Fig. 6. p53 phosphorylation occurs downstream of cyclin B/mTOR upregulation and karyogamy. (A) Chemical inhibition of p53 by cyclic pifithrin-α. Syncytia were generated in the presence of 10 µM cyclic pifithrin-α, and the indicated parameters were determined by in situ fluorescence techniques (columns) or by immunoblotting (insert). Asterisks denote significant (P < 0.01) pifithrin-α effects. (B) Effect of DN p53. Syncytia were generated by co-culture of HeLa CD4 and HeLa Env cells previously transfected with either of two p53 mutants. Note that the level of p53^S15P staining, at per-cell level, actually increased and that karyogamy and the frequency of p53^S15P⁺ cells was not affected, while apoptosis was inhibited corresponding to the transfection efficiency (∼50%). Results are representative of three independent determinations.