p73 and p63 are homotetramers capable of weak heterotypic interactions with each other but not with p53

Mutations in the p53 tumor suppressor gene are the most frequent genetic al terations found in human cancers, Recent identification of two human homolo gues of p53 has raised the prospect of functional interactions between fami ly members via a conserved oligomerization domain. Here we report in vitro and in vivo analysis of homo- and hetero-oligomerization of p53 and its hom ologues, p63 and p73, The oligomerization domains of p63 and p73 can indepe ndently fold into stable homotetramers, as previously observed for p53, How ever, the oligomerization domain of p53 does not associate with that of eit her p73 or p63, even when p53 is in 15-fold excess. On the other hand, the oligomerization domains of p63 and p73 are able to weakly associate with on e another in vitro, In vivo co-transfection assays of the ability of p53 an d its homologues to activate reporter genes showed that a DNA-binding mutan t of p53 was not able to act in a dominant negative manner over wild-type p 73 or p63 but that a p73 mutant could inhibit the activity of wild-type p63 , These data suggest that mutant p53 in cancer cells will not interact with endogenous or exogenous p63 or p73 via their respective oligomerization do mains. It also establishes that the multiple isoforms of p63 as well as tho se of p73 are capable of interacting via their common oligomerization domai n.