Phosphoregulation for Therapeutic Interventions in Cancer? Phosphoregulatory Map of Checkpoint Kinase 1 (CHK1) Uncovers Unexplored Regulatory Layers.

Checkpoint kinase 1 (CHEK1/CHK1) is a serine/threonine kinase that is pivotal in maintaining genomic stability by regulating DNA replication, mitotic progression, and DNA damage response (DDR). Phosphorylation at distinct regulatory sites of CHK1 serves as a central signaling switch that tightly coordinates checkpoint control and DNA repair pathways. However, the broad phosphorylation network associated with the DNA repair pathway and CHK1 phosphorylation remains relatively underexplored, representing an untapped avenue with profound therapeutic potential. To bridge this discovery gap, we systematically analyzed global phosphoproteome datasets to visualize CHK1 phosphosites and their coregulated protein phosphosites, providing new insights into the functional networks governed by DDR signaling. The integrative analysis of 577 qualitative and 120 quantitative cellular phosphoproteomic datasets identified signatures of the CHK1 phosphorylation landscape. Our study visualized a strong co-occurrence of DDR-associated phosphosites in proteins, particularly with S280, and the Ataxia telangiectasia and Rad3-related protein-dependent S317 phosphosites in CHK1 located outside its kinase domain. Their coregulation analysis across CHK1 substrates, kinase regulators, and protein interactions uncovered connectivity between CHK1 phosphosites and DDR regulators. Collectively, our phosphosite-concordance approach reported here provides a regulatory map of CHK1 phosphorylation patterns, uncovering unexplored regulatory layers, and highlights new opportunities to explore mechanistic insights into CHK1 phosphoregulation as a target for therapeutic interventions in cancer.