title: The neurofibromatosis type 1 gene product neurofibromin enhances cell motility by regulating actin filament dynamics via the Rho-ROCK-LIMK2-cofilin pathway.
abstract: Neurofibromin is a neurofibromatosis type 1 (NF1) tumor suppressor gene product with a domain that acts as a GTPase-activating protein and functions, in part, as a negative regulator of Ras. Loss of neurofibromin expression in NF1 patients is associated with elevated Ras activity and increased cell proliferation, predisposing to a variety of tumors of the peripheral and central nervous systems. We show here, using the small interfering RNA (siRNA) technique, that neurofibromin dynamically regulates actin cytoskeletal reorganization, followed by enhanced cell motility and gross cell aggregation in Matrigel matrix. NF1 siRNA induces characteristic morphological changes, such as excessive actin stress fiber formation, with elevated negative phosphorylation levels of cofilin, which regulates actin cytoskeletal reorganization by depolymerizing and severing actin filaments. We found that the elevated phosphorylation of cofilin in neurofibromin-depleted cells is promoted by activation of a Rho-ROCK-LIMK2 pathway, which requires Ras activation but is not transduced through three major Ras-mediated downstream pathways via Raf, phosphatidylinositol 3-kinase, and RalGEF. In addition, the exogenous expression of the NF1-GTPase-activating protein-related domain suppressed the NF1 siRNA-induced phenotypes. Neurofibromin was demonstrated to play a significant role in the machinery regulating cell proliferation and in actin cytoskeletal reorganization, which affects cell motility and adhesion. These findings may explain, in part, the mechanism of multiple neurofibroma formation in NF1 patients.
authors.affiliation: Department of Tumor Genetics and Biology, Graduate School of Medical Sciences, Kumamoto University, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ozawa
authors.forename: Norie
authors.initials: N
authors.lastname: Araki
authors.forename: Shunji
authors.initials: S
authors.lastname: Yunoue
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tokuo
authors.forename: Liping
authors.initials: L
authors.lastname: Feng
authors.forename: Siriporn
authors.initials: S
authors.lastname: Patrakitkomjorn
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Hara
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Ichikawa
authors.forename: Kunio
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Kiyotaka
authors.initials: K
authors.lastname: Fujii
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Saya
mesh_terms: D051339:Actin Depolymerizing Factors / Q000502:physiology; D000199:Actins / Q000737:chemistry / Q000502:physiology*; D001483:Base Sequence; D002460:Cell Line; D002465:Cell Movement / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D054461:Lim Kinases; D009456:Neurofibromatosis 1 / Q000235:genetics / Q000503:physiopathology; D025542:Neurofibromin 1 / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D020741:rho GTP-Binding Proteins / Q000502:physiology; D054460:rho-Associated Kinases
chemical_list: D051339:Actin Depolymerizing Factors; D000199:Actins; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D025542:Neurofibromin 1; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; C102895:LIMK2 protein, human; D054461:Lim Kinases; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D020741:rho GTP-Binding Proteins