Effects of bisphenol A on gap junctions in HaCaT cells as mediated by the estrogen receptor pathway

Bisphenol A (BPA) is widely used as the raw material for the production of plastics and paper products. People can be exposed to BPA through dermal contact, particularly for cashiers in contact with thermal paper every day. BPA is a known endocrine disruptor that has been shown to be carcinogenic. Many tumors show weak gap junctional intercellular communication (GJIC) function. The aim of this study was to investigate the effects and possible mechanisms of BPA's action on GJIC of human HaCaT skin cells. The results showed that BPA increased cell proliferation rates, prolonged GJIC photobleaching fluorescence recovery times and reduced overall fluorescence recovery rates at 0.01, 0.1 and 1 μm. BPA downregulated connexin (Cx)26 mRNA level at 0.1 μm. Estrogen receptor (ER) antagonist ICI 182 780 at 5 nm partially blocked the above effects of BPA indicating involvement of the ER pathway with BPA exposure. However, BPA did not influence Cx43 mRNA and protein levels. Our immunofluorescence data showed that Cx26 was expressed in the cytoplasm and plasma membrane, and was involved in the formation of gap junctions between adjacent cells, while Cx43 was expressed only in the cytoplasm. Therefore, our data indicate that Cx26 gap junctions may be involved in the GJIC inhibition caused by BPA. In conclusion, our results indicate that BPA can promote human skin cell proliferation, inhibit skin cell GJIC function but not formation and downregulate Cx26 mRNA levels partially through the ER pathway. We hypothesize that BPA can exhibit carcinogenicity by inhibiting GJIC.