Signaling events downstream of mammalian target of rapamycin complex 2 are attenuated in cells and tumors deficient for the tuberous sclerosis complex tumor suppressors

Cancer Res. 2009 Aug 1;69(15):6107-14. doi: 10.1158/0008-5472.CAN-09-0975. Epub 2009 Jul 14.

Abstract

Mutations in the TSC1 and TSC2 tumor suppressor genes give rise to the neoplastic disorders tuberous sclerosis complex (TSC) and lymphangioleiomyomatosis. Their gene products form a complex that is a critical negative regulator of mammalian target of rapamycin (mTOR) complex 1 (mTORC1) and cell growth. We recently found that the TSC1-TSC2 complex promotes the activity of mTOR complex 2 (mTORC2), an upstream activator of Akt, and this occurs independent of its inhibitory effects on mTORC1. Loss of mTORC2 activity in cells lacking the TSC1-TSC2 complex, coupled with mTORC1-mediated feedback mechanisms, leads to strong attenuation of the growth factor-stimulated phosphorylation of Akt on S473. In this study, we show that both phosphatidylinositol 3-kinase-dependent and phosphatidylinositol 3-kinase-independent mTORC2 substrates are affected by loss of the TSC1-TSC2 complex in cell culture models and kidney tumors from both Tsc2(+/-) mice (adenoma) and TSC patients (angiomyolipoma). These mTORC2 targets are all members of the AGC kinase family and include Akt, protein kinase Calpha, and serum and glucocorticoid-induced protein kinase 1. We also show that the TSC1-TSC2 complex can directly stimulate the in vitro kinase activity of mTORC2. The interaction between these two complexes is mediated primarily through regions on TSC2 and a core component of mTORC2 called Rictor. Hence, loss of the TSC tumor suppressors results in elevated mTORC1 signaling and attenuated mTORC2 signaling. These findings suggest that the TSC1-TSC2 complex plays opposing roles in tumor progression, both blocking and promoting specific oncogenic pathways through its effects on mTORC1 inhibition and mTORC2 activation, respectively.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Angiomyolipoma / metabolism
  • Animals
  • Carrier Proteins / metabolism
  • Humans
  • Immediate-Early Proteins / metabolism
  • Kidney Neoplasms / metabolism
  • Mice
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphorylation
  • Protein Kinase C-alpha / metabolism
  • Protein Serine-Threonine Kinases / metabolism
  • Rapamycin-Insensitive Companion of mTOR Protein
  • Signal Transduction
  • Transcription Factors / metabolism*
  • Tuberous Sclerosis Complex 1 Protein
  • Tuberous Sclerosis Complex 2 Protein
  • Tumor Suppressor Proteins / deficiency*
  • Tumor Suppressor Proteins / genetics
  • Tumor Suppressor Proteins / metabolism

Substances

  • CRTC2 protein, human
  • Carrier Proteins
  • Immediate-Early Proteins
  • RICTOR protein, human
  • Rapamycin-Insensitive Companion of mTOR Protein
  • TSC1 protein, human
  • TSC2 protein, human
  • Transcription Factors
  • Tsc1 protein, mouse
  • Tsc2 protein, mouse
  • Tuberous Sclerosis Complex 1 Protein
  • Tuberous Sclerosis Complex 2 Protein
  • Tumor Suppressor Proteins
  • rictor protein, mouse
  • Protein Serine-Threonine Kinases
  • serum-glucocorticoid regulated kinase
  • Protein Kinase C-alpha