Noncanonical agonist PPAR gamma ligands modulate the response to DNA damage and sensitize cancer cells to cytotoxic chemotherapy

The peroxisome-proliferator receptor-gamma (PPAR gamma) is expressed in multiple cancer types. Recently, our group has shown that PPAR gamma is phosphorylated on serine 273 (S273), which selectively modulates the transcriptional program controlled by this protein. PPAR gamma ligands, including thiazolidinediones (TZDs), block S273 phosphorylation. This activity is chemically separable from the canonical activation of the receptor by agonist ligands and, importantly, these noncanonical agonist ligands do not cause some of the known side effects of TZDs. Here, we show that phosphorylation of S273 of PPAR gamma occurs in cancer cells on exposure to DNA damaging agents. Blocking this phosphorylation genetically or pharmacologically increases accumulation of DNA damage, resulting in apoptotic cell death. A genetic signature of PPAR gamma phosphorylation is associated with worse outcomes in response to chemotherapy in human patients. Non-canonical agonist ligands sensitize lung cancer xenografts and genetically induced lung tumors to carboplatin therapy. Moreover, inhibition of this phosphorylation results in deregulation of p53 signaling, and biochemical studies show that PPAR gamma physically interacts with p53 in a manner dependent on S273 phosphorylation. These data implicate a role for PPAR gamma in modifying the p53 response to cytotoxic therapy, which can be modulated for therapeutic gain using these compounds