Phosphoinositide 3-kinases (PI 3-kinases) are critical regulators of proliferation, motility, and apoptosis. The Class IA PI 3-kinase is a dimer containing distinct regulatory (p85) and catalytic (p110) subunits, both of which are frequently mutated in human cancer. While a large amount of energy in academia and industry has been applied to the study of these enzymes, there are critical aspects of PI 3-kinase regulation that remain poorly understood. For example, although the p110 catalytic subunit has been crystallized, there is little information as to how the distinct domains of p85 are oriented in space, or how mutants of p85 lead to a loss of PI 3-kinase regulation. A specific role of p110 catalytic subunit in the proliferation and tumorigenesis of PTEN null prostate cancer cells has been identified, but the mechanisms that regulate p110 in these cells are not clear. Although novel mutations of p85 have been identified in colon cancer and glioblastoma, the effects of these mutations on tumorigenesis and metastasis in vivo are not known. The current proposal uses both biochemical and genetic approaches to address fundamental questions concerning PI 3-kinase signaling in cancer.
Aim 1 uses single molecule FRET measurements to produce a spatial map of the p85 regulatory subunit, and to determine how the binding of PI 3-kinase activators alters p85 conformation and interactions with the p110 catalytic subunit.
Aim 2 examines the mechanism of p110 activation by G subunits. Sites of p110-G interactions will be defined using genetic and biochemical methods. These sites will then be mutated, in order to test the requirement for G binding in signaling by p110 in PTEN null prostate cancer cells.
Aim 3 will study the signaling by p85 mutants in colon cancer and glioblastoma cell lines, the tumor types in which the recently described mutants were identified. Lentivirus methods will be used to knock down endogenous p85 and rescue with wild type or mutant p85. The effects of these mutants on in vitro cell growth and motility, and in vivo tumorigenesis and metastasis, will be studied. This proposal will define novel aspects of PI 3-kinase signaling and regulation, and will provide a better understanding of structural features that could be exploited as drug targets.

Public Health Relevance

PI 3-kinases are intracellular enzymes that play an important role in cell proliferation and survival, and which frequently contain activating mutations in human cancers. Understanding the mechanisms that regulate their activity in normal and malignant cells is critical for the design of novel and specific drugs to target these enzymes in human disease.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
Project #
Application #
Study Section
Tumor Cell Biology Study Section (TCB)
Program Officer
Gerratana, Barbara
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Albert Einstein College of Medicine
Schools of Medicine
United States
Zip Code
Dbouk, Hashem A; Backer, Jonathan M (2013) Novel approaches to inhibitor design for the p110* phosphoinositide 3-kinase. Trends Pharmacol Sci 34:149-53
Salamon, Rachel Schnur; Backer, Jonathan M (2013) Phosphatidylinositol-3,4,5-trisphosphate: tool of choice for class I PI 3-kinases. Bioessays 35:602-11
Dbouk, Hashem A; Khalil, Bassem D; Wu, Haiyan et al. (2013) Characterization of a tumor-associated activating mutation of the p110* PI 3-kinase. PLoS One 8:e63833
Jaiswal, Bijay S; Janakiraman, Vasantharajan; Kljavin, Noelyn M et al. (2009) Somatic mutations in p85alpha promote tumorigenesis through class IA PI3K activation. Cancer Cell 16:463-74
Pang, Huan; Flinn, Rory; Patsialou, Antonia et al. (2009) Differential enhancement of breast cancer cell motility and metastasis by helical and kinase domain mutations of class IA phosphoinositide 3-kinase. Cancer Res 69:8868-76
Backer, Jonathan M (2008) The regulation and function of Class III PI3Ks: novel roles for Vps34. Biochem J 410:1-17
Weinger, Jason G; Gohari, Pouyan; Yan, Ying et al. (2008) In brain, Axl recruits Grb2 and the p85 regulatory subunit of PI3 kinase;in vitro mutagenesis defines the requisite binding sites for downstream Akt activation. J Neurochem 106:134-46
El-Sibai, Mirvat; Pertz, Olivier; Pang, Huan et al. (2008) RhoA/ROCK-mediated switching between Cdc42- and Rac1-dependent protrusion in MTLn3 carcinoma cells. Exp Cell Res 314:1540-52
Ciraolo, Elisa; Iezzi, Manuela; Marone, Romina et al. (2008) Phosphoinositide 3-kinase p110beta activity: key role in metabolism and mammary gland cancer but not development. Sci Signal 1:ra3
Yip, Shu-Chin; Eddy, Robert J; Branch, Angie M et al. (2008) Quantification of PtdIns(3,4,5)P(3) dynamics in EGF-stimulated carcinoma cells: a comparison of PH-domain-mediated methods with immunological methods. Biochem J 411:441-8