New insight into the mechanism of p53 inducing leukemia cell apoptosis

Objective To investigate the expression changes of intrinsic cytokines TGF-β 1 and TNF-α,telomerase activity and bcl-2 during ongoing apoptosis of HL-60 and K562 cells induced by p53. Methods pN53cG(Val135), a temperature sensitive p53 mutant, which behaved like wild type p53(wt-p53) at 32.5 ℃, were introduced into p53-null HL-60 and K562 cells respectively by lipofectin . In the presence of G418, HL-60-pN53cG and K562-pN53cG clones expressing p53 protein were selected. The ongoing expression of intrinsic cytokines (TGF-β 1 and TNF-α), bcl-2 oncogene and hTERT mRNA during the apoptosis of HL-60 and K562 cells induced by p53 and the effects of exogenous p53 gene, TGF-β 1 and TNF-α antisense PS-ODNS on the apoptosis of HL-60 and K562 cells and the expression of bcl-2 were studied by RT-PCR,quantitative RT-PCR, DNA fragmentation, TdT-mediated dUTP nick end labeling(TUNEL) and flow cytometery. The levels of secreted TGF-β 1 and telomerase activity were detected by ELISA and PCR-ELISA, respectively. Results ①The expressions of intrinsic TGF-β 1 and TNF-α mRNA were up-regulated, while that of bcl-2 and hTERT down-regulated. The levels of TGF-β 1 in the supernatant of HL-60 and K562 cells were increased, and the level of telomerase activity decreased.②Antisense PS-ODNS of TGF-β 1 and TNF-α could obviously inhibit the p53 inducing cell apoptosis, and restore bcl-2 mRNA and protein to pre-treated level. Conclusions Exogenous p53 induces leukemia cell apoptosis via up-regulating the expression of intrinsic TGF-β 1 and TNF-α and down-regulating the expression of hTERT and bcl-2.