title: The catalytic domain of inositol-1,4,5-trisphosphate 3-kinase-a contributes to ITPKA-induced modulation of F-actin.
abstract: Inositol-1,4,5-trisphosphate-3-kinase-A (ITPKA) has been considered as an actin bundling protein because its N-terminal actin binding domain (ABD) induces formation of linear actin bundles. Since in many cancer cell lines ITPKA is essential for formation of lamellipodia, which consist of cross-linked actin filaments, here we analyzed if full length-ITPKA may induce formation of more complex actin structures. Indeed, we found that incubation of F-actin with ITPKA resulted in formation of dense, branched actin networks. Based on our result that ITPKA does not exhibit an additional C-terminal ABD, we exclude that ITPKA cross-links actin filaments by simultaneous F-actin binding with two different ABDs. Instead, stimulated-emission-depletion-microscopy and measurement of InsP3 Kinase activity give evidence that that N-terminal ABD-homodimers of ITPKA bind to F-actin while the monomeric C-termini insert between adjacent actin filaments. Thereby, they prevent formation of thick actin bundles but induce formation of thin branched actin structures. Interestingly, when embedded in this dense actin network, InsP3 Kinase activity is doubled and the product of InsP3 Kinase activity, Ins(1,3,4,5)P4 , inhibits spontaneous actin polymerization which may reflect a local negative feedback regulation of InsP3 Kinase activity. In conclusion, we demonstrate that not only the ABD of ITPKA modulates actin dynamics but reveal that the InsP3 Kinase domain substantially contributes to this process.
authors.affiliation: Department of Biochemistry and Signal Transduction, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, Hamburg, Germany.
authors.forename: Dina Julia
authors.initials: DJ
authors.lastname: Ashour
authors.forename: Benjamin
authors.initials: B
authors.lastname: Pelka
authors.forename: Patricia
authors.initials: P
authors.lastname: Jaaks
authors.forename: Torsten
authors.initials: T
authors.lastname: Wundenberg
authors.forename: Christine
authors.initials: C
authors.lastname: Blechner
authors.forename: Bernd
authors.initials: B
authors.lastname: Zobiak
authors.forename: Antonio Virgilio
authors.initials: AV
authors.lastname: Failla
authors.forename: Sabine
authors.initials: S
authors.lastname: Windhorst
mesh_terms: D000199:Actins / Q000378:metabolism*; D020134:Catalytic Domain; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D000199:Actins; D011993:Recombinant Fusion Proteins; D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase
keywords: actin bundles; actin cross-linking; actin polymerization; enzyme activity; inositol phosphate