Insulin signalling to mTOR mediated by the Akt/PKB substrate PRAS40

Abstract

Insulin stimulates protein synthesis and cell growth by activation of the protein kinases Akt (also known as protein kinase B, PKB) and mammalian target of rapamycin (mTOR). It was reported that Akt activates mTOR by phosphorylation and inhibition of tuberous sclerosis complex 2 (TSC2)1,2,3,4. However, in recent studies the physiological requirement of Akt phosphorylation of TSC2 for mTOR activation has been questioned5,6. Here, we identify PRAS40 (proline-rich Akt/PKB substrate 40 kDa) as a novel mTOR binding partner that mediates Akt signals to mTOR. PRAS40 binds the mTOR kinase domain and its interaction with mTOR is induced under conditions that inhibit mTOR signalling, such as nutrient or serum deprivation or mitochondrial metabolic inhibition. Binding of PRAS40 inhibits mTOR activity and suppresses constitutive activation of mTOR in cells lacking TSC2. PRAS40 silencing inactivates insulin-receptor substrate-1 (IRS-1) and Akt, and uncouples the response of mTOR to Akt signals. Furthermore, PRAS40 phosphorylation by Akt and association with 14-3-3, a cytosolic anchor protein, are crucial for insulin to stimulate mTOR. These findings identify PRAS40 as an important regulator of insulin sensitivity of the Akt–mTOR pathway and a potential target for the treatment of cancers, insulin resistance and hamartoma syndromes.

Figure 1: PRAS40 interacts with the raptor–mTOR complex.
Figure 2: PRAS40 negatively regulates the mTOR pathway.
Figure 3: PRAS40 phosphorylation is crucial for insulin-regulated mTOR signalling.
Figure 4: Insulin and nutrients regulate the PRAS40–mTOR interaction.

References

  1. 1

    Inoki, K., Li, Y., Zhu, T., Wu, J. & Guan, K. L. TSC2 is phosphorylated and inhibited by Akt and suppresses mTOR signalling. Nature Cell Biol. 4, 648–657 (2002).

    CAS  Article  Google Scholar 

  2. 2

    Manning, B. D., Tee, A. R., Logsdon, M. N., Blenis, J. & Cantley, L. C. Identification of the tuberous sclerosis complex-2 tumor suppressor gene product tuberin as a target of the phosphoinsitide 3-kinase/Akt pathway. Mol. Cell 10, 151–162 (2002).

    CAS  Article  Google Scholar 

  3. 3

    Zhang, Y. et al. Rheb is a direct target of the tuberous sclerosis tumour suppressor proteins. Nature Cell Biol. 5, 578–581 (2003).

    CAS  Article  Google Scholar 

  4. 4

    Long, X., Lin, Y., Ortiz-Vega, S., Yonezawa, K. & Avruch, J. Rheb binds and regulates the mTOR kinase. Curr. Biol. 15, 702–713 (2005).

    CAS  Article  Google Scholar 

  5. 5

    Dong, J. & Pan, D. J. Tsc2 is not a critical target of Akt during normal Drosophila development. Genes Dev. 18, 2479–2484 (2004).

    CAS  Article  Google Scholar 

  6. 6

    Hahn-Windgassen, A. et al. Akt activates the mammalian target of rapamycin by regulating cellular ATP level and AMPK activity. J. Biol. Chem. 280, 32081–32089 (2005).

    CAS  Article  Google Scholar 

  7. 7

    Brunn, G. J. et al. Phosphorylation of the translational repressor PHAS-I by the mammalian target of rapamycin. Science 277, 99–101 (1997).

    CAS  Article  Google Scholar 

  8. 8

    Dennis, P. B. et al. Mammalian TOR, a homeostatic ATP sensor. Science 294, 1102–1105 (2001).

    CAS  Article  Google Scholar 

  9. 9

    Shimji, A. F., Nghiem, P. & Schreiber, S. L. Integration of growth factor and nutrient signaling: implications for cancer biology. Molecular Cell 12, 271–280 (2003).

    Article  Google Scholar 

  10. 10

    Gao, X. et al. Tsc tumour suppressor proteins antagonize amino-acid-TOR signalling. Nature Cell Biol. 4, 699–704 (2002).

    CAS  Article  Google Scholar 

  11. 11

    Corradetti, M. N. Inoki, K., Bardeesy, N., Depinho, R. A. & Guan, K. L. Regulation of the TSC pathway by LKB1: evidence of a molecular link between tuberous sclerosis complex and Peutz-Jeghers syndrome. Genes Dev. 18, 1533–1538 (2004).

    CAS  Article  Google Scholar 

  12. 12

    Um, S. H. et al. Absence of S6K1 protects against age- and diet-induced obesity while enhancing insulin sensitivity. Nature 431, 200–205 (2004).

    CAS  Article  Google Scholar 

  13. 13

    Kenerson, H., Dundon, T. A. & Yeung, R. S. Effects of rapamycin in the Eker rat model of tuberous sclerosis complex. Pediatr Res. 57, 67–75 (2005).

    CAS  Article  Google Scholar 

  14. 14

    Vellai, T. et al. Genetics: influence of TOR kinase on lifespan in C. elegans. Nature 426, 620 (2003).

    CAS  Article  Google Scholar 

  15. 15

    Loewith, R. et al. Two TOR complexes, only one of which is rapamycin sensitive, have distinct roles in cell growth control. Mol. Cell 10, 457–468 (2002).

    CAS  Article  Google Scholar 

  16. 16

    Kim, D.-H. et al. mTOR interacts with raptor to form a nutrient-sensitive complex that signals to the cell growth machinery. Cell 110, 163–175 (2002).

    CAS  Article  Google Scholar 

  17. 17

    Kim, D.-H. et al. GβL, a positive regulator of the rapamycin-sensitive pathway required for the nutrient-sensitive interaction between raptor and mTOR. Mol. Cell 11, 895–904 (2003).

    CAS  Article  Google Scholar 

  18. 18

    Hara, K. et al. Raptor, a binding partner of target of rapamycin (TOR), mediates TOR action. Cell 110, 177–189 (2002).

    CAS  Article  Google Scholar 

  19. 19

    Sarbassov, D. D. et al. Rictor, a novel binding partner of mTOR, defines a rapamycin-insensitive and raptor-independent pathway that regulates the cytoskeleton. Curr. Biol. 14, 1296–1302 (2004).

    CAS  Article  Google Scholar 

  20. 20

    Sarbassov, D. D., Guertin, D. A., Ali, S. M. & Sabatini, D. M. Phosphorylation and regulation of Akt/PKB by the rictor-mTOR complex. Science 307, 1098–1101 (2005).

    CAS  Article  Google Scholar 

  21. 21

    Jacinto, E. et al. Mammalian TOR complex 2 controls the actin cytoskeleton and is rapamycin insensitive. Nature Cell Biol. 6, 1122–1128 (2004).

    CAS  Article  Google Scholar 

  22. 22

    Eng, J., McCormack, A. L. & Yates, J. R. An approach to correlate tandem mass spectral data of peptides with amino acid sequences in a protein database. J. Am. Mass Spectrom. 5, 976–989 (1994).

    CAS  Article  Google Scholar 

  23. 23

    Keller, A., Nesvizhskii, A. I., Kolker, E. & Aebersold, R. Empirical statistical model to estimate the accuracy of peptide identifications made by MS/MS and database search. Anal. Chem. 74, 5383–5392 (2002).

    CAS  Article  Google Scholar 

  24. 24

    Frias, M. A. et al. mSin1 is necessary for Akt/PKB phosphorylation, and its isoforms define three distinct mTORC2s. Curr. Biol. 16, 1–6 (2006).

    Article  Google Scholar 

  25. 25

    Jacinto, E. et al. Sin1/Mip1 maintains rictor-mTOR complex integrity and regulates Akt phosphorylation and substrate specificity. Cell 126, 1–13 (2006).

    Article  Google Scholar 

  26. 26

    Kovacina, K. S. et al. Identification of a proline-rich Akt substrate as a 14-3-3 binding partner. J. Biol. Chem. 278, 10189–10194 (2003).

    CAS  Article  Google Scholar 

  27. 27

    Singh, A., Chan, J., Chern, J. J. & Choi, K.-W. Genetic interaction of lobe with its modifiers in dorsoventral patterning and growth of the Drosophila eye. Genetics 171, 169–183 (2005).

    CAS  Article  Google Scholar 

  28. 28

    Tzatsos, A. & Kandror, K. V. Nutrients suppress phosphatidylinositol 3-kinase/Akt signaling via raptor-dependent mTOR-mediated insulin receptor substrate 1 phosphorylation. Mol. Cell. Biol. 26, 63–76 (2006).

    CAS  Article  Google Scholar 

  29. 29

    Huang, B. & Porter, G. Expression of proline-rich akt-substrate PRAS40 in cell survival pathway and carcinogenesis. Acta. Pharmacol. Sin. 26, 1253–1258 (2005).

    CAS  Article  Google Scholar 

  30. 30

    Saito, A. et al. Neuroprotective role of a proline-rich Akt substrate in apoptotic neuronal cell death after stroke: relationships with nerve growth factor. J. Neurosci. 24, 1584–1593 (2004).

    CAS  Article  Google Scholar 

Download references

Acknowledgements

We thank: R. Roth for PRAS40 cDNA; A. Shaw for 14-3-3 plasmid; R. Yeung for Tsc2 cells; Y.-J. Kim for database search; H. Towle and T. Neufeld for comments on the manuscript; the Mass Spectrometry and Proteomics Center at the University of Minnesota for the mass spectrometry instrumentation; the University of Minnesota Supercomputing Institute for the Sequest cluster. This study was supported by the Tuberous Sclerosis Alliance, the Minnesota Medical Foundation, the Department of Defense TS050039, and the National Institutes of Health (grant DK072004).

Author information

Affiliations

Authors

Corresponding author

Correspondence to Do-Hyung Kim.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supplementary figures S1, S2, S3, S4, Supplementary tables S1 and S2 (PDF 1877 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Haar, E., Lee, Si., Bandhakavi, S. et al. Insulin signalling to mTOR mediated by the Akt/PKB substrate PRAS40. Nat Cell Biol 9, 316–323 (2007). https://doi.org/10.1038/ncb1547

Download citation

Further reading

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing