Role of connexin32 and beta-catenin in tumor promotion in mouse liver

Connexins and Gap Junctions in Cancer of the Urinary Tract

This review focuses on connexins and nexus or gap junctions in the genesis, progression, and therapy of carcinomas of the human urinary tract. Some decades ago, the idea was born that gap junctional intercellular communication might prevent both the onset and the progression of cancer. Later evidence indicated that, on the contrary, synthesis and the presence of connexins as a prerequisite for gap junctional intercellular communication might promote the occurrence of cancer and metastases. The research history of urinary bladder cancer is a good example of the development of scientific perception. So far, the role of gap junctional intercellular communication in carcinogenesis and cancer progression, as well as in therapeutical approaches, remains unclear.

Cx32 exerts anti-apoptotic and pro-tumor effects via the epidermal growth factor receptor pathway in hepatocellular carcinoma

BACKGROUND

Abnormal expression or distribution of connexin 32 (Cx32) is associated with hepatocarcinogenesis, but the role of Cx32 and the underlying mechanisms are still unclear.

METHODS

The expression level of Cx32 in 96 hepatocellular carcinoma (HCC) specimens was determined using western blotting and immunohistochemistry. The correlation between Cx32 expression and clinicopathological parameters was analyzed. The cell apoptosis rate was examined using flow cytometry and western blotting. The role of Cx32 in the Src kinase and epidermal growth factor receptor (EGFR) signaling pathways was measured by quantitative real-time PCR, western blotting and coimmunoprecipitation (CO-IP). The effect of Cx32 overexpression on the streptonigrin (SN)-induced tumor growth suppression and apoptosis was assessed in nude mice.

RESULTS

Our study showed that overexpressed Cx32 accumulated in the cytoplasm and that Cx32-containing gap junctions (GJs) were nearly absent in HCC specimens. Upregulated Cx32 expression was highly correlated with advanced tumor-node-metastasis (TNM) stage and poor tumor differentiation and was an independent predictive marker for poor prognosis in HCC. Overexpression of Cx32 significantly inhibited SN-induced apoptosis by activating the EGFR signaling pathway in vitro and in vivo. Moreover, the expression levels of Cx32 and EGFR were positively correlated in HCC specimens. The CO-IP experiments demonstrated that Cx32 could bind to Src kinase, and the western blotting results revealed that Cx32 increased the levels of EGFR and p-EGFR by upregulating Src expression.

CONCLUSION

The present study demonstrated that overexpressed and internalized Cx32 was associated with advanced TNM stage and poor tumor differentiation and predicted poor prognosis in HCC. Cx32 facilitated HCC progression by blocking chemotherapy-induced apoptosis in vitro and in vivo via interacting with Src and thus promoting the phosphorylation of EGFR, subsequently activating the EGFR signaling pathway. Cx32 may be a potential biomarker and a new therapeutic target for HCC.

Fenofibrate Augments the Sensitivity of Drug-Resistant Prostate Cancer Cells to Docetaxel

Metronomic agents reduce the effective doses and adverse effects of cytostatics in cancer chemotherapy. Therefore, they can enhance the treatment efficiency of drug-resistant cancers. Cytostatic and anti-angiogenic effects of fenofibrate (FF) suggest that it can be used for the metronomic chemotherapy of drug-resistant prostate tumors. To estimate the effect of FF on the drug-resistance of prostate cancer cells, we compared the reactions of naïve and drug-resistant cells to the combined treatment with docetaxel (DCX)/mitoxantrone (MTX) and FF. FF sensitized drug-resistant DU145 and PC3 cells to DCX and MTX, as illustrated by their reduced viability and invasive potential observed in the presence of DCX/MTX and FF. The synergy of the cytostatic activities of both agents was accompanied by the inactivation of P-gp-dependent efflux, dysfunction of the microtubular system, and induction of polyploidy in DCX-resistant cells. Chemical inhibition of PPARα- and reactive oxygen species (ROS)-dependent pathways by GW6471 and N-acetyl-L-cysteine, respectively, had no effect on cell sensitivity to combined DCX/FF treatment. Instead, we observed the signs of adenosine triphosphate (ATP) deficit and autophagy in DCX/FF-treated drug-resistant cells. Furthermore, the cells that had been permanently propagated under DCX- and DCX/FF-induced stress did not acquire DCX/FF-resistance. Instead, relatively slow proliferation of DCX-resistant cells was efficiently inhibited by FF. Collectively, our observations show that FF reduces the effective doses of DCX by interfering with the drug resistance and energy metabolism of prostate cancer cells. Concomitantly, it impairs the chemotherapy-induced microevolution and expansion of DCX/FF-resistant cells. Therefore, FF can be applied as a metronomic agent to enhance the efficiency of palliative chemotherapy of prostate cancer.

Design and development of a robotized system coupled to µCT imaging for intratumoral drug evaluation in a HCC mouse model

Hepatocellular carcinoma (HCC) is one of the most common cancer related deaths worldwide. One of the main challenges in cancer treatment is drug delivery to target cancer cells specifically. Preclinical evaluation of intratumoral drugs in orthotopic liver cancer mouse models is difficult, as percutaneous injection hardly can be precisely performed manually. In the present study we have characterized a hepatoma model developing a single tumor nodule by implantation of Hep55.1C cells in the liver of syngeneic C57BL/6J mice. Tumor evolution was followed up by µCT imaging, and at the histological and molecular levels. This orthotopic, poorly differentiated mouse HCC model expressing fibrosis, inflammation and cancer markers was used to assess the efficacy of drugs. We took advantage of the high precision of a previously developed robotized system for automated, image-guided intratumoral needle insertion, to administer every week in the tumor of the Hep55.1C mouse model. A significant tumor growth inhibition was observed using our robotized system, whereas manual intraperitoneal administration had no effect, by comparison to untreated control mice.

Beta-catenin signaling, liver regeneration and hepatocellular cancer: sorting the good from the bad

Among the adult organs, liver is unique for its ability to regenerate. A concerted signaling cascade enables optimum initiation of the regeneration process following insults brought about by surgery or a toxicant. Additionally, there exists a cellular redundancy, whereby a transiently amplifying progenitor population appears and expands to ensure regeneration, when differentiated cells of the liver are unable to proliferate in both experimental and clinical scenarios. One such pathway of relevance in these phenomena is Wnt/β-catenin signaling, which is activated relatively early during regeneration mostly through post-translational modifications. Once activated, β-catenin signaling drives the expression of target genes that are critical for cell cycle progression and contribute to initiation of the regeneration process. The role and regulation of Wnt/β-catenin signaling is now documented in rats, mice, zebrafish and patients. More recently, a regenerative advantage of the livers in β-catenin overexpressing mice was reported, as was also the case after exogenous Wnt-1 delivery to the liver paving the way for assessing means to stimulate the pathway for therapeutics in liver failure. β-Catenin is also pertinent in hepatic oval cell activation and differentiation. However, aberrant activation of the Wnt/β-catenin signaling is reported in a significant subset of hepatocellular cancers (HCC). While many mechanisms of such activation have been reported, the most functional means of aberrant and sustained activation is through mutations in the β-catenin gene or in AXIN1/2, which encodes for a scaffolding protein critical for β-catenin degradation. Intriguingly, in experimental models hepatic overexpression of normal or mutant β-catenin is insufficient for tumorigenesis. In fact β-catenin loss promoted chemical carcinogenesis in the liver due to alternate mechanisms. Since most HCC occur in the backdrop of chronic hepatic injury, where hepatic regeneration is necessary for maintenance of liver function, but at the same time serves as the basis of dysplastic changes, this Promethean attribute exhibits a Jekyll and Hyde behavior that makes distinguishing good regeneration from bad regeneration essential for targeting selective molecular pathways as personalized medicine becomes a norm in clinical practice. Could β-catenin signaling be one such pathway that may be redundant in regeneration and indispensible in HCC in a subset of cases?

Experimental mouse models for hepatocellular carcinoma research

Every year almost 500,000 new patients are diagnosed with hepatocellular carcinoma (HCC), a primary malignancy of the liver that is associated with a poor prognosis. Numerous experimental models have been developed to define the pathogenesis of HCC and to test novel drug candidates. This review analyses several mouse models useful for HCC research and points out their advantages and weaknesses. Chemically induced HCC mice models mimic the injury-fibrosis-malignancy cycle by administration of a genotoxic compound alone or, if necessary, followed by a promoting agent. Xenograft models develop HCC by implanting hepatoma cell lines in mice, either ectopically or orthotopically; these models are suitable for drug screening, although extrapolation should be considered with caution as multiple cell lines must always be used. The hollow fibre assay offers a solution for limiting the number of test animals in xenograft research because of the ability for implanting multiple cell lines in one mouse. There is also a broad range of genetically modified mice engineered to investigate the pathophysiology of HCC. Transgenic mice expressing viral genes, oncogenes and/or growth factors allow the identification of pathways involved in hepatocarcinogenesis.

Phenobarbital elicits unique, early changes in the expression of hepatic genes that affect critical pathways in tumor-prone B6C3F1 mice

At 2 and 4 weeks following treatment with phenobarbital (PB), the classical nongenotoxic rodent liver carcinogen, we elucidated unique gene expression changes (both induction and repression) in liver tumor-susceptible B6C3F1 mice, as compared with the relatively resistant C57BL/6. Based on their cancer-related roles, we believe that altered expression of at least some of these genes might underlie PB-induced liver tumorigenesis. Putative constitutive active/androstane (CAR) response elements (CAREs), a subset of PB response elements, were present within multiple genes whose expression was uniquely altered in the B6C3F1 mice, suggesting a role for CAR in their regulation. Additionally, three DNA methyltransferase genes (Dnmt1, Dnmt3a, and Dnmt3b) were repressed uniquely in the tumor-prone B6C3F1 mice, and all possess putative CAREs, providing a potential direct link between PB and expression of key genes that regulate DNA methylation status. Previously, we demonstrated that PB-elicited unique regions of altered methylation (RAMs) in B6C3F1 mice, as compared with the relatively resistant C57BL/6, at 2 and 4 weeks, and annotation of the regions harboring these changes revealed 51 genes. This is extended by the current study, which employed RNA isolated from the same liver tissue used in the earlier investigations. Genes elucidated from both the methylation and expression analyses are involved in identical processes/pathways (e.g., cell cycle, apoptosis, angiogenesis, epithelial-mesenchymal cell transition, invasion/metastasis, and mitogen-activated protein kinase, transforming growth factor-beta, and Wnt signaling). Therefore, these changes might represent very early events that directly contribute to PB-induced tumorigenesis. It is instructive to consider the possibility that, in a hypothesis-driven fashion, these genes are initial candidates that could be utilized to develop a biomarker "fingerprint" of early exposure to PB and PB-like compounds.

Altered tumor biology and tumorigenesis in irradiated and chemical carcinogen-treated single and combined connexin32/p27Kip1-deficient mice

Connexin32 knockout mice (Cx32-KO) exhibit increased chemical and radiation-induced liver and lung tumorigenesis. This increased tumor incidence is associated with altered tumor biology including enhanced tumor progression and an increased percent of MAPK-active tumors. Likewise, mice lacking the tumor suppressor/cell cycle regulator p27Kip1 exhibit increased tumorigenesis in a variety of tissues following chemical and radiation induction. Interestingly, in a double-deficient mouse model (DKO), additional loss of p27Kip1 in a Cx32-KO background results in attenuation of liver and lung tumorigenesis as well as MAPK activation profiles, suggesting pathway interaction. While these mouse strains exhibit altered liver and lung tumor susceptibility following both chemical (DEN) and radiation (X-ray) induction protocols, comparisons of the resulting tumor incidence, multiplicity, tumor progression, and MAPK activation in response to these two distinct carcinogens underscores the separate influence of each individual gene on both tumor formation and activation of specific oncogenic pathways. Furthermore, these studies demonstrate that different carcinogens interact disparately with Cx32/p27Kip1 genotypic backgrounds in situ resulting in varied tumorigenic response.

Deficiency in the gap junction protein connexin32 alters p27Kip1 tumor suppression and MAPK activation in a tissue-specific manner

Connexin32 knockout mice (Cx32-KO) exhibit increased chemical- and radiation-induced liver and lung tumor formation with many lung tumors demonstrating decreased levels of the tumor suppressor p27KIP1. To determine if p27 deficiency alters Cx32-influenced tumorigenesis, we have generated a Cx32/p27 double-deficient mouse strain (DKO) and show here that exposure of these mice to X-ray radiation resulted in an increase or decrease in tumorigenesis depending on the tissue. Several tissues were highly sensitive to loss of p27 tumor suppressor function (intestine, adrenal, pituitary) resulting in an increased overall tumor burden in DKO mice compared to both wild-type (P<0.005) and Cx32-KO mice (P=0.066). However, additional deletion of p27 in a Cx32-KO background resulted in a statistically significant decrease in the liver tumor incidence suggesting that Cx32 and p27 pathways mechanistically interact. Immunohistochemical analysis revealed an increased percentage of Cx32-KO liver and lung tumors harboring active mitogen-activated protein kinase (Erk1, Erk2) pathways in contrast to lower percentages of activated wild-type (P<0.005) and DKO tumors (P=0.027). Increased MAPK activation in liver tumors did not correlate with Ha-ras codon-61 mutation status. This study demonstrates that tissues dependent on Cx32 tumor suppression, such as the liver and lung, exhibit altered tumorigenesis and tumor biology (MAPK pathway activation) related to p27 status.

Do the expressions of gap junction gene connexin messenger RNA in noncancerous liver remnants of patients with hepatocellular carcinoma correlate with postoperative recurrences?

AIM: To investigate whether the changes of gap junction gene connexin messenger RNA in the noncancerous liver tissue of patients with hepatocellular carcinoma (HCC) could play a significant role in its postresection recurrence.

METHODS: Seventy-nine consecutive patients having undergone curative resection for HCC entered this study. Using a reverse-transcription polymerase chain reaction (RT-PCR)-based assay, connexin (Cx) 26, connexin (Cx) 32 and connexin (Cx) 43 mRNAs were determined prospectively in noncancerous liver tissues from these 79 patients and in the liver tissues from 15 controls. The correlations between connexin mRNA expression and the clinicopathological variables and outcomes (tumor recurrence and recurrence related mortality) were studied.

RESULTS: Compared with liver tissues of control patients, the expression of Cx 32 mRNA in noncancerous liver tissues was significantly lower (mean: 0.715 vs control 1.225, P<0.01), whereas the decreased Cx 26 mRNA (mean: 0.700 vs of control 1.205, P>0.05) and increased Cx 43 mRNA (mean: 0.241 vs control 0.100, P>0.05) had no statistical significance. We defined the value of Cx 32 mRNA or Cx 26 mRNA below 0.800 as a lower value. By multivariate analysis for noncancerous livers, a lower value of Cx 32 mRNA correlated significantly with a risk of HCC recurrence and recurrence-related mortality. The lower value of Cx 26 mRNA did not correlate with recurrence and mortality. The increased value of Cx43 mRNA also did not correlate with postoperative recurrence and recurrence-related mortality. By multivariate analysis, other significant predictors of HCC recurrence included vascular permeation, cellular dedifferentiation, and less encaps-ulation. The other significant parameter of recurrence related mortality was vascular permeation.

CONCLUSION: The decreased expression of Cx 32 mRNA in noncancerous liver tissues plays a significant role in the prediction of postoperative recurrence of HCC.

Gene Expression Profiling of Early- and Late-Relapse Nonseminomatous Germ Cell Tumor and Primitive Neuroectodermal Tumor of the Testis

PURPOSE

To better understand the molecular mechanisms that underlay the development and progression of nonseminomatous germ cell tumor of testis (NSGCTT) as well as malignant transformation of teratoma and primitive neuroectodermal tumor (PNET).

EXPERIMENTAL DESIGN

We studied the gene expression profiles of 17 retroperitoneal NSGCTTs (10 yolk sac tumors, 3 embryonal carcinomas, 4 teratomas) and 2 PNETs obtained from patients with two clinical outcomes. Tissue samples were obtained from the Indiana University. One group of NSGCTT and PNET patients developed metastases within 2 years (early-relapse) of initial successful treatment, and the other group developed metastases after 2 years (late-relapse). Gene expression in these groups of patients was quantified using cDNA microarrays and real-time relative quantitative PCR.

RESULTS

We demonstrate that the gene expression profiles of these tumors correlate with histological type. In addition, we identify type-specific genes that may serve as novel diagnostic markers. We also identify a gene set that can distinguish between early-relapse and late-relapse yolk sac tumors. The expression differences of these genes may underlie the differences in clinical outcome and drug response of these tumors.

CONCLUSION

This is the first study that used gene expression profiling to examine the molecular characteristics of the NSGCTTs and drug response in early- and late-relapse tumors. These results suggest that two molecularly distinct forms of NSGCTTs exist and that the integration of expression profile data with clinical parameters could enhance the diagnosis and prognosis of NSGCTTs. More importantly, the identified genes provide insight into the molecular mechanisms of aggressive NSGCTTs and suggest intervention strategies.