HL60세포 분화에 따른 p21WAF1 유전자의 발현

Abstract

p21WAF1 is the mammalian cyclin-dependent kinase (CDK) inhibitor to be discovered. p21WAF1 which is found to be induced by p53 mediates growth arrest by inhibiting G1 CDKs. But, recently p21WAF1 was also found to be induced in senescent and quiescent cells which were low in p53 level and in p53-deficient growth-arrested tumor cell lines. The present study has been investigated the effect of differentiation inducing agents on expression of p21WAF1 gene and cyclin genes in p53-mutant HL60 cell lines by using quantitative reverse transcription- polymerase chain reaction. p21WAF1 mRNA was increased within 15 minutes during monocytic and within 6 hours during granulocytic differentiation of HL60 cell lines. Cycloheximide (CHX), potent protein synthesis inhibitor, alone had no detectable effect on the accumulation of p21WAF1 mRNA but combination of CHX and TPA (12-O-tetradecanoyl phorbol-13-acetate) for 6 hours increased levels of p21WAF1 mRNA. Actinomycin D (ACT) alone and combination of ACT and TPA for 6 hours did not increase levels of p21 mRNA. These results indicated that protein synthesis is not required for the induction of p21WAF1 by TPA and p21WAF1 appeared to be an immediate early response gene. In HL60 cells the increased expression of p21WAF1 mRNA by TPA occurred at the transcriptional level and did not result from change in p21WAF1 mRNA stability. We also studied the involvement of cyclins during monocytic differentiation of HL60 ceil lines. While levels of cyclin A, B, C and E mRNA were gradualy decreased but unexpectedly, levels of cyclin D1 remarkably increased after incubation with TPA. These result showed that monocytic differentiation of HL60 cells by TPA were related with transcriptional level inactivations of cyclin A, B, C and E, but the mechanismss of increased expression of • cyclin D1 mRNA during differentiation remains to be elucidate. Key Words: p21WAF1, CDK inhibitor, Cyclin, HL60 Cell