Anti-UBR5 monoclonal antibody, clone FQS5952

The Mre11/Rad50/NBS1 (MRN) protein complex and ATMIN protein mediate ATM kinase signaling in response to ionizing radiation (IR) and chromatin changes, respectively. NBS1 and ATMIN directly compete for ATM binding, but the molecular mechanism favoring either NBS1 or ATMIN in response to specific stimuli is enigmatic. Here, we identify the E3 ubiquitin ligase UBR5 as a key component of ATM activation in response to IR. UBR5 interacts with ATMIN and catalyzes ubiquitination of ATMIN at lysine 238 in an IR-stimulated manner, which decreases ATMIN interaction with ATM and promotes MRN-mediated signaling. We show that UBR5 deficiency, or mutation of ATMIN lysine 238, prevents ATMIN dissociation from ATM and inhibits ATM and NBS1 foci formation after IR, thereby impairing checkpoint activation and increasing radiosensitivity. Thus, UBR5-mediated ATMIN ubiquitination is a vital event for ATM pathway selection and activation in response to DNA damage.

Using proteomic approaches, we uncovered a DNA damage response (DDR) function for peroxisome proliferator activated receptor gamma (PPAR gamma) through its interaction with the DNA damage sensor MRE11-RAD50-NBS1 (MRN) and the E3 ubiquitin ligase UBR5. We show that PPAR gamma promotes ATM signaling and is essential for UBR5 activity targeting ATM interactor (ATMIN). PPAR gamma depletion increases ATMIN protein independent of transcription and suppresses DDR-induced ATM signaling. Blocking ATMIN in this context restores ATM activation and DNA repair. We illustrate the physiological relevance of PPAR gamma DDR functions by using pulmonary arterial hypertension (PAH) as a model that has impaired PPAR gamma signaling related to endothelial cell (EC) dysfunction and unresolved DNA damage. In pulmonary arterial ECs (PAECs) from PAH patients, we observed disrupted PPAR gamma-UBR5 interaction, heightened ATMIN expression, and DNA lesions. Blocking ATMIN in PAH PAEC restores ATM activation. Thus, impaired PPAR gamma DDR functions may explain the genomic instability and loss of endothelial homeostasis in PAH.