Phosphoinositide 3-Kinase Regulates Plasma Membrane Targeting of the Ras-specific Exchange Factor RasGRP1

• Published in: The Journal of biological chemistry 2011-04, Vol.286 (14), p.12712-12723
• Main Authors: Zahedi, Bari, Goo, Hyun-jung, Beaulieu, Nadine, Tazmini, Ghazaleh, Kay, Robert J., Cornell, Rosemary B.
• Format: Article
• Language: English
• Subjects: Animals; Cell Line; Cell Membrane - metabolism; Guanine Nucleotide Exchange Factors - genetics; Guanine Nucleotide Exchange Factors - metabolism; Inositol Phospholipid; Membrane Proteins; Mice; Microscopy, Fluorescence; Mitogen-Activated Protein Kinase 1 - genetics; Mitogen-Activated Protein Kinase 1 - metabolism; NIH 3T3 Cells; Phosphatidylinositol 3-Kinase; Phosphatidylinositol 3-Kinases - genetics; Phosphatidylinositol 3-Kinases - metabolism; Phosphatidylinositol Signaling; Phosphorylation; Plasma Membrane; Protein Structure, Tertiary; Protein Targeting; Ras; Signal Transduction
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M110.189605

Receptor-induced targeting of exchange factors to specific cellular membranes is the predominant mechanism for initiating and compartmentalizing signal transduction by Ras GTPases. The exchange factor RasGRP1 has a C1 domain that binds the lipid diacylglycerol and thus can potentially mediate membrane localization in response to receptors that are coupled to diacylglycerol-generating phospholipase Cs. However, the C1 domain is insufficient for targeting RasGRP1 to the plasma membrane. We found that a basic/hydrophobic cluster of amino acids within the plasma membrane-targeting domain of RasGRP1 is instead responsible for plasma membrane targeting. This basic/hydrophobic cluster binds directly to phospholipid vesicles containing phosphoinositides via electrostatic interactions with polyanionic phosphoinositide headgroups and insertion of a tryptophan into the lipid bilayer. B cell antigen receptor ligation and other stimuli induce plasma membrane targeting of RasGRP1 by activating the phosphoinositide 3-kinase signaling pathway, which generates phosphoinositides within the plasma membrane. Direct detection of phosphoinositides by the basic/hydrophobic cluster of RasGRP1 provides a novel mechanism for coupling and co-compartmentalizing phosphoinositide 3-kinase and Ras signaling and, in coordination with diacylglycerol detection by the C1 domain, gives RasGRP1 the potential to serve as an integrator of converging signals from the phosphoinositide 3-kinase and phospholipase C pathways.