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 t o aberrant proliferation and an enhanced neoplastic phenotype. Many human t umors, 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 dem onstrated a major reduction in Cx43 expression in dysplastic regions compar ed to normal epithelia. To determine whether this loss influences the neopl astic behavior of cervical carcinoma cells, we have constructed HeLa cell l ines in which Cx43 expression can be induced in response to doxycycline. Th is approach allows for the discrimination of Cx43-mediated effects from tho se 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 forma tion when in co-culture with growth-controlled fibroblasts. However, Cx43 i nduction decreased two indices of neoplasia: it reduced anchorage-independe nt growth and attenuated the growth rate of tumor xenografts. These results indicate that established HeLa cell lines are unresponsive to Cx43-mediate d signals which are thought to mediate growth control of non-transformed ce lls, however, Cx43 expression can still reduce aspects of the neoplastic ph enotype of these cells, indicating that loss of connexin signaling in dyspl astic cells may contribute to their neoplastic progression.