title: IQGAP3 regulates cell proliferation through the Ras/ERK signalling cascade.
abstract: Proliferation of epithelial cells must be spatiotemporally regulated to maintain the organization of epithelial sheets. Here we show that the IQGAP family, comprising IQGAP1, 2 and 3, underlies lateral cell-cell contacts of epithelial cells. Of the three proteins, IQGAP3 is unique in that its expression is specifically confined to proliferating cells. Knockdown of IQGAP3 in cultured epithelial cells caused inhibition of proliferation and ERK activity. When exogenously expressed in quiescent cells, IQGAP3 was capable of inducing cell-cycle re-entry, which was completely inhibited by the MEK inhibitor U0126. Thus, IQGAP3 is necessary and sufficient for driving cell proliferation and ERK acts downstream of IQGAP3. Furthermore, IQGAP3 specifically interacted with the active, GTP-bound form of Ras, and in IQGAP3 knockdown cells, the activity of Ras, but not of other small GTPases, was inhibited. Thus, IQGAP3 regulates the promotion of cell proliferation through Ras-dependent ERK activation.
authors.affiliation: Laboratory of Biological Science, Graduate School of Frontier Biosciences/Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Nojima
authors.forename: Makoto
authors.initials: M
authors.lastname: Adachi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Matsui
authors.forename: Katsuya
authors.initials: K
authors.lastname: Okawa
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Tsukita
authors.forename: Sachiko
authors.initials: S
authors.lastname: Tsukita
mesh_terms: D000818:Animals; D049109:Cell Proliferation; D004847:Epithelial Cells / Q000166:cytology; D004848:Epithelium / Q000254:growth & development; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D020690:GTPase-Activating Proteins / Q000502:physiology*; D020935:MAP Kinase Signaling System; D051379:Mice; D020703:ras GTPase-Activating Proteins / Q000502:physiology*; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D020690:GTPase-Activating Proteins; C531126:IQGAP3 protein, mouse; D020703:ras GTPase-Activating Proteins; D048049:Extracellular Signal-Regulated MAP Kinases; D018631:ras Proteins