Phospholipase D2‐derived phosphatidic acid binds to and activates ribosomal p70 S6 kinase independently of mTOR

• DOI: 10.1096/fj.06-6652com
• Publication Date: 2007-01-23T01:51:31Z
• Authors: Nicholas Lehman; Bill Ledford; Mauricio Di Fulvio; Kathleen Frondorf; Linda C. McPhail; Julian Gomez-Camb...
• Keywords: Ribosomal protein s6; Phospholipase D; PLD2; Ribosomal s6 kinase

The product of phospholipase D (PLD) enzymatic action in cell membranes, phosphatidic acid (PA), regulates kinases implicated NADPH oxidase activation, as well the mammalian target rapamycin (mTOR) kinase. However, other protein targets for this lipid second messenger must exist order to explain key PA-mediated cellular functions. In study, PA was found specifically and saturably bind activate recombinant immunoprecipitated endogenous ribosomal S6 kinase (S6K) with a stoichiometry 94:1 lipid/protein. Polyphosphoinositides PI4-P PI4,5P2 cardiolipin could also S6K, albeit different kinetics. Conversely, at least one acyl side chain saturated (10:0) ineffective binding or activating enzyme. Transfection COS-7 cells wild-type myc-(pcDNA)-PLD2 construct resulted high PLD activity, concomitantly an increase p70S6K enzyme activity phosphorylation T389 T421/S424 p70S6K's natural substrate S235/S236. Overexpression lipase inactive mutant (K758R), however, failed induce both S6K phosphorylation, indicating that PLD2 (i.e., synthesis PA) be present affect S6K. Neither inhibiting mTOR nor silencing gene expression altered augmentative effect exerted on activity. This finding indicates binds activates p70S6K, even absence mTOR. Lastly, transfection changed pattern subcellular expression, colocalization observed by immunofluorescence microscopy. These results show first time direct (mTOR-independent) participation pathway implicate nexus brings together phospholipases kinases.