IRF1 and diffuse large B-cell lymphoma: Functionally, PARP9 represses the tumor suppressor IRF1 while upregulating the proto-oncogene IRF2, thereby inhibiting the IFNγ–STAT1–IRF1–p53 signaling axis and promoting proliferation, survival and chemoresistance in DLBCL (Fig. 5B) (Camicia et al., 2013).