Ca(2+)- and phospholipase D-dependent and -independent pathways activate mTOR signaling.
The mammalian target of rapamycin (mTOR) promotes increased protein synthesis required for cell growth. It has been suggested that phosphatidic acid, produced upon activation of phospholipase D (PLD), is a common mediator of growth factor activation of mTOR signaling. We used Rat-1 fibroblasts expressing the alpha(1A) adrenergic receptor to study if this G(q)-coupled receptor uses PLD to regulate mTOR signaling. Phenylephrine (PE) stimulation of the alpha(1A) adrenergic receptor induced mTOR autophosphorylation at Ser2481 and phosphorylation of two mTOR effectors, 4E-BP1 and p70 S6 kinase. These PE-induced phosphorylations were greatly reduced in cells depleted of intracellular Ca(2+). PE activation of PLD was also inhibited in Ca(2+)-depleted cells. Incubation of cells with 1-butanol to inhibit PLD signaling attenuated PE-induced phosphorylation of mTOR, 4E-BP1 and p70 S6 kinase. By contrast, platelet-derived growth factor (PDGF)-induced phosphorylation of these proteins was not blocked by Ca(2+) depletion or 1-butanol treatment. These results suggest that the alpha(1A) adrenergic receptor promotes mTOR signaling via a pathway that requires an increase in intracellular Ca(2+) and activation of PLD. The PDGF receptor, by contrast, appears to activate mTOR by a distinct pathway that does not require Ca(2+) or PLD.
Ballou
Lisa M
LM
Department of Medicine, Division of Hematology, Stony Brook University, Stony Brook, NY 11794-8151, USA.
Jiang
Ya-Ping
YP
Du
Guangwei
G
Frohman
Michael A
MA
Lin
Richard Z
RZ
D020001:1-Butanol / Q000494:pharmacology; D058646:Adrenergic alpha-1 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D010656:Phenylephrine / Q000494:pharmacology; D010739:Phospholipase D / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism; D011494:Protein Kinases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases
C547715:Adra1a protein, rat; D058646:Adrenergic alpha-1 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D002352:Carrier Proteins; C499526:Eif4ebp1 protein, rat; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D010982:Platelet-Derived Growth Factor; D018340:Receptors, Adrenergic, alpha-1; D010656:Phenylephrine; D020001:1-Butanol; D011494:Protein Kinases; C546845:mTOR protein, rat; D017479:Receptors, Platelet-Derived Growth Factor; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D011493:Protein Kinase C; D010739:Phospholipase D; D002118:Calcium