Aberrant Expression of the p53 Tumor Suppressor Gene in Adult T‐Cell Leukemia and HTLV‐I‐infected Cells

By immunoprecipitation analysis, enhanced p53 expression was detected in 3 of 4 adult T‐cell leukemia (ATL) cell lines, 1 of 3 HTLV‐I‐infected cell lines and 1 of 5 fresh ATL samples, compared with phytohemagglutinin‐stimulated peripheral blood lymphocytes. Among these 5 high expressers, p53 missense mutations were indicated in 2 ATL cell lines and 1 fresh ATL sample by extensive p53 cDNA and genomic DNA polymerase chain reaction single‐strand conformation polymorphism analysis. No mutation was found throughout the entire coding region of the remaining 2 high expressers (1 ATL and 1 HTLV‐I‐infected cell lines) and low expressers of p53 (2 HTLV‐I‐infected cell lines). Tax oncoprotein expression was found in these 2 high p53 expressers in which p53 mutation was not present, but not in low p53 expressers or cells carrying this mutation. The levels of p53 mRNA were similar among the samples regardless of p53 levels. Posttranscriptional mechanisms other than missense mutation would thus appear to increase p53 in the Tax‐expressing cells hut not in cells containing undetectablc levels of Tax. No complex formation between p53 and Tax was observed.