Phosphorylation of Protein Inhibitor of Activated STAT1 (PIAS1) by MAPK-Activated Protein Kinase-2 (MK2) Inhibits Endothelial Inflammation via Increasing Both PIAS1 Transrepression and SUMO E3 Ligase Activity
Objective—Protein inhibitor of activated signal transducer and activator of transcription-1 (PIAS1) is known to function as SUMO E3 ligase as well as transrepressor. The aim of the study is to elucidate the regulatory mechanisms for these 2 different functions, especially with respect to endothelial inflammation.
Methods and Results—The MAPK-activated protein kinase-2 is a proinflammatory kinase and phosphorylates PIAS1 at the Ser522 residue. Activation of MAPK-activated protein kinase-2 enhances p53-SUMOylation, but a PIAS1 phosphorylation mutant, PIAS1 S522A, abolished this p53-SUMOylation, suggesting a critical role for PIAS1 S522 phosphorylation in its SUMO ligase activity. Because nuclear p53 can inhibit Kruppel-like factor 2 promoter activity, we investigated the roles for PIAS1 phosphorylation and p53-SUMOylation in the Kruppel-like factor 2 and endothelial NO synthase expression. Both MAPK-activated protein kinase-2 and PIAS1 overexpression increased Kruppel-like factor 2 promoter activity and endothelial NO synthase expression, which were inhibited by expressing a p53-SUMOylation defective mutant, p53-K386R, and PIAS1 S522A. PIAS1 S522A also abolished the anti-inflammatory effect of wild-type PIAS1 in vitro and also in vivo, which was examined by leukocyte rolling in microvessels of skin grafts transduced by adenovirus encoding wild-type PIAS1 or the S522A mutant.
Conclusion—Our study has identified a novel negative feedback regulatory pathway through which MAPK-activated protein kinase-2 limits endothelial inflammation via the PIAS1 S522 phosphorylation-mediated increase in PIAS1 transrepression and SUMO ligase activity.
- endothelial inflammation
- MAPK-activated protein kinase-2
- nuclear factor-κB transrepression
- protein inhibitor of activated signal transducer and activator of transcription-1
- vascular biology
- Received February 2, 2012.
- Accepted October 26, 2012.
- © 2012 American Heart Association, Inc.