Reduced levels of connexin43 in cervical dysplasia: inducible expression in a cervical carcinoma cell line decreases neoplastic potential with implications for tumor progression

Loss of gap junctional intercellular communication (GJIC) has been linked to aberrant proliferation and an enhanced neoplastic phenotype. Many human tumors, including the cervical carcinoma line HeLa, have been reported to be deficient in expression of the gap junction protein connexin43 (Cx43) and GJIC. To determine if this is an early event in carcinogenesis, we utilized immunohistochemistry to screen a series of cervical biopsy samples and demonstrated a major reduction in Cx43 expression in dysplastic regions compared to normal epithelia. To determine whether this loss influences the neoplastic behavior of cervical carcinoma cells, we have constructed HeLa cell lines in which Cx43 expression can be induced in response to doxycycline. This approach allows for the discrimination of Cx43-mediated effects from those due to pre-existing clonal heterogeneity. Cx43 induction in these cells led to assembly of functional junctions but did not alter growth control in vitro as measured by logarithmic growth, saturation density or focus formation when in co-culture with growth-controlled fibroblasts. However, Cx43 induction decreased two indices of neoplasia: it reduced anchorage-independent growth and attenuated the growth rate of tumor xenografts. These results indicate that established HeLa cell lines are unresponsive to Cx43-mediated signals which are thought to mediate growth control of non-transformed cells, however, Cx43 expression can still reduce aspects of the neoplastic phenotype of these cells, indicating that loss of connexin signaling in dysplastic cells may contribute to their neoplastic progression.