Signal transducers and activators of transcription 5b activation enhances hepatocellular carcinoma aggressiveness through induction of epithelial-mesenchymal transition

Hepatitis B virus X protein promotes hepatoma cell invasion and metastasis by stabilizing Snail protein

A high incidence of tumor recurrence and metastasis has been reported in hepatocellular carcinoma (HCC) patients with chronic hepatitis B virus (HBV) infection. Although the pathological relevance and significance of hepatitis B virus X protein (HBx) in HBV-associated hepatocarcinogenesis attracted much attention in recent years, the role and molecular mechanism for HBx in hepatoma invasion and metastasis remains poorly understood. In the present study, we found that HBx expression could induce epithelial-mesenchymal transition in hepatoma and hepatic cells. This effect was shown due to stabilized Snail protein through activating the phosphatidylinositol 3-kinase/protein kinase B/glycogen synthase kinase-3β (PI3K/AKT/GSK-3β) signal pathway by HBx expression. Functional studies revealed that HBx expression could enhance hepatoma cell migration and invasion in vitro. Moreover, stable HBx expression could also facilitate intrahepatic and distant lung metastasis of HCC in a nude mice tumor metastasis model in vivo. The correlation between increased PI3K/AKT/GSK-3β signaling with elevated Snail protein level was also observed in HCC tumor tissues with intrahepatic metastasis or chronic HBV infection. These results revealed a novel function of HBx in promoting epithelial-mesenchymal transition through Snail protein stabilization by activating PI3K/AKT/GSK-3β signaling, thus facilitating tumor invasion and metastasis during HCC progression. This could provide a putative molecular mechanism for tumor recurrence and metastasis in HBV-associated HCC patients.

Hepatic growth hormone and glucocorticoid receptor signaling in body growth, steatosis and metabolic liver cancer development

Growth hormone (GH) and glucocorticoids (GCs) are involved in the control of processes that are essential for the maintenance of vital body functions including energy supply and growth control. GH and GCs have been well characterized to regulate systemic energy homeostasis, particular during certain conditions of physical stress. However, dysfunctional signaling in both pathways is linked to various metabolic disorders associated with aberrant carbohydrate and lipid metabolism. In liver, GH-dependent activation of the transcription factor signal transducer and activator of transcription (STAT) 5 controls a variety of physiologic functions within hepatocytes. Similarly, GCs, through activation of the glucocorticoid receptor (GR), influence many important liver functions such as gluconeogenesis. Studies in hepatic Stat5 or GR knockout mice have revealed that they similarly control liver function on their target gene level and indeed, the GR functions often as a cofactor of STAT5 for GH-induced genes. Gene sets, which require physical STAT5-GR interaction, include those controlling body growth and maturation. More recently, it has become evident that impairment of GH-STAT5 signaling in different experimental models correlates with metabolic liver disease, ranging from hepatic steatosis to hepatocellular carcinoma (HCC). While GH-activated STAT5 has a protective role in chronic liver disease, experimental disruption of GC-GR signaling rather seems to ameliorate metabolic disorders under metabolic challenge. In this review, we focus on the current knowledge about hepatic GH-STAT5 and GC-GR signaling in body growth, metabolism, and protection from fatty liver disease and HCC development.

Upregulation of SATB1 promotes tumor growth and metastasis in liver cancer

BACKGROUND

Special AT-rich binding protein-1 (SATB1) reprograms chromatin organization and transcription profiles to promote tumour growth and metastasis.

AIMS

This study aimed to confirm the effects of SATB1 on the growth and metastasis of liver cancer and its specific regulation mechanism.

METHODS

SATB1 expression was evaluated in human hepatoma tissue, adjacent noncancerous tissue and seven kinds of liver cancer cell lines. Cell cycle, cell proliferation, apoptosis and epithelial-mesenchymal transition (EMT) was investigated after enhanced or silenced expression of SATB1. The regulatory action of SATB1 on the expression of genes that are known to regulate cell cycle progression, apoptosis and EMT and the specific apoptotic pathway on which it acts were further analysed. Nude mice that received subcutaneous implantation were used to study the effects of SATB1 on tumour growth in vivo.

RESULTS

Our data show that the high expression of SATB1 was observed in the human hepatocellular carcinoma tissue (26/45) and liver cancer cell lines with high metastatic potential. SATB1 upregulated CDK4 and downregulated p16 (INK) (4A) to promote cell cycle progression and cell proliferation and prevented apoptosis by inhibiting the FADD-caspase-8-caspase-3 death receptor-mediated apoptosis pathway. SATB1 also induced EMT concomitant with increased expression of Snail1, Slug, Twist and vimentin and decreased expression of E-cadherin, tight junction protein ZO-1 and desmoplakin. SATB1 promoted the growth of tumour in vivo.

CONCLUSION

These data suggest that the SATB1 gene may play an important role in the development and progression of liver cancer by regulation of genes related to cell cycle progression, apoptosis and EMT.

NSC 74859 enhances doxorubicin cytotoxicity via inhibition of epithelial-mesenchymal transition in hepatocellular carcinoma cells

Doxorubicin-based therapy is not effective for the treatment of hepatocellular carcinomas (HCCs), which often undergo epithelial-mesenchymal transition (EMT) during tumor progression. Activation of signal transducer and activator of transcription 3 (STAT3) is associated with chemosensitivity and may contribute to EMT during HCC chemotherapy. Low doses of NSC 78459 (a novel STAT3 inhibitor) have little effect on HCC cell proliferation, but efficiently inhibit STAT3. HuH-7, Hep3B, and HepG2 cells, with epithelial phenotypes, show significantly enhanced doxorubicin cytotoxicity following co-treatment with NSC 74859, whereas mesenchymal SNU-449 cells show no such enhancement. NSC 74859 inhibits STAT3 activity and suppressed doxorubicin-induced EMT in epithelial HCC cells. siRNA-mediated STAT3 knockdown resulted in EMT inhibition, which led to attenuation of NSC 74859-mediated chemosensitivity. Our data indicate NSC 74859 co-administration enhances doxorubicin cytotoxicity by inhibiting STAT3 in epithelial HCC cells. STAT3 deactivation and associated EMT attenuation contribute to the synergistic anti-tumor effects of combined NSC 74859/doxorubicin therapy.

Growth-hormone-induced signal transducer and activator of transcription 5 signaling causes gigantism, inflammation, and premature death but protects mice from aggressive liver cancer

Persistently high levels of growth hormone (GH) can cause liver cancer. GH activates multiple signal-transduction pathways, among them janus kinase (JAK) 2-signal transducer and activator of transcription (STAT) 5 (signal transducer and activator of transcription 5). Both hyperactivation and deletion of STAT5 in hepatocytes have been implicated in the development of hepatocellular carcinoma (HCC); nevertheless, the role of STAT5 in the development of HCC as a result of high GH levels remains enigmatic. Thus, we crossed a mouse model of gigantism and inflammatory liver cancer caused by hyperactivated GH signaling (GH(tg) ) to mice with hepatic deletion of STAT5 (STAT5(Δhep) ). Unlike GH(tg) mice, GH(tg) STAT5(Δhep) animals did not display gigantism. Moreover, the premature mortality, which was associated with chronic inflammation, as well as the pathologic alterations of hepatocytes observed in GH(tg) mice, were not observed in GH(tg) animals lacking STAT5. Strikingly, loss of hepatic STAT5 proteins led to enhanced HCC development in GH(tg) mice. Despite reduced chronic inflammation, GH(tg) STAT5(Δhep) mice displayed earlier and more advanced HCC than GH(tg) animals. This may be attributed to the combination of increased peripheral lipolysis, hepatic lipid synthesis, loss of hepatoprotective mediators accompanied by aberrant activation of tumor-promoting c-JUN and STAT3 signaling cascades, and accumulation of DNA damage secondary to loss of cell-cycle control. Thus, HCC was never observed in STAT5(Δhep) mice.

CONCLUSION

As a result of their hepatoprotective functions, STAT5 proteins prevent progressive fatty liver disease and the formation of aggressive HCC in the setting of hyperactivated GH signaling. At the same time, they play a key role in controlling systemic inflammation and regulating organ and body size.

Intersecting pathways in inflammation and cancer: Hepatocellular carcinoma as a paradigm

Viral infection and chemical carcinogens trigger somatic changes resulting in activation of oncogenes during tumor initiation in the development of cancer. However, a critical interaction resides in the synergism between these somatic changes and an inflamed tumor microenvironment where myeloid and hematopoietic cells are subverted to enhance tumor progression. The causative molecular mechanisms leading to the development of hepatocellular cancer remain incompletely understood but appear to result from multiple factors related to direct hepatocyte injury and the ensuing inflammatory changes mediated by the host response to tissue injury, DNA damage, repair of cellular damage, and chronic, repetitive injury. In this review, the molecular and cellular changes that regulate inflammation and tissue repair will be compared to the activated local tumor microenvironment. Cell-cell signaling within this microenvironment that enhances tumor progression and inhibits anti-tumor immunity will be discussed

Inducible and repressable oncogene-addicted hepatocellular carcinoma in Tet-on xmrk transgenic zebrafish

BACKGROUND & AIMS

Liver cancer, mainly hepatocellular carcinoma, is a major malignancy and currently there are no effective treatment protocols due to insufficient understanding of hepatocarcinogenesis. As a potentially high-throughput and cost-effective experimental model, the zebrafish is increasingly recognized for disease studies. Here, we aim at using the zebrafish to generate a convenient hepatocellular carcinoma model.

METHODS

Using the Tet-on system for liver-specific expression of fish oncogene xmrk, a hyperactive version of epidermal growth factor receptor homolog, we have generated transgenic zebrafish with inducible development of liver cancer.

RESULTS

Liver tumors were rapidly induced with 100% penetrance in both juvenile and adult xmrk transgenic fish. Histological examination indicated that they all showed features of hepatocellular carcinoma. The induced liver tumors regressed rapidly upon inducer withdrawal. During the tumor induction stage, we detected increased cell proliferation and activation of Xmrk downstream targets Erk and Stat5, which were important for liver tumorigenesis as proved by inhibition experiments. When tumors regressed, there were decreased phosphorylated Erk and Stat5 accompanied with an increase in apoptosis.

CONCLUSIONS

Our zebrafish model demonstrates the potential of a hyperactivated epidermal growth factor receptor pathway in initiating heptocarcinogenesis. It provides clear evidence for the requirement of only a single oncogene for HCC initiation and maintenance and is thus a convenient model for further investigation of oncogene addiction and future anti-cancer drug screening.

STAT5A-mediated SOCS2 expression regulates Jak2 and STAT3 activity following c-Src inhibition in head and neck squamous carcinoma

PURPOSE

The inhibition of c-Src results in a striking reduction in cancer cell invasion, but the effect on cell survival is modest. Defining mechanisms that limit apoptosis following c-Src inhibition could result in an ideal therapeutic approach that both inhibits invasion and leads to apoptosis. In this regard, we discovered a novel feedback loop that results in STAT3 reactivation following sustained c-Src inhibition. Here we define the mechanism underlying this feedback loop and examine the effect of inhibiting it in vivo.

EXPERIMENTAL DESIGN

We measured levels and activity of pathway components using PCR, Western blotting, and kinase assays following their manipulation using both molecular and pharmacologic approaches. We used a heterotransplant animal model in which human oral squamous cancer is maintained exclusively in vivo.

RESULTS

Following c-Src inhibition, STAT5 is durably inhibited. The inhibition of STAT5A, but not STAT5B, subsequently reduces the expression of suppressors of cytokine signaling 2 (SOCS2). SOCS2 inhibits Janus kinase 2 (Jak2) activity and Jak2-STAT3 binding. SOCS2 expression is necessary for STAT3 inhibition by c-Src inhibitors. Overexpression of SOCS2 is adequate to prevent STAT3 reactivation and to enhance the cytotoxic effects of c-Src inhibition. Likewise, the combination of Jak and c-Src inhibitors led to significantly more apoptosis than either agent alone in vivo.

CONCLUSIONS

To our knowledge, ours is the first study that fully defines the mechanism underlying this feedback loop, in which sustained c-Src inhibition leads to diminished SOCS2 expression via sustained inhibition of STAT5A, allowing activation of Jak2 and STAT3, Jak2-STAT3 binding, and survival signals.

Proline-rich tyrosine kinase 2 (Pyk2) promotes cell motility of hepatocellular carcinoma through induction of epithelial to mesenchymal transition

AIMS

Proline-rich tyrosine kinase 2 (Pyk2), a non-receptor tyrosine kinase of the focal adhesion kinase (FAK) family, is up-regulated in more than 60% of the tumors of hepatocellular carcinoma (HCC) patients. Forced overexpression of Pyk2 can promote the proliferation and invasion of HCC cells. In this study, we aimed to explore the underlying molecular mechanism of Pyk2-mediated cell migration of HCC cells.

METHODOLOGY/PRINCIPAL FINDINGS

We demonstrated that Pyk2 transformed the epithelial HCC cell line Hep3B into a mesenchymal phenotype via the induction of epithelial to mesenchymal transition (EMT), signified by the up-regulation of membrane ruffle formation, activation of Rac/Rho GTPases, down-regulation of epithelial genes E-cadherin and cytokeratin as well as promotion of cell motility in presence of lysophosphatidic acid (LPA). Suppression of Pyk2 by overexpression of dominant negative PRNK domain in the metastatic HCC cell line MHCC97L transformed its fibroblastoid phenotype to an epithelial phenotype with up-regulation of epithelial genes, down-regulation of mesenchymal genes N-cadherin and STAT5b, and reduction of LPA-induced membrane ruffle formation and cell motility. Moreover, overexpression of Pyk2 in Hep3B cells promoted the phosphorylation and localization of mesenchymal gene Hic-5 onto cell membrane while suppression of Pyk2 in MHCC97L cells attenuated its phosphorylation and localization.

CONCLUSION

These data provided new evidence of the underlying mechanism of Pyk2 in controlling cell motility of HCC cells through regulation of genes associated with EMT.

Constitutive STAT5 activation correlates with better survival in cervical cancer patients treated with radiation therapy

PURPOSE

Constitutively activated signal transducers and activators of transcription (STAT) factors, in particular STAT1, STAT3, and STAT5, have been detected in a wide variety of human primary tumors and have been demonstrated to directly contribute to oncogenesis. However, the expression pattern of these STATs in cervical carcinoma is still unknown, as is whether or not they have prognostic significance. This study investigated the expression patterns of STAT1, STAT3, and STAT5 in cervical cancer and their associations with clinical outcomes in patients treated with radical radiation therapy.

METHODS AND MATERIALS

A total of 165 consecutive patients with International Federation of Gynecology and Obstetrics (FIGO) Stages IB to IVA cervical cancer underwent radical radiation therapy, including external beam and/or high-dose-rate brachytherapy between 1989 and 2002. Immunohistochemical studies of their formalin-fixed, paraffin-embedded tissues were performed. Univariate and multivariate analyses were performed to identify and to evaluate the effects of these factors affecting patient survival.

RESULTS

Constitutive activations of STAT1, STAT3, and STAT5 were observed in 11%, 22%, and 61% of the participants, respectively. While STAT5 activation was associated with significantly better metastasis-free survival (p < 0.01) and overall survival (p = 0.04), STAT1 and STAT3 activation were not. Multivariate analyses showed that STAT5 activation, bulky tumor (≥ 4 cm), advanced stage (FIGO Stages III and IV), and brachytherapy (yes vs. no) were independent prognostic factors for cause-specific overall survival. None of the STATs was associated with local relapse. STAT5 activation (odds ratio = 0.29, 95% confidence interval = 0.13-0.63) and advanced stage (odds ratio = 2.54; 95% confidence interval = 1.03-6.26) were independent predictors of distant metastasis.

CONCLUSIONS

This is the first report to provide the overall expression patterns and prognostic significance of specific STATs in cervical carcinoma. Our results indicate that constitutive STAT5 activation correlates with better metastasis-free survival and overall survival in cervical cancer patients who have received radiation therapy.

Phospho-STAT5 expression is associated with poor prognosis of human colonic adenocarcinoma

The signal transducer and activator of transcription-5 (STAT5) protein has been shown to play an important role in tumor progression through stimulating cell proliferation and preventing apoptosis. STAT5 activation has been observed in a variety of human tumors and cancer cell lines. However, it is not clear how activated STAT5 is expressed in colon cancer. In this study, we aimed to investigate phospho-STAT5 (activated form of STAT5) expression and its relationship with the clinicopathological factors and overall survival of patients with colonic adenocarcinoma. A total of 121 histological samples were selected for this study. Immunohistochemistry was used to detect the expression of phospho-STAT5. Analysis of the immunohistochemical staining was based on the proportion of stained cells in the field: positive, >15% stained cells, and negative, <15% stained cells. Survival times were analyzed using the Kaplan-Meier method, and the differences between groups were assessed with the log-rank test. A multivariate Cox regression model was used for prognostic power analysis. Expression of phospho-STAT5 was observed in the cytoplasms of colonic adenocarcinoma cells. Univariate analysis showed that phospho-STAT5 immunoreactivity was correlated with the depth of tumor invasion (P-value = 0.009), tumor-node-metastasis (TNM) stage (P-value = 0.048) and shorter overall survival times (P-value = 0.026). Lymph node metastasis, distant metastasis and TNM stage were associated with shorter overall survival times (P-value range from 0.003- < 0.001). Multivariate analysis showed that only distant metastasis was an independent predictor of overall survival time (P-value = 0.016). Our findings first demonstrate that phospho-STAT5 is frequently present and active in colonic adenocarcinoma and related to poor prognosis.

Role of the growth hormone-IGF-1 axis in cancer

A substantial body of evidence supports a role for the growth hormone (GH)-IGF-1 axis in cancer incidence and progression. This includes epidemiological evidence relating elevated plasma IGF-1 to cancer incidence as well as a lack of cancers in GH/IGF-1 deficiency. Rodent models lacking GH or its receptor are strikingly resistant to the induction of a wide range of cancers, and treatment with the GH antagonist pegvisomant slows tumor progression. While GH receptor expression is elevated in many cancers, autocrine GH is present in several types, and overexpression of autocrine GH can induce cell transformation. While the mechanism of autocrine action is not clear, it does involve both STAT5 and STAT3 activation, and probably nuclear translocation of the GH receptor. Development of a more potent GH receptor antagonist or secretion inhibitor is warranted for cancer therapy.

Expression of phosphorylated Stat5 predicts expression of cyclin D1 and correlates with poor prognosis of colonic adenocarcinoma

PURPOSE

Constitutive activation of signal transducer and activator of transcription-5 (Stat5) was recently found to be associated with tumor progression through stimulating cell proliferation and preventing apoptosis. However, it is not clear how activated Stat5 is expressed in colon cancer. We aimed to investigate the correlation between phosphorylated Stat5 (p-Stat5) expression and cell cycle regulators (cyclin D1) expression in colonic adenocarcinoma and the relationship between expression of these two proteins and various clinicopathological parameters, including overall survival.

METHODS

P-Stat5 and cyclin D1 expression were determined by immunohistochemical staining from 169 cases of resected colonic adenocarcinoma specimens.

RESULTS

P-Stat5 expression correlated with cyclin D1 expression (r = 0.250, P = 0.001). P-Stat5-positive staining was associated with the depth of tumor invasion (P = 0.002). Univariate survival analysis showed that lymph node metastasis, distant metastasis, TNM stage (all P < 0.0001), T stage (P = 0.024), p-Stat5-positive expression (P = 0.002), and cyclin D1-positive expression (P = 0.039) were associated with shorter survival in patients with colonic adenocarcinoma. Multivariate survival analysis showed that only distant metastasis (P < 0.001; hazard ratio [HR] = 4.96), TNM stage (P < 0.001; HR = 9.80), and p-Stat5 overexpression (P = 0.020; HR = 1.84) were independent predictors of poor prognosis.

CONCLUSIONS

Our findings provide the first evidence that p-Stat5 may play an important role in cyclin D1 overexpression and contribute to colonic adenocarcinoma progression.

The role of Stat5 transcription factors as tumor suppressors or oncogenes

Stat5 is constitutively activated in many human cancers affecting the expression of cell proliferation and cell survival controlling genes. These oncogenic functions of Stat5 have been elegantly reproduced in mouse models. Aberrant Stat5 activity induces also mitochondrial dysfunction and reactive oxygen species leading to DNA damage. Although DNA damage can stimulate tumorigenesis, it can also prevent it. Stat5 can inhibit tumor progression like in the liver and it is a tumor suppressor in fibroblasts. Stat5 proteins are able to regulate cell differentiation and senescence activating the tumor suppressors SOCS1, p53 and PML. Understanding the context dependent regulation of tumorigenesis through Stat5 function will be central to understand proliferation, survival, differentiation or senescence of cancer cells.

ZFP36L1 negatively regulates erythroid differentiation of CD34+ hematopoietic stem cells by interfering with the Stat5b pathway

ZFP36L1 is a member of a family of CCCH tandem zinc finger proteins (TTP family) able to bind to AU-rich elements in the 3'-untranslated region of mRNAs, thereby triggering their degradation. The present study suggests that such mechanism is used during hematopoiesis to regulate differentiation by posttranscriptionally modulating the expression of specific target genes. In particular, it demonstrates that ZFP36L1 negatively regulates erythroid differentiation by directly binding the 3' untranslated region of Stat5b encoding mRNA. Stat5b down-regulation obtained by ZFP36L1 overexpression results, in human hematopoietic progenitors, in a drastic decrease of erythroid colonies formation. These observations have been confirmed by silencing experiments targeting Stat5b and by treating hematopoietic stem/progenitor cells with drugs able to induce ZFP36L1 expression. Moreover, this study shows that different members of ZFP36L1 family act redundantly, because cooverexpression of ZFP36L1 and family member ZFP36 determines a cumulative effect on Stat5b down-regulation. This work describes a mechanism underlying ZFP36L1 capability to regulate hematopoietic differentiation and suggests a new target for the therapy of hematopoietic diseases involving Stat5b/JAK2 pathway, such as chronic myeloproliferative disorders.

Epithelial-mesenchymal transition in the liver

Epithelial-mesenchymal transition (EMT) is a physiological process occurring in the embryo. In adult organism, EMT could be involved in disease development. In the liver, the possibility that EMT of liver epithelial cells participate to liver fibrosis is increasingly discussed. Furthermore, the involvement of hepatocyte EMT to liver cancer biology has also been documented over the past few years. In this review, we will first describe how EMT participates to embryological development. We will then discuss the involvement of hepatocytes and biliary epithelial cells in liver fibrosis. Finally, we will describe how EMT may impact the metastatic process and resistance to therapy in hepatocellular carcinoma.

Oncoproteomic analysis reveals co-upregulation of RELA and STAT5 in carboplatin resistant ovarian carcinoma

Background

Ovarian cancer is one of the most lethal types of female malignancy. Although most patients are initially responsive to platinum-based chemotherapy, almost all develop recurrent chemoresistant tumors and succumb to their diseases. Elucidating the pathogenesis underlying drug resistance is fundamental to the development of new therapeutics, leading to improved clinical outcomes in these patients.

Methods and Findings

We compared the proteomes of paired primary and recurrent post-chemotherapy ovarian high-grade serous carcinomas from nine ovarian cancer patients using CIEF/Nano-RPLC coupled with ESI-Tandem MS. As compared to their primary tumors, more than half of the recurrent tumors expressed higher levels of several proteins including CP, FN1, SYK, CD97, AIF1, WNK1, SERPINA3, APOD, URP2, STAT5B and RELA (NF-κB p65), which were also validated by quantitative RT-PCR. Based on shRNA screening for the upregulated genes in in vitro carboplatin-resistant cells, we found that simultaneous knockdown of RELA and STAT5B was most effective in sensitizing tumor cells for carboplatin treatment. Similarly, the NF-κB inhibitor, BMS-345541, and the STAT5 inhibitor, Dasatinib, significantly enhanced cell sensitivity to carboplatin. Moreover, both RELA and STAT5 are known to bind to the promoter region of Bcl-X, regulating its promoter activity. In this regard, augmented Bcl-xL expression was detected in carboplatin-resistant cells. Combined ectopic expression of RELA and STAT5B enhanced Bcl-xL promoter activity while treatment with BMS-345541 and Dasatinib decreased it. Chromatin immunoprecipitation of the Bcl-X promoter region using a STAT5 antibody showed induction of RELA and STAT5 DNA-binding segments both in naïve cells treated with a high concentration of carboplatin as well as in carboplatin-resistant cells.

Conclusions

Proteomic analysis identified RELA and STAT5 as two major proteins associated with carboplatin resistance in ovarian tumors. Our results further showed that NF-κB and STAT5 inhibitor could sensitize carboplatin-resistant cells and suggest that such inhibitors can be used to benefit patients with carboplatin-resistant recurrent ovarian cancer.

Epithelial-mesenchymal transitions and hepatocarcinogenesis

Epithelial-mesenchymal transitions (EMTs) are believed to play a role in invasion and metastasis of many types of tumors. In this issue of the JCI, Chen et al. show that a gene that has been associated with aggressive biology in hepatocellular carcinomas initiates a molecular cascade that results in EMT.

Epithelial-mesenchymal transition in hepatocellular carcinoma

The transition of epithelial cells to a mesenchymal phenotype is of paramount relevance for embryonic development and adult wound healing. During the past decade, the epithelial-mesenchymal transition (EMT) has been increasingly recognized to occur during the progression of various carcinomas such as hepatocellular carcinoma (HCC). Here, we focus on EMT in both experimental liver models and human HCC, emphasizing the underlying molecular mechanisms which show partial recurrence of embryonic programs such as TGF-beta and Wnt/ beta-catenin signaling, including collaboration with hepatitis viruses. We further discuss the differentiation repertoire of malignant hepatocytes with respect to the potential acquisition of stemness, and the involvement of the mesenchymal to epithelial transition, the reversal of EMT, in cancer dissemination and metastatic colonization. The strong evidence for EMT in HCC patients demands novel strategies in pathological assessments and therapeutic concepts to efficiently combat HCC progression.

Signal transducer and activator of transcription (STAT)-5A and STAT5B differentially regulate human mammary carcinoma cell behavior

Increased activation of signal transducer and activator of transcription (STAT)-5 has been reported in various malignancies including mammary carcinoma. However, it is only recently that potentially distinct roles of STAT5A and STAT5B in neoplasia have begun to emerge. Herein we systematically delineate the functions of STAT5A and STAT5B in human mammary carcinoma cell lines MCF-7 and T47D. Forced expression of constitutively active (CA) STAT5A enhanced both survival and anchorage-independent growth of human mammary carcinoma cells but concordantly suppressed cell motility as revealed in colony scattering, cell migration, and invasion assays. In contrast, forced expression of CA STAT5B exhibited lower potency than CA STAT5A in enhancing survival and anchorage-independent growth of mammary carcinoma cells and exerted no effects on cell motility. Differential expression of genes that regulate cellular survival and motility was concomitantly observed on forced expression of CA STAT5A or CA STAT5B. Small interfering RNA-mediated depletion of STAT5A significantly impaired anchorage-independent growth of human mammary carcinoma cells, whereas a smaller reduction was observed upon small interfering RNA-mediated depletion of STAT5B. Depletion of endogenous STAT5A also significantly enhanced cell motility, whereas depletion of endogenous STAT5B exhibited no effect. Xenograft studies provided data concordant with the in vitro effects of the two STAT5 isoforms. We therefore demonstrate that STAT5A and STAT5B differentially regulate behavior of human mammary carcinoma cells.

Nuclear beta-catenin induces an early liver progenitor phenotype in hepatocellular carcinoma and promotes tumor recurrence

Transforming growth factor-beta cooperates with oncogenic Ras to activate nuclear beta-catenin during the epithelial to mesenchymal transition of hepatocytes, a process relevant in the progression of hepatocellular carcinoma (HCC). In this study we investigated the role of beta-catenin in the differentiation of murine, oncogene-targeted hepatocytes and in 133 human HCC patients scheduled for orthotopic liver transplantation. Transforming growth factor-beta caused dissociation of plasma membrane E-cadherin/beta-catenin complexes and accumulation of nuclear beta-catenin in Ras-transformed, but otherwise normal hepatocytes in p19(ARF)-/- mice. Both processes were inhibited by Smad7-mediated disruption of transforming growth factor-beta signaling. Overexpression of constitutively active beta-catenin resulted in high levels of CK19 and M2-PK, whereas ablation of beta-catenin by axin overexpression caused strong expression of CK8 and CK18. Therefore, nuclear beta-catenin resulted in dedifferentiation of neoplastic hepatocytes to immature progenitor cells, whereas loss of nuclear beta-catenin led to a differentiated HCC phenotype. Poorly differentiated human HCC showed cytoplasmic redistribution or even loss of E-cadherin, suggesting epithelial to mesenchymal transition. Analysis of 133 HCC patient samples revealed that 58.6% of human HCC exhibited strong nuclear beta-catenin accumulation, which correlated with clinical features such as vascular invasion and recurrence of disease after orthotopic liver transplantation. These data suggest that activation of beta-catenin signaling causes dedifferentiation to malignant, immature hepatocyte progenitors and facilitates recurrence of human HCC after orthotopic liver transplantation.

Hepatic tumor-stroma crosstalk guides epithelial to mesenchymal transition at the tumor edge

The tumor-stroma crosstalk is a dynamic process fundamental in tumor development. In hepatocellular carcinoma (HCC), the progression of malignant hepatocytes frequently depends on transforming growth factor (TGF)-beta provided by stromal cells. TGF-beta induces an epithelial to mesenchymal transition (EMT) of oncogenic Ras-transformed hepatocytes and an upregulation of platelet-derived growth factor (PDGF) signaling. To analyse the influence of the hepatic tumor-stroma crosstalk onto tumor growth and progression, we co-injected malignant hepatocytes and myofibroblasts (MFBs). For this, we either used in vitro-activated p19(ARF) MFBs or in vivo-activated MFBs derived from physiologically inflamed livers of Mdr2/p19(ARF) double-null mice. We show that co-transplantation of MFBs with Ras-transformed hepatocytes strongly enhances tumor growth. Genetic interference with the PDGF signaling decreases tumor cell growth and maintains plasma membrane-located E-cadherin and beta-catenin at the tumor-host border, indicating a blockade of hepatocellular EMT. We further generated a collagen gel-based three dimensional HCC model in vitro to monitor the MFB-induced invasion of micro-organoid HCC spheroids. This invasion was diminished after inhibition of TGF-beta or PDGF signaling. These data suggest that the TGF-beta/PDGF axis is crucial during hepatic tumor-stroma crosstalk, regulating both tumor growth and cancer progression.

Inhibition of STAT5 induces G1 cell cycle arrest and reduces tumor cell invasion in human colorectal cancer cells

Abnormalities in the signal transducer and activator of transcription (STAT) pathway are involved in the oncogenesis of several cancers. However, the mechanism by which dysregulated STAT5 signaling contributes to the progression of human colorectal cancer (CRC) has not been elucidated. To investigate the role of STAT5 in CRC progression, we depleted STAT5 with a small interfering RNA (siRNA). Our results demonstrate that STAT5 is involved in CRC cell growth, cell cycle progression, invasion and migration through regulation of gene expression, such as Bcl-2, p16(ink4a), p21(waf1/cip1), p27(kip1), E-cadherin, the focal adhesion kinase (FAK), vascular endothelial growth factor (VEGF) and matrix metalloproteinases. In addition, immunohistochemical staining reveals upregulation of STAT5 during CRC tumorigenesis. Moreover, phospho-STAT5 (pSTAT5) is predominantly localized in the cytoplasm of adenomas cells and colon adenocarcinoma cells, but primarily presented in the nucleus of normal colonic epithelium cells. Thus, pSTAT5 protein is shuttled from the nucleus to the cytoplasm in the oncogenesis of CRC, suggesting that activated STAT5 may also have cytoplasmic functions. In support of this hypothesis, we found that STAT5 formed a complex with p44/42 MAPK and SAPK/JNK in CRC cells, suggesting cross talk between STAT5 signaling and the MAPK pathway in the development of human CRC. Our findings illustrate the biological significance of STAT5 signaling in CRC progression, and provide novel evidence that intervention in STAT5 signaling may have potential therapeutic value in the prevention of human colorectal cancer.

Deregulated direct targets of the hepatitis B virus (HBV) protein, HBx, identified through chromatin immunoprecipitation and expression microarray profiling

The hepatitis B-X (HBx) protein is strongly associated with hepatocellular carcinoma. It is implicated not to directly cause cancer but to play a role in hepatocellular carcinoma as a co-factor. The oncogenic potential of HBx primarily lies in its interaction with transcriptional regulators resulting in aberrant gene expression and deregulated cellular pathways. Utilizing ultraviolet irradiation to simulate a tumor-initiating event, we integrated chip-based chromatin immunoprecipitation (ChIP-chip) with expression microarray profiling and identified 184 gene targets directly deregulated by HBx. One-hundred forty-four transcription factors interacting with HBx were computationally inferred. We experimentally validated that HBx interacts with some of the predicted transcription factors (pTF) as well as the promoters of the deregulated target genes of these pTFs. Significantly, we demonstrated that the pTF interacts with the promoters of the deregulated HBx target genes and that deregulation by HBx of these HBx target genes carrying the pTF consensus sequences can be reversed using pTF small interfering RNAs. The roles of these deregulated direct HBx target genes and their relevance in cancer was inferred via querying against biogroup/cancer-related microarray databases using web-based NextBio(TM) software. Six pathways, including the Jak-STAT pathway, were predicted to be significantly deregulated when HBx binds indirectly to direct target gene promoters. In conclusion, this study represents the first ever demonstration of the utilization of ChIP-chip to identify deregulated direct gene targets from indirect protein-DNA binding as well as transcriptional factors directly interacting with HBx. Increased knowledge of the gene/transcriptional factor targets of HBx will enhance our understanding of the role of HBx in hepatocellular carcinogenesis and facilitate the design of better strategies in combating hepatitis B virus-associated hepatocellular carcinoma.

Loss of STAT5 causes liver fibrosis and cancer development through increased TGF-{beta} and STAT3 activation

The molecular mechanisms underlying the development of hepatocellular carcinoma are not fully understood. Liver-specific signal transducer and activator of transcription (STAT) 5A/B–null mice (STAT5-LKO) were treated with carbon tetrachloride (CCl₄), and histological analyses revealed liver fibrosis and tumors. Transforming growth factor (TGF)–β levels and STAT3 activity were elevated in liver tissue from STAT5-LKO mice upon CCl₄ treatment. To define the molecular link between STAT5 silencing and TGF-β up-regulation, as well as STAT3 activation, we examined STAT5-null mouse embryonic fibroblasts and primary hepatocytes. These cells displayed elevated TGF-β protein levels, whereas messenger RNA levels remained almost unchanged. Protease inhibitor studies revealed that STAT5 deficiency enhanced the stability of mature TGF-β. Immunoprecipitation and immunohistochemistry analyses demonstrated that STAT5, through its N-terminal sequences, could bind to TGF-β and that retroviral-mediated overexpression of STAT5 decreased TGF-β levels. To confirm the in vivo significance of the N-terminal domain of STAT5, we treated mice that expressed STAT5 lacking the N terminus (STAT5-ΔN) with CCl₄. STAT5-ΔN mice developed CCl₄-induced liver fibrosis but no tumors. In conclusion, loss of STAT5 results in elevated TGF-β levels and enhanced growth hormone–induced STAT3 activity. We propose that a deregulated STAT5–TGF-β–STAT3 network contributes to the development of chronic liver disease.

Hepatocyte-specific activation of NF-kappaB does not aggravate chemical hepatocarcinogenesis in transgenic mice

The NF-kappaB signalling pathway plays important roles in liver organogenesis and carcinogenesis. Mouse embryos deficient in IKKbeta die in mid-gestation, due to excessive apoptosis of hepatoblasts. Although activation of the NF-kappaB signalling pathway has been demonstrated in human hepatocellular carcinoma, the role of NF-kappaB is controversial. Here, we have generated transgenic mice in which a constitutively active form of IKKbeta was expressed in a hepatocyte-specific manner. Using electrophoretic mobility shift assay, we documented increased NF-kappaB activities and up-regulated levels of NF-kappaB downstream target genes, Bcl-xL and STAT5, in the transgenic mouse livers. These results confirmed that the NF-kappaB pathway was activated in the livers of the transgenic mice. However, there was no significant difference in tumour formation between transgenic and wild-type mice up to an age of 50 weeks. When we treated the transgenic mice with the chemical carcinogen diethylnitrosamine (DEN), we observed no significant differences in the incidence and size of liver tumours formed in these mice with and without DEN treatment at 35 weeks of age, suggesting that the activated NF-kappaB pathway in the livers of the transgenic mice did not enhance hepatocarcinogenesis. Interestingly, some of the transient transgenic embryos (E12.5) had abnormal excessive accumulation of nucleated red blood cells in their developing livers. In summary, NF-kappaB activation in hepatocytes did not significantly affect chemical hepatocarcinogenesis. In addition, the TTR/IKKCA transgenic mice may serve as a useful model for studying the role of NF-kappaB activation in hepatocarcinogenesis as well as inflammatory and metabolic diseases.

Constitutive activation of signal transducer and activator of transcription 5 contributes to tumor growth, epithelial-mesenchymal transition, and resistance to epidermal growth factor receptor targeting

PURPOSE

Signal transducer and activator of transcription 5 (STAT5) is activated in squamous cell carcinoma of the head and neck (SCCHN), where targeting of STAT5 inhibits tumor growth in vitro and in vivo. The role of STAT5 activation in carcinogenesis, tumor progression, and response to therapy remains incompletely understood. In this study, we investigated the effects of STAT5 activation on squamous epithelial carcinogenesis and response to therapy.

EXPERIMENTAL DESIGN

The functional consequences of STAT5 activation in squamous epithelial carcinogenesis were examined using cells derived from normal (Het-1A) and transformed mucosal epithelial cells engineered to express constitutive-active mutants of STAT5.

RESULTS

The growth rate of stable clones derived from both normal and transformed squamous epithelial cells expressing the constitutive-active STAT5 was increased. In SCCHN xenografts, tumor volumes were increased in constitutive-active STAT5 mutant cells compared with vector-transfected controls. Constitutive activation of STAT5 significantly increased cell migration and invasion through Matrigel, as well as the transforming efficiency of SCCHN cells in vitro, as assessed by soft agar assays. The constitutive-active STAT5 clones derived from SCCHN cells showed changes consistent with an epithelial-mesenchymal transition including decreased expression of E-cadherin and increased vimentin in comparison with control transfectants. In these cells, STAT5 activation was associated with resistance to cisplatin-mediated apoptosis and growth inhibition induced by the epidermal growth factor receptor tyrosine kinase inhibitor, erlotinib.

CONCLUSIONS

These results suggest that constitutive STAT5 signaling enhances tumor growth, invasion, and epithelial-to-mesenchymal transition in squamous epithelial carcinogenesis and may contribute to resistance to epidermal growth factor receptor tyrosine kinase inhibitor and chemotherapy.

Association of autophagy defect with a malignant phenotype and poor prognosis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is an aggressive cancer with a poor prognosis. The role of autophagy and the prognostic value of autophagic genes are largely unknown in HCC. Here, we showed decreased expression of autophagic genes and their corresponding autophagic activity and increased expression of the antiapoptotic gene Bcl-xL in HCC cell lines compared with a normal hepatic cell line. We also found decreased expression of the autophagic gene Beclin 1 in 44 HCC tissue samples compared with adjacent nontumor tissues. In addition, we found that the most aggressive malignant HCC cell lines and HCC tissues with recurrent disease displayed much lower autophagic levels, especially when Bcl-xL was overexpressed. Interestingly, in a tissue microarray study consisting of 300 HCC patients who underwent curative resection, the expression of Beclin 1 was only significantly correlated with disease-free survival (DFS; P < 0.0001) and overall survival (OS; P < 0.0001) in the Bcl-xL(+) group. Multivariate and univariate analyses also revealed that Beclin 1 expression was an independent predictor for DFS and OS in Bcl-xL(+) patients. In addition, we found a significant correlation between Beclin 1 expression and tumor differentiation in Bcl-xL(+) but not in Bcl-xL(-) HCC patients. In conclusion, our data showed expression of autophagic genes and their corresponding autophagic activities were suppressed in HCC. The autophagy defects synergized with altered apoptotic activity might facilitate tumor malignant differentiation, which results in a more aggressive cancer cell phenotype and poor prognosis of HCC.

ILEI requires oncogenic Ras for the epithelial to mesenchymal transition of hepatocytes and liver carcinoma progression

In human hepatocellular carcinoma (HCC), epithelial to mesenchymal transition (EMT) correlates with aggressiveness of tumors and poor survival. We employed a model of EMT based on immortalized p19(ARF) null hepatocytes (MIM), which display tumor growth upon expression of oncogenic Ras and undergo EMT through the synergism of Ras and transforming growth factor (TGF)-beta. Here, we show that the interleukin-related protein interleukin-like EMT inducer (ILEI), a novel EMT-, tumor- and metastasis-inducing protein, cooperates with oncogenic Ras to cause TGF-beta-independent EMT. Ras-transformed MIM hepatocytes overexpressing ILEI showed cytoplasmic E-cadherin, loss of ZO-1 and induction of alpha-smooth muscle actin as well as platelet-derived growth factor (PDGF)/PDGF-R isoforms. As shown by dominant-negative PDGF-R expression in these cells, ILEI-induced PDGF signaling was required for enhanced cell migration, nuclear accumulation of beta-catenin, nuclear pY-Stat3 and accelerated growth of lung metastases. In MIM hepatocytes expressing the Ras mutant V12-C40, ILEI collaborated with PI3K signaling resulting in tumor formation without EMT. Clinically, human HCC samples showed granular or cytoplasmic localization of ILEI correlating with well and poorly differentiated tumors, respectively. In conclusion, these data indicate that ILEI requires cooperation with oncogenic Ras to govern hepatocellular EMT through mechanisms involving PDGF-R/beta-catenin and PDGF-R/Stat3 signaling.

Molecular basis of parthenolide-dependent proapoptotic activity in cancer cells

This review outlines the molecular events that accompany the anti-tumor action of parthenolide (PN). Parthenolide (PN) is naturally derived compound, isolated from plant Tanacetum parthenium. PN has been previously shown to withdraw cells from cell cycle or to promote cell differentiation, and finally to induce programmed cell death. Recent advances in molecular biology indicate that this sesquiterpene lactone might evoke the above-mentioned effects by indirect action on genes. PN was shown to inhibit NF-kappaB- and STATs-mediated antiapoptotic gene transcription. On one hand, the proapoptotic activity of PN includes stimulation of intrinsic apoptotic pathway with the higher level of intracellular ROS and modifications of Bcl-2 family proteins (conformational changes of Bak and Bax, Bid cleavage). On the other hand, PN amplifies the apoptotic signal through the sensitization of cancer cells to extrinsic apoptosis, induced by TNF-alpha. These effects are specific to tumor cells. Unique properties of PN make this agent a promising metabolic inhibitor to retard tumorigenesis and to suppress tumor growth.

Mutations in the C-terminus of the X protein of hepatitis B virus regulate Wnt-5a expression in hepatoma Huh7 cells: cDNA microarray and proteomic analyses

Background: The hepatitis B virus x gene (HBx) is a promiscuous transactivator implicated in the development of hepatocellular carcinoma (HCC). The present study was designed to investigate the molecular events regulated by HBx. Methods: Genomic and proteomic expression profiling was performed in Huh7 HCC cells transfected with HBx mutants with a C-terminal deletion. The gene and protein expression of wingless-type murine-mammary-tumour virus (MMTV) integration site family, member 5A (Wnt-5a) was validated by analyses of reverse transcription–polymerase chain reaction (RT–PCR), real-time RT–PCR, western blot and immunohistochemistry. Results: Differentially expressed genes and proteins were found in the transfected Huh7 HCC cells; most of them were involved in transcriptional regulation, although others including oncogenes or tumor suppressor genes, and molecules involved in cell junctions, signal transduction pathways, metabolism or the immune response were also observed. The expression of the Wnt-5a gene was elevated >10-fold in Huh7 cells transfected with the HBx3′-30 amino acid deletion mutant. However, the expression was downregulated by the transfection with the HBx3′-40 amino acid deletion mutant. The changes in Wnt-5a expression were also observed in human HCC tissues, compared with corresponding non-cancerous liver tissues. A negative correlation was found between the expression of Wnt-5a and HBx COOH mutations in HCC tissues. Conclusions: HBx mutants may participate in the development and progression of HCC, at least in part through the Wnt-5a pathway.

Genomic dissection of the cytokine-controlled STAT5 signaling network in liver

Growth hormone (GH) controls the physiology and pathophysiology of the liver, and its signals are conducted by two members of the family of signal transducers and activators of transcription, STAT5A and STAT5B. Mice in which the Stat5a/b locus has been inactivated specifically in hepatocytes display GH resistance, the sex-specific expression of genes associated with liver metabolism and the cytochrome P-450 system is lost, and they develop hepatosteatosis. Several groups have shown by global gene expression profiling that a cadre of STAT5A/B target genes identify genetic cascades induced by GH and other cytokines. Evidence is accumulating that in the absence of STAT5A/B GH aberrantly activates STAT1 and STAT3 and their downstream target genes and thereby offers a partial explanation of some of the physiological alterations observed in Stat5a/b-null mice and human patients. We hypothesize that phenotypic changes observed in the absence of STAT5A/B are due to two distinct molecular consequences: first, the failure of STAT5A/B target genes to be activated by GH and second, the rerouting of GH signaling to other members of the STAT family. Rerouting of GH signaling to STAT1 and STAT3 might partially compensate for the loss of STAT5A/B, but it certainly activates biological programs distinct from STAT5A/B. Here we discuss the extent to which studies on global gene expression profiling have fostered a better understanding of the biology behind cytokine-STAT5A/B networks in hepatocytes. We also explore whether this wealth of information on gene activity can be used to further understand the roles of cytokines in liver disease.

Lupeol Suppresses Cisplatin-Induced Nuclear Factor-κB Activation in Head and Neck Squamous Cell Carcinoma and Inhibits Local Invasion and Nodal Metastasis in an Orthotopic Nude Mouse Model

A poor prognosis in head and neck squamous cell carcinoma (HNSCC) patients is commonly associated with the presence of regional metastasis. Cisplatin-based chemotherapy concurrent with radiation therapy is commonly used in the treatment of locally advanced HNSCC. However, the result is dismal due to common acquisition of chemoresistance and radioresistance. Epidemiologic studies have shown the importance of dietary substances in the prevention of HNSCC. Here, we found that lupeol, a triterpene found in fruits and vegetables, selectively induced substantial HNSCC cell death but exhibited only a minimal effect on a normal tongue fibroblast cell line in vitro. Down-regulation of NF-kappaB was identified as the major mechanism of the anticancer properties of lupeol against HNSCC. Lupeol alone was not only found to suppress tumor growth but also to impair HNSCC cell invasion by reversal of the NF-kappaB-dependent epithelial-to-mesenchymal transition. Lupeol exerted a synergistic effect with cisplatin, resulting in chemosensitization of HNSCC cell lines with high NF-kappaB activity in vitro. In in vivo studies, using an orthotopic metastatic nude mouse model of oral tongue squamous cell carcinoma, lupeol at a dose of 2 mg/animal dramatically decreased tumor volume and suppressed local metastasis, which was more effective than cisplatin alone. Lupeol exerted a significant synergistic cytotoxic effect when combined with low-dose cisplatin without side effects. Our results suggest that lupeol may be an effective agent either alone or in combination for treatment of advanced tumors.