Figure 5. Cisplatin induces dissociation of the ΔNp63α/TAp73 complex.

(A) Quantitative binding of TAp73 to ΔNp63α in HCC-1937 cells and dissociation following cisplatin treatment. Left, IPs of control or cisplatin-treated cultures (IC₇₀ for 6 hours); right, corresponding post-IP supernatants (Sup). IP for either p63 or p73 resulted in complete immunodepletion of TAp73 (lanes 11 and 12). Following cisplatin treatment, less TAp73 was associated with ΔNp63α (lanes 3 and 7), resulting in detectable “free” TAp73 in the depleted post-IP supernatant (lanes 11 and 15). Note the absence of change in ΔNp63α or TAp73 protein levels following cisplatin treatment (lanes 2, 6, 10, and 14). Controls demonstrated these antibodies to be non–cross-reactive (ref. 24 and data not shown). (B) MDA-MB-468 cells showed quantitative ΔNp63α/TAp73 binding similar to that of HCC-1937 cells and partial dissociation following cisplatin treatment. Cells were treated as in A. Left, IP product; right, post-IP supernatant. Note the decrease in TAp73 associated with ΔNp63α following cisplatin treatment (lanes 3 and 7), despite no change in ΔNp63α or TAp73 protein levels (lanes 10 and 14). HCC-1937 cells expressed TAp73α (A), while MDA-MB-468 cells expressed both TAp73α and TAp73β (B).