Unravelling the phosphoregulatory network of protein kinase C-delta (PKC-δ)

Protein kinase C Delta (PRKCD) is a serine/threonine kinase involved in transcription regulation, cytoskeleton organization, DNA damage response, DNA repair and carcinogenesis. Several PRKCD phosphopeptides are frequently detected to be differentially regulated through mass spectrometry-based phosphoproteomics analysis. Here, we utilize publicly available phosphoproteomics data to decipher phosphoregulatory networks associated with PRKCD. Among 315 phosphoproteomics datasets demonstrating the differential regulation of phosphopeptides of PRKCD, the phosphosites S304, Y313, S645, S299, S302, S664, Y334, Y374, T295 and T507 predominantly represent PRKCD hyperphosphorylation in over 83 % of cases. Further, through co-differential regulation analysis of the predominant sites and associated phosphosites on other proteins, we propose that the autophosphorylation sites S302 and S304 are critically associated with the kinase activity of PRKCD and play a crucial role in modulating its downstream signaling pathways. Compared to known activation sites of PRKCD including Y313, Y334 and Y374, the sites S302 and S304 coregulated the most with the experimentally validated and predicted substrates. Besides that, phosphosites Y313, Y334 and Y374 are associated with stress signaling and cancer progression. Current study focuses on critical kinase-activation associated with phosphosites in kinases. This study highlights the sites S302 and S304 as activation sites and as key players in various cellular processes including cell cycle regulation, motility, adhesion and migration. Our approach and the stringent criteria adopted sets a robust platform to analyze differentially regulated phosphoproteome data in diverse biological contexts to interpret the predominant phosphosites, their co-regulation and the overall biological relevance of such regulation in pathophysiological processes.