title: Tuberous sclerosis complex tumor suppressor-mediated S6 kinase inhibition by phosphatidylinositide-3-OH kinase is mTOR independent.
abstract: The evolution of mitogenic pathways has led to the parallel requirement for negative control mechanisms, which prevent aberrant growth and the development of cancer. Principally, such negative control mechanisms are represented by tumor suppressor genes, which normally act to constrain cell proliferation (Macleod, K. 2000. Curr. Opin. Genet. Dev. 10:81-93). Tuberous sclerosis complex (TSC) is an autosomal-dominant genetic disorder, characterized by mutations in either TSC1 or TSC2, whose gene products hamartin (TSC1) and tuberin (TSC2) constitute a putative tumor suppressor complex (TSC1-2; van Slegtenhorst, M., M. Nellist, B. Nagelkerken, J. Cheadle, R. Snell, A. van den Ouweland, A. Reuser, J. Sampson, D. Halley, and P. van der Sluijs. 1998. Hum. Mol. Genet. 7:1053-1057). Little is known with regard to the oncogenic target of TSC1-2, however recent genetic studies in Drosophila have shown that S6 kinase (S6K) is epistatically dominant to TSC1-2 (Tapon, N., N. Ito, B.J. Dickson, J.E. Treisman, and I.K. Hariharan. 2001. Cell. 105:345-355; Potter, C.J., H. Huang, and T. Xu. 2001. Cell. 105:357-368). Here we show that loss of TSC2 function in mammalian cells leads to constitutive S6K1 activation, whereas ectopic expression of TSC1-2 blocks this response. Although activation of wild-type S6K1 and cell proliferation in TSC2-deficient cells is dependent on the mammalian target of rapamycin (mTOR), by using an S6K1 variant (GST-DeltaC-S6K1), which is uncoupled from mTOR signaling, we demonstrate that TSC1-2 does not inhibit S6K1 via mTOR. Instead, we show by using wortmannin and dominant interfering alleles of phosphatidylinositide-3-OH kinase (PI3K) that increased S6K1 activation is contingent upon the suppression of TSC2 function by PI3K in normal cells and is PI3K independent in TSC2-deficient cells.
authors.affiliation: Cancer Research UK Centre for Cell and Molecular Biology, Institute for Cancer Research, 237 Fulham Road, London SW3 6JB, UK.
authors.forename: Anja
authors.initials: A
authors.lastname: Jaeschke
authors.forename: Joerg
authors.initials: J
authors.lastname: Hartkamp
authors.forename: Masao
authors.initials: M
authors.lastname: Saitoh
authors.forename: Wendy
authors.initials: W
authors.lastname: Roworth
authors.forename: Takahiro
authors.initials: T
authors.lastname: Nobukuni
authors.forename: Angela
authors.initials: A
authors.lastname: Hodges
authors.forename: Julian
authors.initials: J
authors.lastname: Sampson
authors.forename: George
authors.initials: G
authors.lastname: Thomas
authors.forename: Richard
authors.initials: R
authors.lastname: Lamb
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D039642:Eukaryotic Initiation Factors; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology; D016147:Genes, Tumor Suppressor / Q000502:physiology; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D014176:Protein Biosynthesis / Q000502:physiology; D011494:Protein Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D058570:TOR Serine-Threonine Kinases; D014162:Transfection; D014402:Tuberous Sclerosis / Q000378:metabolism*; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D039642:Eukaryotic Initiation Factors; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D011494:Protein Kinases; D011506:Proteins; D011994:Recombinant Proteins; D012097:Repressor Proteins; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D000077004:Tuberous Sclerosis Complex 1 Protein; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; C499527:Eif4ebp1 protein, mouse; C000624651:Tsc1 protein, mouse; C000624654:Tsc2 protein, mouse; C546843:mTOR protein, mouse