B56 alpha subunit of protein phosphatase 2A mediates retinoic acid-induced decreases in phosphorylation of endothelial nitric oxide synthase at serine 1179 and nitric oxide production in bovine aortic endothelial cells

作者：Park Jung Hyun; Sung Hye Youn; Lee Jee Young; Kim Hyun Jin; Ahn Jung Hyuck^*; Jo Inho

来源：Biochemical and Biophysical Research Communications, 2013, 430(2): 476-481.

DOI：10.1016/j.bbrc.2012.12.011

• Endothelial nitric oxide synthase
• All-trans retinoic acid
• Dephosphorylation
• Protein phosphatase 2A
• PP2A B56 alpha subunit

We previously showed that all-trans retinoic acid (atRA) decreased nitric oxide (NO) production through Akt-mediated decreased phosphorylation of endothelial NO synthase at serine 1179 (eNOS-Ser(1179)) in bovine aortic endothelial cells (BAEC). Since protein phosphatase 2A (PP2A) was also reported to decrease eNOS-Ser(1179) phosphorylation, we investigated using BAEC whether PP2A mediates atRA-induced eNOS-Ser(1179) dephosphorylation and subsequent decreased NO production. Treatment with okadaic acid (5 nM), a selective PP2A inhibitor, or ectopic expression of small interference RNA (siRNA) of PP2A catalytic subunit alpha (PP2A C alpha) significantly increased eNOS-Ser(1179) phosphorylation and NO production. Each treatment also significantly reversed atRA-induced observed effects, suggesting a role for PP2A. We also found that atRA significantly increased cellular PP2A activity. However, Western blot analysis revealed that atRA did not increase the expression of PP2A C alpha, although it significantly increased the level of B56 alpha of PP2A regulatory B subunit (PP2A B56 alpha), but not PP2A B55 alpha and PP2A B56 delta. Real-time PCR assay confirmed a significant increase in PP2A B56 alpha mRNA expression in atRA-treated cells. Ectopic expression of siRNA of PP2A B56 alpha significantly reversed atRA-induced inhibitory effects on eNOS-Ser(1179) phosphorylation and NO production, suggesting a role for PP2A B56 alpha. Our study demonstrates for the first time that atRA decreases eNOS-Ser(1179) phosphorylation and NO release at least in part by increasing PP2A B56 alpha-mediated PP2A activity in BAEC.

• 出版日期2013-1-11