Functional characterization of naturally occurring mutants (P405R and P425L) of p73 alpha and p73 beta found in neuroblastoma and lung cancer

The novel candidate tumor suppressor p73, a structural and functional homol og of p53, activates various p53 responsive promoters and induces tumor cel l apoptosis, Although p73 is infrequently mutated in human cancers, we ha, e previously found two types of p73 mutation with amino acid substitution ( P405R and P425L) in primary neuroblastoma and lung cancer. Here we report g enerations of the p73 mutants with either P405R or P425L substitution and f unctional analysis of these naturally occurring mutants, Indirect immunoflu orescence staining revealed that nuclear accumulation of p73 alpha or p73 b eta was not affected by these mutations. The P425L substitution reduced the ability of p73a to transactivate various p53 responsive promoters (p21(Waf 1), Mdm2, and Bax), Moreover, this down-regulation was correlated with the reduced capability of p73 alpha (P425L) to suppress cell growth in p53-defi cient SAOS-2 cells. In contrast, p73 beta (P425L) was as effective as wild- type p73 beta in transactivation and growth inhibition. On the other hand, the P405R substitution had no significant effect on both the transcriptiona l activity and the growth-suppressive ability of p73 alpha or p73 beta. The se results suggested that, at least, one of the naturally occurring p73 mut ants, p73 alpha (P425L), was a functionally defective mutant of p73.