Systematic Analysis of MRTFB Phosphoproteomic Datasets Reveals Co-Regulated Kinase Networks and Co-Occurring Phosphosites Associated with the Actin Cytoskeleton Pathway.

Background: Myocardin-related transcription factor B (MRTFB) acts as a transcriptional coactivator for serum response factor (SRF) and regulates actin cytoskeletal dynamics. Despite its biological significance, the phosphoregulatory network, upstream kinases, and interactors remain poorly understood. Methods: To explore this, we analyzed global phosphoproteomic datasets to identify predominant phosphosites. We categorized phosphosites in other proteins as positively or negatively co-regulated with the predominant phosphosites of MRTFB and also integrated predicted upstream kinases and interactors of MRTFB. Further, phosphosite conservation, co-occurrence patterns, and functional and pathway enrichment analyses of co-regulated proteins were also performed. Results: We identified S66 and S921 as predominant phosphosites in MRTFB, with the highest detection frequency across multiple experimental conditions. These phosphosites were found to be conserved within the MRTF family and across multiple species. From the predicted upstream kinases, MAPK1, MAPK3, MAST3, and CSNK1A1 were identified as predicted upstream kinases. Co-occurrence analysis revealed high positive co-occurrence between the predominant phosphosites, S66 and S921, suggesting similar functional roles. Functional enrichment analysis highlighted the involvement of co-regulated proteins in the actin cytoskeleton pathway. Conclusions: This study provides the detailed phosphoproteomic landscape of MRTFB, mapping its upstream kinases and co-regulated proteins involved in actin cytoskeleton regulation.