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Hypoxia modulates protein phosphatase 2A through HIF‐1α dependent and independent mechanisms in human aortic smooth muscle cells and ventricular cardiomyocytes
Author(s) -
Elgenaidi Ismail Suliman,
Spiers James Paul
Publication year - 2019
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/bph.14648
Subject(s) - protein phosphatase 2 , phosphatase , hypoxia (environmental) , microbiology and biotechnology , biology , messenger rna , gene silencing , protein phosphatase 1 , cell culture , protein subunit , alkaline phosphatase , chemistry , phosphorylation , biochemistry , enzyme , gene , genetics , organic chemistry , oxygen
Background and Purpose Although protein phosphatases regulate multiple cellular functions, their modulation under hypoxia remains unclear. We investigated expression of the protein phosphatase system under normoxic/hypoxic conditions and the mechanism by which hypoxia alters protein phosphatase 2A (PP2A) activity. Experimental Approach Human cardiovascular cells were cultured in cell type specific media under normoxic or hypoxic conditions (1% O 2 ). Effects on mRNA expression, phosphatase activity, post‐translational modification, and involvement of hypoxia inducible factor 1α (HIF‐1α) were assessed using RT‐PCR, immunoblotting, an activity assay, and siRNA silencing. Key Results All components of the protein phosphatase system studied were expressed in each cell line. Hypoxia attenuated mRNA expression of the transcripts in a cell line‐ and time‐dependent manner. In human aortic smooth muscle cells (HASMC) and AC16 cells, hypoxia decreased PP2Ac activity and mRNA expression without altering PP2Ac abundance. Hypoxia increased demethylated PP2Ac (DPP2Ac) and phosphatase methylesterase 1 (PME‐1) abundance but decreased leucine carboxyl methyltransferase 1 (LCMT‐1) abundance. HIF‐1α siRNA prevented the hypoxia‐mediated decrease in phosphatase activity and expression of the catalytic subunit of protein phosphatase 2A (PPP2CA), independently of altering pPP2Ac, DPP2Ac, LCMT‐1, or PME‐1 abundance. Conclusion and Implications Cardiovascular cells express multiple components of the PP2A system. In HASMC and AC16 cells, hypoxia inhibits PP2A activity through HIF‐1α‐dependent and ‐independent mechanisms, with the latter being consistent with altered PP2A holoenzyme assembly. This indicates a complex inhibitory effect of hypoxia on the PP2A system, and highlights PP2A as a therapeutic target for diseases associated with dysregulated protein phosphorylation.