Premium
Stretch‐induced Akt phosphorylation/dephosphorylation in cardiomyocytes
Author(s) -
Samarel Allen Mark,
Hall William A,
Iyengar Rekha,
Henderson Kyle K,
Russell Brenda
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.6.a1259-d
Subject(s) - protein kinase c , protein kinase b , phosphorylation , dephosphorylation , phosphatase , chemistry , kinase , protein phosphatase 2 , microbiology and biotechnology , okadaic acid , threonine , endocrinology , medicine , serine , biology , biochemistry
The serine‐threonine protein kinase Akt plays an essential role in cardiomyocyte metabolism, growth, and survival. Here we examine whether static stretch of neonatal rat ventricular myocytes (NRVM) increases Akt activation (assessed by Akt phosphorylation at S473 (pAkt)), and whether pAkt is dependent on upstream activation of protein kinase C (PKC). NRVM plated on collagen‐coated silicone membranes were stretched (20% maximal strain, 10 min), or stimulated with IGF‐1 (100ng/ml; 10 min). Stretch increased pAkt 2.9±0.5‐fold, which was similar to IGF‐1 (3.9±0.2‐fold). Surprisingly, the PKC inhibitor GF109203X (GFX; 10 μM; 1h pretreatment) increased basal pAkt (1.6±0.6‐fold), and stretch‐induced pAkt (5.0±1.4 fold), but had no effect on pAkt by IGF‐1. These results suggested that stretch, but not IGF‐1, activates a PKC‐dependent protein phosphatase that partially reduces pAkt. This suggestion was supported by treating NRVM with phorbol myristate acetate (PMA; 200nM; 15 min), which decreased basal pAkt by 38±6%. To identify which PKC is involved, NRVM were infected (25moi, 24h) with adenoviruses expressing wildtype and mutant forms of PKCα, PKCδ, and PKCε. Overexpression of constitutively active PKCε, but not PKCα or PKCδ, also decreased basal pAkt to 39±0.4% of control. Furthermore, the protein phosphatase 2A (PP2A) inhibitor okadaic acid (50nM; 1hr pretreatment), increased basal pAkt, and also blocked the PMA‐induced decrease in pAkt, suggesting that PKCε activates a signaling pathway that stimulates PP2A. Thus, stretch‐induced pAkt involves a complex signaling pathway with both positive and negative regulators of the enzyme. PP2A inhibitors may enhance Akt activation and promote cardiomyocyte growth and survival. Supported by NIH 2PO1 HL062426 and the Falk Foundation.