A diacylglycerol-protein kinase C-RasGRP1 pathway directs Ras activation upon antigen receptor stimulation of T cells.
Ras GTPases are on/off switches regulating numerous cellular responses by signaling to various effector molecules. In T lymphocytes, Ras can be activated by two Ras exchange factors, SOS and RasGRP1, which are recruited through the adapters Grb2 and LAT and via the second-messenger diacylglycerol (DAG), respectively. Mitogen-activated protein (MAP) kinase phosphorylation patterns induced by active Ras can vary and contribute to distinct cellular responses. The different consequences of Ras activation by either guanine exchange factor are unknown. DAG also recruits and activates the kinase protein kinase Ctheta (PKCtheta) turning on the Erk MAP kinase pathway, but the biochemical mechanism responsible is unclear. We generated T-cell clones deficient in phorbol myristate acetate (a surrogate for DAG)-induced Ras activation. Analysis of a RasGRP1-deficient Jurkat T-cell clone and RasGRP1 RNA interference in wild-type cells revealed that RasGRP1 is required for optimal, antigen receptor-triggered Ras-Erk activation. RasGRP1 relies on its DAG-binding domain to selectively activate Erk kinases. Activation of Erk correlates with the phosphorylation of threonine residue 184 in RasGRP1. This phosphorylation event requires the activities of novel PKC kinases. Conversely, active PKCtheta depends on RasGRP1 sufficiency to effectively trigger downstream events. Last, DAG-PKC-RasGRP1-driven Ras-Erk activation in T cells is a unique signaling event, not simply compensated for by SOS activity.
Roose
Jeroen P
JP
Department of Medicine, UCSF, 533 Parnassus Avenue, Room U-330, San Francisco, CA 94143, USA.
Mollenauer
Marianne
M
Gupta
Vikas A
VA
Stone
James
J
Weiss
Arthur
A
D000098:Acetophenones / Q000494:pharmacology; D015703:Antigens, CD / Q000378:metabolism; D000945:Antigens, Differentiation, T-Lymphocyte / Q000378:metabolism; D001578:Benzopyrans / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004075:Diglycerides / Q000378:metabolism*; D004789:Enzyme Activation; D020662:Guanine Nucleotide Exchange Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019169:Jurkat Cells; D037181:Lectins, C-Type; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000074121:Protein Kinase C-theta; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D034622:RNA Interference; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000378:metabolism*; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000187:drug effects / Q000201:enzymology* / Q000276:immunology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D020703:ras GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism*; D000099192:CD69 Antigens
D000098:Acetophenones; D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D001578:Benzopyrans; D002118:Calcium; D004268:DNA-Binding Proteins; D004075:Diglycerides; D020662:Guanine Nucleotide Exchange Factors; D007527:Isoenzymes; D037181:Lectins, C-Type; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D011493:Protein Kinase C; D000074121:Protein Kinase C-theta; D047428:Protein Kinase Inhibitors; D016693:Receptors, Antigen, T-Cell, alpha-beta; D013755:Tetradecanoylphorbol Acetate; D020703:ras GTPase-Activating Proteins; D018631:ras Proteins; D000099192:CD69 Antigens; C491790:RASGRP1 protein, human; C085746:rottlerin; C076233:PRKCQ protein, human