Identification of p63 target genes in keratinocytes

One single gene, p63, coding for a developmentally regulated transcription factor, causes three human syndromes, the Hay Wells AEC, the EEC and the split hand/split foot malformation (SHFM). The molecular defects have been charaterized and reside in dominant negative missense mutations within the DNA-binding domain (EEC), or in the C-termnal SAM domain (AEC). More specifically p63 seems to play a master regulatory role in the keratinocites stem cell compartment. The p63 transcriptional circuitry is still poorly understood, mainly because the genes targeted and the proteins regulating its activity are essentially unknown. It was shown that the related p73 protein inhibits transcription by interacting with the common activator NF-Y, a protein that regulates most of the cell growth genes: I verified that p63 is also capable to interact in vivo. interestingly, all AEC mutants affecting the SAM domain were incapable to associate NF-Y, suggesting that inhibition of growth regulated genes through NF-Y might be an important function of p63. I have functionally inactivated the p63 gene in HaCat cells by siRNA technology and identified genes activated and repressed by Affimetrix microarray analysis. To confirm the data, I set up the Chromatin Immunoprecipitations (ChIP) technique from the same cell line and in human primary keratinocytes. More than 30 new p63 target gene were identified. The products of these genes have been tested upon differentiation of HaCat cells and in normal human skin sections: my data suggest that the DN is a pro-growth, anti-differentiation isoform, with the capacity to both activate and repress transcription. Furthermore, some of the genes under p63 control confirm its central role at the cross-road between cell growth and differentiation, as demonstrated by immunostaining on p63-/- mice.