The mTOR/S6K signalling pathway: The role of the tsc1/2 tumour suppressor complex and the proto-oncogene rheb

Takahiro Nobukuni, George Thomas

Research output: Chapter in Book/Report/Conference proceedingChapter

Abstract

Gene deletion studies in mice and in Drosophila have shown that the 40S ribosomal protein S6 Kinases, dS6K in Drosophila and S6K1 and S6K2 in mice are important regulators of cell growth in response to insulin stimulation and nutrition availability. Here we chiefly focus on dS6k and S6K1, whose activities are regulated by an upstream kinase termed the mammalian target of rapamycin (mTOR, or dTOR in Drosophila). Our understanding of the mechanisms regulating the mTOR/S6K1-signalling pathway will be fundamental in determining the mechanisms which control cell growth in response to insulin signalling. Recent findings from this laboratory and others suggests that the tumour suppressor complex made of two proteins TSC1/ hamartin and TSC2/tuberin, acts as a negative regulator of mTOR/S6K1 signalling. Mutations in either TSC1 or TSC2 are genetically linked to tuberous sclerosis complex (TSC) syndrome, which can lead to severe pathological consequences, including mental retardation, epilepsy and autism, as well as cardiac, pulmonary and renal failure. Despite a large number of initial reports on the TSC1/TSC2 complex, and the finding that its activity is regulated by protein kinase B (PKB), the direct target of the TSC1/TSC2 inhibitory complex was unknown until recently. Since TSC2 has a GTPase-activating domain, or GAP-like sequence, others and we searched for a small GTP binding protein, which may serve as the target of TSC1/TSC2 inhibitory complex. In our case we took advantage of a genome wide screen in Drosophila for effectors of cell growth and in parallel searched for a small GTPase whose activity is up-regulated in TSC2-deficient cells. The identified gene was a member of the Ras family of GTPases termed Ras homologue enriched in brain or Rheb. Here we review recent findings demonstrating that the TSC1/TSC2 inhibitory complex normally acts on Rheb to mediate mTOR/S6K1-signalling.

Original languageEnglish
Title of host publicationBiology of IGF-1
Subtitle of host publicationIts Interaction with Insulin in Health and Malignant States
Publisherwiley
Pages148-154
Number of pages7
Volume262
ISBN (Electronic)9780470869970
ISBN (Print)9780470869987
DOIs
Publication statusPublished - 2008 Oct 7
Externally publishedYes

Keywords

  • DTsc1/2 tumour suppressor complex
  • Endogenous Rheb activity
  • MTOR/S6K1- signalling pathway
  • PI3K inhibitor
  • Proto-oncogene Rheb
  • Rheb and insulin signal
  • Rheb overexpression
  • S6K1 as cell regulator

ASJC Scopus subject areas

  • Medicine(all)

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