Aberrant distributions and relationships among E-cadherin, beta-catenin, and connexin 26 and 43 in endometrioid adenocarcinomas

The role of connexins in breast cancer: from misregulated cell communication to aberrant intracellular signaling

In spite of clinical advancements and improved diagnostic techniques, breast cancers are the leading cause of cancer-associated deaths in women worldwide. Although 70% of early breast cancers can be cured, there are no efficient therapies against metastatic breast cancers. Several factors including connexins and gap junctions play roles in breast tumorigenesis. Connexins are critical for cellular processes as a linkage between connexin mutations and hereditary disorders demonstrated their importance for tissue homeostasis. Further, alterations in their expression, localization and channel activities were observed in many cancers including breast cancer. Both channel-dependent and independent functions of connexins were reported in initiation and progression of cancers. Unlike initial reports suggesting tumor suppressor functions, connexins and gap junctions have stage, context and isoform dependent effects in breast cancers similar to other cancers. In this review, we tried to describe the current understanding of connexins in tumorigenesis specifically in breast cancers.

Direct Cell⁻Cell Interactions in the Endometrium and in Endometrial Pathophysiology

Cell contacts exhibit a considerable influence on tissue physiology and homeostasis by controlling paracellular and intercellular transport processes, as well as by affecting signaling pathways. Since they maintain cell polarity, they play an important role in cell plasticity. The knowledge about the junctional protein families and their interactions has increased considerably during recent years. In contrast to most other tissues, the endometrium undergoes extensive physiological changes and reveals an extraordinary plasticity due to its crucial role in the establishment and maintenance of pregnancy. These complex changes are accompanied by changes in direct cell–cell contacts to meet the various requirements in the respective developmental stage. Impairment of this sophisticated differentiation process may lead to failure of implantation and embryo development and may be involved in the pathogenesis of endometrial diseases. In this article, we focus on the knowledge about the distribution and regulation of the different junctional proteins in the endometrium during cycling and pregnancy, as well as in pathologic conditions such as endometriosis and cancer. Decoding these sophisticated interactions should improve our understanding of endometrial physiology as well as of the mechanisms involved in pathological conditions.

Comparison of E-cadherin with STAT3 and apoptosis regulators: Bak and Bcl-xL in endometrioid adenocarcinomas of different ER-alpha immunoprofile

E-cadherin is a factor of good prognosis in endometrioid adenocarcinomas, while STAT3 is an oncogenic driver of carcinogenesis. E-cadherin, Bak, Bcl-xL and STAT3 were immunohistochemically detected in 78 human endometrioid adenocarcinomas. E-cadherin correlated with STAT3 (p <. 001, r = 0.537) as well as Bak (p = .005, r = 0.314) and Bcl-xL (p = .002, r = 0.340) in the whole study group. In G2 tumors, E-cadherin associated with Bak (p = .021, r = 0.319), Bcl-xL (p = .026, r = 0.309) and STAT3 (p <.001, r = 0.513) but not in G3 adenocarcinomas. E-cadherin correlated with Bak and Bcl-xL in both G1- and estrogen receptor (ER)-negative tumors with significant relation of E-cadherin and STAT3 in G1- and ER-negative tumors. Antigrowth synergy of expression was preserved for antiapoptotic Bak and proliferation-suppressing E-cadherin in IA adenocarcinomas (p = .031, r = 0.342) with no significance between Bak and E-cadherin or STAT3 and emerging correlation between E-cadherin and Bcl-xL in IB + II tumors instead (p = .003, r = 0.472). E-cadherin correlated with Bak and Bcl-xL in ER-positive adenocarcinomas (p =  .002, r = 0.382 and p <.001, r = 0.439, respectively) but not in ER-negative tumors. In conclusion, expression deregulation of studied proteins is reflected in selective loss of correlation between suppressors of tumor growth (E-cadherin and Bak) presumably due to progressing impairment of growth-inhibitory properties of clone of neoplastic cells within higher staging and poorer differentiation.

Gap junctions and cancer: communicating for 50 years

Fifty years ago, tumour cells were found to lack electrical coupling, leading to the hypothesis that loss of direct intercellular communication is commonly associated with cancer onset and progression. Subsequent studies linked this phenomenon to gap junctions composed of connexin proteins. Although many studies support the notion that connexins are tumour suppressors, recent evidence suggests that, in some tumour types, they may facilitate specific stages of tumour progression through both junctional and non-junctional signalling pathways. This Timeline article highlights the milestones connecting gap junctions to cancer, and underscores important unanswered questions, controversies and therapeutic opportunities in the field.

E-cadherin and β-catenin adhesion proteins correlate positively with connexins in colorectal cancer

The majority of solid cancers present with qualitative and quantitative aberrations of adhesion proteins, including E-cadherin and β-catenin, and connexin (Cx) gap junction proteins, which is consistent with alterations in the expression and location of such proteins in neoplastic cells. Since there are no data on the correlation between adhesion proteins and Cxs in human colorectal cancer (CRC), the aim of the present study was to evaluate the expression and correlation between these proteins. Tissue specimens were obtained from 151 cases of surgically removed colorectal adenocarcinomas. The samples were examined by immunohistochemistry with the use of antibodies against E-cadherin, β-catenin and the three Cxs: Cx26, Cx32 and Cx43. The aberrant expression of the studied adhesion proteins (primarily cytoplasmic for E-cadherin and cytoplasmic and/or nuclear for β-catenin) was observed, whereas only a minority of cases revealed normal membranous distribution of the labeling. The present study is the first in the literature to reveal a correlation between the expression of E-cadherin and β-catenin and the examined Cxs in CRC in humans. The positive correlation between the Cxs, particularly Cx26 and Cx32, and the adhesive proteins occurred in patients without lymph node metastases and in the moderately differentiated tumors (G2). Such a dependency was not observed in the analysis of the correlation between Cx43 and E-cadherin. However, a positive correlation between these proteins was observed in patients with lymph nodes metastases. Additionally, a link between the expression of these adhesion proteins was observed. The present study indicates, for the first time, that the expression of adhesion proteins, E-cadherin and β-catenin, is closely associated with the expression of three studied Cxs in CRC, and that this correlation may improve an understanding of the carcinogenic process in this cancer.

The molecular basis for the pharmacokinetics and pharmacodynamics of curcumin and its metabolites in relation to cancer

This review addresses the oncopharmacological properties of curcumin at the molecular level. First, the interactions between curcumin and its molecular targets are addressed on the basis of curcumin's distinct chemical properties, which include H-bond donating and accepting capacity of the β-dicarbonyl moiety and the phenylic hydroxyl groups, H-bond accepting capacity of the methoxy ethers, multivalent metal and nonmetal cation binding properties, high partition coefficient, rotamerization around multiple C-C bonds, and the ability to act as a Michael acceptor. Next, the in vitro chemical stability of curcumin is elaborated in the context of its susceptibility to photochemical and chemical modification and degradation (e.g., alkaline hydrolysis). Specific modification and degradatory pathways are provided, which mainly entail radical-based intermediates, and the in vitro catabolites are identified. The implications of curcumin's (photo)chemical instability are addressed in light of pharmaceutical curcumin preparations, the use of curcumin analogues, and implementation of nanoparticulate drug delivery systems. Furthermore, the pharmacokinetics of curcumin and its most important degradation products are detailed in light of curcumin's poor bioavailability. Particular emphasis is placed on xenobiotic phase I and II metabolism as well as excretion of curcumin in the intestines (first pass), the liver (second pass), and other organs in addition to the pharmacokinetics of curcumin metabolites and their systemic clearance. Lastly, a summary is provided of the clinical pharmacodynamics of curcumin followed by a detailed account of curcumin's direct molecular targets, whereby the phenotypical/biological changes induced in cancer cells upon completion of the curcumin-triggered signaling cascade(s) are addressed in the framework of the hallmarks of cancer. The direct molecular targets include the ErbB family of receptors, protein kinase C, enzymes involved in prostaglandin synthesis, vitamin D receptor, and DNA.

TCF12 protein functions as transcriptional repressor of E-cadherin, and its overexpression is correlated with metastasis of colorectal cancer

A correlation of TCF12 mRNA overexpression with colorectal cancer (CRC) metastasis was suggested by microarray data and validated by the survey of 120 patients. Thirty-three (27.5%) of the 120 patients showed tumor TCF12 mRNA overexpression and had a higher rate of metastatic occurrence (p = 0.020) and a poorer survival outcome (p = 0.014). Abundant TCF12 levels were also observed in human CRC cell lines such as SW620 and LoVo, but a relatively low level was detected in SW480 cells. Knockdown of TCF12 expression in SW620 and LoVo cells drastically reduced their activities of migration, invasion, and metastasis. Tight cell-cell contact and an increase in E-cadherin but a concomitant decrease in fibronectin were observed in TCF12-knockdown cells. Connexin 26, connexin 43, and gap-junction activity were also increased upon TCF12-knockdown. In contrast, ectopic TCF12 overexpression in SW480 cells facilitated fibronectin expression and cell migration and invasion activities but diminished cellular levels of E-cadherin, connexin 26, connexin 43, and gap junction. A physical association of TCF12 with the E-cadherin promoter was evidenced by chromatin immunoprecipitation assay. TCF12 was tightly correlated with cellular expression of Bmi1 and EZH2 and was co-immunoprecipitable with Bmi1 and EZH2, suggesting that TCF12 transcriptionally suppressed E-cadherin expression via polycomb group-repressive complexes. Clinically, TCF12 mRNA overexpression was also correlated with E-cadherin mRNA down-regulation in the tumor tissues of our 120 patients (p = 0.013). These studies suggested that TCF12 functioned as a transcriptional repressor of E-cadherin and its overexpression was significantly correlated with the occurrence of CRC metastasis.

Connexin43 acts as a colorectal cancer tumor suppressor and predicts disease outcome

This article is the first to show that loss of connexin43 (Cx43) expression in colorectal tumors is correlated with significantly shorter relapse-free and overall survival. Cx43 was further found to negatively regulate growth of colon cancer cells, in part by enhancing apoptosis. In addition, Cx43 was found to colocalize with β-catenin and reduce Wnt signaling. The study represents the first evidence that Cx43 acts as a colorectal cancer tumor suppressor and that loss of Cx43 expression during colorectal cancer development is associated with reduced patient survival. The study has important implications for the assessment of Cx43 as a prognostic marker and target in colorectal cancer prevention and therapy. Gap junctions consist of intercellular channels that permit direct transfer of ions and small molecules between adjacent cells. The gap junction channel protein Cx43 plays important roles in cell growth control and differentiation and is frequently dysregulated in human cancers. However, the functional importance and clinical relevance of Cx43 in cancer development has remained elusive. Here, we show that Cx43 is downregulated or aberrantly localized in colon cancer cell lines and colorectal carcinomas, which is associated with loss of gap junction intercellular communication. The in situ protein expression of Cx43 was analyzed in colorectal tumors in a cohort of 674 patients and related to established clinicopathological variables and survival. A subgroup of the patients had weak or no expression of Cx43 in tumors. Loss of Cx43 expression was significantly correlated with shorter relapse-free and overall survival. Loss of Cx43 further identified a high-risk subgroup among stage I and stage II patients with reduced relapse-free and overall survival. Ectopic expression of Cx43 in the colon cancer cell line HT29 was associated with reduced growth in monolayer and soft agar cultures and in tumor xenografts. Cx43 was found to colocalize with β-catenin and negatively regulate the Wnt signaling pathway, and expression of Cx43 was associated with increased levels of apoptosis. Altogether, these data indicate that Cx43 is a colorectal cancer tumor suppressor protein that predicts clinical outcome.