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Original Article |
Regulates Ras Activation by a Novel Mechanism
Correspondence to: Stephen M. Prescott, The Huntsman Cancer Institute, University of Utah, 2000 Circle of Hope, Salt Lake City, UT 84132. Tel:(801) 585-3401 Fax:(801) 585-6345 E-mail:stephen.prescott{at}hci.utah.edu.
Guanine nucleotide exchange factors (GEFs) activate Ras by facilitating its GTP binding. Ras guanyl nucleotide-releasing protein (GRP) was recently identified as a Ras GEF that has a diacylglycerol (DAG)-binding C1 domain. Its exchange factor activity is regulated by local availability of signaling DAG. DAG kinases (DGKs) metabolize DAG by converting it to phosphatidic acid. Because they can attenuate local accumulation of signaling DAG, DGKs may regulate RasGRP activity and, consequently, activation of Ras. DGK
, but not other DGKs, completely eliminated Ras activation induced by RasGRP, and DGK activity was required for this mechanism. DGK
also coimmunoprecipitated and colocalized with RasGRP, indicating that these proteins associate in a signaling complex. Coimmunoprecipitation of DGK
and RasGRP was enhanced in the presence of phorbol esters, which are DAG analogues that cannot be metabolized by DGKs, suggesting that DAG signaling can induce their interaction. Finally, overexpression of kinase-dead DGK
in Jurkat cells prolonged Ras activation after ligation of the T cell receptor. Thus, we have identified a novel way to regulate Ras activation: through DGK
, which controls local accumulation of DAG that would otherwise activate RasGRP.
Key Words: diacylglycerols, diacylglycerol kinase, signal transduction, H-Ras oncogenes, RasGRP protein
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