RNF2 is the target for phosphorylation by the p38 MAPK and ERK signaling pathways

RNF2, a member of polycomb group (PcG) proteins, is involved in chromatin remodeling. However, mechanisms that regulate RNF2 function are unknown. To identify such mechanisms, RNF2 was expressed in HEK-293 cells and analyzed by 2-D electrophoresis. RNF2 was resolved into at least seven protein spots, migrating toward the lower pI from its expected pI of 6.38, suggesting that RNF2 undergoes post-translational modifications. Western blotting indicated that majority of these RNF2 spots contained phosphoserine(s), which were completely dephosphorylated upon treatment with a phosphatase. SB203580, a specific inhibitor of p38 MAPK, inhibited RNF2 phosphorylation at one site. On the other hand, PD98059, an inhibitor of MEK1/2, inhibited majority of the phosphorylation events in RNF2. Mass spectrometry analysis identified that RNF2 expressed in Sf9 insect cells undergoes co-translational excision of (1)Met coupled to N-acetylation of (2)Ser, and phosphorylation of (41)Ser. Interestingly, (41)Ser is a predicted p38/MAPK phosphorylation site, consistent with the loss of phosphorylation induced by SB203580. Further analysis indicated that RNF2 phosphorylation differentially modulates the expression of transcription factors and histone 2B acetylation. These results provide first evidence for phosphorylation of RNF2, and suggest that the mitogen activated protein kinases including p38 MAPK and ERK1/2 regulate growth, stress response, differentiation and other cellular processes, through phosphorylation of RNF2.