title: Valproic acid-inducible Arl4D and cytohesin-2/ARNO, acting through the downstream Arf6, regulate neurite outgrowth in N1E-115 cells.
abstract: The mood-stabilizing agent valproic acid (VPA) potently promotes neuronal differentiation. As yet, however, little is known about the underlying molecular mechanism. Here, we show that VPA upregulates cytohesin-2 and mediates neurite outgrowth in N1E-115 neuroblastoma cells. Cytohesin-2 is the guanine-nucleotide exchange factor (GEF) for small GTPases of the Arf family; it regulates many aspects of cellular functions including morphological changes. Treatment with the specific cytohesin family inhibitor SecinH3 or knockdown of cytohesin-2 with its siRNA results in blunted induction of neurite outgrowth in N1E-115 cells. The outgrowth is specifically inhibited by siRNA knockdown of Arf6, but not by that of Arf1. Furthermore, VPA upregulates Arl4D, an Arf-like small GTPase that has recently been identified as the regulator that binds to cytohesin-2. Arl4D knockdown displays an inhibitory effect on neurite outgrowth resulting from VPA, while expression of constitutively active Arl4D induces outgrowth. We also demonstrate that the addition of cell-permeable peptide, coupling the cytohesin-2-binding region of Arl4D into cells, reduces the effect of VPA. Thus, Arl4D is a previously unknown regulator of neurite formation through cytohesin-2 and Arf6, providing another example that the functional interaction of two different small GTPases controls an important cellular function.
authors.affiliation: Department of Pharmacology, National Research Institute for Child Health and Development, Setagaya, Tokyo 157-8535, Japan. jyamauchi@nch.go.jp
authors.forename: Junji
authors.initials: J
authors.lastname: Yamauchi
authors.forename: Yuki
authors.initials: Y
authors.lastname: Miyamoto
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Torii
authors.forename: Reiko
authors.initials: R
authors.lastname: Mizutani
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Nakamura
authors.forename: Atsushi
authors.initials: A
authors.lastname: Sanbe
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Koide
authors.forename: Shinji
authors.initials: S
authors.lastname: Kusakawa
authors.forename: Akito
authors.initials: A
authors.lastname: Tanoue