Identification of ΔNp63α Protein Interactions by Mass Spectrometry

p63, a transcription factor related to the p53 tumor suppressor, plays a key role in epidermal differentiation and limb development. The gene has two distinct promoters that allow the formation of proteins that either contain (TA) or lack (ΔN) a transactivation domain. ΔNp63α is the most widely expressed isoform, at all stages of development and in adult tissues. It supports the regenerative capacity of basal keratinocytes and its upregulation is a hallmark of human squamous carcinomas. To get insight into the complex biology of ΔNp63α, we set out to identify ΔNp63α interacting proteins by co-immunoprecipitation in mammalian cells and mass spectrometry analysis. A total of 49 potential ΔNp63α binding proteins, including several heterogeneous ribonucleoproteins (hnRNPs), were identified. Integration of the proteomic data with a Human Coexpression Network highlighted 5 putative p63 protein interactors whose expression is significantly comodulated with p63: hnRNPA/B, hnRNPK, hnRNPQ, FUS/TLS and Keratin 5. hnRNPA/B was already described as a p63 partner, but the others were novel. Interaction of ΔNp63α with hnRNPQ, hnRNPK and FUS/TLS was confirmed by reciprocal co-immunoprecipitations in human keratinocytes. The finding that ΔNp63α exists in complexes with several RNA-binding proteins lays the premises for the analysis of the role of ΔNp63α in mRNA metabolism and transport.