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Akt regulates growth by directly phosphorylating Tsc2


The direct mechanism by which the serine/threonine kinase Akt (also known as protein kinase B (PKB)) regulates cell growth is unknown. Here, we report that Drosophila melanogaster Akt/PKB stimulates growth by phosphorylating the tuberous sclerosis complex 2 (Tsc2) tumour suppressor and inhibiting formation of a Tsc1–Tsc2 complex. We show that Akt/PKB directly phosphorylates Drosophila Tsc2 in vitro at the conserved residues, Ser 924 and Thr 1518. Mutation of these sites renders Tsc2 insensitive to Akt/PKB signalling, increasing the stability of the Tsc1–Tsc2 complex within the cell. Stimulating Akt/PKB signalling in vivo markedly increases cell growth/size, disrupts the Tsc1–Tsc2 complex and disturbs the distinct subcellular localization of Tsc1 and Tsc2. Furthermore, all Akt/PKB growth signals are blocked by expression of a Tsc2 mutant lacking Akt phosphorylation sites. Thus, Tsc2 seems to be the critical target of Akt in mediating growth signals for the insulin signalling pathway.

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Figure 1: Akt alters the localization of Tsc1 and Tsc2.
Figure 2: Insulin/Akt inhibits the stability of the Tsc1–Tsc2 complex.
Figure 3: Akt phosphorylates Tsc2 at Ser 924 and Thr 1518 in vitro.
Figure 4: Mutation of Ser 924 and Thr 1518 in Tsc2 results in an activated Tsc2 protein.
Figure 5: Mutation of Ser 924 and Thr 1518 in Tsc2 inhibits Akt-stimulated growth.
Figure 6: Akt-stimulated growth in the wing can be abolished by Tsc2ΔAkt-P.
Figure 7: S6K suppresses Tsc1–Tsc2ΔAkt-P-mediated growth reduction.
Figure 8: Akt regulates growth by phosphorylating and inhibiting the Tsc1–Tsc2 complex.


  1. 1

    Gomez, M. R., Sampson, J. R. & Whittemore, V. H. Tuberous Sclerosis Complex (Oxford University Press, New York, 1999).

    Google Scholar 

  2. 2

    Gomez, M. R. Tuberous Sclerosis (Raven Press, New York, 1988).

    Google Scholar 

  3. 3

    van Slegtenhorst, M. et al. Identification of the tuberous sclerosis gene TSC1 on chromosome 9q34. Science 277, 805–808 (1997).

    CAS  Article  Google Scholar 

  4. 4

    Consortium, T. E. C. T. S. Identification and characterization of the tuberous sclerosis gene on chromosome 16. Cell 75, 1305–1315 (1993).

    Article  Google Scholar 

  5. 5

    Maheshwar, M. M. et al. The GAP-related domain of tuberin, the product of the TSC2 gene, is a target for missense mutations in tuberous sclerosis. Hum. Mol. Genet. 6, 1991–1996 (1997).

    CAS  Article  Google Scholar 

  6. 6

    Cheadle, J. P., Reeve, M. P., Sampson, J. R. & Kwiatkowski, D. J. Molecular genetic advances in tuberous sclerosis. Hum. Genet. 107, 97–114 (2000).

    CAS  Article  Google Scholar 

  7. 7

    Lupas, A., Van Dyke, M. & Stock, J. Predicting coiled coils from protein sequences. Science 252, 1162–1164 (1991).

    CAS  Article  Google Scholar 

  8. 8

    van Slegtenhorst, M. et al. Interaction between hamartin and tuberin, the TSC1 and TSC2 gene products. Hum. Mol. Genet. 7, 1053–1057 (1998).

    CAS  Article  Google Scholar 

  9. 9

    Plank, T. L., Yeung, R. S. & Henske, E. P. Hamartin, the product of the tuberous sclerosis 1 (TSC1) gene, interacts with tuberin and appears to be localized to cytoplasmic vesicles. Cancer Res. 58, 4766–4770 (1998).

    CAS  PubMed  Google Scholar 

  10. 10

    Nellist, M. et al. Characterization of the cytosolic tuberin–hamartin complex. Tuberin is a cytosolic chaperone for hamartin. J. Biol. Chem. 274, 35647–35652 (1999).

    CAS  Article  Google Scholar 

  11. 11

    Miloloza, A. et al. The TSC1 gene product, hamartin, negatively regulates cell proliferation. Hum. Mol. Genet. 9, 1721–1727 (2000).

    CAS  Article  Google Scholar 

  12. 12

    Xu, T., Wang, W., Zhang, S., Stewart, R. A. & Yu, W. Identifying tumor suppressors in genetic mosaics: the Drosophila lats gene encodes a putative protein kinase. Development 121, 1053–1063 (1995).

    CAS  PubMed  Google Scholar 

  13. 13

    Theodosiou, N. A., Zhang, S., Wang, W. Y. & Xu, T. slimb coordinates wg and dpp expression in the dorsal–ventral and anterior–posterior axes during limb development. Development 125, 3411–3416 (1998).

    CAS  PubMed  Google Scholar 

  14. 14

    Ito, N. & Rubin, G. M. gigas, a Drosophila homolog of tuberous sclerosis gene product-2, regulates the cell cycle. Cell 96, 529–539 (1999).

    CAS  Article  Google Scholar 

  15. 15

    Huang, H. et al. PTEN affects cell size, cell proliferation and apoptosis during Drosophila eye development. Development 126, 5365–5372 (1999).

    CAS  PubMed  Google Scholar 

  16. 16

    Oldham, S., Montagne, J., Radimerski, T., Thomas, G. & Hafen, E. Genetic and biochemical characterization of dTOR, the Drosophila homolog of the target of rapamycin. Genes Dev. 14, 2689–2694 (2000).

    CAS  Article  Google Scholar 

  17. 17

    Gao, X., Neufeld, T. P. & Pan, D. Drosophila PTEN regulates cell growth and proliferation through PI3K-dependent and -independent pathways. Dev. Biol. 221, 404–418 (2000).

    CAS  Article  Google Scholar 

  18. 18

    Potter, C. J., Huang, H. & Xu, T. Drosophila Tsc1 functions with Tsc2 to antagonize insulin signaling in regulating cell growth, cell proliferation, and organ size. Cell 105, 357–368 (2001).

    CAS  Article  Google Scholar 

  19. 19

    Tapon, N., Ito, N., Dickson, B. J., Treisman, J. E. & Hariharan, I. K. The Drosophila tuberous sclerosis complex gene homologs restrict cell growth and cell proliferation. Cell 105, 345–355 (2001).

    CAS  Article  Google Scholar 

  20. 20

    Gao, X. & Pan, D. TSC1 and TSC2 tumor suppressors antagonize insulin signaling in cell growth. Genes Dev. 15, 1383–1392 (2001).

    CAS  Article  Google Scholar 

  21. 21

    Moberg, K. H., Bell, D. W., Wahrer, D. C., Haber, D. A. & Hariharan, I. K. Archipelago regulates Cyclin E levels in Drosophila and is mutated in human cancer cell lines. Nature 413, 311–316 (2001).

    CAS  Article  Google Scholar 

  22. 22

    Goberdhan, D. C., Paricio, N., Goodman, E. C., Mlodzik, M. & Wilson, C. Drosophila tumor suppressor PTEN controls cell size and number by antagonizing the Chico/PI3-kinase signaling pathway. Genes Dev. 13, 3244–3258 (1999).

    CAS  Article  Google Scholar 

  23. 23

    Maehama, T. & Dixon, J. E. The tumor suppressor, PTEN/MMAC1, dephosphorylates the lipid second messenger, phosphatidylinositol 3,4,5-trisphosphate. J. Biol. Chem. 273, 13375–13378 (1998).

    CAS  Article  Google Scholar 

  24. 24

    Cantley, L. C. & Neel, B. G. New insights into tumor suppression: PTEN suppresses tumor formation by restraining the phosphoinositide 3-kinase/AKT pathway. Proc. Natl Acad. Sci. USA 96, 4240–4245 (1999).

    CAS  Article  Google Scholar 

  25. 25

    Lehner, C. F. The beauty of small flies. Nature Cell Biol. 1, E129–E130 (1999).

    CAS  Article  Google Scholar 

  26. 26

    Edgar, B. A. From small flies come big discoveries about size control. Nature Cell Biol. 1, E191–E193 (1999).

    CAS  Article  Google Scholar 

  27. 27

    Weinkove, D. & Leevers, S. J. The genetic control of organ growth: insights from Drosophila. Curr. Opin. Genet. Dev. 10, 75–80 (2000).

    CAS  Article  Google Scholar 

  28. 28

    Stocker, H. & Hafen, E. Genetic control of cell size. Curr. Opin. Genet. Dev. 10, 529–535 (2000).

    CAS  Article  Google Scholar 

  29. 29

    Alessi, D. R. & Cohen, P. Mechanism of activation and function of protein kinase B. Curr. Opin. Genet. Dev. 8, 55–62 (1998).

    CAS  Article  Google Scholar 

  30. 30

    Brazil, D. P. & Hemmings, B. A. Ten years of protein kinase B signalling: a hard Akt to follow. Trends Biochem. Sci. 26, 657–664 (2001).

    CAS  Article  Google Scholar 

  31. 31

    Scheid, M. P. & Woodgett, J. R. PKB/AKT: functional insights from genetic models. Nature Rev. Mol. Cell Biol. 2, 760–768 (2001).

    CAS  Article  Google Scholar 

  32. 32

    Verdu, J., Buratovich, M. A., Wilder, E. L. & Birnbaum, M. J. Cell-autonomous regulation of cell and organ growth in Drosophila by Akt/PKB. Nature Cell Biol. 1, 500–506 (1999).

    CAS  Article  Google Scholar 

  33. 33

    Shioi, T. et al. Akt/protein kinase B promotes organ growth in transgenic mice. Mol. Cell. Biol. 22, 2799–2809 (2002).

    CAS  Article  Google Scholar 

  34. 34

    Stambolic, V. et al. Negative regulation of PKB/Akt-dependent cell survival by the tumor suppressor PTEN. Cell 95, 29–39 (1998).

    CAS  Article  Google Scholar 

  35. 35

    Aoki, M., Blazek, E. & Vogt, P. K. A role of the kinase mTOR in cellular transformation induced by the oncoproteins P3k and Akt. Proc. Natl Acad. Sci. USA 98, 136–141 (2001).

    CAS  Article  Google Scholar 

  36. 36

    Alessi, D. R., Caudwell, F. B., Andjelkovic, M., Hemmings, B. A. & Cohen, P. Molecular basis for the substrate specificity of protein kinase B; comparison with MAPKAP kinase-1 and p70 S6 kinase. FEBS Lett. 399, 333–338 (1996).

    CAS  Article  Google Scholar 

  37. 37

    Brand, A. H. & Perrimon, N. Targeted gene expression as a means of altering cell fates and generating dominant phenotypes. Development 118, 401–415 (1993).

    CAS  Google Scholar 

  38. 38

    Scanga, S. E. et al. The conserved PI3′K/PTEN/Akt signaling pathway regulates both cell size and survival in Drosophila. Oncogene 19, 3971–3977 (2000).

    CAS  Article  Google Scholar 

  39. 39

    Ito, K., Awano, W., Suzuki, K., Hiromi, Y. & Yamamoto, D. The Drosophila mushroom body is a quadruple structure of clonal units each of which contains a virtually identical set of neurones and glial cells. Development 124, 761–771 (1997).

    CAS  PubMed  Google Scholar 

  40. 40

    Struhl, G. & Basler, K. Organizing activity of wingless protein in Drosophila. Cell 72, 527–540 (1993).

    CAS  Article  Google Scholar 

  41. 41

    Schmelzle, T. & Hall, M. N. TOR, a central controller of cell growth. Cell 103, 253–262 (2000).

    CAS  Article  Google Scholar 

  42. 42

    Dufner, A. & Thomas, G. Ribosomal S6 kinase signaling and the control of translation. Exp. Cell Res. 253, 100–109 (1999).

    CAS  Article  Google Scholar 

  43. 43

    Bunch, T. A., Grinblat, Y. & Goldstein, L. S. Characterization and use of the Drosophila metallothionein promoter in cultured Drosophila melanogaster cells. Nucleic Acids Res. 16, 1043–1061 (1988).

    CAS  Article  Google Scholar 

  44. 44

    Halder, G. et al. Eyeless initiates the expression of both sine oculis and eyes absent during Drosophila compound eye development. Development 125, 2181–2191 (1998).

    CAS  PubMed  Google Scholar 

  45. 45

    Hay, B. A., Maile, R. & Rubin, G. M. P element insertion-dependent gene activation in the Drosophila eye. Proc. Natl Acad. Sci. USA 94, 5195–5200 (1997).

    CAS  Article  Google Scholar 

  46. 46

    Zhang, H., Stallock, J. P., Ng, J. C., Reinhard, C. & Neufeld, T. P. Regulation of cellular growth by the Drosophila target of rapamycin dTOR. Genes Dev. 14, 2712–2724 (2000).

    CAS  Article  Google Scholar 

  47. 47

    Fehon, R. G. et al. Molecular interactions between the protein products of the neurogenic loci Notch and Delta, two EGF-homologous genes in Drosophila. Cell 61, 523–534 (1990).

    CAS  Article  Google Scholar 

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We thank K. Wehner for helpful discussions, M. Birnbaum for Dakt1 reagents, the Developmental Studies Hybridoma bank for anti-gigas antibodies and X. Fei for injections. This work was supported in part by a National Institutes of Health grant (CA69408) and the Rothberg Courage Award, TS Alliance. T.X. is an investigator of the Howard Hughes Medical Institute. C.J.P. was a predoctoral candidate in the Department of Genetics.

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Correspondence to Tian Xu.

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Supplementary figure

Figure S1. Akt expression does not enhance the Tsc1 mutant phenotype. (PDF 170 kb)

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Potter, C., Pedraza, L. & Xu, T. Akt regulates growth by directly phosphorylating Tsc2. Nat Cell Biol 4, 658–665 (2002).

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