Regulation of the cyclin-dependent kinase inhibitor p57Kip2 expression by p63.

The cyclin-dependent kinase (CDK) inhibitor p57Kip2 is a negative regulator of cell proliferation, binding to a variety of cyclin-CDK complexes and inhibiting their kinase activities. The p57Kip2 gene was recognized as a target gene for p73beta, one member of the p53 family. In spite of this, the phenotypes of p73 and p57Kip2 knockout mice do not resemble each other while there is a phenotypic overlap between the p57Kip2 null mice, the p63 null mice and patients affected by p63 associated syndromes, suggesting that p57Kip2 could be indeed a downstream target of p63. By ChIP we determined that in the HaCaT cell line the DeltaNp63alpha protein is associated to three different regions of the p57Kip2 gene. DeltaNp63 can activate both the endogenous p57Kip2 gene and a reporter vector containing a -2191 promoter fragment of the p57Kip2 gene. Natural p63 mutants, associated to the AEC syndrome, show a partial or complete lack of transactivation potential of the p57Kip2 promoter, while three other natural p63 mutants, associated to the EEC, LMS and SHFM-4 syndromes, were less affected. These data suggests that p63 play an important role in the regulation of p57Kip2 expression and that this regulation is subverted in AEC p63 mutants.