Effects of Aroclor 1254 on intercellular communication in human keratinocytes

It has been previously described that Aroclor 1254 can inhibit GJIC in rodent liver cells where it is known to be a tumor promoter, while the possibility that Aroclor 1254 exerts its inhibitory effects on GJIC in human keratinocytes and acts as a human skin tumor promoter, deserves further attention. In the present study the effects of Aroclor 1254 were examined on gap junction channel permeability, on connexin 43 (Cx 43) expression at mRNA and protein level and on ultrastructural modification to add further experimental evidence to its inhibitory effect on GJIC. The results were compared to those induced by 12-O-tetradecanoylphorbol-13 acetate (TPA), a tumor promoter known to be a potent inhibitor of GJIC in human skin cells and to those induced by benzo[a]pyrene (B[a]P) known for its genotoxic activity. Our data show increased Cx 43 protein expression in Aroclor 1254 and TPA-treated cultures compared to controls, decreased Cx 43 protein level in those exposed to B[a]P, while Cx 43 gene expression (Cx 43 mRNA) was unaffected by the treatments. In Aroclor and TPA-treated keratinocytes, the ultrastructural examination showed residues of junctional systems expressed by specular, short tracts of the faced plasma membranes. In contrast, the contacts between plasma membranes of adjacent B[a]P treated keratinocytes were more extended. A clear inhibition of gap junction channel permeability due to Aroclor 1254 and TPA was also manifest by Lucifer yellow dye test compared to B[a]P-treated cultures where dye spreading to the neighbouring cells and to the extracellular space occurred. The present data, in addition to confirming inhibition of GJIC mediated by Aroclor 1254 in human keratinocytes, which were found to be comparable to those induced by TPA, suggest that GJIC inhibition is associated with increased Cx 43 protein expression without significant modification of its gene expression.