mTORC1 signaling can regulate growth factor activation of p44/42 mitogen-activated protein kinases through protein phosphatase 2A

作者：Harwood Franklin C; Shu Lili; Houghton Peter J^*

来源：Journal of Biological Chemistry, 2008, 283(5): 2575-2585.

DOI：10.1074/jbc.M706173200

The mTORC1 complex ( mammalian target of rapamycin (mTOR)-raptor) is modulated by mitogen-activated protein (p44/42 MAP) kinases (p44/42) through phosphorylation and inactivation of the tuberous sclerosis complex. However, a role for mTORC1 signaling in modulating activation of p44/42 has not been reported. We show that in two cancer cell lines regulation of the p44/42 MAPKs is mTORC1-dependent. In Rh1 cells rapamycin inhibited insulin-like growth factor-I (IGF-I)-stimulated phosphorylation of Thr(202) but not Tyr(204) and suppressed activation of p44/42 kinase activity. Down-regulation of raptor, which inhibits mTORC1 signaling, had a similar effect to rapamycin in blocking IGF-I- stimulated Tyr204 phosphorylation. Rapamycin did not block maximal phosphorylation of Tyr204 but retarded the rate of dephosphorylation of Tyr204 following IGF-I stimulation. IGF-I stimulation of MEK1 phosphorylation (Ser(217/221)) was not inhibited by rapamycin. Higher concentrations of rapamycin (>= 100 ng/ml) were required to inhibit epidermal growth factor (EGF)induced phosphorylation of p44/42 ( Thr202). Rapamycin-induced inhibition of p44/42 ( Thr202) phosphorylation by IGF-I was reversed by low concentrations of okadaic acid, suggesting involvement of protein phosphatase 2A(PP2A). Both IGF-I and EGF caused dissociation of PP2A catalytic subunit (PP2Ac) from p42. Whereas low concentrations of rapamycin ( 1 ng/ml) inhibited dissociation of PP2Ac after IGF-I stimulation, it required higher concentrations (> 100 ng/ ml) to block EGF-induced dissociation, consistent with the ability for rapamycin to attenuate growth factor-induced activation of p44/42. The effect of rapamycin on IGF-I or insulin activation of p44/42 was recapitulated by amino acid deprivation. Rapamycin effects altering the kinetics of p44/42 phosphorylation were completely abrogated in Rh1mTORrr cells that express a rapamycin-resistant mTOR, whereas the effects of amino acid deprivation were similar in Rh1 and Rh1mTORrr cells. These results indicate complex regulation of p44/42 by phosphatases downstream of mTORC1. This suggests a model in which mTORC1 modulates the phosphorylation of Thr202 on p44/42 MAPKs through direct or indirect regulation of PP2Ac.

• 出版日期2008-2-1