Inhibition of human glioblastoma cell growth by WAF1/Cip1 can be attenuated by mutant p53.
The WAF1/Cip1 protein is an important regulator at the G1 checkpoint in the cell cycle. The WAF1/Cip1 protein binds to the cyclin-dependent kinase complexes and inhibits the kinase activity that is required for cell cycle progression. We investigated the expression of WAF1/Cip1 protein in 14 glioblastoma cell lines and found that WAF1/Cip1 expression was detectable in many of the cell lines, even when mutant p53 was present. We also showed that WAF1/Cip1 protein level was very low in LN-Z308 cells that do not express endogenous p53. Transfection of the wild-type p53 into this cell line activated WAF1/Cip1 expression and inhibited cell growth. In contrast, transfection of the p53 mutant 248Trp failed to activate WAF1/Cip1 expression. Transfection of WAF1/Cip1 alone also inhibited LN-Z308 cell proliferation. However, cotransfection of the p53 mutant 248Trp with WAF1/Cip1 attenuated the growth-suppression effect of WAF1/Cip1. Our analysis with Western blot showed that the levels of cyclin E increased in cells transfected with p53 mutants. We conclude that p53 mutants may counter the negative regulators, such as WAF1/Cip1, by the elevation of positive cell cycle regulators, and the presence of WAF1/Cip1 in tumor cells is not sufficient for growth inhibition.
Jung
J M
JM
Department of Neuro-Oncology, University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
Li
H
H
Kobayashi
T
T
Kyritsis
A P
AP
Langford
L A
LA
Bruner
J M
JM
Levin
V A
VA
Zhang
W
W
D001932:Brain Neoplasms / Q000188:drug therapy* / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics; D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors*; D016213:Cyclins / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D016158:Genes, p53; D005909:Glioblastoma / Q000188:drug therapy* / Q000473:pathology; D006801:Humans; D009154:Mutation; D014162:Transfection; D014407:Tumor Cells, Cultured
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D018844:Cyclin-Dependent Kinases