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1.  Corrigendum 
Carcinogenesis  2014;35(3):737.
PMCID: PMC3989579
2.  Corrigendum 
Carcinogenesis  2014;35(3):738.
PMCID: PMC3989580
3.  Role of CYP2A13 in the bioactivation and lung tumorigenicity of the tobacco-specific lung procarcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone: in vivo studies using a CYP2A13-humanized mouse model 
Carcinogenesis  2013;35(1):131-137.
The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), which is abundant in tobacco smoke, is a potent lung procarcinogen. The present study was aimed to prove that transgenic expression of human cytochrome P450 2A13 (CYP2A13), known to be selectively expressed in the respiratory tract and be the most efficient enzyme for NNK bioactivation in vitro, will enhance NNK bioactivation and NNK-induced tumorigenesis in the mouse lung. Kinetic parameters of NNK bioactivation in vitro and incidence of NNK-induced lung tumors in vivo were determined for wild-type, Cyp2a5-null and CYP2A13-humanized (CYP2A13-transgenic/Cyp2a5-null) mice. As expected, in both liver and lung microsomes, the loss of CYP2A5 resulted in significant increases in Michaelis constant (K m) values for the formation of 4-oxo-4-(3-pyridyl)-butanal, representing the reactive intermediate that can lead to the formation of O6-methylguanine (O6-mG) DNA adducts; however, the gain of CYP2A13 at a fraction of the level of mouse lung CYP2A5 led to recovery of the activity in the lung, but not in the liver. The levels of O6-mG, the DNA adduct highly correlated with lung tumorigenesis, were significantly higher in the lungs of CYP2A13-humanized mice than in Cyp2a5-null mice. Moreover, incidences of lung tumorigenesis were significantly greater in CYP2A13-humanized mice than in Cyp2a5-null mice, and the magnitude of the differences in incidence was greater at low (30mg/kg) than at high (200mg/kg) NNK doses. These results indicate that CYP2A13 is a low K m enzyme in catalyzing NNK bioactivation in vivo and support the notion that genetic polymorphisms of CYP2A13 can influence the risks of tobacco-induced lung tumorigenesis in humans.
PMCID: PMC3871935  PMID: 23917075
4.  Dihydroartemisinin inhibits the mammalian target of rapamycin-mediated signaling pathways in tumor cells 
Carcinogenesis  2013;35(1):192-200.
Dihydroartemisinin (DHA), an antimalarial drug, has previously unrecognized anticancer activity, and is in clinical trials as a new anticancer agent for skin, lung, colon and breast cancer treatment. However, the anticancer mechanism is not well understood. Here, we show that DHA inhibited proliferation and induced apoptosis in rhabdomyosarcoma (Rh30 and RD) cells, and concurrently inhibited the signaling pathways mediated by the mammalian target of rapamycin (mTOR), a central controller for cell proliferation and survival, at concentrations (<3 μM) that are pharmacologically achievable. Of interest, in contrast to the effects of conventional mTOR inhibitors (rapalogs), DHA potently inhibited mTORC1-mediated phosphorylation of p70 S6 kinase 1 and eukaryotic initiation factor 4E binding protein 1 but did not obviously affect mTORC2-mediated phosphorylation of Akt. The results suggest that DHA may represent a novel class of mTORC1 inhibitor and may execute its anticancer activity primarily by blocking mTORC1-mediated signaling pathways in the tumor cells.
PMCID: PMC3871936  PMID: 23929438
5.  Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) promotes glioblastoma cell chemotaxis via Lyn activation 
Carcinogenesis  2013;35(1):218-226.
The long-term survival of patients with glioblastoma is compromised by the proclivity for local invasion into the surrounding normal brain, escaping surgical resection and contributing to therapeutic resistance. Tumor necrosis factor-like weak inducer of apoptosis (TWEAK), a member of the tumor necrosis factor superfamily, can stimulate glioma cell invasion via binding to fibroblast growth factor-inducible 14 (Fn14) and subsequent activation of the Rho guanosine triphosphatase family member Rac1. Here, we demonstrate that TWEAK acts as a chemotactic factor for glioma cells, a potential process for driving cell invasion into the surrounding brain tissue. TWEAK exposure induced the activation of Src family kinases (SFKs), and pharmacologic suppression of SFK activity inhibited TWEAK-induced chemotactic migration. We employed a multiplexed Luminex assay and identified Lyn as a candidate SFK activated by TWEAK. Depletion of Lyn suppressed TWEAK-induced chemotaxis and Rac1 activity. Furthermore, Lyn gene expression levels increase with primary glioma tumor grade and inversely correlate with patient survival. These results show that TWEAK-induced glioma cell chemotaxis is dependent upon Lyn kinase function and, thus, provides opportunities for therapeutic targeting of this deadly disease.
PMCID: PMC3871937  PMID: 23975833
6.  Occult progression by Apc-deficient intestinal crypts as a target for chemoprevention 
Carcinogenesis  2013;35(1):237-246.
Although Apc mutation is widely considered an initiating event in colorectal cancer, little is known about the earliest stages of tumorigenesis following sporadic Apc loss. Therefore, we have utilized a novel mouse model that facilitates the sporadic inactivation of Apc via frameshift reversion of Cre in single, isolated cells and subsequently tracks the fates of Apc-deficient intestinal cells. Our results suggest that consistent with Apc being a ‘gatekeeper’, loss of Apc early in life during intestinal growth leads to adenomas or increased crypt fission, manifested by fields of mutant but otherwise normal-appearing crypts. In contrast, Apc loss occurring later in life has minimal consequences, with mutant crypts being less prone to either increased crypt fission or adenoma formation. Using the stem cell-specific Lgr5-CreER mouse, we generated different sized fields of Apc-deficient crypts via independent recombination events and found that field size correlates with progression to adenoma. To evaluate this early stage prior to adenoma formation as a therapeutic target, we examined the chemopreventive effects of sulindac on Apc-deficient occult crypt fission. We found that sulindac treatment started early in life inhibits the morphologically occult spread of Apc-deficient crypts and thus reduces adenoma numbers. Taken together these results suggest that: (i) earlier Apc loss promotes increased crypt fission, (ii) a field of Apc-deficient crypts, which can form via occult crypt fission or independent neighboring events, is an important intermediate between loss of Apc and adenoma formation and (iii) normal-appearing Apc-deficient crypts are potential unappreciated targets for cancer screening and chemoprevention.
PMCID: PMC3871938  PMID: 23996931
7.  Estrogen receptor α or β loss in the colon of Min/+ mice promotes crypt expansion and impairs TGFβ and HNF3β signaling 
Carcinogenesis  2013;35(1):96-102.
ER activity in the colon prevents tumorigenesis by suppressing inflammation, regulating cytokine, Wnt and Ihh availability and providing maintenance of the ISC microenvironment through modulation of crosstalk in the ECM.
Adenomatous polyposis coli (APC)-regulated Wnt and transforming growth factor-β (TGFβ) signaling cooperate in the intestine to maintain normal enterocyte functions. Human clinical trials showed that estrogen [17β-estradiol (E2)], the ligand of nuclear receptors estrogen receptor α (ERα) and ERβ, inhibited colorectal cancer (CRC) in women. Consistent with this finding, we reported that E2, ERα and ERβ suppressed intestinal tumorigenesis in the C57BL/6J-Min/+ (Min/+) mouse, a CRC model. Here, we extended our results with further comparisons of colon and small intestine from intact female Apc +/+ (WT), Min/+ and ER-deficient Min/+ mice. In the colon of ER-deficient Min/+ mice, ER loss reduced TGFβ signaling in crypt base cells as evidenced by minimal expression of the effectors Smad 2, 3 and 4 in these strains. We also found reduced expression of Indian hedgehog (Ihh), bone morphogenetic protein 4 and hepatocyte nuclear factor 3β or FoxA2, factors needed for paracrine signaling between enterocytes and mesenchyme. In proximal colon, ER loss produced a >10-fold increased incidence of crypt fission, a marker for wound healing and tumor promotion. These data, combined with our previous work detailing the specific roles of E2, ERα and ERβ in the colon, suggest that ER activity helps to maintain the intestinal stem cell (ISC) microenvironment by modulating epithelial–stromal crosstalk in ways that regulate cytokine, Wnt and Ihh availability in the extracellular matrix (ECM).
PMCID: PMC3871939  PMID: 24104551
8.  Potentially functional variants of p14 ARF are associated with HPV-positive oropharyngeal cancer patients and survival after definitive chemoradiotherapy 
Carcinogenesis  2013;35(1):62-68.
Since p14 ARF and human papillomavirus (HPV) 16 E6/E7 oncoproteins are important regulators participating in the p53/Rb pathways, genetic variations of p14 ARF may modify tumor HPV16 status and survival of HPV16-positive squamous cell carcinoma of the oropharynx (SCCOP) patients. We determined tumor HPV16 status and expression of p14/p53 and genotyped p14 ARF-rs3731217 and -rs3088440 polymorphisms in 552 incident SCCOP patients. We found that patients having variant genotypes for each p14 ARF polymorphism were approximately two or three times as likely to have HPV16-positive tumors compared with patients with corresponding common homozygous genotype, and such an association was particularly pronounced in patients with variant genotypes of both polymorphisms. After definitive chemoradiotherapy, patients having p14 ARF rs3731217 TG/GG variant genotypes had significantly better overall, disease-specific and disease-free survival than those having TT genotype, respectively. Multivariable analysis found that patients with p14 ARF-rs3731217 TT genotype had an ~7-, 11- and 3-fold increased risk for death overall, death due to SCCOP and recurrence than those with TG/GG variant genotypes, respectively. Furthermore, such significantly prognostic effect was also found when survival analysis was limited to HPV16-positive patients. Additionally, potentially functional relevance of the two variants was characterized to explore the genotype–phenotype correlation. Our findings indicate p14 ARF variants may predict tumor HPV16-positive SCCOP patients and survival.
PMCID: PMC3871940  PMID: 24104554
9.  Significant interactions between maternal PAH exposure and haplotypes in candidate genes on B[a]P-DNA adducts in a NYC cohort of non-smoking African-American and Dominican mothers and newborns 
Carcinogenesis  2013;35(1):69-75.
Our study, conducted within a New York City-based cohort, identified novel interactions between maternal PAH exposure and maternal and newborn genetic haplotypes in key B[a]P metabolism genes on B[a]P-DNA adducts in paired cord blood samples.
Polycyclic aromatic hydrocarbons (PAH) are a class of chemicals common in the environment. Certain PAH are carcinogenic, although the degree to which genetic variation influences susceptibility to carcinogenic PAH remains unclear. Also unknown is the influence of genetic variation on the procarcinogenic effect of in utero exposures to PAH. Benzo[a]pyrene (B[a]P) is a well-studied PAH that is classified as a probable human carcinogen. Within our New York City-based cohort, we explored interactions between maternal exposure to airborne PAH during pregnancy and maternal and newborn haplotypes (and in one case, a single-nucleotide polymorphism) in key B[a]P metabolism genes on B[a]P-DNA adducts in paired cord blood samples. The study subjects included non-smoking African-American (n = 132) and Dominican (n = 235) women with available data on maternal PAH exposure, paired cord adducts and genetic data who resided in the Washington Heights, Central Harlem and South Bronx neighborhoods of New York City. We selected seven maternal and newborn genes related to B[a]P metabolism, detoxification and repair for our analyses: CYP1A1, CYP1A2, CYP1B1, GSTM3, GSTT2, NQO1 and XRCC1. We found significant interactions between maternal PAH exposure and haplotype on cord B[a]P-DNA adducts in the following genes: maternal CYP1B1, XRCC1 and GSTM3, and newborn CYP1A2 and XRCC1 in African-Americans; and maternal XRCC1 and newborn NQO1 in Dominicans. These novel findings highlight differences in maternal and newborn genetic contributions to B[a]P-DNA adduct formation, as well as ethnic differences in gene–environment interactions, and have the potential to identify at-risk subpopulations who are susceptible to the carcinogenic potential of B[a]P.
PMCID: PMC3871941  PMID: 24177223
10.  The P110 subunit of PI3-K is a therapeutic target of acacetin in skin cancer 
Carcinogenesis  2013;35(1):123-130.
The identification of primary molecular targets of cancer-preventive phytochemicals is essential for a comprehensive understanding of their mechanism of action. In the present study, we investigated the chemopreventive effects and molecular targets of acacetin, a flavonoid found in Robinia p seudoacacia, also known as black locust. Acacetin treatment significantly suppressed epidermal growth factor (EGF)-induced cell transformation. Immunoblot analysis revealed that acacetin attenuated EGF-induced phosphorylation of Akt and p70S6K, which are downstream effectors of phosphatidylinositol 3-kinase (PI3-K). An immunoprecipitation kinase assay of PI3-K and pull-down assay results demonstrated that acacetin substantially inhibits PI3-K activity by direct physical binding. Acacetin exhibited stronger inhibitory effects against anchorage-dependent and -independent cell growth in cells expressing higher PI3-K activity compared with those exhibiting relatively low PI3-K activity. Binding assay data combined with computational modeling suggest that acacetin binds in an adenosine triphosphate (ATP)-competitive manner with the p110α subunit of PI3-K and interacts with Val828, Glu826, Asp911, Trp760, Ile777, Ile825, Tyr813, Ile910 and Met900 residues. Acacetin was also found to significantly reduce SK-MEL-28 tumor growth and Akt phosphorylation in vivo. Taken together, these results indicate that acacetin is an ATP-competitive PI3-K inhibitor and a promising agent for melanoma chemoprevention.
PMCID: PMC3895936  PMID: 23913940
11.  Metformin inhibits pancreatic cancer cell and tumor growth and downregulates Sp transcription factors 
Carcinogenesis  2013;34(12):2870-2879.
Metformin is a widely used antidiabetic drug, and epidemiology studies for pancreatic and other cancers indicate that metformin exhibits both chemopreventive and chemotherapeutic activities. Several metformin-induced responses and genes are similar to those observed after knockdown of specificity protein (Sp) transcription factors Sp1, Sp3 and Sp4 by RNA interference, and we hypothesized that the mechanism of action of metformin in pancreatic cancer cells was due, in part, to downregulation of Sp transcription factors. Treatment of Panc1, L3.6pL and Panc28 pancreatic cancer cells with metformin downregulated Sp1, Sp3 and Sp4 proteins and several pro-oncogenic Sp-regulated genes including bcl-2, survivin, cyclin D1, vascular endothelial growth factor and its receptor, and fatty acid synthase. Metformin induced proteasome-dependent degradation of Sps in L3.6pL and Panc28 cells, whereas in Panc1 cells metformin decreased microRNA-27a and induced the Sp repressor, ZBTB10, and disruption of miR-27a:ZBTB10 by metformin was phosphatase dependent. Metformin also inhibited pancreatic tumor growth and downregulated Sp1, Sp3 and Sp4 in tumors in an orthotopic model where L3.6pL cells were injected directly into the pancreas. The results demonstrate for the first time that the anticancer activities of metformin are also due, in part, to downregulation of Sp transcription factors and Sp-regulated genes.
PMCID: PMC3845888  PMID: 23803693
12.  Expression of a phosphorylated substrate domain of p130Cas promotes PyMT-induced c-Src-dependent murine breast cancer progression 
Carcinogenesis  2013;34(12):2880-2890.
Elevated expression of p130Cas (Crk-associated substrate)/BCAR1 (breast cancer antiestrogen resistance 1) in human breast tumors is a marker of poor prognosis and poor overall survival. p130Cas is a downstream target of the tyrosine kinase c-Src. Signaling mediated by p130Cas through its phosphorylated substrate domain (SD) and interaction with effector molecules directly promotes tumor progression. We previously developed a constitutively phosphorylated p130Cas SD molecule, Src*/SD (formerly referred to as Src*/CasSD), which acts as decoy molecule and attenuates the transformed phenotype in v-crk-transformed murine fibroblasts and human breast cancer cells. To test the function of this molecule in vivo, we established mouse mammary tumor virus (MMTV)-long terminal repeat-Src*/SD transgenic mice in which mammary gland development and tumor formation were analyzed. Transgenic expression of the Src*/SD molecule under the MMTV-long terminal repeat promoter did not interfere with normal mammary gland development or induce tumors in mice observed for up to 11 months. To evaluate the effects of the Src*/SD molecule on tumor development in vivo, we utilized the MMTV-polyoma middle T-antigen (PyMT) murine breast cancer model that depends on c-Src. PyMT mice crossed with Src*/SD mice displayed accelerated tumor formation. The earlier onset of tumors can be explained by the interaction of the Src* domain with PyMT and targeting the fused phosphorylated SD to the membrane. At membrane compartments, it might integrate membrane-associated active signaling complexes leading to increased proliferation measured by phospho-Histone H3 staining. Although these results were unexpected, they emphasize the importance of preventing the membrane association of Src*/SD when employed as decoy molecule.
PMCID: PMC3845889  PMID: 23825155
13.  Macrophage migratory inhibitory factor promotes bladder cancer progression via increasing proliferation and angiogenesis 
Carcinogenesis  2013;34(12):2891-2899.
Macrophage migratory inhibitory factor (MIF) is a proinflammatory cytokine shown to promote tumorigenesis. Using the N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN) model of bladder cancer, we previously showed that MIF knockout mice display decreased angiogenesis and invasion compared with wild-type. This study examines the role of MIF in bladder cancer via use of oral inhibitors of MIF. In vitro, high-grade bladder cancer cells were treated with recombinant human MIF +/− (rhMIF+/−) inhibitor. Measurements included cell counts, proliferation by 3H-thymidine incorporation (TdR), extracellular signal-regulated kinase (ERK) phosphorylation by western blot analysis, messenger RNA (mRNA) expression by quantitative PCR and protein secretion by enzyme-linked immunosorbent assay. Treatment with rhMIF increased ERK phosphorylation, cell counts, TdR and mRNA expression and protein secretion of vascular endothelial growth factor, which were blocked by specific inhibitors of ERK and MIF. In vivo, 3-month-old male C57Bl/6 mice were given BBN for 22 and 16 weeks in study 1 and study 2, respectively. Mice (n = 8–10 per group) were gavaged with vehicle or doses of MIF inhibitors daily from weeks 16–22 in both studies. Average bladder weights, reflecting tumor mass, tumor stage/burden, mitotic rate and proliferation indices, and microvessel densities were reduced in inhibitor groups versus controls. In summary, MIF promotes bladder cancer via increasing cell proliferation and angiogenesis and oral inhibitors of MIF may prove useful in treatment of this disease.
PMCID: PMC3845890  PMID: 23825153
14.  Insulin-like growth factor-I receptor is suppressed through transcriptional repression and mRNA destabilization by a novel energy restriction-mimetic agent 
Carcinogenesis  2013;34(12):2694-2705.
Insulin-like growth factor-I receptor (IGF-IR) represents one of the major targets by which dietary or chemically induced energy restriction mediates chemopreventive effects in animal tumor models. However, the mechanism underlying this cellular response remains unclear. In the course of investigating the suppressive effect of the energy restriction-mimetic agent CG-5 on IGF-IR expression in prostate cancer cells, we identified a novel posttranscriptional mechanism by which the RNA-binding protein human antigen R (HuR) regulates IGF-IR expression through messenger RNA (mRNA) stabilization. Previously, we demonstrated that Sp1 and HuR proteins were concomitantly targeted for ubiquitin-dependent degradation by β-transducin repeat-containing protein in response to CG-5. Although this loss of Sp1 expression contributed to CG-5-mediated IGF-IR downregulation, enforced specific protein 1 (Sp1) expression could only partially protect cells from the drug effect. The small interfering RNA-mediated silencing of HuR suppressed IGF-IR expression by reducing mRNA stability, whereas ectopic HuR expression increased IGF-IR mRNA stability and protein expression and, when coexpressed with Sp1, blocked CG-5-mediated IGF-IR ablation. RNA pull-down and immunoprecipitation analyses indicated that HuR selectively bound to the distal region of the IGF-IR 3′ untranslated region (UTR), whereas no interaction with the 5′UTR was noted. Evaluation of a series of truncated HuR mutants revealed that the RNA recognition motifs (RRM2 and RRM3) were involved in IGF-IR 3′UTR binding and the consequent increase in IGF-IR mRNA stability. Although these data contrast with a previous report that HuR acted as a translation repressor of IGF-IR mRNA through 5′UTR binding, our finding is consistent with the reported oncogenic role of HuR in conferring stability to target mRNAs encoding tumor-promoting proteins.
PMCID: PMC3845891  PMID: 23864387
15.  Genome-wide methylation analysis shows similar patterns in Barrett’s esophagus and esophageal adenocarcinoma 
Carcinogenesis  2013;34(12):2750-2756.
Barrett’s esophagus (BE) is a precursor of esophageal adenocarcinoma (EAC). To identify novel tumor suppressors involved in esophageal carcinogenesis and potential biomarkers for the malignant progression of BE, we performed a genome-wide methylation profiling of BE and EAC tissues. Using Illumina’s Infinium HumanMethylation27 BeadChip microarray, we examined the methylation status of 27 578 CpG sites in 94 normal esophageal (NE), 77 BE and 117 EAC tissue samples. The overall methylation of CpG sites within the CpG islands was higher, but outside of the CpG islands was lower in BE and EAC tissues than in NE tissues. Hierarchical clustering analysis showed an excellent separation of NE tissues from BE and EAC tissues; however, the clustering of BE and EAC tissues was less clear, suggesting that methylation occurs early during the progression of EAC. We confirmed many previously reported hypermethylated genes and identified a large number of novel hypermethylated genes in BE and EAC tissues, particularly genes encoding ADAM (A Disintegrin And Metalloproteinase) peptidase proteins, cadherins and protocadherins, and potassium voltage-gated channels. Pathway analysis showed that a number of channel and transporter activities were enriched for hypermethylated genes. We used pyrosequencing to validate selected candidate genes and found high correlations between the array and pyrosequencing data (rho > 0.8 for each validated gene). The differentially methylated genes and pathways may provide biological insights into the development and progression of BE and become potential biomarkers for the prediction and early detection of EAC.
PMCID: PMC3845893  PMID: 23996928
16.  Circulating C-reactive protein and colorectal cancer risk: a report from the Shanghai Men’s Health Study 
Carcinogenesis  2013;34(12):2799-2803.
Chronic inflammation has been implicated in the pathogenesis of colorectal cancer. The objective of this study was to evaluate the association of prediagnostic circulating levels of C-reactive protein (CRP), a biomarker of systemic inflammation, with subsequent development of colorectal cancer. Prediagnostic plasma CRP levels were examined among 288 colorectal cancer cases and 576 individually-matched controls nested within the Shanghai Men’s Health Study (2002–06), a population-based cohort study of 61 482 Chinese men. The association between CRP levels and colorectal cancer risk was investigated. Baseline plasma CRP levels were 53% higher among men who subsequently developed colorectal cancer than among those who remained free of the disease (1.15 versus 0.75 μg/ml; P < 0.001). Multivariate analyses showed a dose-dependent relationship between CRP and colorectal cancer risk (P trend = 0.003); men in the highest tertile (CRP > 1.19 μg/ml) had 1.88-fold (95% confidence interval (CI): 1.24–2.86) increased odds of developing colorectal cancer compared with men in the lowest tertile (CRP < 0.45 μg/ml). The association was only significant for colon cancer, when cancer site was considered, and was predominantly seen for cases diagnosed within 4 years of blood collection; adjusted odds ratios for the highest versus the lowest tertiles were 3.28 (95% CI: 1.28–8.37), 3.68 (95% CI: 1.62–8.38) and 1.05 (95% CI: 0.56–1.97), respectively, for cases diagnosed <2, 2–4 and >4 years after blood collection. The findings from our study suggest that circulating CRP level is positively associated with colorectal cancer risk in Chinese men, and this association, at least in part, is explained by inflammation-related cancerous or precancerous processes.
PMCID: PMC3845894  PMID: 23985781
17.  Metformin targets c-MYC oncogene to prevent prostate cancer 
Carcinogenesis  2013;34(12):2823-2832.
Prostate cancer (PCa) is the second leading cause of cancer-related death in American men and many PCa patients develop skeletal metastasis. Current treatment modalities for metastatic PCa are mostly palliative with poor prognosis. Epidemiological studies indicated that patients receiving the diabetic drug metformin have lower PCa risk and better prognosis, suggesting that metformin may have antineoplastic effects. The mechanism by which metformin acts as chemopreventive agent to impede PCa initiation and progression is unknown. The amplification of c-MYC oncogene plays a key role in early prostate epithelia cell transformation and PCa growth. The purpose of this study is to investigate the effect of metformin on c-myc expression and PCa progression. Our results demonstrated that (i) in Hi-Myc mice that display murine prostate neoplasia and highly resemble the progression of human prostate tumors, metformin attenuated the development of prostate intraepithelial neoplasia (PIN, the precancerous lesion of prostate) and PCa lesions. (ii) Metformin reduced c-myc protein levels in vivo and in vitro. In Myc-CaP mouse PCa cells, metformin decreased c-myc protein levels by at least 50%. (iii) Metformin selectively inhibited the growth of PCa cells by stimulating cell cycle arrest and apoptosis without affecting the growth of normal prostatic epithelial cells (RWPE-1). (iv) Reduced PIN formation by metformin was associated with reduced levels of androgen receptor and proliferation marker Ki-67 in Hi-Myc mouse prostate glands. Our novel findings suggest that by downregulating c-myc, metformin can act as a chemopreventive agent to restrict prostatic neoplasia initiation and transformation.
Summary: Metformin, an old antidiabetes drug, may inhibit prostate intraepithelial neoplasia transforming to cancer lesion via reducing c-MYC, an ‘old’ overexpressed oncogene. This study explores chemopreventive efficacy of metformin in prostate cancer and its link to cMYC in vitro and in vivo.
PMCID: PMC3845895  PMID: 24130167
18.  Dietary black raspberries modulate DNA methylation in dextran sodium sulfate (DSS)-induced ulcerative colitis 
Carcinogenesis  2013;34(12):2842-2850.
Ulcerative colitis (UC) is characterized by chronic inflammation of the colon. During inflammation, NF-κB is increased in colonic epithelial cells and in immune cells, leading to increases in proinflammatory cytokines. These events then increase DNA methyltransferases (DNMTs), which silence a subset of tumor suppressor genes by promoter methylation. Negative regulators of the Wnt pathway are frequently methylated in UC, leading to dysregulation of the pathway and, potentially, to colorectal cancer. We determined if black raspberries (BRBs) influence promoter methylation of suppressors in the Wnt pathway in dextran sodium sulfate (DSS)-induced UC. C57BL/6J mice received 1% DSS and were fed either control or 5% BRB diets. Mice were euthanized on days 7, 14 and 28, and their colons, spleen and bone marrow were collected. Berries reduced ulceration at day 28. This was accompanied by decreased staining of macrophages and neutrophils and decreased NF-κB p65 nuclear localization in the colon at all time points. At day 7, BRBs demethylated the promoter of dkk3, leading to its increased messenger RNA (mRNA) expression in colon, spleen and bone marrow. β-Catenin nuclear localization, c-Myc staining as well as protein expression of DNMT3B, histone deacetylases 1 and 2 (HDAC1 and HDAC2) and methyl-binding domain 2 (MBD2) were all decreased in colon; mRNA expression of these four proteins was decreased in bone marrow cells by BRBs. These results suggest that BRBs suppress colonic ulceration by correcting promoter hypermethylation of suppressor genes in the colon, as well as in the spleen and bone marrow that systematically regulate inflammation.
Summary: Our results suggest that dietary BRBs suppress colonic ulceration by correcting promoter hypermethylation of suppressor genes in the colon, as well as in the spleen and bone marrow that systematically regulate inflammation in DSS-induced UC.
PMCID: PMC3845896  PMID: 24067901
19.  Tpl2 knockout keratinocytes have increased biomarkers for invasion and metastasis 
Carcinogenesis  2013;34(12):2789-2798.
Skin cancer is the most common form of cancer in the USA, with an estimated two million cases diagnosed annually. Tumor progression locus 2 (Tpl2), also known as MAP3K8, is a serine/threonine protein kinase in the mitogen-activated protein kinase signal transduction cascade. Tpl2 was identified by our laboratory as having a tumor suppressor function in skin carcinogenesis, with the absence of this gene contributing to heightened inflammation and increased skin carcinogenesis. In this study, we used gene expression profiling to compare expression levels between Tpl2 +/+ and Tpl2 − /− keratinocytes. We identified over 2000 genes as being differentially expressed between genotypes. Functional annotation analysis identified cancer, cell growth/proliferation, cell death, cell development, cell movement and cell signaling as the top biological processes to be differentially regulated between genotypes. Further microarray analysis identified several candidate genes, including Mmp1b, Mmp2, Mmp9 and Mmp13, involved in migration and invasion to be upregulated in Tpl2 − /− keratinocytes. Moreover, Tpl2 −/− keratinocytes had a significant downregulation in the matrix metalloproteinase (MMP) inhibitor Timp3. Real-time PCR validated the upregulation of the MMPs in Tpl2 −/− keratinocytes and zymography confirmed that MMP2 and MMP9 activity was higher in conditioned media from Tpl2 −/− keratinocytes. Immunohistochemistry confirmed higher MMP9 staining in 12-O-tetradecanoylphorbol-13-acetate-treated skin from Tpl2 −/− mice and grafted tumors formed from v-rasHa retrovirus-infected Tpl2 −/− keratinocytes. Additionally, Tpl2 −/− keratinocytes had significantly higher invasion, malignant conversion rates and increased endothelial cell tube formation when compared with Tpl2 +/+ keratinocytes. In summary, our studies reveal that keratinocytes from Tpl2 −/− mice demonstrate a higher potential to be invasive and metastatic.
Tpl2has a tumor suppressor function in skin carcinogenesis. Moreover, using microarray complemented with cellular assays we identified a role for Tpl2 in skin cancer progression and demonstrated the absence of the gene contributes to increased invasive and metastatic potential.
PMCID: PMC3845897  PMID: 24067898
20.  Trichostatin-A modulates claudin-1 mRNA stability through the modulation of Hu antigen R and tristetraprolin in colon cancer cells 
Carcinogenesis  2013;34(11):2610-2621.
Expression of claudin-1, a tight junction protein, is highly upregulated in colon cancer. We have reported that claudin-1 expression in colon cancer cells is epigenetically regulated as histone deacetylase (HDAC) inhibitors decrease claudin-1 messenger RNA (mRNA) stability and thus expression. In this regard, our data suggested a role of the 3′-untranslated region (UTR) in the regulation of HDAC-dependent regulation of claudin-1 mRNA stability. In the current study, we demonstrate, based on our continued investigation, that the ELAV-like RNA-binding proteins (RBPs), human antigen R (HuR) and tristetraprolin (TTP) associate with the 3′-UTR of claudin-1 mRNA to modulate the latter’s stability. Ribonomic and site-directed mutagenesis approaches were used to confirm the binding of HuR and TTP to the 3′-UTR of claudin-1. We further confirmed their roles in the stabilization of claudin-1 mRNA, under conditions of HDAC inhibition. In summary, we report that HuR and TTP are the critical regulators of the posttranscriptional regulation of claudin-1 expression in colon cancer cells. We also demonstrate that inhibition of HDACs by trichostatin treatment decreased the binding of HuR while increasing the binding of TTP to the 3′-UTR of claudin-1. Additionally, we provide data showing transcriptional regulation of claudin-1 expression, through the regulation of transcription factor Sp1. Taken together, we demonstrate epigenetic regulation of claudin-1 expression in colon cancer cells at the transcriptional and posttranscriptional levels.
PMCID: PMC3810835  PMID: 23880304
21.  IMP1 promotes tumor growth, dissemination and a tumor-initiating cell phenotype in colorectal cancer cell xenografts 
Carcinogenesis  2013;34(11):2647-2654.
Igf2 mRNA binding protein 1 (IMP1, CRD-BP, ZBP-1) is a messenger RNA binding protein that we have shown previously to regulate colorectal cancer (CRC) cell growth in vitro. Furthermore, increased IMP1 expression correlates with enhanced metastasis and poor prognosis in CRC patients. In the current study, we sought to elucidate IMP1-mediated functions in CRC pathogenesis in vivo. Using CRC cell xenografts, we demonstrate that IMP1 overexpression promotes xenograft tumor growth and dissemination into the blood. Furthermore, intestine-specific knockdown of Imp1 dramatically reduces tumor number in the Apc Min/+ mouse model of intestinal tumorigenesis. In addition, IMP1 knockdown xenografts exhibit a reduced number of tumor cells entering the circulation, suggesting that IMP1 may directly modulate this early metastatic event. We further demonstrate that IMP1 overexpression decreases E-cadherin expression, promotes survival of single tumor cell-derived colonospheres and promotes enrichment and maintenance of a population of CD24+CD44+ cells, signifying that IMP1 overexpressing cells display evidence of loss of epithelial identity and enhancement of a tumor-initiating cell phenotype. Taken together, these findings implicate IMP1 as a modulator of tumor growth and provide evidence for a novel role of IMP1 in early events in CRC metastasis.
PMCID: PMC3810836  PMID: 23764754
22.  The molecular features of tongue epithelium treated with the carcinogen 4-nitroquinoline-1-oxide and alcohol as a model for HNSCC 
Carcinogenesis  2013;34(11):2673-2681.
Head and neck squamous cell carcinoma (HNSCC) is the sixth most common type of cancer affecting humans worldwide. To determine the potential mechanisms by which chronic tobacco and alcohol abuse lead to HNSCC of the oral cavity, we have used both the 4-nitroquinoline-1-oxide (4-NQO) murine oral carcinogenesis and the Meadows–Cook alcohol models. In this study, we treated mice with 4-NQO in drinking water for 10 weeks and then administered 20% (w:v) ethanol (EtOH) for another 10 weeks. We observed increased levels and/or activation of signaling proteins [p38 mitogen-activated protein kinase (MAPK), β-catenin and Erk 1/2] that are typically altered during HNSCC initiation in humans. We found that EtOH administration alone increased the expression of p38 MAPK but not Erk 1/2 MAPK. Total β-catenin levels in the tongues increased by 2- to 3-fold after 4-NQO treatment, with or without EtOH. However, EtOH combined with 4-NQO reduced phosphorylated β-catenin levels, whereas 4-NQO treatment alone did not. These data implicate EtOH as a regulator of β-catenin signaling in this HNSCC model. We also utilized K14-CreERTAM; ROSA26 mice to mark permanently stem/progenitor cells in the tongue epithelia. We found that 4-NQO alone and 4-NQO plus EtOH treatment resulted in massive, horizontal expansion of stem/progenitor cell populations arising from single stem cells in the basal layer of the epithelia. This expansion is consistent with carcinogen-associated, symmetric division of stem/progenitor cells. Our data suggest that specific therapeutic targets for prevention of HNSCC of the oral cavity associated with both alcohol and tobacco use are p38 MAPK and β-catenin.
PMCID: PMC3810837  PMID: 23784083
23.  Innate immunity gene polymorphisms and the risk of colorectal neoplasia 
Carcinogenesis  2013;34(11):2512-2520.
Inherited variation in genes that regulate innate immunity and inflammation may contribute to colorectal neoplasia risk. To evaluate this association, we conducted a nested case–control study of 451 colorectal cancer cases, 694 colorectal advanced adenoma cases and 696 controls of European descent within the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial. A total of 935 tag single-nucleotide polymorphisms (SNPs) in 98 genes were evaluated. Logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the association with colorectal neoplasia. Sixteen SNPs were associated with colorectal neoplasia risk at P < 0.01, but after adjustment for multiple testing, only rs2838732 (ITGB2) remained suggestively associated with colorectal neoplasia (ORper T allele = 0.68, 95% CI: 0.57–0.83, P = 7.7 × 10–5, adjusted P = 0.07). ITGB2 codes for the CD18 protein in the integrin beta chain family. The ITGB2 association was stronger for colorectal cancer (ORper T allele = 0.41, 95% CI: 0.30–0.55, P = 2.4 × 10− 9) than for adenoma (ORper T allele = 0.84, 95%CI: 0.69–1.03, P = 0.08), but it did not replicate in the validation study. The ITGB2 rs2838732 association was significantly modified by smoking status (P value for interaction = 0.003). Among never and former smokers, it was inversely associated with colorectal neoplasia (ORper T allele = 0.5, 95% CI: 0.37–0.69 and ORper T allele = 0.72, 95% CI: 0.54–0.95, respectively), but no association was seen among current smokers. Other notable findings were observed for SNPs in BPI/LBP and MYD88. Although the results need to be replicated, our findings suggest that genetic variation in inflammation-related genes may be related to the risk of colorectal neoplasia.
PMCID: PMC3810838  PMID: 23803696
24.  Association of mitochondrial DNA copy number in peripheral blood leukocytes with risk of esophageal adenocarcinoma 
Carcinogenesis  2013;34(11):2521-2524.
Alterations of mitochondrial DNA (mtDNA) have been associated with the risk of a number of human cancers; however, the relationship between mtDNA copy number in peripheral blood leukocytes and the risk of esophageal adenocarcinoma (EAC) has not been reported. In this study, we determined relative mtDNA copy number in peripheral blood leukocytes of 218 EAC cases and 218 frequency-matched controls. We calculated odds ratios and 95% confidence intervals using unconditional logistic regression, adjusting for age, sex and smoking status. MtDNA copy number was significantly lower in cases than in controls (mean ± SD, 1.16 ± 0.30 versus 1.27 ± 0.43, P = 0.002). Dichotomized at the median value of mtDNA copy number in the controls, low mtDNA copy number was significantly associated with an increased risk of EAC (odds ratio: 1.55, 95% confidence interval: 1.05–2.29). A significant dose–response relationship was observed between mtDNA copy number and risk of EAC in quartile analysis. Our results suggest that low mtDNA copy number in peripheral blood leukocytes is associated with increased susceptibility to EAC.
PMCID: PMC3810839  PMID: 23803692
25.  TNFRSF10B polymorphisms and haplotypes associated with increased risk of death in non-small cell lung cancer 
Carcinogenesis  2013;34(11):2525-2530.
Presently, there are few validated biomarkers that can predict survival or treatment response for non-small cell lung cancer (NSCLC) and most are based on tumor markers. Biomarkers based on germ line DNA variations represent a valuable complementary strategy, which could have translational implications by subclassifying patients to tailored, patient-specific treatment. We analyzed single nucleotide polymorphisms (SNPs) in 53 inflammation-related genes among 651 NSCLC patients. Multivariable Cox proportional hazard models, adjusted for lung cancer prognostic factors, were used to assess the association of genotypes and haplotypes with overall survival. Four of the top 15 SNPs associated with survival were located in the TNF-receptor superfamily member 10b (TNFRSF10B) gene. The T-allele of the top ranked SNP (rs11785599) was associated with a 41% increased risk of death (95% confidence interval [CI] = 1.16–1.70) and the other three TNFRSF10B SNPs (rs1047275, rs4460370 and rs883429) exhibited a 35% (95% CI = 1.11–1.65), 29% (95% CI = 1.06–1.57) and 24% (95% CI = 0.99–1.54) increased risk of death, respectively. Haplotype analyses revealed that the most common risk haplotype (TCTT) was associated with a 78% (95% CI = 1.25–2.54) increased risk of death compared with the low-risk haplotype (CGCC). When the data were stratified by treatment, the risk haplotypes exhibited statistically significantly increased risk of death among patients who had surgery only and no statistically significant effects among patients who had surgery and adjuvant chemotherapy. These data suggest that possessing one or more risk alleles in TNFRSF10B is associated with an increased risk of death. Validated germ line biomarkers may have potential important clinical implications by optimizing patient-specific treatment.
PMCID: PMC3810840  PMID: 23839018

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