Increased cell growth due to a new lipase-GEF (Phospholipase D2) fastly acting on Ras

Abstract

We report the novel finding that Phospholipase D2 (PLD2), through its PX and PH domains, binds specifically to Ras and catalyzes the GDP/GTP exchange (i.e., is a GEF), with potency comparable to Ras-GRF-1, a known Ras-GEF. Cells overexpressing PLD2-GEF inactive mutants (F129Y and R172C/L173A) fail to stimulate cell proliferation compared to the wild type-expressing cells. The GEF effect on Ras follows a faster kinetics than other GTPase substrates (such as Rac2 or Rac1) and is a better substrate, too. The GEF action is due to PLD2 (protein) itself, independent of the lipase product PA. PA can still have a fine-tuning regulatory effect on Ras-GTP depending upon its cellular concentration. Rapidly growing human breast cancer cells MDA-MB 231 (but not the slow growing MCF7 counterpart) have high levels of endogenous PLD2-GEF which correlates with high Ras activation. The PLD2-“GEF” activity is even higher than the classical “lipase” activity and is abrogated with GEF single point mutants, particularly F129Y, and concomitantly with a slow rate of cell growth. This can be crucial to cancer biology in that not only Ras mutations explain abnormal growth, but the existence of a new GEF for Ras: a GEF molecule that happens to be a phospholipase.