Updated project metadata. PPM1D (also known as WIP1) is a p53-regulated protein phosphatase that modulates the DNA damage response (DDR) by dephosphorylation of DDR proteins. Amplification of PPM1D gene or gain-of-function mutations are commonly found in cancer. Here, we employed chemical inhibition of PPM1D and quantitative mass spectrometry-based phosphoproteomics to identify the substrates of PPM1D upon induction of DNA double strand breaks (DSBs) by topoisomerase II poison etoposide. We identified 73 putative PPM1D substrates that are involved in DNA repair, regulation of transcription and RNA processing. One third of DSB-induced S/TQ phosphorylation sites are dephosphorylated by PPM1D, demonstrating that PPM1D only partially counteracts ATM/ATR/DNA-PK signaling. PPM1D-targeted phosphorylation sites are found in a specific amino acid sequence motif that is characterized by glutamic acid residues, high intrinsic disorder and poor evolutionary conservation. We identified a functionally uncharacterized protein Kanadaptin as ATM and PPM1D substrate upon DSB induction. We propose that PPM1D plays a role during the response to DSBs formation by regulating the phosphorylation of DNA- and RNA-binding proteins in intrinsically disordered regions.