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 treat ed 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 gluta thione S-transferase P (GST-P) and p53 protein. Ten percent of the GST -P-immunonegative cells were p53-immunopositive. Thymidine incorporati on was blocked in these cells. Both p53 expression and the block in th ymidine incorporation could be eliminated by p53 antisense oligonucleo tides. Less than 1% of the GST-P-positive cells in the same cultures w ere 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 ce lls 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 incor porated thymidine, Virtually none of the GST-P-negative cells with DNA strand breaks demonstrated thymidine incorporation, We suggest that G ST-P-positive cells lack functional p53 protein and that this permits cells with damaged DNA to replicate.