title: Rab27b regulates c-kit expression by controlling the secretion of stem cell factor.
abstract: Rab27b, a subfamily of Rab27 small GTPases, was originally identified in platelets. However, the role of Rab27b in megakaryocytic lineage cells remains unknown. Here, using a human megakaryoblastic cell line, CMK, we show that Rab27b negatively regulates c-kit-expression. We found that transfection of shRNA-Rab27b into CMK cells led to specific increase in the amount of the receptor-type tyrosine kinase c-kit. To elucidate the molecular mechanisms by which Rab27b regulates c-kit expression, we analyzed the dynamics of c-kit by the stimulation with its ligand, stem cell factor (SCF). We found that cell surface expression of c-kit was promptly reduced and rapidly degraded in both CMK and Rab27b-knockdown CMK cells. Pretreatment with a lysosome inhibitor bafilomycin suppressed the degradation of c-kit, indicating that c-kit expression is controlled by SCF-induced endolysosomal degradation system. We therefore focused on the potential involvement of SCF in Rab27b-mediated effects on c-kit expression levels. We found that autocrine secretion of SCF was downregulated in Rab27b-knockdown cells as compared with parental CMK cells. These results suggest that Rab27b negatively regulates the cell surface expression of c-kit via secretion of SCF and that ligation of SCF leads to the endolysosomal degradation system of c-kit.
authors.affiliation: Division of Epidemiology, Department of Community Medicine and Social Healthcare Science, Kobe University Graduate School of Medicine, Kobe, Japan.
authors.forename: Chisato
authors.initials: C
authors.lastname: Tanaka
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kaji
authors.forename: Jinsong
authors.initials: J
authors.lastname: He
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Hazama
authors.forename: Kunio
authors.initials: K
authors.lastname: Yokoyama
authors.forename: Emi
authors.initials: E
authors.lastname: Kinoshita
authors.forename: Takayuki
authors.initials: T
authors.lastname: Tsujioka
authors.forename: Kaoru
authors.initials: K
authors.lastname: Tohyama
authors.forename: Hirohei
authors.initials: H
authors.lastname: Yamamura
authors.forename: Hisahide
authors.initials: H
authors.lastname: Nishio
authors.forename: Yumi
authors.initials: Y
authors.lastname: Tohyama
mesh_terms: D019898:Autocrine Communication; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D059748:Proteolysis; D019009:Proto-Oncogene Proteins c-kit / Q000096:biosynthesis / Q000378:metabolism*; D019089:Stem Cell Factor / Q000378:metabolism*; D015854:Up-Regulation; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D019089:Stem Cell Factor; D019009:Proto-Oncogene Proteins c-kit; C512960:Rab27B protein, human; D020691:rab GTP-Binding Proteins