title: LIM kinase has a dual role in regulating lamellipodium extension by decelerating the rate of actin retrograde flow and the rate of actin polymerization.
abstract: Lamellipodium extension is crucial for cell migration and spreading. The rate of lamellipodium extension is determined by the balance between the rate of actin polymerization and the rate of actin retrograde flow. LIM kinase 1 (LIMK1) regulates actin dynamics by phosphorylating and inactivating cofilin, an actin-depolymerizing protein. We examined the role of LIMK1 in lamellipodium extension by measuring the rates of actin polymerization, actin retrograde flow, and lamellipodium extension using time-lapse imaging of fluorescence recovery after photobleaching. In the non-extending lamellipodia of active Rac-expressing N1E-115 cells, LIMK1 expression decelerated and LIMK1 knockdown accelerated actin retrograde flow. In the extending lamellipodia of neuregulin-stimulated MCF-7 cells, LIMK1 knockdown accelerated both the rate of actin polymerization and the rate of actin retrograde flow, but the accelerating effect on retrograde flow was greater than the effect on polymerization, thus resulting in a decreased rate of lamellipodium extension. These results indicate that LIMK1 has a dual role in regulating lamellipodium extension by decelerating actin retrograde flow and polymerization, and in MCF-7 cells endogenous LIMK1 contributes to lamellipodium extension by decelerating actin retrograde flow more effectively than decelerating actin polymerization.
authors.affiliation: Department of Biomolecular Sciences, Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi 980-8578, Japan. kohashi@biology.tohoku.ac.jp
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Ohashi
authors.forename: Sachiko
authors.initials: S
authors.lastname: Fujiwara
authors.forename: Takuya
authors.initials: T
authors.lastname: Watanabe
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kondo
authors.forename: Tai
authors.initials: T
authors.lastname: Kiuchi
authors.forename: Masaaki
authors.initials: M
authors.lastname: Sato
authors.forename: Kensaku
authors.initials: K
authors.lastname: Mizuno
mesh_terms: D000199:Actins / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D045744:Cell Line, Tumor; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D006801:Humans; D054461:Lim Kinases / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D010766:Phosphorylation / Q000502:physiology; D038761:Photobleaching; D011554:Pseudopodia / Q000201:enzymology* / Q000235:genetics
chemical_list: D000199:Actins; C515892:LIMK1 protein, human; D054461:Lim Kinases; C515893:Limk1 protein, mouse