RESTORATION OF WILD-TYPE P53 ACTIVITY IN P53-NULL HL-60 CELLS CONFERSMULTIDRUG SENSITIVITY

HL-60 cells that stably express transfected wild-type (wt) p53 were us ed to determine whether restoration of wt p53 increased the chemosensi tivity of cells that normally lack p53 activity. The wt p53 HL-60 tran sfectants (SN3 cells) were more sensitive than the parental (S) cells to a number of common anticancer drugs representing various mechanisms of action, whereas HL-60 cells transfected with p53 genes mutated at codons 248 and 143 were not sensitized. The sensitization ratio due to the transfected wt p53 varied from about 2-fold for cisplatin to over 50-fold for thymidine. Cells treated with the thymidylate synthase in hibitor 5-fluoro-2'-deoxyuridine (FdUrd) were used to study changes in various p53-associated gene expressions, A higher percentage of apopt otic cells among the SN3 cells was observed than among the S cells at each concentration of FdUrd, The S cells had undetectable levels of ba r and high levels of bcl-2, whereas the SN3 cells had undetectable lev els of bcl-2 levels and appreciable basal levels of bar. After FdUrd t reatment of SN3 cells, both p53 and bar levels increased, but the indu ction of bar was faster than that of p53 and paralleled the appearance of apoptotic DNA laddering. FdUrd treatment induced p21 expression an d increased the G(1) fraction of the SN3 cells but did not induce p21 or change the phase distribution in the S cells, FdUrd treatment also induced the expression and phosphorylation of cyclin D1 in the SN3 cel ls but not in the S cells. These results shown that transfected wt p53 confers multidrug sensitivity to HL-60 cells by re-adjustment of the expressions of apoptosis genes and displays other properties character istic of endogenously originated wt p53.