The Class IA phosphatidylinositol 3-kinases (PI3Ks) p110a and p110b isoforms are ubiquitously expressed and respond to membrane receptor signals. They PI(3,4,5)P3, which acts as a signaling molecule to activate downstream signaling pathways including the Akt/mTOR pathway. Despite their similarities, two isoforms have distinct biochemical and biological features, one of which is that p110b has a kinase-independent function. We have reported that p110b positively regulates the small GTPase Rab5 in a manner that is independent of its catalytic activity. p110b, through a direct binding and as a molecular scaffold, keeps Rab5 in its ?active? GTP- bound form by preventing Rab5 from interacting with its GTPase-activating protein (GAP), which inactivates Rab5 by hydrolyzing its GTP to GDP. Rab5 is well known for regulating endocytosis. Our preliminary data strongly indicate that p110b can regulate endocytic turnover of cell surface nutrient transporters such as glucose transporter 1 (GLUT1) in response to growth factor deprivation. We found that genetic ablation or shRNA silencing of p110b decreased the level of Rab5-GTP. This resulted in increased cell surface GLUT1 that led to increased glucose utilization of cell lines and promoted their oncogenic transformation. These findings lead us to propose the hypothesis that p110b, as a molecular scaffold, activates Rab5 and endocytic turnover of nutrient transporters. We further propose that this novel function of p110b regulates membrane trafficking and cell metabolism and homeostasis. We have designed two Specific Aims to test this hypothesis and establish its biological relevance.
Aim 1 : Test the hypothesis that p110b facilitates Rab5-mediated endocytic turnover of nutrient transporters. We will use FL5.12, MEFs, HK-2, and MCF10A cells to determine that p110b deficiency can lead to the stabilization of nutrient transporters, and to determine if the failure of endocytic turnover is the result of Rab5 inactivation.
Aim 2. Determine the molecular and cell biological consequence of the stabilized nutrient transporters in p110b-deficient cells (with a focus on GLUT1). We will characterize the metabolic features associated with the nutrient transporter stabilization, and characterize the growth/proliferation signaling in p110b-deficient cells. We will also determine the physiological effects of the p110b-Rab5 interaction in vivo. !

Public Health Relevance

PI3 kinases are important players in human diseases. Our study is designed to test the hypothesis that PI3K p110b isoform functions to regulate intracellular membrane trafficking and metabolism. This will provide new molecular connection between PI3K, cell metabolism, and many human physiological and pathological conditions such as cancer development.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA232246-02
Application #
9741665
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Salnikow, Konstantin
Project Start
2018-09-01
Project End
2023-08-31
Budget Start
2019-09-01
Budget End
2020-08-31
Support Year
2
Fiscal Year
2019
Total Cost
Indirect Cost
Name
Rutgers University
Department
Biology
Type
Schools of Pharmacy
DUNS #
001912864
City
Piscataway
State
NJ
Country
United States
Zip Code
08854