Characterization of p53 isoforms by 2D-PAGE immunoblotting. Phosphorylated p53 was detected by 2D-PAGE in resting and irradiated (A) Molm-13 and (B) LNCaP cells that express wild-type p53. Following IR, expression of total full-length p53 increased, a characteristic laddering was detected, and phosphorylation occurred at serines 37, 46, and 392, primarily in the full-length p53 isoform group. Following IR, no change in reactivity with phospho-specific antibodies was observed for p63 or Δp53 isoforms. (C) The 63-kDa isoform reactive with the BP53-12 antibody in normal PBMCs was p63. Also seen was a triplet of low-molecular-weight α-p63–reactive spots that were not detected by BP53-12. (D) p63, full-length p53, and the putative p53 truncation (designated Δp53) were the 3 major isoform groups reactive with BP53-12.