MET-dependent modulation of cellular responses to ionizing radiation by quantitative phosphoproteomics

Increasing evidence suggests that inhibiting growth factor receptor tyrosine kinases (RTKs) signaling may modulate cellular responses to DNA-damaging agents widely used in cancer treatment. In that respect, the MET RTK is deregulated in abundance and/or activity in a variety of human tumors. Using two proteomic techniques, we explored how the MET inhibitor tepotinib modulates global cellular phosphorylation response to ionizing radiation (IR). Following an immunoaffinity-based phosphoproteomic discovery survey we selected candidate phosphorylation sites for extensive characterization by targeted proteomics focusing on phosphosites that consist of the SQ motif recognized by the PIKK-related kinases ATM, ATR and PRKDC. Several substrates of the DNA damage response (DDR) were confirmed to be modulated by sequential MET inhibition and IR, or MET inhibition alone.