Effect of c-myc on p21Cipl and apoptosis of breast cancer cells via a p53,independent manner

Abstract

Objective To investigate the effect of mutant （T58A） and wild type （ WT） c-myc onp21Clpl and apoptosis of breast cancer cells in a p53-independent way. Methods Lentiviral vectors contai-ning c-myc T58A and WT were transfected into breast cancer cells HCC1937 （ cell transfection rate exceeds85% ） . Untreated cells （ group A） and cells transfected by lentivirus without c-myc gene （group B） servedas blank control group and transfection control group respectively. Cells stably expressing c-myc T58A（group C） and WT （group D） served as experiment groups. All the cells were then transfected by p21Cipi/siRNA. RT-PCR and Western blotting were used to detect the mRNA and protein levels of c-myc andp21Cipl,and the apoptosis was examined by using TdT-mediated dUTP nick end labeling （TUNEL） . Re-sults As compared with groups A and B,the c-myc was overexpressed in groups C and D （ all p 〈0. 01 ） . Before transfection, the p21c,pl in group C was highest （P 〈0. 01 ）,while group D had the lowestexpression of p21Cipl （p 〈0. 01 ） ; the apoptosis rate in group C was lower than in other groups, and that ingroup D was the highest： （5. 5 ±0. 5）% , （5. 8 ±0. 3）% , （2. 8 ±0. 3）% and （9. 8 ±0. 8）% in groupsA,B,C and D, respectively （p 〈0.01）. After transfection, the apoptosis rate in all groups were im-proved obviously （P 〈0.05）. Conclusion Normally,in a non-p53 background,c-myc WT can suppressthe expression of p21c,pI,resulting in the increased apoptosis rate, but after mutation （T58A）,the abilityof c-myc to induce apoptosis is decreased. Key words: Breast cancer; c-myc ; p21 cip1 ; Apoptosis