Expression and function of connexin in normal and transformed human keratinocytes in culture

We have studied the gap junctional intercellular communication(GJIC) of immortalized and tumourigenic human keratinocyte celllines and of a spontaneously immortalized non-tumourigenic anda highly differentiating keratinocyte cell line (HaCaT) as thecontrol. In homologous cultures, the GJIC capacity of five squamouscell carcinoma-derived cell lines was 1–27% that of theHaCaT cells. Ha-ras-transfected HaCaT cells with tumourigenicpotential and an SV40 DNA-immortalized cell line had markedlyreduced GJIC capacities. Northern analysis and immunohisto-chemistryshowed that connexin (Cx) 43 is the major gap junction proteinexpressed in the communicating cells. They do not express Cx26 or 32. The low or absent communication observed in certaincell lines was due in some to a lack of Cx 43 gene expression,but in others to aberrant localization of the gap junction protein.GJIC of these cell lines, as well as that of primary normalhuman epidermal keratinocytes, was susceptible to 12-O-tetra-decanoylphorbol-13-acetate-mediatedinhibition. Moreover, GJIC of HaCaT cells and their tumourigenicderivatives is Ca²⁺-dependent. These results, when comparedwith those previously obtained for mouse keratinocyte cell lines,reveal that GJIC of human keratinocytes was correlated to thedegree of differentiation and is controlled in a similar wayto that of murine keratinocytes. Aberrant GJIC seems to be acommon feature of human and murine skin carcinogenesis.