title: Phosphoinositide binding inhibits alpha-actinin bundling activity.
abstract: alpha-Actinin is an abundant actin-bundling and adhesion protein that directly links actin filaments to integrin receptors. Previously, in platelet-derived growth factor-treated fibroblasts, we demonstrated that phosphoinositides bind to alpha-actinin, regulating its localization (Greenwood, J. A., Theibert, A. B., Prestwich, G. D., and Murphy-Ullrich, J. E. (2000) J. Cell Biol. 150, 627- 642). In this study, phosphoinositide binding and regulation of alpha-actinin function is further characterized. Phosphoinositide binding specificity, determined using a protein-lipid overlay procedure, suggests that alpha-actinin interacts with phosphates on the 4th and 5th position of the inositol head group. Binding assays and mutational analyses demonstrate that phosphoinositides bind to the calponin homology domain 2 of alpha-actinin. Phosphoinositide binding inhibited the bundling activity of alpha-actinin by blocking the interaction of the actin-binding domain with actin filaments. Consistent with these results, excessive bundling of actin filaments was observed in fibroblasts expressing an alpha-actinin mutant with decreased phosphoinositide affinity. We conclude that the interaction of alpha-actinin with phosphoinositides regulates actin stress fibers in the cell by controlling the extent to which microfilaments are bundled.
authors.affiliation: Department of Biochemistry and Biophysics, Oregon State University, Corvallis, Oregon 97331, USA.
authors.forename: Tamara S
authors.initials: TS
authors.lastname: Fraley
authors.forename: Thuan C
authors.initials: TC
authors.lastname: Tran
authors.forename: Anne Marie
authors.initials: AM
authors.lastname: Corgan
authors.forename: Coral A
authors.initials: CA
authors.lastname: Nash
authors.forename: Jie
authors.initials: J
authors.lastname: Hao
authors.forename: David R
authors.initials: DR
authors.lastname: Critchley
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Greenwood
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000185:Actinin / Q000037:antagonists & inhibitors* / Q000502:physiology*; D000199:Actins / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002645:Chickens; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000737:chemistry; D009154:Mutation; D010716:Phosphatidylinositols / Q000494:pharmacology*; D011485:Protein Binding; D051381:Rats; D022502:Stress Fibers / Q000378:metabolism
chemical_list: D000199:Actins; D010716:Phosphatidylinositols; D000185:Actinin