title: Unphosphorylated MARCKS is involved in neurite initiation induced by insulin-like growth factor-I in SH-SY5Y cells.
abstract: Myristoylated alanine-rich C kinase substrate (MARCKS) has been suggested to be involved in various aspects of neuronal cell differentiation, including neurite outgrowth. However, the precise mechanisms by which MARCKS phosphorylation is regulated, and how MARCKS contributes to neurite outgrowth, are poorly understood. Here, we found that treatment of SH-SY5Y cells with insulin-like growth factor-I (IGF-I) induced a rapid and transient decrease in the level of phosphorylated MARCKS (P-MARCKS) to below the basal level. The decrease in P-MARCKS induced by IGF-I was blocked by pretreatment of cells with phosphoinositide 3-kinase (PI3K) inhibitors, LY294002 and wortmannin. A decrease in P-MARCKS was also observed in cells treated with a Rho-dependent kinase (ROCK) inhibitor, Y27632. Furthermore, IGF-I induced transient inactivation of RhoA, an upstream effector of ROCK. We showed that MARCKS was translocated to the membrane and colocalized with F-actin at the lamellipodia and the tips of neurites in the cells stimulated with IGF-I. Finally, overexpression of wild-type MARCKS or an unphosphorylatable mutant of MARCKS enhanced the number of neurite-bearing cells relative to vector-transfected cells. Taken together, these findings suggest that unphosphorylated MARCKS is involved in neurite initiation, and highlight the important role played by MARCKS in organization of the actin cytoskeleton.
authors.affiliation: Laboratory of Pharmacology, School of Pharmaceutical Science, Kitasato University, Shirokane 5-9-1, Minato-ku, Tokyo 108-8641, Japan. shiraishim@pharm.kitasato-u.ac.jp
authors.forename: Mitsuya
authors.initials: M
authors.lastname: Shiraishi
authors.forename: Atsuhiro
authors.initials: A
authors.lastname: Tanabe
authors.forename: Naoaki
authors.initials: N
authors.lastname: Saito
authors.forename: Yasuharu
authors.initials: Y
authors.lastname: Sasaki
mesh_terms: D000199:Actins / Q000378:metabolism; D000730:Androstadienes / Q000378:metabolism; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002867:Chromones / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009025:Morpholines / Q000378:metabolism; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D016501:Neurites / Q000187:drug effects* / Q000378:metabolism* / Q000648:ultrastructure; D009447:Neuroblastoma / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D000077191:Wortmannin; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D000199:Actins; D000730:Androstadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D007334:Insulin-Like Growth Factor I; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009025:Morpholines; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010749:Phosphoprotein Phosphatases; D017346:Protein Serine-Threonine Kinases; D000077191:Wortmannin; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein; C000619710:MARCKS protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one