Gelsolin and functionally similar actin-binding proteins are regulated by lysophosphatidic acid.
An extensive survey was carried out for compounds capable of regulating actin-binding proteins in a manner similar to phosphatidylinositol 4,5 bisphosphate (PI 4,5-P2). For this purpose we developed a sensitive assay involving release of radioactively phosphorylated actin from the fragminP-actin complex. We found that the structurally simplest lysophospholipid, lysophosphatidic acid (LPA), dissociated the complex between fragminP and actin, whereas other lysophospholipids or sphingosine-1-phosphate were inactive. Furthermore, LPA inhibited the F-actin severing activity of human gelsolin, purified from plasma or as recombinant protein, mouse adseverin and Physarum fragminP. Dissociation of actin-containing complexes by LPA analyzed by gelfiltration indicated that LPA is active as a monomer, in contrast to PI 4,5-P2. We further show that binding of LPA to these actin-regulatory proteins promotes their phosphorylation by pp60(c-src). A PI 4,5-P2-binding peptide counteracted the effects mediated by LPA, suggesting that LPA binds to the same target region in these actin-binding proteins. When both LPA and PI 4,5-P2 were used in combination we found that LPA reduced the threshold concentration at which PI 4,5-P2 was active. Significantly, LPA promoted the release of gelsolin from barbed actin filaments in octylglucoside-permeabilized human platelets. These results suggest that lysophosphatidic acid could act as an intracellular modulator of actin-binding proteins. Our findings can also explain agonist-induced changes in the actin cytoskeleton that are not mediated by polyphosphoinositides.
Flanders Interuniversity Institute for Biotechnology (V.I.B.) and Department of Biochemistry, Faculty of Medicine, Universiteit Gent, Ledeganckstraat 35, B-9000 Gent, Belgium.
K
K
Meerschaert
V
V
De Corte
Y
Y
De Ville
J
J
Vandekerckhove
J
J
Gettemans
D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D004533:Egtazic Acid / Q000378:metabolism; D018260:Gelsolin / Q000378:metabolism*; D006801:Humans; D008246:Lysophospholipids / Q000494:pharmacology*; D051379:Mice; D008840:Microfilament Proteins / Q000037:antagonists & inhibitors; D008969:Molecular Sequence Data; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects
D000199:Actins; D018260:Gelsolin; D008246:Lysophospholipids; D008840:Microfilament Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D004533:Egtazic Acid