In previous reports, PARP14 suppressed apoptosis by inhibiting JNK1 phosphorylation in hepatocellular carcinoma and multiple myeloma cells.21, 23 Indeed, we observed a small but reproducible increase in JNK phosphorylation in FaDu and HeLa when PARP14, PARP9 or DTX3L was knocked down (1.2–1.9-fold increase Figure S4A). Here, MAPK8 is linked to plasma cell myeloma.