Molecular Chaperone Inducers Facilitate the Functional Restoration of Temperature-sensitive Mutant p53 Protein

The tumor suppressor gene p53 encodes a transcription factor and is known to be the most frequently mutated gene (approximately 50%) in human cancer. The functional restoration of mutant p53 protein is considered to be one type of anticancer treatment ; and some chemical compounds, including CP-31398, PRIMA-1 (p53 reactivation and induction of massive apoptosis), and glycerol, have been shown to restore its function. We here investigated whether molecular chaperone inducers such as carbenoxolone (CBX), paeoniflorin (PF), and sodium salicylate (SA) could restore the functional defect of a temperature-sensitive mutant p53 protein (V143A). Functional restoration of p53 was detected by the induction of wild-type p53 activated fragment 1 (WAF1) and mouse double minute 2 (MDM2), both of which are gene products transactivated by an active p53. When H1299/tsp53 cells were cultured continuously at a nonpermissive temperature (37°C), no apparent expression of WAF1 and MDM2 was observed. Upon the temperature shift-down from 37°C to a permissive temperature (32°C), WAF1 and MDM2 gradually accumulated in the cells at 6 to 12 h later, probably owing to the gradual appearance of wild-type p53. When the cells were treated with molecular chaperone inducers at 37°C and then the temperature was shifted down, WAF1 and MDM2 appeared much earlier at 3 to 6 h, and also in much higher amounts than those in the control cells. Inhibition of molecular chaperone induction by quercetin or heat shock factor 1 (HSF1) siRNA diminished the facilitative effect of molecular chaperone inducers. Also, long-term overexpression (48 h) of molecular chaperones by CBX led to the accumulation of wild-type p53 even at 37°C. These results suggested that moderately overexpressed molecular chaperones could facilitate the correct folding and functional restoration of mutant p53 protein.