Illuminating the Co-Phosphoregulatory Network of the Dark Kinase STK10 by Omics Approaches.

Serine/threonine-protein kinase 10 (STK10), an ERM protein kinase, functions as a membrane-cytoskeleton linker and regulates lymphocyte cortical rigidity, cell shape, adhesion, and migration. Despite its emerging relevance in immune regulation and cancer, the phosphoregulatory mechanisms governing STK10 remain poorly understood. To address this, we systematically assembled and mapped the global phosphoproteomic datasets on the dark STK10 phosphosites. From 453 quantitative differential profiles representing STK10 Class 1 phosphosites, 12 predominant sites were identified based on frequency. Of these, four phosphosites (T185, S191, S514, and T952) were conserved with the homologous kinase SLK, indicating evolutionary conservation. Notably, S450, S455, T14, S448, and S454 were predicted as potential autophosphorylation sites, suggesting intrinsic regulatory control. Predictions indicated that PAK2 and MAP3K2 may act as both upstream kinases and downstream substrates of STK10, with their phosphosites (MAP3K2_S153 and PAK2_S141) consistently co-regulated, suggesting a common regulatory axis. These findings stacked the phosphorylation landscape of STK10, extending regulatory insights beyond its kinase domain. This phosphoproteomics data-driven study establishes a framework for prioritizing functional validation and structural investigations to define the physiological and pathological significance of dark phosphosites in STK10 in immunity and cancer.