Aberrant expression of gap junction proteins (connexins) is associated with tumor progression during multistage mouse skin carcinogenesis in vivo

Abstract

To elucidate what changes in the expression of gap junction proteins (connexins) occur at what stages during multistage mouse skin carcinogenesis in vivo, we immunohistochemically and morphometrically analyzed the expression of connexin 26 (Cx26) and connexin 43 (Cx43) in papillomas, well-, moderately- and poorly-differentiated squamous cell carcinomas, as well as in squamous cell carcinomas at invasion sites and those metastasized into lymph nodes in female CD-1 mice as a result of treatment with dimethylbenz[a]anthracene and 12-O-tetradecanoylphorbol-13-acetate. In papillomas, no clear reduction of the two connexins was observed; however, Cx26 and Cx43 were frequently co-localized in the same gap junction plaques, whereas the two kinds of Cxs were differentially expressed in normal and surrounding non-tumorous epidermis. In squamous cell carcinomas, the expression of both Cx26 and Cx43 significantly decreased compared with surrounding non-tumorous epidermis and papillomas. The Western blot analysis confirmed that both Cx26 and Cx43 proteins were reduced in squamous cell carcinomas compared with papillomas. Furthermore, the expression of Cx26 was reduced as cancer cells became morphologically less differentiated, while that of Cx43 did not change. Squamous cell carcinomas at invasive sites showed clear reduction of Cx26 and Cx43. In squamous cell carcinomas metastasized into lymph nodes, Cx26 was expressed, but few carcinoma cells expressed Cx43. The localization of E-cadherin on the plasma membrane between cancer cells was maintained even at invasive and metastatic sites. Our data suggest that quantitative and qualitative changes in connexin expression are associated with tumor progression, including the loss of differentiation, and invasion and metastasis, during multistage mouse skin carcinogenesis.

Enhanced Tumorigenicity of Rat Bladder Squamous Cell Carcinoma Cells after Abrogation of Gap Junctional Intercellular Communication

“…Although connexin 43 expression is increased in these tumors compared to normal transitional cells, the expression is primarily in areas of squamous differentiation. The level of expression in these areas is comparable to or lower than in normal squamous cells [23][24][25] , with which comparison is more appropriate. To clarify whether this is indeed the case, studies of the mechanisms of transcriptional activation of the connexin 43 gene are necessary, although change of connexin 43 expression alone was not enough to alter the morphology of the cells.…”

Connexins: a connection with the skin

“…Recently, multiple in vitro and in vivo studies confirmed that expression and function of Cx play an important role in cell growth control and demonstrated a significant down-regulation of GJIC and loss of Cx expression in epithelial neoplasia (71,75,80,84). Both major gap junctional proteins, Cx26 and Cx43, are almost completely abolished in basal cell carcinoma and squamous cell carcinoma (71,80). Only a few, small gap junctions are developed in such tumor cells, and Cxs often show an aberrant cytoplasmic distribution (75).…”

“…In contrast to fetal skin, Cx45 and Cx26 cannot be detected in the upper epidermal layers. Thus, maturation of rodent epidermis is associated with a down-regulation of the expression of Cx26, Cx37, and Cx45, and an up-regulation of Cx31, Cx31.1, and Cx30.3 expression during terminal differentiation (44,49,58,61,(69)(70)(71). However, the switch in Cx expression is obviously not associated with a descriptive change in pattern of dye transfer, and thus, GJIC (45).…”

The stage-specific function of gap junctions during tumourigenesis

“…Although a correlation between the loss of gap junctions and the metastatic capability of cancerous cells was reported (see [35]), several studies have revealed relatively high levels of connexins and gap junctional coupling in populations of invasive tumour cells. Kamibayashi et al [36] demonstrated that even though the expression of Cx26 and Cx43 was reduced in the early stages of mouse skin carcinogenesis, both connexins were expressed on the plasma membranes of cells invading the lymph nodes. Similar observations were made for breast cancer [35], prostate cancer [37,38] and glioma cell populations [39].…”