Ca²⁺‐ and phospholipase D‐dependent and ‐independent pathways activate mTOR signaling

Abstract

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 ¢broblasts expressing the K K 1A adrenergic receptor to study if this G qcoupled receptor uses PLD to regulate mTOR signaling. Phenylephrine (PE) stimulation of the K K 1A adrenergic receptor induced mTOR autophosphorylation at Ser2481 and phosphorylation of two mTOR e¡ectors, 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 K K 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. ß

Testosterone induces cardiomyocyte hypertrophy through mammalian target of rapamycin complex 1 pathway

“…Lysophosphatidic acid stimulation of Swiss 3T3 fibroblasts promotes a fast S6K1 activation, which depends on PLC activity and intracellular Ca 2C increase (Willard et al 2001). In Rat1 fibroblasts expressing the a 1A -adrenergic receptor, phenylephrine induces mTOR, S6K1, and 4E-BP1 activation dependent on both Ca 2C influx and Ca 2C release (Ballou et al 2003). However, there are no detailed studies showing which Ca 2C pools are involved in mTOR activation or any evidence describing mTORC1 activation through the Ca 2C /MEK/ERK1/2 pathway.…”

Glibenclamide activates translation in rat pancreatic beta cells through calcium-dependent mTOR, PKA and MEK signalling pathways

“…The phosphorylation of both proteins was completely suppressed by the mTOR inhibitor rapamycin, resulting in partial inhibition of protein synthesis. As in other cell types and experimental conditions, the glibenclamide activation of mTOR can be explained by the rise in intracellular calcium [31,32], which acts through phosphorylation of PKB [33] and activation of PKA [8] or an as yet undefined intermediate. Glibenclamide induced phosphorylation of PKB, a well-known upstream kinase of mTOR [10,34,35]; this effect was not influenced by rapamycin, but was completely abolished by verapamil and the PKA inhibitor.…”

Regulation of mTOR by Phosphatidic Acid?

“…Serum-induced increases in S6 kinase activity and 4E-BP1 phosphorylation were blocked by 1-butanol in HEK293 cells (3). Phenylephrine (a-adrenergic receptor agonist)-induced mTOR was also sensitive to treatment with 1-butanol (12). In skeletal muscle, PA stimulated S6 kinase phosphorylation, and 1-butanol suppressed S6 kinase phosphorylation (13).…”