EXPRESSION OF DIFFERENTIALLY PHOSPHORYLATED RB AND MUTANT-P53 PROTEINS IN MYELOID-LEUKEMIA CELL-LINES

We studied the structure and expression of Rb and p53 genes in six mye loid leukemia cell lines (HL-60, KBM3, K562, KBM5, EM2, KBM7) in the l ight of the published reports that structural abnormalities of these g enes are rarely seen in leukemic cells and also a recent finding that Rb gene expression can be regulated by the p53 protein. Except for HL- 60 cells which have a truncated p53 gene, none of the other cell lines revealed any gross structural abnormalities in the Rb and p53 genes. KBM3, KBM5 and EM-2 expressed lower levels of Rb mRNA than HL-60, K562 and KBM7. The amount of Rb protein was lowest in KBM3 cells and in th is and two other cell lines (KBM5, KBM7) Rb was markedly hypophosphory lated compared to the other three cell lines. HL-60 and K562 did not e xpress p53 m-RNA, while the other four cell lines all expressed high l evels of mutant p53 protein. Thus even in the absence of gross structu ral alterations, subtle abnormalities in the expression pattern of Rb and p53 genes occur in myeloid leukemia cells.