ALTERATION IN EXPRESSION OF GAP JUNCTION PROTEINS IN RAT-LIVER AFTER TREATMENT WITH THE TUMOR PROMOTER 3,4,5,3',4'-PENTACHLOROBIPHENYL

Polychlorinated biphenyls (PCBs) are industrial chemicals which are hi ghly persistent and widely distributed in the environment. We have pre viously shown that 3,4,5,3',4'-pentachlorobiphenyl (PCB 126) is a pote nt tumour promoter in two separate 20 week initiation-promotion studie s. In the present study, rat livers from these two studies were furthe r investigated for connexin expression. The results demonstrated that treatment with PCB 126 caused a decrease in the amount of the two majo r liver connexins, cx 26 and cx 32, in livers of treated animals. This reduction was also prominent after treatment at low doses, although g amma-glutamyl transpeptidase-positive foci had not developed in these livers. The quantity of cx 26 and cx 32 in immunostained liver section s was determined using a computerized fluorescence image analyzer. wes tern blot analysis of liver extracts confirmed these results. No chang es in the RNA levels in the treated rats were seen, suggesting that th e down-regulation of cx 26 and cx 32 is post-transcriptional.