Reciprocal regulation of p63 by C/EBP delta in human keratinocytes

Background: Genetic experiments have clarified that p63 is a key transcription factor governing the establishment and maintenance of multilayered epithelia. Key to our understanding of p63 strategy is the identification of target genes. We perfomed an RNAi screening in keratinocytes for p63, followed by profiling analysis. Results: C/EBP delta, member of a family with known roles in differentiation pathways, emerged as a gene repressed by p63. We validated C/EBP delta as a primary target of Delta Np63 alpha by RT-PCR and ChIP location analysis in HaCaT and primary cells. C/EBP delta is differentially expressed in stratification of human skin and it is up-regulated upon differentiation of HaCaT and primary keratinocytes. It is bound to and activates the Delta Np63 promoter. Overexpression of C/EBP delta leads to alteration in the normal profile of p63 isoforms, with the emergence of Delta Np63 beta and gamma, and of the TA isoforms, with different kinetics. In addition, there are changes in the expression of most p63 targets. Inactivation of C/EBP delta leads to gene expression modifications, in part due to the concomitant repression of Delta Np63 alpha. Finally, C/EBP delta is found on the p63 targets in vivo by ChIP analysis, indicating that coregulation is direct. Conclusion: Our data highlight a coherent cross-talk between these two transcription factors in keratinocytes and a large sharing of common transcriptional targets.