GST-P-positive hepatocytes isolated from rats bearing enzyme-altered foci show no signs of p53 protein induction and replicate even when their DNA contains strand breaks.

Hepatocytes were isolated from rats with enzyme-altered foci (EAF) in their livers and were studied in primary cultures. Cultures were treated with two doses of 0.6 mM diethylnitrosamine (DEN) at 1.5 and 24 h. At 48 h the cultures were double stained with antibodies against glutathione S-transferase P (GST-P) and p53 protein. Ten percent of the GST-P-immunonegative cells were p53-immunopositive. Thymidine incorporation was blocked in these cells. Both p53 expression and the block in thymidine incorporation could be eliminated by p53 antisense oligonucleotides. Less than 1% of the GST-P-positive cells in the same cultures were p53-immunopositive. Thymidine incorporation was less affected than in GST-P-negative cells. DNA strand breaks were also monitored by an immunological technique. Twenty-three percent of the GST-P-negative cells and 7% of the GST-P-positive cells were positive for this marker. Seven percent of the GST-P-positive cells with DNA strand breaks incorporated thymidine. Virtually none of the GST-P-negative cells with DNA strand breaks demonstrated thymidine incorporation. We suggest that GST-P-positive cells lack functional p53 protein and that this permits cells with damaged DNA to replicate.