Characterization of p38α Signaling Networks in Cancer Cells Using Quantitative Proteomics and Phosphoproteomics

p38 alpha (encoded by MAPK14) is a protein kinase that reg-ulates cellular responses to almost all types of environ-mental and intracellular stresses. Upon activation, p38 alpha phosphorylates many substrates both in the cytoplasm and nucleus, allowing this pathway to regulate a wide variety of cellular processes. While the role of p38 alpha in the stress response has been widely investigated, its impli-cation in cell homeostasis is less understood. To investi-gate the signaling networks regulated by p38 alpha in proliferating cancer cells, we performed quantitative pro-teomic and phosphoproteomic analyses in breast cancer cells in which this pathway had been either genetically targeted or chemically inhibited. Our study identified with high confidence 35 proteins and 82 phosphoproteins (114 phosphosites) that are modulated by p38 alpha and highlighted the implication of various protein kinases, including MK2 and mTOR, in the p38 alpha-regulated signaling networks. Moreover, functional analyses revealed an important contribution of p38 alpha to the regulation of cell adhesion, DNA replication, and RNA metabolism. Indeed, we provide experimental evidence supporting that p38 alpha facilitates cancer cell adhesion and showed that this p38 alpha function is likely mediated by the modulation of the adaptor protein ArgBP2. Collectively, our results illustrate the complexity of the p38 alpha-regulated signaling networks, provide valu-able information on p38 alpha-dependent phosphorylation events in cancer cells, and document a mechanism by which p38 alpha can regulate cell adhesion.