Forchheimer Building 230
Professor, Department of Molecular Pharmacology
Director, Belfer Institute for Advanced Biomedical Studies
SIGNALING BY PHOSPHOINOSITIDE KINASES
Phosphoinositide 3-kinases are lipid kinases that mediate signaling by tyrosine kinase and G-protein coupled receptors. PI 3-kinases are important regulators of cellular proliferation, motility, apoptosis, and vesicular trafficking. They are critical for insulin signaling, and are important in clinical diabetes. Mutational activation of PI 3-kinases is commonly found in human cancers. We are interested in the mechanisms that regulate PI 3'-kinase activity and the role of PI 3-kinases in intracellular signaling in diabetes, cancer and aging.
1. Activating mutations of PI 3-kinase in human cancer. The Class IA PI 3'-kinase is a heterodimer composed of a catalytic subunit (p110) and a regulatory subunit (p85). In normal cells, PI 3-kinase is activated when p85 binds to phosphotyrosine residues in receptor tyrosine kinases and their substrates, or when Gbg subunits from trimeric G-proteins bind to p110. p85 and p110 are frequently mutated in human breast, colon, prostate and brain cancer. Using biochemical, cell biological and biophysical methods, we are studying the mechanism of PI3K activation by both receptor tyrosine kinases and G-protein coupled receptors in normal cells, and how mutations in the regulatory and catalytic subunits of PI 3-kinase can lead to constitutive activity in cancer cells.
2. PI 3'-kinases in autophagy. Autophagy is a cellular response to nutrient deprivation in which cytosolic contents are engulfed and delivered to the lysosome for degradation. Autophagy is required for the viability of pancreatic beta cells, hepatocytes and neurons and for innate immune responses to pathogens. Downregulation of autophagic degradation has been implicated in neurodegenerative syndromes and in aging. The mammalian Class III PI 3-kinase, hVps34, plays essential roles in both vesicular trafficking and autophagy. We are studying the role of hVps34 in autophagy, and the mechanisms that regulate hVps34 activity, using both cell culture and animal models (mice and zebrafish).
3. PI 3'-kinases in tumor metastasis. Activating mutations of PI 3-kinases are frequently found in human breast cancer and other tumors. Using genetic methods, we have engineered human breast cancer cells to express physiological levels of wild type or mutant PI 3-kinase. We are studying the effects of the mutants on tumor metastasis in vivo, using xenograft tumors in SCID mice. We hope to uncover the mechanisms by which oncogenic PI 3-kinase mutations lead to enhanced metastasis.
Selected Publications 2008-
Yip, S.-C, Eddy, R.J., Branch, A.M., Pang, H., Wu, H., Yan, Y., Drees, B.E. Neilsen, P.O., Condeelis, J.S., and Backer, J.M. Quantitation of PI[3,4,5]P3 dynamics in EGF-stimulated carcinoma cells: A comparison of PH domain-mediated versus immunological methods. (2008) Biochemical Journal 411:441-448.
El-Sibai, M, Pertz, O., Pang, H., Yip, S.C., Lorenz, M., Symons, M., Condeelis, J.S., Hahn, K.M., and Backer, J.M. RhoA/ROCK-mediated switching between Cdc42- and Rac1-dependent protrusion in MTLn3 carcinoma cells. (2008) Exp. Cell Res. 314:1540-52.
Juhasz, G, Hill, JH, Yan, Y, Sass, M, Baehrecke, EH, Backer, JM, and Neufeld, TP. The class III PI(3)K Vps34 promotes autophagy and endocytosis but not TOR signaling in Drosophila. (2008) J. Cell Biol. 18:655-66
Yan, Y., Flinn, R.J., Wu, H., Schnur, R.S., and Backer, J.M. hVps15 but not calcium/calmodulin is required for the activity and regulation of hVps34 in mammalian cells. (2009) Biochemical Journal 417:747-755.
Jaiswal, BS, Janakiraman, V., Kljavin, NM, Chaudhari, S, Stern, HM, Wang, W, Kan, Z, Dbouk, HA, Peters, BA, Waring, P, Dela Vega, T, Kenski, DM, Bowman, K, Lorenzo, M, Wu, J, Modrusan, Z, Stinson, J, Eby, M, Yue, P, Kaminker, J, de Sauvage, FJ, Backer, JM, and Seshagiri, S. Somatic mutations in p85a promote tumorigenesis through class IA PI3K activation. (2009) Cancer Cell 16:463-474.
Pang, H., Flinn, R, Patsialou, A, Wyckoff, J, Roussos, ET, Wu, H, Puzutto, M, Goswami, S, Condeelis, JS, Bresnick, AR, Segall, JE and Backer, JM. Differential enhancement of breast cancer cell motility and metastasis by helical and kinase domain mutations of class IA PI3K. (2009) Cancer Research 69:8868-8876.
Wu, H, Shekar, SC, Flinn, RJ, El-Sibai, M, Jaiswal, B.S., Sen, KI, Janakiraman, V, Seshagiri, S, Gerfen, GJ, Girvin, ME, Backer, JM. Regulation of Class IA PI 3-kinases: C2 domain-iSH2 domain contacts inhibit p85/p110 and are disrupted in oncogenic p85 mutants. (2009) PNAS 106:20258-20263.
Flinn, RJ, Yan, Y, Goswami, S, Parker, PJ and Backer, JM. The late endosome is essential for mTORC1 signaling. (2010) Mol Biol Cell 21:833-841
Sen, I, Wu, H. Backer, JM and Gerfen, GJ. The Structure of p85ni in Class IA PI 3-Kinase Exhibits Inter-Domain Disorder. (2010) Biochemistry 16:2159-2166
Dbouk, HA, Pang, H, Fiser, A, and Backer, JM. A biochemical mechanism for the oncogenic potential of the p110 catalytic subunit of phosphoinositide 3-kinase. (2010) PNAS 107:19897-19902.