Direct transactivation of c-Ha-Ras gene by p53: evidence for its involvement in p53 transactivation activity and p53-mediated apoptosis.
p53 protein is a sequence-specific transcriptional activator which induces the expression of a number of cellular genes involved in different metabolic pathways. We report that the computer-selected sequence in human and mouse C-Ha-Ras gene confers to a reporter gene the ability to be directly transactivated by wild-type p53 either overexpressed or activated in response to a cellular stress. By analysing human transformed cell lines, we showed, at both mRNA and protein level, that the endogenous c-Ha-Ras gene expression is positively regulated by wt p53 protein. The stimulation of c-Ha-Ras gene expression in Saos-2Ts cells by a temperature shift down to the permissive temperature for the p53-wt conformation is associated with a significant increase in the activated form of p21c-Ha-Ras protein. Furthermore, in human transformed cell lines, the transient expression of a dominant interfering mutant of c-Ha-Ras greatly reduced the ability of p53 to induce apoptosis and inhibited the p53-dependent transactivation. This is due, at least in part, to a decrease in the protein (but not mRNA) level of the transiently expressed p53, indicating that inactivation of p21c-Ha-Ras signalling pathways led to a specific degradation of p53 protein. We therefore suggest that, by inducing c-Ha-Ras, p53 activates a positive feedback loop that counteracts the negative feedback loop mediated by Mdm2.
Deguin-Chambon
V
V
Commissariat a l'Energie Atomique, Laboratoire de Cancérogenèse Moléculaire, UMR217 CEA-CNRS, Fontenay-aux-Roses, France.
Vacher
M
M
Jullien
M
M
May
E
E
Bourdon
J C
JC
D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D001483:Base Sequence; D017124:Conserved Sequence; D005246:Feedback; D005786:Gene Expression Regulation; D011905:Genes, ras / Q000235:genetics*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D020218:Response Elements / Q000235:genetics; D012689:Sequence Homology, Nucleic Acid; D015398:Signal Transduction / Q000235:genetics*; D013696:Temperature; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics* / Q000502:physiology
D016159:Tumor Suppressor Protein p53; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)