Rapamycin inhibits mSin1 phosphorylation independently of mTORC1 and mTORC2

Abstract

Current knowledge indicates that the mammalian target of rapamycin (mTOR) functions as two complexes, mTORC1 and mTORC2, regulating cell growth, proliferation, survival, differentiation, and motility. Recently mSin1 has been identified as a critical component of mTORC2, which is essential for phosphorylation of Akt and other signaling molecules. Studies have shown that rapamycin inhibits phosphorylation of mSin1. However, the underlying mechanism is unknown. Here we found that rapamycin inhibited phosphorylation of mSin1 potently and rapidly. Expression of rapamycin-resistant mutant of mTOR (mTOR-T), but not rapamycin-resistant and kinase dead mutant of mTOR (mTOR-TE), prevented rapamycin from inhibiting mSin1 phosphorylation, suggesting that rapamycin-induced dephosphorylation of mSin1 is mTOR-dependent. Surprisingly, ectopic expression of rapamycin-resistant and constitutively active p70 S6 kinase 1 (S6K1) did not confer resistance to rapamycin-induced dephosphorylation of mSin1. Furthermore, disruption of mTORC1 and mTORC2 by silencing raptor and rictor, respectively, or downregulation of S6K1 or Akt did not induce the dephosphorylation of mSin1 as rapamycin did. However, silencing mTOR or mLST8 mimicked the effect of rapamycin, inhibiting mSin1 phosphorylation. Our findings suggest that rapamycin inhibits mSin1 phosphorylation, which is independent of mTORC1 and mTORC2, but is possibly dependent on a new mTOR complex, which at least contains mTOR and mLST8.

A high-throughput kinome screen reveals serum/glucocorticoid-regulated kinase 1 as a therapeutic target for NF2-deficient meningiomas

“…Rapamycin is merely cytostatic in our cells, consistent with the clinical outcome thus far observed with RAD001/everolimus. Moreover, rapamycin treatment is known to relieve the negative feedback inhibition on IRS-1 [ 45 , 46 ], Grb10 [ 47 , 48 ] as well as other negative regulation of mTORC2 independent of IRS-1 and Grb10 [ 49 , 50 ], and thus can activate PI3K/Akt and ERK/MAPK prosurvival pathways. Similarly, here we have shown that rapamycin treatment can also upregulate mTORC2-SGK1 signaling (Figure 5D ).…”

Peptidylprolyl Isomerases as In Vivo Carriers for Drugs That Target Various Intracellular Entities

“…It has been shown that in some cell lines, rapamycin actions were not correlated with the inhibition of mTORC1 and mTORC2 [ 79 , 80 ]. A prolonged clinical use of rapamycin leads to dysfunction of glucose homeostasis [ 81 ].…”

Proteomic analysis reveals GIT1 as a novel mTOR complex component critical for mediating astrocyte survival

“…Support for additional mTOR complexes derives from studies examining oxygeninduced mTOR-mediated translational activation of terminal oligopyrimidine (TOP) mRNA in fibroblasts (Miloslavski et al 2014), where mTOR regulation of TOP mRNA translation was independent of Rictor or Raptor and occurred in the absence of S6K and 4EBPI activation. Additionally, rapamycin inhibition of mSin1 phosphorylation in human rhabdomyosarcoma cells was mimicked by mTOR or mLST8 silencing but not by Raptor, Rictor, S6K1, or AKT loss (Luo et al 2015), suggesting the presence of a new mTOR complex containing only mSIN1 and mLST8. Third, mTOR function can be regulated by different upstream modulators.…”