Cell and Developmental Biology University of Michigan

Research

Regulation of signal transduction by the conserved protein kinase mTOR, the mammalian target of rapamycin

Research in the Fingar Lab focuses on signal transduction by the evolutionarily conserved mammalian target of rapamycin (mTOR) protein kinase. mTOR integrates signals from diverse cellular stimuli to control cellular physiology. mTOR associates with partner proteins to form functionally distinct, evolutionarily conserved signaling complexes with differing sensitivities to acute rapamycin, a naturally-occurring mTOR inhibitory compound. The rapamycin-sensitive mTOR complex 1 (mTORC1), which contains mTOR, raptor, mLST8, and PRAS40, promotes cellular biosynthetic processes such as protein synthesis, cell growth, cell proliferation, and cell metabolism only during growth factor, amino acid, and energy sufficiency. Thus, mTORC1 functions as an environmental sensor. The rapamycin-insensitive mTOR complex 2 (mTORC2), which contains mTOR, rictor, mLST8, mSin, and PRR5/protor, responds to growth factors to modulate the organization of the actin cytoskeleton. Currently, rapamycin is employed clinically as an immunosuppressive agent to reduce kidney transplant rejection and as a cardiology drug to inhibit coronary artery restenosis following angioplasty. Additionally, rapamycin analogs (rapalogs) and second generation mTOR catalytic inhibitors hold promise as anti-neoplastic compounds. The clinical efficacy of rapamycin, as well as the emerging idea that aberrant mTOR signaling contributes to several prevalent human diseases (e.g. cancer; insulin-resistant diabetes; cardiovascular diseases), underscores the importance of elucidating all aspects of mTOR biology.

Diverse environmental stimuli regulate mTORC1 and mTORC2 signaling. Although many mTORC1 regulatory molecules have been identified, the molecular mechanisms by which cellular signals directly modulate mTOR activity in either TORC1 or TORC2 are not known. As phosphorylation controls the activity of many proteins in the TORC1 pathway, we hypothesized that phosphorylation of mTOR itself or its partners in response to cellular signals may regulate mTOR signaling and biological function. Thus, a major focus of the lab has been to employ tandem mass spectrometry to identify novel sites of phosphorylation on mTOR and its partners and to elucidate their regulation and function in mTOR complex signal transduction. Thus, our studies investigate the individual and combined roles of site-specific mTOR complex phosphorylation in regulation of mTOR complex function at the cellular level using immortalized cells in culture and a variety of molecular, biochemical, and cellular techniques. In the future, we hope to generate animal models in order to understand the role of mTOR complex phosphorylation in control of organismal physiology.

Lab Members

• Kezhen Huang
  Research Fellow
• Brian Magnuson
  Research Fellow
• Hugo Acosta-Jaquez
  Research Lab Specialist
• Bilgen Ekim
  Graduate Student

Publications

Representative Publications

1. ERK1/2 phosphorylate Raptor to promote Ras-dependent activation of mTOR complex 1 (mTORC1). ; Carriere A, Romeo Y, Acosta-Jaquez HA, Moreau J, Bonneil E, Thibault P, Fingar DC, Roux PP.; J Biol Chem. 2011 Jan 7;286(1):567-77.
2. mTORC1 inhibition via rapamycin promotes triacylglycerol lipolysis and release of free fatty acids in 3T3-L1 adipocytes. ; Soliman GA, Acosta-Jaquez HA, Fingar DC.; Lipids. 2010 Dec;45(12):1089-100.
3. p70 Ribosomal S6 kinase is required for airway smooth muscle cell size enlargement but not increased contractile protein expression. ; Deng H, Hershenson MB, Lei J, Bitar KN, Fingar DC, Solway J, Bentley JK.; Am J Respir Cell Mol Biol. 2010 Jun;42(6):744-52.
4. Mammalian target of rapamycin (mTOR): conducting the cellular signaling symphony. ; Foster KG, Fingar DC.; J Biol Chem. 2010 May 7;285(19):14071-7. Review.
5. mTOR Ser-2481 autophosphorylation monitors mTORC-specific catalytic activity and clarifies rapamycin mechanism of action. ; Soliman GA, Acosta-Jaquez HA, Dunlop EA, Ekim B, Maj NE, Tee AR, Fingar DC.; J Biol Chem. 2010 Mar 12;285(11):7866-79. Epub 2009 Dec 18.
6. Regulation of mTOR complex 1 (mTORC1) by raptor Ser863 and multisite phosphorylation. ; Foster KG, Acosta-Jaquez HA, Romeo Y, Ekim B, Soliman GA, Carriere A, Roux PP, Ballif BA, Fingar DC.; J Biol Chem. 2010 Jan 1;285(1):80-94. Epub 2009 Oct 28.
7. Complex regulation of mammalian target of rapamycin complex 1 in the basomedial hypothalamus by leptin and nutritional status. ; Villanueva EC, Münzberg H, Cota D, Leshan RL, Kopp K, Ishida-Takahashi R, Jones JC, Fingar DC, Seeley RJ, Myers MG Jr.; Endocrinology. 2009 Oct;150(10):4541-51.
8. Site-specific mTOR phosphorylation promotes mTORC1-mediated signaling and cell growth. ; Acosta-Jaquez HA, Keller JA, Foster KG, Ekim B, Soliman GA, Feener EP, Ballif BA, Fingar DC.; Mol Cell Biol. 2009 Aug;29(15):4308-24.
9. Airway smooth muscle hyperplasia and hypertrophy correlate with glycogen synthase kinase-3(beta) phosphorylation in a mouse model of asthma. ; Bentley JK, Deng H, Linn MJ, Lei J, Dokshin GA, Fingar DC, Bitar KN, Henderson WR Jr, Hershenson MB.; Am J Physiol Lung Cell Mol Physiol. 2009 Feb;296(2):L176-84.
10. Inhibition of glycogen synthase kinase-3beta is sufficient for airway smooth muscle hypertrophy. ; Deng H, Dokshin GA, Lei J, Goldsmith AM, Bitar KN, Fingar DC, Hershenson MB, Bentley JK.; J Biol Chem. 2008 Apr 11;283(15):10198-207.
11. The long form of the leptin receptor regulates STAT5 and ribosomal protein S6 via alternate mechanisms. ; Gong Y, Ishida-Takahashi R, Villanueva EC, Fingar DC, Münzberg H, Myers MG Jr.; J Biol Chem. 2007 Oct 19;282(42):31019-27.
12. A simple qPCR-based method to detect correct insertion of homologous targeting vectors in murine ES cells. ; Soliman GA, Ishida-Takahashi R, Gong Y, Jones JC, Leshan RL, Saunders TL, Fingar DC, Myers MG Jr.; Transgenic Res. 2007 Oct;16(5):665-70.
13. Transforming growth factor-beta induces airway smooth muscle hypertrophy. ; Goldsmith AM, Bentley JK, Zhou L, Jia Y, Bitar KN, Fingar DC, Hershenson MB.; Am J Respir Cell Mol Biol. 2006 Feb;34(2):247-54.
14. 4E-binding protein phosphorylation and eukaryotic initiation factor-4E release are required for airway smooth muscle hypertrophy. ; Zhou L, Goldsmith AM, Bentley JK, Jia Y, Rodriguez ML, Abe MK, Fingar DC, Hershenson MB.; Am J Respir Cell Mol Biol. 2005 Aug;33(2):195-202.
15. SKAR is a specific target of S6 kinase 1 in cell growth control. ; Richardson CJ, Bröenstrup M, Fingar DC, Jülich K, Ballif BA, Gygi S, Blenis J.; Curr Biol. 2004 Sep 7;14(17):1540-9.
16. Target of rapamycin (TOR): an integrator of nutrient and growth factor signals and coordinator of cell growth and cell cycle progression. ; Fingar DC, Blenis J.; Oncogene. 2004 Apr 19;23(18):3151-71. Review.
17. The mTOR/p70 S6K1 pathway regulates vascular smooth muscle cell differentiation. ; Martin KA, Rzucidlo EM, Merenick BL, Fingar DC, Brown DJ, Wagner RJ, Powell RJ.; Am J Physiol Cell Physiol. 2004 Mar;286(3):C507-17.
18. mTOR controls cell cycle progression through its cell growth effectors S6K1 and 4E-BP1/eukaryotic translation initiation factor 4E. ; Fingar DC, Richardson CJ, Tee AR, Cheatham L, Tsou C, Blenis J.; Mol Cell Biol. 2004 Jan;24(1):200-16.
19. TOS motif-mediated raptor binding regulates 4E-BP1 multisite phosphorylation and function. ; Schalm SS, Fingar DC, Sabatini DM, Blenis J.; Curr Biol. 2003 May 13;13(10):797-806.
20. Mammalian cell size is controlled by mTOR and its downstream targets S6K1 and 4EBP1/eIF4E. ; Fingar DC, Salama S, Tsou C, Harlow E, Blenis J.; Genes Dev. 2002 Jun 15;16(12):1472-87.