Objective    To investigate the effect of geldanamycin (GA) on the expression of HSP (HSP90

HSP70

HSP27) and oncoprotein (mutant p53

CDK4) in human breast cancer cell line MDA-MB-435s.     Methods    Proliferation of MDA-MB-435s cells was measured with MTT assay. The mRNA expression levels of HSP90

HSP70 and HSP27 were detected by RT-PCR. The protein expression levels of HSP90

HSP70

HSP27

mutant p53 and CDK4 were detected by Western blot.     Results    GA inhibited the proliferation of MDA-MB-435s cells in a time-dose dependent manner. The expression level of mRNA and protein of HSP90

HSP70 and HSP27 were increased

and the increasing of HSP70 was the most significant

while the protein expression level of mutant p53 and CDK4 in MDA-MB-435s cells were reduced obviously after 48-hour treatment with 400 nmol/L GA as compared with that of control cells.     Conclusion    GA inhibits the proliferation of MDA-MB-435s cells by down-regulating the level of mutant p53 and CDK4 protein

and GA involves in the protection of cell stress through increasing the expression of HSP90

HSP70 and HSP27.