title: Activation of protein synthesis in cardiomyocytes by the hypertrophic agent phenylephrine requires the activation of ERK and involves phosphorylation of tuberous sclerosis complex 2 (TSC2).
abstract: The hypertrophic Gq-protein-coupled receptor agonist PE (phenylephrine) activates protein synthesis. We showed previously that activation of protein synthesis by PE requires MEK [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase] and mTOR (mammalian target of rapamycin). However, it remained unclear whether ERK activation was required and which downstream components were involved in activating mTOR and protein synthesis. Using an adenovirus encoding the MKP3 (MAPK phosphatase 3) to inhibit ERK activity, we demonstrate that ERK is essential for the activation of protein synthesis by PE. Activation and phosphorylation of S6K1 (ribosomal protein S6 kinase 1) and phosphorylation of eIF4E (eukaryotic initiation factor 4E)-binding protein (both are mTOR targets) were also inhibited by MKP3, suggesting that ERK is also required for the activation of mTOR signalling. PE stimulation of cardiomyocytes induced the phosphorylation of TSC2 (tuberous sclerosis complex 2), a negative regulator of mTOR activity. TSC2 was phosphorylated only weakly at Thr1462, but phosphorylated at additional sites within the sequence RXRXX(S/T). This differs from the phosphorylation induced by insulin, indicating that MEK/ERK signalling targets distinct sites in TSC2. This phosphorylation may be mediated by p90RSK (90 kDa ribosomal protein S6K), which is activated by ERK, and appears to involve phosphorylation at Ser1798. Activation of protein synthesis by PE is partially insensitive to the mTOR inhibitor rapamycin. Inhibition of the MAPK-interacting kinases by CGP57380 decreases the phosphorylation of eIF4E and PE-induced protein synthesis. Moreover, CGP57380+rapamycin inhibited protein synthesis to the same extent as blocking ERK activation, suggesting that MAPK-interacting kinases and regulation of mTOR each contribute to the activation of protein synthesis by PE in cardiomyocytes.
authors.affiliation: Division of Molecular Physiology, School of Life Sciences, University of Dundee, MSI/WTB Complex, Dow Street, Dundee DD1 5EH, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Rolfe
authors.forename: Laura E
authors.initials: LE
authors.lastname: McLeod
authors.forename: Phillip F
authors.initials: PF
authors.lastname: Pratt
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Proud
mesh_terms: D000814:Aniline Compounds / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D008297:Male; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D010656:Phenylephrine / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D014176:Protein Biosynthesis / Q000187:drug effects*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011687:Purines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
chemical_list: D000814:Aniline Compounds; C466997:CGP 57380; D007328:Insulin; D011687:Purines; C000624653:TSC2 protein, human; C000624655:Tsc2 protein, rat; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D010656:Phenylephrine; D017346:Protein Serine-Threonine Kinases; C069329:RPS6KA1 protein, human; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C512963:Rps6ka1 protein, rat; D048049:Extracellular Signal-Regulated MAP Kinases; D017027:Protein Tyrosine Phosphatases; D020123:Sirolimus