Search tips
Search criteria

Results 1-9 (9)

Clipboard (0)

Select a Filter Below

Year of Publication
Document Types
1.  GARP Is Regulated by miRNAs and Controls Latent TGF-β1 Production by Human Regulatory T Cells 
PLoS ONE  2013;8(9):e76186.
GARP is a transmembrane protein present on stimulated human regulatory T lymphocytes (Tregs), but not on other T lymphocytes (Th cells). It presents the latent form of TGF-β1 on the Treg surface. We report here that GARP favors the cleavage of the pro-TGF-β1 precursor and increases the amount of secreted latent TGF-β1. Stimulated Tregs, which naturally express GARP, and Th cells transfected with GARP secrete a previously unknown form of latent TGF-β1 that is disulfide-linked to GARP. These GARP/TGF-β1 complexes are possibly shed from the T cell surface. Secretion of GARP/TGF-β1 complexes was not observed with transfected 293 cells and may thus be restricted to the T cell lineage. We conclude that in stimulated human Tregs, GARP not only displays latent TGF-β1 at the cell surface, but also increases its secretion by forming soluble disulfide-linked complexes. Moreover, we identified six microRNAs (miRNAs) that are expressed at lower levels in Treg than in Th clones and that target a short region of the GARP 3’ UTR. In transfected Th cells, the presence of this region decreased GARP levels, cleavage of pro-TGF-β1, and secretion of latent TGF-β1.
PMCID: PMC3787020  PMID: 24098777
2.  Mutant Kras Promotes Hyperplasia and Alters Differentiation in the Colon Epithelium But Does Not Expand the Presumptive Stem Cell Pool 
Gastroenterology  2011;141(3):1003-1013.e10.
Adenomatous polyps are precursors to colorectal cancer (CRC), whereas hyperplastic polyps (HPPs) have a small risk of progression to CRC. Mutations in KRAS are found in ~40% of CRCs and large adenomas and a subset of HPPs. We investigated the reasons that HPPs with KRAS mutations lack malignant potential; we compared the effects of Kras/KRAS activation to those of Adenomatous polyposis coli (Apc)/APC inactivation, which promotes adenoma formation.
We activated a KrasG12D mutant allele or inactivated Apc alleles in mouse colon epithelium and analyzed phenotypes and expression of selected genes and proteins. The mouse data were validated using samples of human HPPs and adenomas. Signaling pathways and factors that contribute to Kras/KRAS-induced phenotypes were studied in intestinal epithelial cells.
Activation of Kras led to hyperplasia and serrated crypt architecture akin to that observed in human HPPs. We also observed loss of Paneth cells and increases in goblet cell numbers. Abnormalities in Kras-mediated differentiation and proliferation required mitogen-activated protein kinase (MAPK) signaling and were linked to activation of the Hes1 transcription factor. Human HPPs also had activation of HES1. In contrast to Apc/APC inactivation, Kras/KRAS activation did not increase expression of crypt stem cell markers in colon epithelium or colony formation in vitro. Kras/KRAS activation was not associated with substantial induction of p16INK4a protein expression in mouse colon epithelium or human HPPs.
Although Kras/KRAS mutation promotes serrated and hyperplastic morphological features in colon epithelium, it is not able to initiate adenoma development, perhaps in part because activated Kras/KRAS signaling does not increase the number of presumptive stem cells in affected crypts.
PMCID: PMC3163826  PMID: 21699772
Colon cancer; oncogene; tumor suppressor; transgenic mice
3.  Regulation of lipid homeostasis by the bifunctional SREBF2-miR33a locus 
Cell metabolism  2011;13(3):241-247.
The sterol regulatory element-binding factor-2 (SREBF2) gene is a bifunctional locus encoding SREBP-2, a well-known transcriptional regulator of genes involved in cholesterol biosynthesis, and microRNA-33a, which has recently been shown to reduce expression of proteins involved in export of cholesterol and β-oxidation of fatty acids, thus adding an unexpected layer of complexity and fine-tuning to regulation of lipid homeostasis.
PMCID: PMC3062104  PMID: 21356514
4.  Peroxisome Proliferator Activated Receptor-γ Activation Inhibits Tumor Metastasis by Antagonizing Smad3 Mediated Epithelial Mesenchymal Transition 
Molecular cancer therapeutics  2010;9(12):3221-3232.
Epithelial-mesenchymal transition (EMT) was shown to confer tumor cells with abilities essential for metastasis, including migratory phenotype, invasiveness, and resistance to apoptosis, evading immune surveillance and tumor stem cell traits. Therefore, inhibition of EMT can be an important therapeutic strategy to inhibit tumor metastasis. Here we demonstrate that activation of peroxisome proliferator activated receptor (PPAR) -γ inhibits TGF-β-induced EMT in lung cancer cells and prevents metastasis by antagonizing Smad3 function. Activation of PPAR-γ by synthetic ligands (Troglitazone and Rosiglitazone) or by a constitutively-active form of PPAR-γ prevents TGF-β-induced loss of E-cadherin expression and inhibited the induction of mesenchymal markers (vimentin, N-cadherin, fibronectin) and MMPs. Consistently, activation of PPAR-γ also inhibited EMT-induced migration and invasion of lung cancer cells. Furthermore, effects of PPAR-γ ligands were attenuated by siRNA mediated knockdown of PPAR-γ, indicating that the ligand induced responses are PPAR-γ dependent. Selective knockdown of Smad2 and Smad3 by siRNA demonstrated that TGF-β-induced EMT is Smad3 dependent in lung cancer cells. Activation of PPAR-γ inhibits TGF-β-induced Smad transcriptional activity but had no effect on the phosphorylation or nuclear translocation of Smads. Consistently PPAR-γ activation prevented TGF-ß-induced transcriptional repression of E-cadherin promoter and inhibited transcriptional activation of N-cadherin promoter. Finally, treatment of mice with troglitazone or knockdown of Smad3 in tumor cells both significantly inhibited TGF-β-induced experimental metastasis in Scid-Beige mice. Together, with the low toxicity profile of PPAR-γ ligands, our data demonstrates that these ligands may serve as potential therapeutic agents to inhibit metastasis.
PMCID: PMC3044476  PMID: 21159608
TGF-β; lung cancer; epithelial-mesenchymal transition; PPAR-γ; metastasis
5.  GSK3β and β-Catenin Modulate Radiation Cytotoxicity in Pancreatic Cancer1 
Neoplasia (New York, N.Y.)  2010;12(5):357-365.
Knowledge of factors and mechanisms contributing to the inherent radioresistance of pancreatic cancer may improve cancer treatment. Irradiation inhibits glycogen synthase kinase 3β (GSK3β) by phosphorylation at serine 9. In turn, release of cytosolic membrane β-catenin with subsequent nuclear translocation promotes survival. Both GSK3β and β-catenin have been implicated in cancer cell proliferation and resistance to death.
We investigated pancreatic cancer cell survival after radiation in vitro and in vivo, with a particular focus on the role of the function of the GSK3β/β-catenin axis.
Lithium chloride, RNAi-medicated silencing of GSK3β, or the expression of a kinase dead mutant GSK3β resulted in radioresistance of Panc1 and BxPC3 pancreatic cancer cells. Conversely, ectopic expression of a constitutively active form of GSK3β resulted in radiosensitization of Panc1 cells. GSK3β silencing increased radiation-induced β-catenin target gene expression asmeasured by studies of AXIN2 and LEF1 transcript levels. Western blot analysis of total and phosphorylated levels of GSK3β and β-catenin showed that GSK3β inhibition resulted in stabilization of β-catenin. Xenografts of both BxPC3 and Panc1 with targeted silencing of GSK3β exhibited radioresistance in vivo. Silencing of β-catenin resulted in radiosensitization, whereas a nondegradable β-catenin construct induced radioresistance.
These data support the hypothesis that GSK3β modulates the cellular response to radiation in a β-catenin-dependent mechanism. Further understanding of this pathway may enhance the development of clinical trials combining drugs inhibiting β-catenin activation with radiation and chemotherapy in locally advanced pancreatic cancer.
PMCID: PMC2864473  PMID: 20454507
6.  IRS1 Regulation by Wnt/β-Catenin Signaling and Varied Contribution of IRS1 to the Neoplastic Phenotype* 
The Journal of Biological Chemistry  2009;285(3):1928-1938.
Dysregulation of β-catenin levels and localization and constitutive activation of β-catenin/TCF (T cell factor)-regulated gene expression occur in many cancers, including the majority of colorectal carcinomas and a subset of ovarian endometrioid adenocarcinomas. Based on the results of microarray-based gene expression profiling we found the insulin receptor substrate 1 (IRS1) gene as one of the most highly up-regulated genes upon ectopic expression of a mutant, constitutively active form of β-catenin in the rat kidney epithelial cell line RK3E. We demonstrate expression of IRS1 can be directly activated by β-catenin, likely in part via β-catenin/TCF binding to TCF consensus binding elements located in the first intron and downstream of the IRS1 transcriptional start site. Consistent with the proposal that β-catenin is an important regulator of IRS1 expression in vivo, we observed that IRS1 is highly expressed in many cancers with constitutive stabilization of β-catenin, such as colorectal carcinomas and ovarian endometrioid adenocarcinomas. Using a short hairpin RNA approach to abrogate IRS1 expression and function, we found that IRS1 function is required for efficient de novo neoplastic transformation by β-catenin in RK3E cells. Our findings add to the growing body of data implicating IRS1 as a critical signaling component in cancer development and progression.
PMCID: PMC2804351  PMID: 19843521
7.  MicroRNA miR-34 Inhibits Human Pancreatic Cancer Tumor-Initiating Cells 
PLoS ONE  2009;4(8):e6816.
MicroRNAs (miRNAs) have been implicated in cancer initiation and progression via their ability to affect expression of genes and proteins that regulate cell proliferation and/or cell death. Transcription of the three miRNA miR-34 family members was recently found to be directly regulated by p53. Among the target proteins regulated by miR-34 are Notch pathway proteins and Bcl-2, suggesting the possibility of a role for miR-34 in the maintenance and survival of cancer stem cells.
Methodology/Principal Findings
We examined the roles of miR-34 in p53-mutant human pancreatic cancer cell lines MiaPaCa2 and BxPC3, and the potential link to pancreatic cancer stem cells. Restoration of miR-34 expression in the pancreatic cancer cells by either transfection of miR-34 mimics or infection with lentiviral miR-34-MIF downregulated Bcl-2 and Notch1/2. miR-34 restoration significantly inhibited clonogenic cell growth and invasion, induced apoptosis and G1 and G2/M arrest in cell cycle, and sensitized the cells to chemotherapy and radiation. We identified that CD44+/CD133+ MiaPaCa2 cells are enriched with tumorsphere-forming and tumor-initiating cells or cancer stem/progenitor cells with high levels of Notch/Bcl-2 and loss of miR-34. More significantly, miR-34 restoration led to an 87% reduction of the tumor-initiating cell population, accompanied by significant inhibition of tumorsphere growth in vitro and tumor formation in vivo.
Our results demonstrate that miR-34 may restore, at least in part, the tumor suppressing function of the p53 in p53-deficient human pancreatic cancer cells. Our data support the view that miR-34 may be involved in pancreatic cancer stem cell self-renewal, potentially via the direct modulation of downstream targets Bcl-2 and Notch, implying that miR-34 may play an important role in pancreatic cancer stem cell self-renewal and/or cell fate determination. Restoration of miR-34 may hold significant promise as a novel molecular therapy for human pancreatic cancer with loss of p53–miR34, potentially via inhibiting pancreatic cancer stem cells.
PMCID: PMC2729376  PMID: 19714243
8.  Mesenchymal cells reactivate Snail1 expression to drive three-dimensional invasion programs 
The Journal of Cell Biology  2009;184(3):399-408.
Epithelial–mesenchymal transition (EMT) is required for mesodermal differentiation during development. The zinc-finger transcription factor, Snail1, can trigger EMT and is sufficient to transcriptionally reprogram epithelial cells toward a mesenchymal phenotype during neoplasia and fibrosis. Whether Snail1 also regulates the behavior of terminally differentiated mesenchymal cells remains unexplored. Using a Snai1 conditional knockout model, we now identify Snail1 as a regulator of normal mesenchymal cell function. Snail1 expression in normal fibroblasts can be induced by agonists known to promote proliferation and invasion in vivo. When challenged within a tissue-like, three-dimensional extracellular matrix, Snail1-deficient fibroblasts exhibit global alterations in gene expression, which include defects in membrane type-1 matrix metalloproteinase (MT1-MMP)-dependent invasive activity. Snail1-deficient fibroblasts explanted atop the live chick chorioallantoic membrane lack tissue-invasive potential and fail to induce angiogenesis. These findings establish key functions for the EMT regulator Snail1 after terminal differentiation of mesenchymal cells.
PMCID: PMC2646556  PMID: 19188491
9.  Generating somatic mosaicism with a Cre recombinase–microsatellite sequence transgene 
Nature methods  2008;5(3):231-233.
Strategies for altering constitutional or somatic genotype in mice are well established, but approaches to generate mosaic genotypes in mouse tissues are limited. We showed that a functionally inactive Cre recombinase transgene with a long mononucleotide tract altering the reading frame was stochastically activated in the mouse intestinal tract. We demonstrated the utility of this approach by inducing colonic polyposis after Cre-mediated bi-allelic inactivation of the Apc gene.
PMCID: PMC2279183  PMID: 18264107

Results 1-9 (9)