title: Phosphoinositide 3-kinase-mediated activation of cofilin phosphatase Slingshot and its role for insulin-induced membrane protrusion.
abstract: Cofilin plays an essential role in actin filament dynamics and membrane protrusion in motile cells. Cofilin is inactivated by phosphorylation at Ser-3 by LIM kinase and reactivated by dephosphorylation by cofilin-phosphatase Slingshot (SSH). Although cofilin is dephosphorylated in response to various extracellular stimuli, signaling pathways regulating SSH activation and cofilin dephosphorylation have remained to be elucidated. Here we show that insulin stimulates the phosphatase activity of Slingshot-1L (SSH1L) and cofilin dephosphorylation in cultured cells, in a manner dependent on phosphoinositide 3-kinase (PI3K) activity. Consistent with this, the level of Ser-3-phosphorylated cofilin is increased in PTEN (phosphatase and tensin homolog deleted in chromosome 10)-overexpressing cells and decreased in PTEN-deficient cells. Insulin induced the accumulation of SSH1L and active Akt (a downstream effector of PI3K), together with a PI3K product phosphatidylinositol 3,4,5-trisphosphate, onto membrane protrusions. Cofilin, but not Ser-3-phosphorylated cofilin, accumulated in membrane protrusions in insulin-stimulated cells, indicating that cofilin is dephosphorylated in these areas. Finally, suppression of SSH1L expression by RNA interference abolished insulin-induced cofilin dephosphorylation and the membrane protrusion. These findings suggest that SSH1L is activated downstream of PI3K and plays a critical role in insulin-induced membrane protrusion by dephosphorylating and activating cofilin.
authors.affiliation: Department of Biomolecular Sciences, Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi 980-8578, USA.
authors.forename: Michiru
authors.initials: M
authors.lastname: Nishita
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.forename: Chinatsu
authors.initials: C
authors.lastname: Tomizawa
authors.forename: Akira
authors.initials: A
authors.lastname: Suzuki
authors.forename: Ryusuke
authors.initials: R
authors.lastname: Niwa
authors.forename: Tadashi
authors.initials: T
authors.lastname: Uemura
authors.forename: Kensaku
authors.initials: K
authors.lastname: Mizuno
mesh_terms: D051339:Actin Depolymerizing Factors; D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D029721:Drosophila Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D008840:Microfilament Proteins / Q000737:chemistry / Q000378:metabolism*; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism / Q000502:physiology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism* / Q000502:physiology*; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D034622:RNA Interference; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D013997:Time Factors; D025521:Tumor Suppressor Proteins / Q000737:chemistry
chemical_list: D051339:Actin Depolymerizing Factors; D029721:Drosophila Proteins; D007328:Insulin; D008840:Microfilament Proteins; D025521:Tumor Suppressor Proteins; D012694:Serine; D019869:Phosphatidylinositol 3-Kinases; C448559:ssh protein, Drosophila; D010749:Phosphoprotein Phosphatases; C484329:SSH1 protein, human; D010744:Phosphoric Monoester Hydrolases; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human