The cytoskeletal protein Spectrin, beta, non-erythrocytic 1 (SPTBN1), an adapter protein to SMAD3 in TGF-β signaling, may prevent hepatocellular carcinoma (HCC) development by downregulating the expression of signal transducer and activator of transcription 3 (STAT3). To elucidate the as yet undefined mechanisms that regulate this process, we demonstrate that higher levels of STAT3 transcription are found in livers of heterozygous SPTBN1+/– mice as compared to that of wild type mice. We also found increased levels of STAT3 mRNA, STAT3 protein, and p-STAT3 in human HCC cell-lines after knockdown of SPTBN1 or SMAD3, which promoted cell colony formation. Inhibition of STAT3 overrode the increase in cell colony formation due to knockdown of SPTBN1 or SMAD3. We also found that inhibition of SPTBN1 or SMAD3 upregulated STAT3 promoter activity in HCC cell-lines, which is dependent upon the cAMP-response element (CRE) and STAT-binding element (SBE) sites of the STAT3 promoter. Mechanistically, suppression of SPTBN1 and SMAD3 augmented the transcription of STAT3 by upregulating the CRE-binding proteins ATF3 and CREB2 and augmented the binding of those proteins to the regions within or upstream of the CRE site of the STAT3 promoter. Finally, in human HCC tissues, SPTBN1 expression correlated negatively with expression levels of STAT3, ATF3, and CREB2; SMAD3 expression correlated negatively with STAT3 expression; and the level of phosphorylated SMAD3 (p-SMAD3) correlated negatively with ATF3 and CREB2 protein levels. SPTBN1 and SMAD3 collaborate with CRE-binding transcription factors to inhibit STAT3, thereby preventing HCC development.
Genetic mutations in pancreatic ductal adenocarcinoma (PDAC) with critical roles have been well examined. The recent discovery of alterations in genes encoding histone modifiers suggests their possible roles in the complexity of cancer development. We previously reported loss of heterozygosity of the KDM6B gene, which encodes a histone demethylase for trimethylated histone H3 lysine 27, a repressive chromatin mark, in PDAC cells. In this study, we demonstrated that loss of KDM6B enhanced aggressiveness of PDAC cells. KDM6B has been regarded as a tumor suppressor that mediates oncogenic KRAS-induced senescence. Consistently, KDM6B was highly expressed in pancreatic precancerous lesions (pancreatic intraepithelial neoplasms); then, the expression decreased as the malignant grade progressed. We found that knockdown of KDM6B in PDAC cells promoted tumor sphere formation and increased peritoneal dissemination and liver metastasis in vivo. Microarray and chromatin immunoprecipitation analysis implicated CEBPA for aggressiveness induced by KDM6B knockdown. CEBPA knockdown recapitulated the phenotypic change of PDAC cells after KDM6B knockdown, which was reversed by forced expression of C/EBPα. Moreover, similar protein expression patterns of KDM6B and C/EBPα in human PDAC emphasized their functional correlation. Notably, pharmacological inhibition of the H3K27 methylase EZH2 in PDAC cells inhibited tumor sphere formation along with the upregulation of CEBPA expression, and this effect was impaired in KDM6B knockdown cells, highlighting the role for KDM6B in the activation of CEBPA. Together, our results propose a significant role for the KDM6B-C/EBPα axis in the PDAC phenotype.
RECQL4, a member of the RecQ helicase family, is a multifunctional participant in DNA metabolism. RECQL4 protein participates in several functions both in the nucleus and in the cytoplasm of the cell, and mutations in human RECQL4 are associated with three genetic disorders: Rothmund-Thomson, RAPADILINO and Baller-Gerold syndromes. We previously reported that RECQL4 is recruited to laser-induced DNA double-strand breaks (DSB). Here, we have characterized the functional roles of RECQL4 in the non-homologous end joining (NHEJ) pathway of DSB repair. In an in vitro NHEJ assay that depends on the activity of DNA-dependent protein kinase (DNA-PK), extracts from RECQL4 knockdown cells display reduced end-joining activity on DNA substrates with cohesive and non-cohesive ends. Depletion of RECQL4 also reduced the end joining activity on a GFP reporter plasmid in vivo. Knockdown of RECQL4 increased the sensitivity of cells to -irradiation and resulted in accumulation of 53BP1 foci after irradiation, indicating defects in the processing of DSB. We find that RECQL4 interacts with the Ku70/Ku80 heterodimer, part of the DNA-PK complex, via its N-terminal domain. Further, RECQL4 stimulates higher order DNA binding of Ku70/Ku80 to a blunt end DNA substrate. Taken together, these results implicate that RECQL4 participates in the NHEJ pathway of DSB repair via a functional interaction with the Ku70/Ku80 complex. This is the first study to provide both in vitro and in vivo evidence for a role of a RecQ helicase in NHEJ.
Metastatic disease is the leading cause of cancer mortality. Identifying biomarkers and regulatory mechanisms is important toward developing diagnostic and therapeutic tools against metastatic cancer. In this study, we demonstrated that podocalyxin-like 1 (PODXL) is overexpressed in breast tumor cells and increased in lymph node metastatic cancer. Mechanistically, we found that the expression of PODXL was associated with cell motility and invasiveness. Suppression of PODXL in MDA-MB-231 cells reduced lamellipodia formation and focal adhesion kinase (FAK) and paxillin phosphorylation. PODXL knockdown reduced the formation of invadopodia, such as inhibiting the colocalization of F-actin with cortactin and suppressing phosphorylation of cortactin and neural Wiskott–Aldrich syndrome protein. Conversely, overexpression of PODXL in MCF7 cells induced F-actin/cortactin colocalization and enhanced invadopodia formation and activation. Invadopodia activity and tumor invasion in PODXL-knockdown cells are similar to that in cortactin-knockdown cells. We further found that the DTHL motif in PODXL is crucial for regulating cortactin phosphorylation and Rac1/Cdc42 activation. Inhibition of Rac1/Cdc42 impeded PODXL-mediated cortactin activation and FAK and paxillin phosphorylation. Moreover, inhibition of PODXL in MDA-MB-231 cells significantly suppressed tumor colonization in the lungs and distant metastases, similar to those in cortactin-knockdown cells. These findings show that overexpression of PODXL enhanced invadopodia formation and tumor metastasis by inducing Rac1/Cdc42/cortactin signaling network.
5-Aza-2'-deoxycytidine (5-azaCdR) not only inhibits growth of non-invasive breast cancer cells but also increases their invasiveness through induction of pro-metastatic genes. Methylated DNA binding protein 2 (MBD2) is involved in silencing methylated tumor suppressor genes as well as activation of pro-metastatic genes. In this study, we show that a combination of MBD2 depletion and DNA methyltransferases (DNMT) inhibition in breast cancer cells results in a combined effect in vitro and in vivo, enhancing tumor growth arrest on one hand, while inhibiting invasiveness triggered by 5-azaCdR on the other hand. The combined treatment of MBD2 depletion and 5-azaCdR suppresses and augments distinct gene networks that are induced by DNMT inhibition alone. These data point to a potential new approach in targeting the DNA methylation machinery by combination of MBD2 and DNMT inhibitors.
Estetrol (E4) is a fetal estrogen with estrogenic effects on reproductive organs and bone in preclinical models and in postmenopausal women. However, E4 exerts antiestrogenic effects on breast cancer (BC) cell growth in vitro and in vivo. We have investigated the effect of 14 days preoperative treatment with 20mg E4 per day on tumor proliferation markers, sex steroid receptor expression and endocrine parameters in a prospective, randomized, placebo-controlled, preoperative window trial in 30 pre- and post-menopausal women with estrogen-receptor positive early BC. E4 had a significant pro-apoptotic effect on tumor tissue, whereas Ki67 expression remained unchanged in both pre- and post-menopausal women. E4 increased sex-hormone-binding globulin significantly thereby reducing the concentrations of bioavailable estradiol. Follicle-stimulating hormone levels decreased in postmenopausal women only and luteinizing hormone levels remained unchanged. Systemic insulin growth factor-1 levels decreased significantly. Intratumoral epithelial ERα expression decreased significantly and a trend was found towards an increased expression of ERβ. This clinical data support the preclinical findings that E4 has antiestrogenic effects on BC cells, whereas earlier studies have shown that E4 has estrogenic effects on reproductive tissues and bone. Further clinical studies seem acceptable and are needed to confirm the safety and efficacy of E4 for the breast in hormone replacement therapy, including hormone replacement therapy in women who have or have had BC, especially in those BC patients treated with aromatase inhibitors and suffering from serious complaints due to estrogen deficiency.
Oncogenic fusion of the RET (rearranged during transfection) gene was recently identified as a novel driver gene aberration not only for the development of thyroid carcinoma but also of lung adenocarcinoma, the most frequent histological type of lung cancer. This study constructed and analyzed transgenic mice expressing KIF5B-RET, the predominant form of RET fusion gene specific for lung adenocarcinoma, under the control of the SPC (surfactant protein C) gene promoter. The mice expressed the KIF5B-RET fusion gene specifically in lung alveolar epithelial cells, and developed multiple tumors in the lungs. Treatment of the transgenic mice with vandetanib, which is a RET tyrosine kinase inhibitor approved by the U.S. Food and Drug Administration for the treatment of thyroid carcinoma, for 8 or 20 weeks led to a marked reduction in the number of lung tumors (3.3 versus 0 and 6.5 versus 0.2 per tissue section, respectively; P < 0.01, t-test). The results suggest that the RET fusion functions as a driver for the development of lung tumors, whose growth is inhibited by RET tyrosine kinase inhibitors.
Acquired chemoresistance is a major challenge in cancer therapy. While the oncoprotein Mucin-1 (MUC1) performs multiple roles in the development of diverse human tumors, whether MUC1 is involved in acquired chemoresistance has not been determined. Using an acquired chemoresistance lung cancer cell model, we show that MUC1 expression was substantially increased in cells with acquired apoptosis resistance (AR). Knockdown of MUC1 expression effectively increased the sensitivity of these cells to the apoptotic cytotoxicity of anticancer therapeutics, suggesting that MUC1 contributes to acquired chemoresistance. Decreased catalase expression and increased cellular reactive oxygen species (ROS) accumulation were found to be associated with MUC1 overexpression. Scavenging ROS with butylated hydroxyanisole or supplying exogenous catalase dramatically suppressed MUC1 expression through destabilizing MUC1 protein, suggesting that reduced catalase expression mediated ROS accumulation is accounted for MUC1 overexpression. Further, we found that increased miR-551b expression in the AR cells inhibited the expression of catalase and potentiated ROS accumulation and MUC1 expression. Finally, by manipulating MUC1 expression, we found that MUC1 promotes EGFR-mediated activation of the cell survival cascade involving Akt/c-FLIP/COX-2 in order to protect cancer cells from responding to anticancer agents. Thus, our results establish a pathway consisting of miR-551b/catalase/ROS that results in MUC1 overexpression, and intervention against this pathway could be exploited to overcome acquired chemoresistance.
Growth hormone (GH) and/or insulin-like growth factor I (IGF-I) are thought to promote breast cancer based on reports showing circulating IGF-I levels correlate, in epidemiological studies, with breast cancer risk. Also, mouse models with developmental GH/IGF-I deficiency/resistance are less susceptible to genetic- or chemical-induced mammary tumorigenesis. However, given the metabolic properties of GH, medical strategies have been considered to raise GH to improve body composition and metabolic function in elderly and obese patients. Since hyperlipidemia, inflammation, insulin resistance and obesity increase breast cancer risk, elevating GH may serve to exacerbate cancer progression. To better understand the role GH/IGF-I plays in tumor formation, this study used unique mouse models to determine if reducing GH/IGF-I in adults protects against 7,12-dimethylbenz[α]anthracene (DMBA)-induced mammary tumor development, and if moderate elevations in endogenous GH/IGF-I alter DMBA-induced tumorigenesis in mice fed a standard-chow diet or in mice with altered metabolic function due to high-fat feeding. We observed that adult-onset isolated GH-deficient mice, which also have reduced IGF-I levels, were less susceptible to DMBA-treatment. Specifically, fewer adult-onset isolated GH-deficient mice developed mammary tumors compared with GH-replete controls. In contrast, chow-fed mice with elevated endogenous GH/IGF-I (HiGH mice) were not more susceptible to DMBA-treatment. However, high-fat-fed, HiGH mice showed reduced tumor latency and increased tumor incidence compared with diet-matched controls. These results further support a role of GH/IGF-I in regulating mammary tumorigenesis but suggest the ultimate consequences of GH/IGF-I on breast tumor development are dependent on the diet and/or metabolic status.
Nur77, an orphan member of the nuclear receptor superfamily, has been implicated in tumorigenesis. However, its contributions to colorectal cancer (CRC) invasion and metastasis are largely under characterized. Here, we present the first evidence that the invasion and metastasis of CRC is regulated by Nur77. High expression of Nur77 was observed in clinical CRC tissues, and this elevated expression was significantly associated with advanced tumor, lymph nodes, distant metastasis stage (P = 0.003), lymph node metastasis (P = 0.001) and poor survival (P = 0.03). Overexpression of Nur77 in CRC cells enhanced cell invasion in vitro, whereas knockdown of Nur77 diminished cell invasion and metastasis both in vitro and in vivo. In studying the possible mechanism by which overexpression of Nur77 contributes to CRC invasion and metastasis, we observed that the nuclear protein Nur77 promoted the expression of matrix metalloproteinase (MMP)-9, a novel downstream target of Nur77, and subsequently decreased the expression of E-cadherin. Examination of clinical samples further showed that Nur77 expression is positively correlated with MMP-9, whereas negatively correlated with E-cadherin. Interestingly, Nur77-mediated CRC invasion via MMP-9 and E-cadherin could be mimicked by some metastasis-inducible factors including hypoxia and prostaglandin E2. Collectively, our study demonstrated that Nur77 could promote the invasion and metastasis of CRC cells through regulation of MMP-9/E-cadherin signaling. These observations provide a possible new strategy for potentially treating or preventing the metastasis of CRC through targeting of Nur77.
Granulin-epithelin precursor (GEP) is a pluripotent secretory growth factor which promotes cancer progression in a number of human cancers. However, how cancer cells interact with GEP remains unknown. In this study, we aimed to identify the cell surface-binding partner of GEP on liver cancer cells. Human recombinant GEP (rGEP) was expressed and purified to homogeneity. The rGEP was shown to trigger phosphorylation of AKT and ERK1/2 in liver cancer cells. We demonstrated cell surface attachment of rGEP, which was blocked by prebinding of platelet-derived growth factor-AA, platelet-derived growth factor-BB and fibroblast growth factor-2. Therefore, heparan sulfate (HS) had been reasoned as the binding partner of rGEP. Heparinase digestion validated the role of HS on supporting the attachment. The heparin-binding domain of GEP was mapped to RRH(555-557) in the C-terminal region. Suppression of the HS polymerase exostosin-1 reduced the rGEP binding and rGEP-mediated signaling transduction. Suppression of a specific HS proteoglycan, glypican-3, also showed a partial reduction of rGEP binding and an inhibition on rGEP-mediated activation of AKT. Furthermore, glypican-3 was shown to correlate with the expressions of GEP in clinical samples (Spearman’s = 0.363, P = 0.001). This study identified HS, partly through glypican-3, as a novel binding partner of GEP on the surface of liver cancer cells.
Cancer susceptibility varies between people, affected by genotoxic exposures, genetic makeup and physiological state. Yet, how these factors interact among each other to define cancer risk is largely unknown. Here, we uncover the interactive effects of genetical, environmental and physiological factors on genome rearrangements driven by homologous recombination (HR). Using FYDR mice to quantify HR-driven rearrangements in pancreas tissue, we show that DNA methylation damage (induced by methylnitrosourea) and cell proliferation (induced by thyroid hormone) each induce HR and together act synergistically to induce HR-driven rearrangements in vivo. These results imply that developmental or regenerative proliferation as well as mitogenic exposures may sensitize tissues to DNA damaging exposures. We exploited mice genetically deficient in alkyl-adenine DNA glycosylase (Aag) to analyse the relative contributions of unrepaired DNA base lesions versus intermediates formed during base excision repair (BER). Remarkably, results show that, in the pancreas, Aag is a major driver of spontaneous HR, indicating that BER intermediates (including abasic sites and single strand breaks) are more recombinogenic than the spontaneous base lesions removed by Aag. Given that mammals have about a dozen DNA glycosylases, these results point to BER as a major source of pressure on the HR pathway in vivo. Taken together, methylation damage, cell proliferation and Aag interact to define the risk of HR-driven sequence rearrangements in vivo. These data identify important sources of sequence changes in a cancer-relevant organ, and advance the effort to identify populations at high-risk for cancer.
Gem is a small guanosine triphosphate (GTP)-binding protein within the Ras superfamily, involved in the regulation of voltage-gated calcium channel activity and cytoskeleton reorganization. Gem overexpression leads to stress fiber disruption, actin and cell shape remodeling and neurite elongation in interphase cells. In this study, we show that Gem plays a crucial role in the regulation of cortical actin cytoskeleton that undergoes active remodeling during mitosis. Ectopic expression of Gem leads to cortical actin disruption and spindle mispositioning during metaphase. The regulation of spindle positioning by Gem involves its downstream effector Gmip. Knockdown of Gmip rescued Gem-induced spindle phenotype, although both Gem and Gmip accumulated at the cell cortex. In addition, we implicated RhoA GTPase as an important effector of Gem/Gmip signaling. Inactivation of RhoA by overexpressing dominant-negative mutant prevented normal spindle positioning. Introduction of active RhoA rescued the actin and spindle positioning defects caused by Gem or Gmip overexpression. These findings demonstrate a new role of Gem/Gmip/RhoA signaling in cortical actin regulation during early mitotic stages.
Only a fraction of colorectal cancer heritability is explained by known risk-conferring genetic variation. This study was designed to identify novel risk alleles in Europeans. We conducted a genome-wide association study (GWAS) meta-analysis of colorectal cancer in participants from a population-based case–control study in Israel (n = 1616 cases, 1329 controls) and a consortium study from the Colon Cancer Family Registry (n = 1977 cases, 999 controls). We used a two-stage (discovery–replication) GWAS design, followed by a joint meta-analysis. A combined analysis identified a novel susceptibility locus that reached genome-wide significance on chromosome 4q32.2 [rs35509282, risk allele = A (minor allele frequency = 0.09); odds ratio (OR) per risk allele = 1.53; P value = 8.2 x 10–9; nearest gene = FSTL5]. The direction of the association was consistent across studies. In addition, we confirmed that 14 of 29 previously identified susceptibility variants were significantly associated with risk of colorectal cancer in this study. Genetic variation on chromosome 4q32.2 is significantly associated with risk of colorectal cancer in Ashkenazi Jews and Europeans in this study.
Previous studies indicated that smoking exposure is associated with an increased risk of breast cancer, and α9-nicotine acetylcholine receptors (α9-nAChRs) are involved in breast tumorigenesis. However, no studies have explored the joint effect of α9-nAChRs (CHRNA9) genes and cigarette smoking exposure on breast cancer risk. A case–control study was conducted on 737 breast cancer patients and 719 age-matched healthy controls. Three single-nucleotide polymorphisms (SNPs) of CHRNA9 located in the promoter region were genotyped and compared between cases and controls to identify those SNPs associated with breast cancer susceptibility. A dual-luciferase reporter assay was used to analyze the promoter activities of these SNPs of the CHRNA9 gene. After a Bonferroni correction, the G allele of the CHRNA9 rs7329797 SNP was significantly associated with an increased risk of developing breast cancer compared with A/A genotype carriers (odds ratio, 1.8; 95% confidence interval, 1.2–2.6). A multiplicative interaction between passive smoking exposure and the CHRNA9 rs73229797 SNP on the risk of breast malignancy was observed. A functional assay further showed that rs73229797 was associated with increased promoter activity of the CHRNA9 gene. Our findings support a significant interaction effect existing between the CHRNA9 gene and smoking exposure on the risk of breast cancer development.
Nicotine metabolism influences smoking behavior and differences in metabolism probably contribute to ethnic variability in lung cancer risk. We report here on the proportion of nicotine metabolism by cytochrome P450 2A6-catalyzed C-oxidation, UDP-glucuronosyl transferase 2B10 (UGT2B10)-catalyzed N-glucuronidation and flavin monooxygenase 3-catalyzed N-oxidation in five ethnic/racial groups and the role of UGT2B10 genotype on the metabolic patterns observed. Nicotine and its metabolites were quantified in urine from African American (AA, n = 364), Native Hawaiian (NH, n = 311), White (n = 437), Latino (LA, n = 453) and Japanese American (JA, n = 674) smokers. Total nicotine equivalents, the sum of nicotine and six metabolites, and nicotine metabolism phenotypes were calculated. The relationship of UGT2B10 genotype to nicotine metabolic pathways was determined for each group; geometric means were computed and adjusted for age, sex, creatinine, and body mass index. Nicotine metabolism patterns were unique across the groups, C-oxidation was lowest in JA and NH (P < 0.0001), and N-glucuronidation lowest in AA (P < 0.0001). There was no difference in C-oxidation among Whites and AA and LA. Nicotine and cotinine glucuronide ratios were 2- and 3-fold lower in AA compared with Whites. Two UGT variants, a missense mutation (Asp67Tyr, rs61750900) and a splice variant (rs116294140) accounted for 33% of the variation in glucuronidation. In AA, the splice variant accounted for the majority of the reduced nicotine glucuronidation. UGT2B10 variant allele carriers had increased levels of C-oxidation (P = 0.0099). Our data indicate that the relative importance of nicotine metabolic pathways varies by ethnicity, and all pathways should be considered when characterizing the role of nicotine metabolism on smoking behavior and cancer risk.
Cytochrome P450 1B1 (CYP1B1) is an enzyme that has a unique tumor-specific pattern of expression and is capable of bioactivating a wide range of carcinogenic compounds. We have reported previously that coordinated upregulation of CYP1B1 by inflammatory cytokines, such as tumor necrosis factor-α (TNF-α) and the aryl hydrocarbon receptor ligands, may increase bioactivation of promutagens, such as benzo[a]pyrene (BaP) in epithelial cells. Here, we extend those studies by describing a novel mechanism participating in the regulation of CYP1B1 expression, which involves activation of the p38 mitogen-activated protein kinase (p38) and mitogen- and stress-activated protein kinase 1 (MSK1). Using inhibitors of p38 and MSKs, as well as mouse embryonic cells derived from p38α-deficient and MSK1/2 double knockout mice, we show here that TNF-α potentiates CYP1B1 upregulation via the p38/MSK1 kinase cascade. Effects of this inflammatory cytokine on CYP1B1 expression further involve the positive transcription elongation factor b (P-TEFb). The inhibition of the P-TEFb subunit, cyclin-dependent kinase 9 (CDK9), which phosphorylates RNA polymerase II (RNAPII), prevented the enhanced CYP1B1 induction by a combination of BaP and inflammatory cytokine. Furthermore, using chromatin immunoprecipitation assays, we found that cotreatment of epithelial cells with TNF-α and BaP resulted in enhanced recruitment of both CDK9 and RNAPII to the Cyp1b1 gene promoter. Overall, these results have implications concerning the contribution of inflammatory factors to carcinogenesis, since enhanced CYP1B1 induction during inflammation may alter metabolism of exogenous carcinogens, as well as endogenous CYP1B1 substrates playing role in tumor development.
Accumulating evidence suggests that β-catenin signaling in breast cancer stem cells (CSCs) is closely correlated to chemoresistance and adenosine triphosphate (ATP)-binding cassette subfamily G2 (ABCG2) expression. Targeting the aberrant β-catenin signaling in CSCs has become a promising strategy to improve chemosensitivity in cancer treatment. In a pilot screening study, we found that the natural compound isoliquiritigenin (ISL) blocked β-catenin transcription activity with the highest inhibition ratio. Here, we investigated the chemosensitizing effects of ISL on breast CSCs and the underlying mechanisms regulating the β-catenin pathway. ISL could have synergistic effects with chemotherapeutic drugs to inhibit breast cancer cell proliferation and colony formation. In addition, ISL could significantly limit the side population and CSC ratios in breast cancer cells, accompanied by inhibited self-renewal and multidifferentiation abilities. A mechanistic study revealed that ISL could inhibit β-catenin/ABCG2 signaling by activating the proteasome degradation pathway. The drug affinity responsive target stability strategy further identified GRP78 as the direct target of ISL. Subsequent molecular docking analysis and functional studies demonstrated that ISL could dock into the ATP domain of GRP78 and thereby inhibit its ATPase activity, resulting in its dissociation from β-catenin. An in vivo study also suggested that ISL could chemosensitize breast CSCs via the GRP78/β-catenin/ABCG2 pathway, with little toxicity in normal tissues and mammary stem cells. Taken together, the data from this study not only suggest ISL as a natural candidate to enhance breast CSC chemosensitivity but also highlight the significance of GRP78 in mediating cancer drug resistance and β-catenin signaling in CSCs.
Nuclear factors of activated T cells (NFAT) are critical modulators of cancer cell growth and survival. However, the mechanisms of their oncogenic dysregulation and strategies for targeting in tumors remain elusive. Here, we report coupling of anti- apoptotic NFAT (NFAT2) activation to cholesterol-enriched lipid raft microdomains of malignant melanoma cells and interruption of this pathway by the aminobisphosphonate zoledronic acid (Zol). The pathway was indicated by capability of Zol to promote apoptosis and to retard in vivo outgrowth of tumorigenic melanoma cell variants through inhibition of permanently active NFAT2. NFAT2 inhibition resulted from disintegration of cholesterol-enriched rafts due to reduction of cellular cholesterol by Zol. Mechanistically, raft disruption abolished raft-localized robust store-operated Ca2+ (SOC) entry, blocking constitutive activation of protein kinase B/Akt (PKB) and thereby reactivating the NFAT repressor glycogen synthase kinase 3β (GSK3β). Pro-apoptotic inactivation of NFAT2 also followed reactivation of GSK3β by direct inhibition of PKB or SOC, whereas GSK3β blockade prevented Zol-induced NFAT2 inhibition and cell death. The rescuing effect of GSK3β blockade was reproduced by recovery of entire SOC/PKB/GSK3β cascade after reconstitution of rafts by cholesterol replenishment of Zol-treated tumorigenic cells. Remarkably, these malignant cells displayed higher cholesterol and lipid raft content than non-tumorigenic cells, which expressed weak SOC, PKB and NFAT2 activities and resisted raft-ablating action of Zol. Together, the results underscore the functional relevance of amplified melanoma rafts for tumor-promoting NFAT2 signaling and reveal these distinctive microdomains as a target for in vitro and in vivo demise of tumorigenic cells through NFAT2 inhibition by the clinical agent Zol.
The tumor suppressor p53 is the most frequently mutated gene in human cancers, mutated in 25–30% of breast cancers. However, mutation rates differ according to breast cancer subtype, being more prevalent in aggressive estrogen receptor-negative tumors and basal-like and HER2-amplified subtypes. This heterogeneity suggests that p53 may function differently across breast cancer subtypes. We used RNAi-mediated p53 knockdown (KD) and antagomir-mediated KD of microRNAs to study how gene expression and cellular response to p53 loss differ in luminal versus basal-like breast cancer. As expected, p53 loss caused downregulation of established p53 targets (e.g. p21 and miR-34 family) and increased proliferation in both luminal and basal-like cell lines. However, some p53-dependent changes were subtype specific, including expression of miR-134, miR-146a and miR-181b. To study the cellular response to miR-146a upregulation in p53-impaired basal-like lines, antagomir KD of miR-146a was performed. KD of miR-146a caused decreased proliferation and increased apoptosis, effectively ablating the effects of p53 loss. Furthermore, we found that miR-146a upregulation decreased NF-B expression and downregulated the NF-B-dependent extrinsic apoptotic pathway (including tumor necrosis factor, FADD and TRADD) and antagomir-mediated miR-146a KD restored expression of these components, suggesting a plausible mechanism for miR-146a-dependent cellular responses. These findings are relevant to human basal-like tumor progression in vivo, since miR-146a is highly expressed in p53 mutant basal-like breast cancers. These findings suggest that targeting miR-146a expression may have value for altering the aggressiveness of p53 mutant basal-like tumors.
The forkhead box transcription factor A2 (FOXA2) is a member of the hepatocyte nuclear factor family and plays an important role in liver development and metabolic homeostasis, but its role in the metastasis of hepatocellular carcinoma (HCC) has not been evaluated. In this study, we found that the expression of FOXA2 was decreased in 68.1% (49/72) of human HCC tissues compared with their paired non-cancerous adjacent tissues. Clinicopathological analysis revealed that reduced FOXA2 expression was correlated with aggressive characteristics (venous invasion, poor differentiation, high tumor node metastasis grade). FOXA2 level was even lower in portal vein tumor thrombus compared with primary tumor tissues and correlated with epithelial–mesenchymal transition in HCC cells. Overexpression of FOXA2 inhibited migration and invasion of Focus cells, whereas knockdown of FOXA2 in HepG2 showed the opposite effect. Moreover, upregulation of FOXA2 suppressed HCC metastasis to bone, brain and lung in two distinct mouse models. Finally, we proved that FOXA2 repressed the transcription of matrix metalloproteinase (MMP)-9 and exerted its antimetastasis effect partially through downregulation of MMP-9. In conclusion, our findings indicate that FOXA2 plays a critical role in HCC metastasis and may serve as a novel therapeutic target for HCC.
Cytochrome P450 (P450) enzymes encoded by the mouse Cyp2abfgs gene cluster are preferentially expressed in the respiratory tract. Previous studies have demonstrated that pulmonary P450-mediated bioactivation is necessary for lung tumorigenesis induced by the tobacco-specific lung procarcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and that CYP2A5 mediates a noteworthy fraction, but not all, of NNK bioactivation in the lung. The aim of this study was to determine whether other P450s encoded by the Cyp2abfgs gene cluster also play significant roles in NNK lung tumorigenesis. A novel Cyp2abfgs-null mouse was generated, in which all Cyp2a, 2b, 2g, 2f and 2s genes are deleted. The Cyp2abfgs-null mouse was viable, fertile and without discernible physiological abnormalities or compensatory increases in the expression of other P450s. NNK bioactivation in vitro and NNK-induced DNA adduction and lung tumorigenesis in vivo were determined for wild-type (WT) and Cyp2abfgs-null mice; the results were compared with previous findings from Cyp2a5-null mice. The Cyp2abfgs-null mice exhibited significantly lower rates of NNK bioactivation in lung and liver microsomes, compared with either WT or Cyp2a5-null mice. The levels of lung O6-methyl guanine DNA adduct were also substantially reduced in Cyp2abfgs-null mice, compared with either WT or Cyp2a5-null mice. Moreover, the Cyp2abfgs-null mice were largely resistant to NNK-induced lung tumorigenesis at both low (50mg/kg) and high (200mg/kg) NNK doses, in contrast to the WT or Cyp2a5-null mice. These results indicate for the first time that, collectively, the CYP2A, 2B, 2F, 2G, and 2S enzymes are indispensable for NNK-induced lung tumorigenesis.
Poly (ADP-ribose) polymerase (PARP) is involved in key cellular processes such as DNA replication and repair, gene transcription, cell proliferation and apoptosis. The role of PARP-1 in prostate cancer development and progression is not fully understood. The present study investigated the function of PARP-1 in prostate growth and tumorigenesis in vivo. Functional inactivation of PARP-1 by gene-targeted deletion led to a significant reduction in the prostate gland size in young PARP-1–/– mice (6 weeks) compared with wild-type (WT) littermates. To determine the effect of PARP-1 functional loss on prostate cancer onset, PARP-1–/– mice were crossed with the transgenic adenocarcinoma of the mouse prostate (TRAMP) mice. Pathological assessment of prostate tumors revealed that TRAMP+/–, PARP-1–/– mice exhibited higher grade prostate tumors compared with TRAMP+/– PARP-1+/+ (16–28 weeks) that was associated with a significantly increased proliferative index and decreased apoptosis among the epithelial cells in TRAMP+/– PARP-1–/– prostate tumors. Furthermore tumors harboring PARP-1 loss, exhibited a downregulation of nuclear androgen receptor. Impairing PARP-1 led to increased levels of transforming growth factor-β (TGF-β) and Smads that correlated with induction of epithelial–mesenchymal transition (EMT), as established by loss of E-cadherin and β-catenin and upregulation of N-cadherin and ZEB-1. Our findings suggest that impaired PARP-1 function promotes prostate tumorigenesis in vivo via TGF-β-induced EMT. Defining the EMT control by PARP-1 during prostate cancer progression is of translational significance for optimizing PARP-1 therapeutic targeting and predicting response in metastatic castration-resistant prostate cancer.
Although the etiology of squamous cell carcinomas of the oral mucosa is well understood, the cellular origin and the exact molecular mechanisms leading to their formation are not. Previously, we observed the coordinated loss of E-cadherin (CDH1) and transforming growth factor beta receptor II (TGFBR2) in esophageal squamous tumors. To investigate if the coordinated loss of Cdh1 and Tgfbr2 is sufficient to induce tumorigenesis in vivo, we developed two mouse models targeting ablation of both genes constitutively or inducibly in the oral–esophageal epithelium. We show that the loss of both Cdh1 and Tgfbr2 in both models is sufficient to induce squamous cell carcinomas with animals succumbing to the invasive disease by 18 months of age. Advanced tumors have the ability to invade regional lymph nodes and to establish distant pulmonary metastasis. The mouse tumors showed molecular characteristics of human tumors such as overexpression of Cyclin D1. We addressed the question whether TGFβ signaling may target known stem cell markers and thereby influence tumorigenesis. From our mouse and human models, we conclude that TGFβ signaling regulates key aspects of stemness and quiescence in vitro and in vivo. This provides a new explanation for the importance of TGFβ in mucosal homeostasis.
Promoter methylation of the transcription factor PRDM14 (PRDI-BF1 and RIZ domain containing 14) represents a highly frequent event in human papillomavirus (HPV)-induced cervical cancers and cancer precursor lesions. Here, we aimed to assess the functional consequences of PRDM14 promoter methylation in HPV-induced carcinogenesis. PRDM14 promoter methylation, expression and consequences of ectopic PRDM14 expression were studied in HPV16-positive cervical and oral cancer cell lines (SiHa, CaSki and 93VU147T), human embryonic kidney 293 (HEK293T) cells and primary human foreskin keratinocytes (HFK). PRDM14 mRNA expression was restricted to HEK293T and HFK cells, and could be upregulated in SiHa cells upon DNA methylation inhibition. Ectopic expression of PRDM14 in SiHa, CaSki and 93VU147T cells resulted in significantly more apoptotic cells, as measured by annexin V labelling, compared to HEK293T and HFK cells. MRNA profiling of 41 apoptosis regulators identified NOXA and PUMA as candidate target genes involved in PRDM14-mediated apoptosis induction. Full-length PRDM14 transactivated both NOXA and PUMA promoters. Transactivation was abolished upon deletion of the PRDM14 DNA binding domain. This suggests that NOXA and PUMA expression is directly regulated by PRDM14, which in case of NOXA was linked to a consensus PRDM14 binding motif in the promoter region. Taken together, these results suggest that PRDM14 acts as a regulator of NOXA and PUMA-mediated apoptosis induction, thereby providing evidence for a tumour suppressive role in HPV-induced carcinogenesis. The contribution of methylation-mediated gene silencing of PRDM14 to apoptosis evasion in HPV-positive cancer cells offers novel therapeutic options for HPV-induced cancers.
Helicobacter pylori CagA directly injected by the bacterium into epithelial cells via a type IV secretion system, leads to cellular changes such as morphology, apoptosis, proliferation and cell motility, and stimulates gastric carcinogenesis. We investigated the effects of cytotoxin-associated gene A (CagA) and gastrokine 1 (GKN1) on cell proliferation, apoptosis, reactive oxygen species (ROS) production, epithelial–mesenchymal transition (EMT) and cell migration in CagA- or GKN1-transfected gastric epithelial cells and mucosal tissues from humans and mice infected with H.pylori. On the molecular level, H.pylori CagA induced increased cell proliferation, ROS production, antiapoptotic activity, cell migration and invasion. Moreover, CagA induced activation of NF-B and PI3K/Akt signaling pathways and EMT-related proteins. In addition, H.pylori CagA reduced GKN1 gene copy number and expression in gastric cells and mucosal tissues of humans and mice. However, GKN1 overexpression successfully suppressed the carcinogenic effects of CagA through binding to CagA. These results suggest that GKN1 might be a target to inhibit the effects from H.pylori CagA.