Diacylglycerol kinase zeta regulates Ras activation by a novel mechanism

Guanine nucleotide exchange factors (GEFs) activate Ras by facilitating its GTP binding. Ras guanyl nucleotide-releasing protein (GRP) was recently id entified as a Ras GEF that has a diacylglycerol (DAG)binding C1 domain. Its exchange factor activity is regulated by local availability of signaling D AG, DAG kinases (DGKs) metabolize DAG by converting it to phosphatidic acid . Because they can attenuate local accumulation of signaling DAG, DGKs may regulate Ras-GRP activity and, consequently, activation of Ras, DGK zeta, b ut not other DGKs, completely eliminated Ras activation induced by RasGRP, and DGK activity was required for this mechanism. DGK zeta also coimmunopre cipitated and colocalized with RasGRP, indicating that these proteins assoc iate in a signaling complex. Coimmunoprecipitation of DGK zeta and RasGRP w as enhanced in the presence of phorbol esters, which are DAG analogues that cannot be metabolized by DGKs, suggesting that DAG signaling can induce th eir interaction. Finally overexpression of kinase-dead DGK zeta in Jurkat c ells prolonged Ras activation after ligation of the T cell receptor. Thus, we have identified a novel way to regulate Ras activation: through DGK zeta , which controls local accumulation of DAG that would otherwise activate Ra sGRP.