;12(5):3811-3817.
Overexpression of Crk-like (CrkL) adapter protein has been implicated in a number of types of human cancer. However, its involvement in human cervical carcinoma remains unclear. The present study aimed to explore the clinical significance and biological characteristics of CrkL in human cervical carcinoma. CrkL protein expression was examined in tissue samples from 92 cases of cervical carcinoma using immunohistochemistry, and was found to be overexpressed in 48.9% (45/92 cases). CrkL was transfected into HeLa and CaSki cervical carcinoma cell lines and its effects on biological behavior were examined. CrkL overexpression was revealed to promote cell proliferation, invasion and chemoresistance. In addition, CrkL overexpression increased the level of Src and Akt phosphorylation. Treatment with the Src inhibitor dasatinib eliminated the effect of CrkL on cell invasion. In conclusion, the current results demonstrate that CrkL is an oncoprotein overexpressed in cervical carcinoma which contributes to malignant cell growth and chemoresistance. In addition, the findings indicate that CrkL promotes cervical cancer cell invasion through a Src-dependent pathway.
doi:10.3892/ol.2016.5160
PMCID: PMC5104173  PMID: 27895735
Crk-like; cervical carcinoma; invasion; Src
6.  Integrative Genomic Analyses Identify BRF2 as a Novel Lineage-Specific Oncogene in Lung Squamous Cell Carcinoma 
PLoS Medicine  2010;7(7):e1000315.
William Lockwood and colleagues show that the focal amplification of a gene, BRF2, on Chromosome 8p12 plays a key role in squamous cell carcinoma of the lung.
Background
Traditionally, non-small cell lung cancer is treated as a single disease entity in terms of systemic therapy. Emerging evidence suggests the major subtypes—adenocarcinoma (AC) and squamous cell carcinoma (SqCC)—respond differently to therapy. Identification of the molecular differences between these tumor types will have a significant impact in designing novel therapies that can improve the treatment outcome.
Methods and Findings
We used an integrative genomics approach, combing high-resolution comparative genomic hybridization and gene expression microarray profiles, to compare AC and SqCC tumors in order to uncover alterations at the DNA level, with corresponding gene transcription changes, which are selected for during development of lung cancer subtypes. Through the analysis of multiple independent cohorts of clinical tumor samples (>330), normal lung tissues and bronchial epithelial cells obtained by bronchial brushing in smokers without lung cancer, we identified the overexpression of BRF2, a gene on Chromosome 8p12, which is specific for development of SqCC of lung. Genetic activation of BRF2, which encodes a RNA polymerase III (Pol III) transcription initiation factor, was found to be associated with increased expression of small nuclear RNAs (snRNAs) that are involved in processes essential for cell growth, such as RNA splicing. Ectopic expression of BRF2 in human bronchial epithelial cells induced a transformed phenotype and demonstrates downstream oncogenic effects, whereas RNA interference (RNAi)-mediated knockdown suppressed growth and colony formation of SqCC cells overexpressing BRF2, but not AC cells. Frequent activation of BRF2 in >35% preinvasive bronchial carcinoma in situ, as well as in dysplastic lesions, provides evidence that BRF2 expression is an early event in cancer development of this cell lineage.
Conclusions
This is the first study, to our knowledge, to show that the focal amplification of a gene in Chromosome 8p12, plays a key role in squamous cell lineage specificity of the disease. Our data suggest that genetic activation of BRF2 represents a unique mechanism of SqCC lung tumorigenesis through the increase of Pol III-mediated transcription. It can serve as a marker for lung SqCC and may provide a novel target for therapy.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Lung cancer is the commonest cause of cancer-related death. Every year, 1.3 million people die from this disease, which is mainly caused by smoking. Most cases of lung cancer are “non-small cell lung cancers” (NSCLCs). Like all cancers, NSCLC starts when cells begin to divide uncontrollably and to move round the body (metastasize) because of changes (mutations) in their genes. These mutations are often in “oncogenes,” genes that, when activated, encourage cell division. Oncogenes can be activated by mutations that alter the properties of the proteins they encode or by mutations that increase the amount of protein made from them, such as gene amplification (an increase in the number of copies of a gene). If NSCLC is diagnosed before it has spread from the lungs (stage I disease), it can be surgically removed and many patients with stage I NSCLC survive for more than 5 years after their diagnosis. Unfortunately, in more than half of patients, NSCLC has metastasized before it is diagnosed. This stage IV NSCLC can be treated with chemotherapy (toxic chemicals that kill fast-growing cancer cells) but only 2% of patients with stage IV lung cancer are alive 5 years after diagnosis.
Why Was This Study Done?
Traditionally, NSCLC has been regarded as a single disease in terms of treatment. However, emerging evidence suggests that the two major subtypes of NSCLC—adenocarcinoma and squamous cell carcinoma (SqCC)—respond differently to chemotherapy. Adenocarcinoma and SqCC start in different types of lung cell and experts think that for each cell type in the body, specific combinations of mutations interact with the cell type's own unique characteristics to provide the growth and survival advantage needed for cancer development. If this is true, then identifying the molecular differences between adenocarcinoma and SqCC could provide targets for more effective therapies for these major subtypes of NSCLC. Amplification of a chromosome region called 8p12 is very common in NSCLC, which suggests that an oncogene that drives lung cancer development is present in this chromosome region. In this study, the researchers investigate this possibility by looking for an amplified gene in the 8p12 chromosome region that makes increased amounts of protein in lung SqCC but not in lung adenocarcinoma.
What Did the Researchers Do and Find?
The researchers used a technique called comparative genomic hybridization to show that focal regions of Chromosome 8p are amplified in about 40% of lung SqCCs, but that DNA loss in this region is the most common alteration in lung adenocarcinomas. Ten genes in the 8p12 chromosome region were expressed at higher levels in the SqCC samples that they examined than in adenocarcinoma samples, they report, and overexpression of five of these genes correlated with amplification of the 8p12 region in the SqCC samples. Only one of the genes—BRF2—was more highly expressed in squamous carcinoma cells than in normal bronchial epithelial cells (the cell type that lines the tubes that take air into the lungs and from which SqCC develops). Artificially induced expression of BRF2 in bronchial epithelial cells made these normal cells behave like tumor cells, whereas reduction of BRF2 expression in squamous carcinoma cells made them behave more like normal bronchial epithelial cells. Finally, BRF2 was frequently activated in two early stages of squamous cell carcinoma—bronchial carcinoma in situ and dysplastic lesions.
What Do These Findings Mean?
Together, these findings show that the focal amplification of chromosome region 8p12 plays a role in the development of lung SqCC but not in the development of lung adenocarcinoma, the other major subtype of NSCLC. These findings identify BRF2 (which encodes a RNA polymerase III transcription initiation factor, a protein that is required for the synthesis of RNA molecules that help to control cell growth) as a lung SqCC-specific oncogene and uncover a unique mechanism for lung SqCC development. Most importantly, these findings suggest that genetic activation of BRF2 could be used as a marker for lung SqCC, which might facilitate the early detection of this type of NSCLC and that BRF2 might provide a new target for therapy.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000315.
The US National Cancer Institute provides detailed information for patients and professionals about all aspects of lung cancer, including information on non-small cell carcinoma (in English and Spanish)
Cancer Research UK also provides information about lung cancer and information on how cancer starts
MedlinePlus has links to other resources about lung cancer (in English and Spanish)
doi:10.1371/journal.pmed.1000315
PMCID: PMC2910599  PMID: 20668658
7.  Genomic profiling identifies TITF1 as a lineage-specific oncogene amplified in lung cancer 
Oncogene  2008;27(25):3635-3640.
Lung cancer is a leading cause of cancer death, where the amplification of oncogenes contributes to tumorigenesis. Genomic profiling of 128 lung cancer cell lines and tumors revealed frequent focal DNA amplification at cytoband 14q13.3, a locus not amplified in other tumor types. The smallest region of recurrent amplification spanned the homeobox transcription factor TITF1 (thyroid transcription factor 1; also called NKX2-1), previously linked to normal lung development and function. When amplified, TITF1 exhibited increased expression at both the RNA and protein levels. Small interfering RNA (siRNA)- mediated knockdown of TITF1 in lung cancer cell lines with amplification led to reduced cell proliferation, manifested by both decreased cell-cycle progression and increased apoptosis. Our findings indicate that TITF1 amplification and overexpression contribute to lung cancer cell proliferation rates and survival and implicate TITF1 as a lineage-specific oncogene in lung cancer.
doi:10.1038/sj.onc.1211012
PMCID: PMC2903002  PMID: 18212743
TITF1; lineage-specific oncogene; genomic profiling; lung cancer; TTF-1; NKX2-1
8.  Structural Requirements for Function of the Crkl Adapter Protein in Fibroblasts and Hematopoietic Cells 
Molecular and Cellular Biology  1998;18(9):5082-5090.
Crkl is an adapter protein and phosphotyrosine-containing substrate implicated in transformation by the bcr-abl oncogene and in signaling by cytokines. When phosphorylated, Crkl binds through its Src homology 2 (SH2) domain to other tyrosine phosphoproteins such as paxillin and Cbl. Overexpression of Crkl in fibroblasts induces transformation. Here we examine the role of Crkl in hematopoietic cells and find that overexpression of Crkl confers a signal leading to increased adhesion to fibronectin. In both fibroblasts and hematopoietic cells, individual mutations or deletions of each SH2 and SH3 domain abrogated transformation and adhesion, respectively, indicating that interactions with other proteins such as Cbl and paxillin (SH2 domain) and Abl, Sos, and C3G (N-terminal SH3 domain) are essential for biological activity. In vivo and in vitro tryptic phosphopeptide mapping studies show that Crkl is phosphorylated on multiple tyrosine residues when overexpressed or when activated by Bcr-Abl. Mutation at tyrosine 207, a residue conserved in c-Crk, abrogates all in vivo tyrosine phosphorylation of Crkl. Despite this loss of phosphotyrosine, mutation at this site enhanced Crkl function as measured by complex formation with SH2 binding proteins, signal transduction to Jun Kinase, and fibroblast transformation. These observations implicate Crkl in cellular adhesion and demonstrate that Y207 functions as a negative regulatory site.
PMCID: PMC109093  PMID: 9710592
9.  CRKL mediates EML4-ALK signaling and is a potential therapeutic target for ALK-rearranged lung adenocarcinoma 
Oncotarget  2016;7(20):29199-29210.
Anaplastic lymphoma kinase (ALK) gene rearrangements are oncogenic drivers in a small subset of patients with non-small-cell lung cancer (NSCLC). The ALK inhibitors are highly effective in NSCLC patients harboring ALK rearrangements; however, most patients acquire resistance to the therapy following an initial response. Mechanisms of acquired resistance are complex. We used LC-MS/MS-based phosphotyrosine-peptide profiling in the EML4-ALK rearranged H3122 and H2228 cells treated with ALK inhibitors, to identify downstream effectors of ALK. We then used Western blot, siRNA experiments, cell proliferation, viability and migration assays to validate our findings. We identified CRKL as a novel downstream effector of ALK signaling. We demonstrated that CRKL tyrosine phosphorylation was repressed by pharmacological inhibition or small interfering RNA (siRNA) knockdown of ALK in the ALK-rearranged cells. More importantly, CRKL knockdown attenuated their cell proliferation, viability, and migration, but it had no effect on ALK phosphorylation and expression in these cells. Furthermore, CRKL tyrosine phosphorylation was inhibited by dasatinib (an inhibitor of ABL and SRC kinases), which in combination with the ALK inhibitor crizotinib displayed a synergistic inhibitory effect in vitro. In conclusion, our study suggests that CRKL is a key downstream effector of ALK, and combined inhibition of ALK and CRKL may represent an effective strategy for treating ALK-rearranged NSCLC patients.
doi:10.18632/oncotarget.8638
PMCID: PMC5045389  PMID: 27078848
EML4-ALK; NSCLC; CRKL; ALK
10.  CRKL oncogene is downregulated by p53 through miR-200s 
Cancer Science  2015;106(8):1033-1040.
Tumor suppressive miRNAs that target oncogenes are frequently downregulated in cancers, and this downregulation leads to oncogene pathway activation. Thus, tumor suppressive miRNAs and their target oncogenes have been proposed as useful targets in cancer treatment. miR-200 family downregulation has been reported in cancer progression and metastasis. The miR-200 family consists of two gene clusters, miR-200b/200a/429 and miR-200c/141, which are located on human chromosomes 1 and 12, respectively. Here, we identified that p53 response elements are located around both clusters of the miR-200 family and confirmed that miR-200s are transcriptional targets of the p53 family. In silico analyses of miRNA targets established the CRKL oncogene as a potential target for miR-200b/200c/429. Moreover, miR-200b/200c/429 inhibited CRKL mRNA and protein expression by directly targeting its 3′-UTR region. Importantly, endogenous CRKL expression was decreased in cancer cells through the introduction of p53 family and endogenous p53 activation. Moreover, the downregulation of CRKL by siRNA inhibited cancer cell growth. The Oncomine database demonstrates that CRKL is overexpressed in a subset of cancer types. Furthermore, CRKL is significantly overexpressed in primary breast cancer tissues harboring mutant TP53. Our results demonstrate that the p53 target miR-200b/200c/429 miRNAs are negative regulators of the CRKL oncogene.
doi:10.1111/cas.12713
PMCID: PMC4556393  PMID: 26079153
Cell growth; CRKL; miR-200 family; p53; p53 family
11.  Genomic Profiling Identifies GATA6 as a Candidate Oncogene Amplified in Pancreatobiliary Cancer 
PLoS Genetics  2008;4(5):e1000081.
Pancreatobiliary cancers have among the highest mortality rates of any cancer type. Discovering the full spectrum of molecular genetic alterations may suggest new avenues for therapy. To catalogue genomic alterations, we carried out array-based genomic profiling of 31 exocrine pancreatic cancers and 6 distal bile duct cancers, expanded as xenografts to enrich the tumor cell fraction. We identified numerous focal DNA amplifications and deletions, including in 19% of pancreatobiliary cases gain at cytoband 18q11.2, a locus uncommonly amplified in other tumor types. The smallest shared amplification at 18q11.2 included GATA6, a transcriptional regulator previously linked to normal pancreas development. When amplified, GATA6 was overexpressed at both the mRNA and protein levels, and strong immunostaining was observed in 25 of 54 (46%) primary pancreatic cancers compared to 0 of 33 normal pancreas specimens surveyed. GATA6 expression in xenografts was associated with specific microarray gene-expression patterns, enriched for GATA binding sites and mitochondrial oxidative phosphorylation activity. siRNA mediated knockdown of GATA6 in pancreatic cancer cell lines with amplification led to reduced cell proliferation, cell cycle progression, and colony formation. Our findings indicate that GATA6 amplification and overexpression contribute to the oncogenic phenotypes of pancreatic cancer cells, and identify GATA6 as a candidate lineage-specific oncogene in pancreatobiliary cancer, with implications for novel treatment strategies.
Author Summary
Pancreatic cancer is a devastating disease, having among the lowest survival rates of any cancer. A better understanding of the molecular basis of pancreatic cancer may lead to improved rationale therapies. We report here the discovery of amplification (i.e. extra copies) of the GATA6 gene in many human pancreatic cancers. GATA6 is a regulator of gene expression and functions in the development of the normal pancreas. Our findings indicate that its amplification and aberrant overexpression contribute to pancreatic cancer development. GATA6 joins a growing list of cancer genes with key roles in normal human development but pathogenic roles in cancer when aberrantly expressed. Our discovery of GATA6 amplification provides a new foothold into understanding the pathogenic mechanisms underlying pancreatic cancer, and suggests new strategies for therapy by targeting GATA6 or the genes it regulates.
doi:10.1371/journal.pgen.1000081
PMCID: PMC2413204  PMID: 18535672
12.  The microRNA-200/Zeb1 axis regulates ECM-dependent β1-integrin/FAK signaling, cancer cell invasion and metastasis through CRKL 
Scientific Reports  2016;6:18652.
Tumor cell metastasis is a complex process that has been mechanistically linked to the epithelial-mesenchymal transition (EMT). The double-negative feedback loop between the microRNA-200 family and the Zeb1 transcriptional repressor is a master EMT regulator, but there is incomplete understanding of how miR-200 suppresses invasion. Our recent efforts have focused on the tumor cell-matrix interactions essential to tumor cell activation. Herein we utilized both our Kras/p53 mutant mouse model and human lung cancer cell lines to demonstrate that upon miR-200 loss integrin β1-collagen I interactions drive 3D in vitro migration/invasion and in vivo metastases. Zeb1-dependent EMT enhances tumor cell responsiveness to the ECM composition and activates FAK/Src pathway signaling by de-repression of the direct miR-200 target, CRKL. We demonstrate that CRKL serves as an adaptor molecule to facilitate focal adhesion formation, mediates outside-in signaling through Itgβ1 to drive cell invasion, and inside-out signaling that maintains tumor cell-matrix contacts required for cell invasion. Importantly, CRKL levels in pan-cancer TCGA analyses were predictive of survival and CRKL knockdown suppressed experimental metastases in vivo without affecting primary tumor growth. Our findings highlight the critical ECM-tumor cell interactions regulated by miR-200/Zeb1-dependent EMT that activate intracellular signaling pathways responsible for tumor cell invasion and metastasis.
doi:10.1038/srep18652
PMCID: PMC4700473  PMID: 26728244
13.  SLC7A5 Functions as a Downstream Target Modulated by CRKL in Metastasis Process of Gastric Cancer SGC-7901 Cells 
PLoS ONE  2016;11(11):e0166147.
SLC7A5, who is also named LAT-1, has been validated as a promoter regulated by miRNA-126 in our previous research for gastric cancer cells. However, the mechanisms driving SLC7A5 to affect the bio-function of gastric cancer cells are unclear, remaining us lots of to elucidate. The aim of this study is to investigate the regulating effect of CRKL, one of the critical genes involving with gastric cancer progression, on SLC7A5 expression. By studying the gastric cancer cell lines and clinical pathological specimens, we found that the expression of SLC7A5 was significantly correlated to CRKL. By depleting CRKL in gastric cancer SGC-7901 cells, the SLC7A5 expression was impaired, and the invasion and migration of SGC-7901 cells were suppressed. Ectopic expression of SLC7A5 could drastically rescue the phenotypes induced by CRKL depletion in this study. Accordingly, we conclude that SLC7A5 functions as a promoter in gastric cancer metastasis, and CRKL could be one of its regulators modulating the expression of SLC7A5 and consequentially affect the metastatic feature of SGC-7901 cells. The findings in this study indicate a regulation relationship between CRKL and SLC7A5, and provide useful evidence for gastric cancer therapeutic strategies.
doi:10.1371/journal.pone.0166147
PMCID: PMC5112787  PMID: 27846244
14.  Modeling of Molecular Interaction between Apoptin, BCR-Abl and CrkL - An Alternative Approach to Conventional Rational Drug Design 
PLoS ONE  2012;7(1):e28395.
In this study we have calculated a 3D structure of apoptin and through modeling and docking approaches, we show its interaction with Bcr-Abl oncoprotein and its downstream signaling components, following which we confirm some of the newly-found interactions by biochemical methods. Bcr-Abl oncoprotein is aberrantly expressed in chronic myelogenous leukaemia (CML). It has several distinct functional domains in addition to the Abl kinase domain. The SH3 and SH2 domains cooperatively play important roles in autoinhibiting its kinase activity. Adapter molecules such as Grb2 and CrkL interact with proline-rich region and activate multiple Bcr-Abl downstream signaling pathways that contribute to growth and survival. Therefore, the oncogenic effect of Bcr-Abl could be inhibited by the interaction of small molecules with these domains. Apoptin is a viral protein with well-documented cancer-selective cytotoxicity. Apoptin attributes such as SH2-like sequence similarity with CrkL SH2 domain, unique SH3 domain binding sequence, presence of proline-rich segments, and its nuclear affinity render the molecule capable of interaction with Bcr-Abl. Despite almost two decades of research, the mode of apoptin's action remains elusive because 3D structure of apoptin is unavailable. We performed in silico three-dimensional modeling of apoptin, molecular docking experiments between apoptin model and the known structure of Bcr-Abl, and the 3D structures of SH2 domains of CrkL and Bcr-Abl. We also biochemically validated some of the interactions that were first predicted in silico. This structure-property relationship of apoptin may help in unlocking its cancer-selective toxic properties. Moreover, such models will guide us in developing of a new class of potent apoptin-like molecules with greater selectivity and potency.
doi:10.1371/journal.pone.0028395
PMCID: PMC3254606  PMID: 22253690
15.  Characterization of fibroblast growth factor receptor 2 overexpression in the human breast cancer cell line SUM-52PE 
Breast Cancer Research : BCR  2000;2(4):311-320.
The fibroblast growth factor receptor (FGFR)2 gene has been shown to be amplified in 5-10% of breast cancer patients. A breast cancer cell line developed in our laboratory, SUM-52PE, was shown to have a 12-fold amplification of the FGFR2 gene, and FGFR2 message was found to be overexpressed 40-fold in SUM-52PE cells as compared with normal human mammary epithelial (HME) cells. Both human breast cancer (HBC) cell lines and HME cells expressed two FGFR2 isoforms, whereas SUM-52PE cells overexpressed those two isoforms, as well as several unique FGFR2 polypeptides. SUM-52PE cells expressed exclusively FGFR2-IIIb isoforms, which are high-affinity receptors for fibroblast growth factor (FGF)-1 and FGF-7. Differences were identified in the expression of the extracellular Ig-like domains, acid box and carboxyl termini, and several variants not previously reported were isolated from these cells.
Introduction:
The FGFR family of receptor tyrosine kinases includes four members, all of which are highly alternatively spliced and glycosylated. For FGFR2, alternative splicing of the second half of the third Ig-like domain, involving exons IIIb and IIIc, is a mutually exclusive choice that affects ligand binding specificity and affinity [1,2,3]. It appears that the second half of the third Ig-like domain can dictate high affinity for FGF-2 or keratinocyte growth factor (KGF), whereas affinity for FGF-1 appears to remain the same [3]. Alternative splicing of the carboxyl terminus has been shown to involve at least two different exons that can produce at least three different variants. The C1-type and C2-type carboxyl termini are encoded by the same exon, and have two different splice acceptor sites, whereas the C3-type carboxyl terminus is encoded by a separate exon [4]. The biologic significance of the C1 carboxyl terminus, as compared with the shorter C3 variant found primarily in tumorigenic samples, has been studied in NIH3T3 transfection assays, in which C3 variants were able to produce three times more transformed foci in soft agar than C1 variants (both IIIb), whereas full length FGFR2 and FGFR1 (both IIIc variants) showed no transforming activity [4].
Previous studies [5,6] have found amplification and overexpression of FGFR2 in 5-10% of primary breast cancer specimens. A recent study [7] done using a tissue array consisting of 372 primary breast cancer specimens found a 5% incidence of FGFR2 amplification. To our knowledge, none of the HBC cell lines studied thus far have an FGFR2 gene amplification, although overexpression of FGFR2 message and protein has been documented for some breast cancer cell lines [6,8,9].
SUM-52PE is a breast cancer cell line previously isolated in our laboratory that grows under serum-free and epidermal growth factor-free conditions, has high levels of tyrosine-phosphorylated membrane proteins, and has the capacity to invade and grow under anchorage-independent conditions [10,11,12]. This cell line exhibits all of the important hallmarks of transformed, highly malignant cells. Therefore, SUM-52PE was used as a model to study the diversity of FGFR2 expression in a breast cancer cell line that has true amplification and overexpression of FGFR2.
Objectives:
This study was conducted to examine the degree of FGFR2 amplification and overexpression in the breast cancer cell line SUM-52PE. Subsequent sequencing and characterization of individual FGFR2 variants cloned from the SUM-52PE cell line was completed to determine the complexity of FGFR2 alternative splicing in the context of a highly metastatic breast cancer cell line.
Methods:
Southern, Northern and Western blot analyses were done in order to determine the degree of FGFR2 amplification and overexpression in the breast cancer cell line SUM-52PE. Individual FGFR2 variants were cloned out of SUM-52PE using FGFR2-specific primers in a reverse transcription (RT) polymerase chain reaction (PCR). FGFR2 cDNAs were characterized by restriction fragment analysis, sequencing and transient transfection into 293 cells to examine the protein expression of each FGFR2 clone.
Results:
The results of the Southern blot showed that there was a 12-fold amplification of FGFR2 in the SUM-52PE cell line. Northern blot analysis of SUM-52PE showed FGFR2 transcripts to be highly overexpressed compared with other breast cancer cell lines and normal HME cells. Several overexpressed bands of approximately 6.3, 5.0, 4.0, and 2.8kb were observed in SUM-52PE cells. The most prominent band, at 2.8kb, was so abundant that it was difficult to discern other individual bands clearly. Western blot analysis showed that both normal HME and HBC cells expressed two FGFR2 variants of 95 and 135kDa. The SUM-52PE cell line greatly overexpressed not only these two polypeptides, as compared with HME and HBC cells, but also overexpressed two unique variants of FGFR2 - 85 and 109kDa polypeptides - as well as several smaller polypeptides in the 46-53kDa range. The antibody used in Western blot analysis only recognizes FGFR2 isoforms that express the C1 carboxyl termini, therefore greatly underestimating the actual number of different FGFR2 variants that are overexpressed in this cell line.
PCR was performed to determine the proportion of C1/C2 variants as compared with C3 variants in the SUM-52PE cell line. Results of this analysis indicated the presence of all three types of variants in this cell line, although the C1/C2 variants were predominant as compared with the C3 variants in SUM-52PE.
Four different FGFR2-C1 clones were isolated and sequenced from SUM-52PE cells, which differed in their signal sequence, first Ig-like loop, and acid box. Two FGFR2-C2 clones were isolated from the SUM-52PE cell line, which were identical to each other except for the variable expression of the number of Ig-like domains (two or three). Three C3 clones were isolated and sequenced, two of which have not previously been described in the literature. Clone C3-#3 contained two Ig-like domains, but no acid box. C3-#5 was missing the first two Ig-like domains and the acid box, but did contain the third Ig-like domain.
Discussion:
There is an extensive amount of evidence implicating erbB-2, a gene that is overexpressed in approximately 30% of breast cancer cases, as a breast cancer gene [13]. The identification of other breast oncogenes that function in the remaining 70% of cases is an ongoing challenge, as is establishing a causal role for such oncogenes in HME cell transformation.
FGFR1 and FGFR2, previously established oncogenes, were found to be amplified within large amplicons on 8p11 and 10q26, respectively, in the breast cancer cell line SUM-52PE [14]. Previous studies have shown that the FGFR2 gene is amplified in about 5-10% of breast cancer cases.
Our results showed that SUM-52PE cells overexpressed many alternatively spliced isoforms of FGFR2 at both the transcript and protein level as compared with normal HME cells. The variability in FGFR2 isoform expression is complex and involves exon IIIb/c, which encodes the second half of the third Ig-like loop; variations in the carboxyl terminal end of the receptor, involving the C1/C2 or C3 domains; and variable expression of the Ig-like loops and acid box in the extracellular portion of the receptor. The characterization of three unique FGFR2 isoforms that were cloned from SUM-52PE may build on the findings of others concerning the transforming potential of FGFR2 variants [4]. In particular, because it has been demonstrated that expression of C3-IIIb variants may have more transforming activity than C1-IIIb variants, differences between the three C3 clones we have isolated may provide information regarding the influence of particular structural domains on transforming potential.
Ongoing studies are aimed at characterizing the transforming ability of FGFR2 isoforms obtained from SUM-52PE cells by transducing these genes into normal HME cells. By overexpressing FGFR2 isoforms in a physiologically relevant system, we hope to determine the isoform(s) that acts in a dominant way in the process of cell transformation, and to determine whether different regions present in individual clones drive specific phenotypes associated with transformation.
PMCID: PMC13919  PMID: 11056689
alternative splicing; breast cancer; fibroblast growth factor receptor; receptor tyrosine kinase; SUM-52PE
16.  Differential expression of CRKL and AXL genes in lung adenocarcinoma subtypes according to the epidermal growth factor receptor and anaplastic lymphoma kinase gene status 
Biomedical Reports  2014;2(4):481-489.
Non-small-cell lung cancer (NSCLC) is the most common cause of cancer-related mortality. Adenocarcinoma (AC) is the predominant histological type of NSCLC; however, AC consists of several subtypes. It has not yet been determined whether there is a correlation of CRKL and AXL expression with epidermal growth factor receptor (EGFR) and anaplastic lymphoma kinase (ALK) gene status in lung AC. We assayed exons 18 through 21 of the EGFR gene by direct sequencing; ALK rearrangement and the expression of CRKL and AXL were detected by immunostaining. A total of 212 cases of AC were included in this study, diagnosed using the novel classification system established by the International Association for the Study of Lung Cancer, the American Thoracic Society and the European Respiratory Society in 2011, including 69 acinar ACs, 17 lepidic predominant ACs (LPAs), 63 papillary, 14 mucinous, 17 micropapillary and 32 solid ACs. Of the 212 cases, 101 harbored EGFR mutations. The most common subtypes carrying delK745-S753 were papillary and acinar ACs. ALK rearrangement was found in 23 cases (11%) of lung ACs. Acinar and solid ACs were the most frequent subtypes with ALK aberrance, particularly in acinar ACs with cribriform structure (4/5 cases, 80%). The expression of CRKL was significantly different among the AC subtypes (P=0.01), with the highest and lowest expression levels of CRKL protein in papillary ACs and LPAs, respectively (P<0.05). AXL expression was also significantly different among the AC subtypes (P=0.002) and was correlated with lymph node infiltration in acinar ACs. ACs with EGFR mutations exhibited high levels of AXL protein expression compared to those without mutations (P<0.001). Acinar AC with cribriform structure is a distinct subtype that frequently harbors ALK rearrangement. The activation of AXL may be one of the factors contributing to the invasion of acinar and micropapillary ACs.
doi:10.3892/br.2014.261
PMCID: PMC4051477  PMID: 24944792
lung adenocarcinoma; epidermal growth factor receptor gene mutation; anaplastic lymphoma kinase gene rearrangement; CRKL; AXL
17.  Global gene expression profiling reveals a suppressed immune response pathway associated with 3q amplification in squamous carcinoma of the lung 
Genomics Data  2015;5:272-274.
Chromosome 3q26–28 is a critical region of genomic amplification in non-small cell lung cancer (NSCLC), particularly lung squamous cell carcinomas (SCCs). No molecular therapeutic target has shown clinical utility for SCC, in contrast with adenocarcinomas of the lung. To identify novel candidate drivers in this region, we performed both Array Comparative Genomic Hybridization (array CGH, Agilent Human Genome CGH 244A oligo-microarrays) and Gene Expression Microarray (Agilent Human Gene Expression 4 × 44 K microarray) on 24 untreated lung SCC specimens. Using our previously published integrative genomics approach, we identified 12 top amplified driver genes within this region that are highly correlated and overexpressed in lung SCC. We further demonstrated one of the 12 top amplified driver Fragile X mental retardation-related protein 1 (FXR1) as a novel cancer gene in NSCLC and FXR1 executes its regulatory function by forming a novel complex with two other oncogenes, protein kinase C, iota ( PRKCI) and epithelial cell transforming 2 (ECT2) within the same amplicon in lung cancer cell. Here we report that immune response pathways are significantly suppressed in lung SCC and negatively associated with 3q driver gene expression, implying a potential role of 3q drivers in cancer immune-surveillance. In light of the attractive immunotherapy strategy using blockade of negative regulators of T cell function for multiple human cancer including lung SCC, our findings may provide a rationale for targeting 3q drivers in combination of immunotherapies for human tumors harboring the 3q amplicon. The data have been deposited in NCBI's Gene Expression Omnibus and are accessible through GEO Series accession number GSE40089.
doi:10.1016/j.gdata.2015.06.014
PMCID: PMC4583673  PMID: 26484266
Squamous carcinoma of the lung; 3q amplification; Immune response
18.  Loss-of-function screen in rhabdomyosarcoma identifies CRKL-YES as a critical signal for tumor growth 
Oncogene  2013;32(47):5429-5438.
To identify novel signaling pathways necessary for rhabdomyosarcoma (RMS) survival, we performed a loss-of-function screen using an inducible small hairpin RNA (shRNA) library in an alveolar and an embryonal RMS cell line. This screen identified CRKL expression as necessary for growth of alveolar RMS and embryonal RMS both in vitro and in vivo. We also found that CRKL was uniformly highly expressed in both RMS cell lines and tumor tissue. As CRKL is a member of the CRK adapter protein family that contains an SH2 and two SH3 domains and is involved in signal transduction from multiple tyrosine kinase receptors, we evaluated CRKL interaction with multiple tyrosine kinase receptor signaling pathways in RMS cells. While we saw no interaction of CRKL with IGFIR, MET or PI3KAKT/mTOR pathways, we determined that CRKL signaling was associated with SRC family kinase (SFK) signaling, specifically with YES kinase. Inhibition of SFK signaling with dasatinib or another SFK inhibitor, sarcatinib, suppressed RMS cell growth in vitro and in vivo. These data identify CRKL as a novel critical component of RMS growth. This study also demonstrates the use of functional screening to identify a potentially novel therapeutic target and treatment approach for these highly aggressive pediatric cancers.
doi:10.1038/onc.2012.590
PMCID: PMC3898328  PMID: 23318429
rhabdomyosarcoma; CRKL; SRC; YES; dasatinib
19.  SOX2 Is an Oncogene Activated by Recurrent 3q26.3 Amplifications in Human Lung Squamous Cell Carcinomas 
PLoS ONE  2010;5(1):e8960.
Squamous cell carcinoma (SCC) of the lung is a frequent and aggressive cancer type. Gene amplifications, a known activating mechanism of oncogenes, target the 3q26-qter region as one of the most frequently gained/amplified genomic sites in SCC of various types. Here, we used array comparative genomic hybridization to delineate the consensus region of 3q26.3 amplifications in lung SCC. Recurrent amplifications occur in 20% of lung SCC (136 tumors in total) and map to a core region of 2 Mb (Megabases) that encompasses SOX2, a transcription factor gene. Intense SOX2 immunostaining is frequent in nuclei of lung SCC, indicating potential active transcriptional regulation by SOX2. Analyses of the transcriptome of lung SCC, SOX2-overexpressing lung epithelial cells and embryonic stem cells (ESCs) reveal that SOX2 contributes to activate ESC-like phenotypes and provide clues pertaining to the deregulated genes involved in the malignant phenotype. In cell culture experiments, overexpression of SOX2 stimulates cellular migration and anchorage-independent growth while SOX2 knockdown impairs cell growth. Finally, SOX2 over-expression in non-tumorigenic human lung bronchial epithelial cells is tumorigenic in immunocompromised mice. These results indicate that the SOX2 transcription factor, a major regulator of stem cell function, is also an oncogene and a driver gene for the recurrent 3q26.33 amplifications in lung SCC.
doi:10.1371/journal.pone.0008960
PMCID: PMC2813300  PMID: 20126410
20.  CRKL as a lung cancer oncogene and mediator of acquired resistance to EGFR inhibitors: is it all that it is cracked up to be? 
Cancer discovery  2011;1(7):560-561.
Summary
Cheung et al show that amplified CRKL can function as a driver oncogene in lung adenocarcinoma, activating both RAS and RAP1 to induce MAPK signaling. In addition, they show that CRKL amplification may be another mechanism for primary or acquired resistance to EGFR kinase inhibitors.
doi:10.1158/2159-8290.CD-11-0295
PMCID: PMC3247017  PMID: 22211192
21.  Small nucleolar RNA 42 acts as an oncogene in lung tumorigenesis 
Mei, Y | Liao, J | Shen, J | Yu, L | Liu, B | Liu, L | Li, R | Ji, L | Dorsey, SG | Jiang, Z | Katz, RL | Wang, J-Y | Jiang, F
Oncogene  2011;31(22):2794-2804.
Non-small cell lung cancer (NSCLC) is the leading cause of cancer death, reflecting the need for better understanding the oncogenesis, and developing new diagnostic and therapeutic targets for the malignancy. Emerging evidence suggests that small nucleolar RNAs (snoRNAs) have malfunctioning roles in tumorigenesis. Our recent study demonstrated that small nucleolar RNA 42 (SNORA42) was overexpressed in lung tumors. Here, we investigate the role of SNORA42 in tumorigenesis of NSCLC. We simultaneously assess genomic dosages and expression levels of SNORA42 and its host gene, KIAA0907, in 10 NSCLC cell lines and a human bronchial epithelial cell line. We then determine in vitro functional significance of SNORA42 in lung cancer cell lines through gain- and loss-of-function analyses. We also inoculate cancer cells with SNORA42-siRNA into mice through either tail vein or subcutaneous injection. We finally evaluate expression level of SNORA42 on frozen surgically resected lung tumor tissues of 64 patients with stage I NSCLC by using quantitative reverse transcriptase PCR assay. Genomic amplification and associated high expression of SNORA42 rather than KIAA0907 are frequently observed in lung cancer cells, suggesting that SNORA42 overexpression is activated by its genomic amplification. SNORA42 knockdown in NSCLC cells inhibits in vitro and in vivo tumorigenicity, whereas enforced SNORA42 expression in bronchial epitheliums increases cell growth and colony formation. Such pleiotropy of SNORA42 suppression could be achieved at least partially through increased apoptosis of NSCLC cells in a p53-dependent manner. SNORA42 expression in lung tumor tissue specimens is inversely correlated with survival of NSCLC patients. Therefore, SNORA42 activation could have an oncogenic role in lung tumorigenesis and provide potential diagnostic and therapeutic targets for the malignancy.
doi:10.1038/onc.2011.449
PMCID: PMC4966663  PMID: 21986946
small nucleolar RNA; tumorigenesis; bio-markers; apoptosis; p53
22.  Emerging Roles for Crk in Human Cancer 
Genes & Cancer  2010;1(11):1132-1139.
Adaptor proteins are named for their function in assembling complexes of cellular proteins to execute and facilitate transmission of signals. The Crk family of adaptors consists of 2 members, Crk and CrkL. Crk, which was originally isolated as an oncogene, v-Crk, that transforms CEFs, has at least 2 splice variants, CrkI and CrkII, with differing biological activities. All Crk family proteins serve to act as molecular bridges between tyrosine kinases and their substrates and also modulate the specificity and stoichiometry of signaling processes. Signaling via CrkII and CrkL can be negatively regulated via tyrosine phosphorylation–mediated autoinhibition, while such a mechanism is not known to exist for CrkI. Although v-Crk clearly functions as a bona fide oncogene, in recent years, an emerging body of evidence suggests that cellular Crk proteins are overexpressed in human tumors and the expression levels correlate with aggressive and malignant behavior of cancer cells. These properties of Crk proteins make them potential cancer prognosis markers and therapeutic targets.
doi:10.1177/1947601910397188
PMCID: PMC3092275  PMID: 21779437
Crk adaptor proteins; human cancer; malignant phenotype; cell motility
23.  LASP1 is a novel BCR-ABL substrate and a phosphorylation-dependent binding partner of CRKL in chronic myeloid leukemia 
Oncotarget  2014;5(14):5257-5271.
Chronic myeloid leukemia (CML) is characterized by a genomic translocation generating a permanently active BCR-ABL oncogene with a complex pattern of atypically tyrosine-phosphorylated proteins that drive the malignant phenotype of CML. Recently, the LIM and SH3 domain protein 1 (LASP1) was identified as a component of a six gene signature that is strongly predictive for disease progression and relapse in CML patients. However, the underlying mechanisms why LASP1 expression correlates with dismal outcome remained unresolved.
Here, we identified LASP1 as a novel and overexpressed direct substrate of BCR-ABL in CML. We demonstrate that LASP1 is specifically phosphorylated by BCR-ABL at tyrosine-171 in CML patients, which is abolished by tyrosine kinase inhibitor therapy. Further studies revealed that LASP1 phosphorylation results in an association with CRKL – another specific BCR-ABL substrate and bona fide biomarker for BCR-ABL activity. pLASP1-Y171 binds to non-phosphorylated CRKL at its SH2 domain. Accordingly, the BCR-ABL-mediated pathophysiological hyper-phosphorylation of LASP1 in CML disrupts normal regulation of CRKL and LASP1, which likely has implications on downstream BCR-ABL signaling. Collectively, our results suggest that LASP1 phosphorylation might serve as an additional candidate biomarker for assessment of BCR-ABL activity and provide a first step toward a molecular understanding of LASP1 function in CML.
PMCID: PMC4170624  PMID: 24913448
LASP1; CML; BCR-ABL; CRKL; nilotinib
24.  Peroxisome proliferator-activated receptor γ agonist efatutazone impairs transforming growth factor β2-induced motility of epidermal growth factor receptor tyrosine kinase inhibitor-resistant lung cancer cells 
Cancer Science  2014;105(6):683-689.
Epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKI) are effective for non-small cell lung cancers (NSCLC) with EGFR-activating mutations. However, most responders develop resistance. Efatutazone, a novel peroxisome proliferator-activated receptor gamma (PPARγ) agonist, is currently under clinical evaluation; it has antiproliferative effects and induces cellular morphological changes and differentiation. The present study investigated the effects of efatutazone in EGFR-TKI-resistant NSCLC cells, while focusing on cell motility. The PC-9-derived NSCLC cell lines PC-9ER and PC-9ZD, resistant to EGFR-TKI due to v-crk avian sarcoma virus CT10 oncogene homolog-like (CRKL) amplification-induced phosphatidylinositol 3-kinase (PI3K)/v-akt murine thymoma viral oncogene homolog (AKT) activation and an EGFR T790M mutation, respectively, were used. These cells exhibit enhanced cell motility due to transforming growth factor β (TGF-β)/Smad2 family member 2 (Smad2) pathway activation. Efatutazone had no growth-inhibitory effect on the tested cells but inhibited the motility of EGFR-TKI-resistant cells in wound closure and transwell assays. Efatutazone plus erlotinib treatment provided greater inhibition of PC-9ER cell migration than efatutazone or erlotinib alone. Efatutazone suppressed increased TGF-β2 secretion from both cell lines (shown by ELISA) and downregulation of TGF-β2 transcription (observed by quantitative RT-PCR). Immunoblot analysis and luciferase assays revealed that efatutazone suppressed Smad2 phosphorylation and its transcriptional activity. These results suggest that efatutazone inhibits cell motility by antagonizing the TGF-β/Smad2 pathway and effectively prevents metastasis in NSCLC patients with acquired resistance to EGFR-TKI regardless of the resistance mechanism.
doi:10.1111/cas.12411
PMCID: PMC4317891  PMID: 24698130
Efatutazone; epidermal growth factor receptor-tyrosine kinase inhibitor resistance; motility; non-small cell lung cancer; peroxisome proliferator-activated receptor gamma
25.  Crk adaptor proteins act as key signaling integrators for breast tumorigenesis 
Introduction
CT10 regulator of kinase (Crk) adaptor proteins (CrkI, CrkII and CrkL) play a role in integrating signals for migration and invasion of highly malignant breast cancer cell lines. This has important implications, as elevated CrkI/II protein levels were observed in a small cohort of breast cancer patients, which identified a potential role for Crk proteins in breast cancer progression. Numerous in vitro studies identified a role for Crk proteins in cell motility, but little is known about how Crk proteins contribute to breast cancer progression in vivo.
Methods
The clinical significance of Crk proteins in human breast cancer was assessed by analyzing published breast cancer datasets using a gene expression signature that was generated following CrkII over-expression and by examining Crk protein expression in tissue microarrays of breast tumors (n = 254). Stable knockdown of Crk (CrkI/CrkII/CrkL) proteins was accomplished using a short hairpin RNA (shRNA)-mediated approach in two basal breast cancer cell lines, MDA-231 1833TR and SUM1315, where the former have a high affinity to form bone metastases. Both in vitro assays (cell migration, invasion, soft agar growth) and in vivo experiments (intra-cardiac, tibial and mammary fat pad injections) were performed to assess the functional significance of Crk proteins in breast cancer.
Results
A gene signature derived following CrkII over-expression correlated significantly with basal breast cancers and with high grade and poor outcome in general. Moreover, elevated Crk immunostaining on tissue microarrays revealed a significant association with highly proliferative tumors within the basal subtype. RNAi-mediated knockdown of all three Crk proteins in metastatic basal breast cancer cells established a continued requirement for Crk in cell migration and invasion in vitro and metastatic growth in vivo. Furthermore, Crk ablation suppressed anchorage independent growth and in vivo orthotopic tumor growth. This was associated with diminished cell proliferation and was rescued by expression of non-shRNA targeted CrkI/II. Perturbations in tumor progression correlated with altered integrin signaling, including decreased cell spreading, diminished p130Cas phosphorylation, and Cdc42 activation.
Conclusions
These data highlight the physiological importance of Crk proteins in regulating growth of aggressive basal breast cancer cells and identify Crk-dependent signaling networks as promising therapeutic targets.
doi:10.1186/bcr3183
PMCID: PMC3446336  PMID: 22569336

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