CELL-TYPE-DEPENDENT AND PROMOTER-DEPENDENT TS PHENOTYPE OF P53 VAL(135)

The p53 mutant Val(135) is widely considered to have a wild-type (wt) phenotype at 32.5 degrees C, but not at 37 degrees C. The ability of w t murine p53 and its Val(135) mutant to modulate transcription from th e muscle-specific creatine kinase promoter (- 3.3 kb pMCK), from a rep orter construct containing two copies of the p53-binding DNA element f rom within MCK (p50-2), and from the interleukin-6 (IL-6) promoter (pT C225) was evaluated in transient transfection experiments in CV1 and H eLa cells. In CV1 cells, wt p53 was confirmed to activate the pMCK and p50-2 reporters, but to repress the IL-6 promoter. However, although in these cells p53 Val(135) had the expected wt-like phenotype with re spect to activation of the p50-2 reporter at 32.5 degrees C (32.5 degr ees C) 37 degrees C), this mutant had little effect on expression from pMCK at either temperature, and activated rather than repressed the I L-6 promoter at 32.5 degrees C. In HeLa cells, although wt p53 activat ed p50-2 but repressed the MCK and IL-6 promoters, p53 Val(135) activa ted all three reporters. Unexpectedly, in these cells the upregulation of p50-2 and pIC225 was basically temperature-independent, and that o f pMCK was inversely ts (37 degrees C>32.5 degrees C). The novel ts pr operties of p53 Val(135) show that this mutant is not always wt-like a t 32.5 degrees C but exhibits strong cell-type and promoter-dependent differences in its ts phenotype for transcriptional modulation.