Rab27b regulates c-kit expression by controlling the secretion of stem cell factor

• Published in: Biochemical and biophysical research communications Vol. 419; no. 2; pp. 368 - 373
• Main Authors: Tanaka, Chisato, Kaji, Hiroaki, He, Jinsong, Hazama, Ryoichi, Yokoyama, Kunio, Kinoshita, Emi, Tsujioka, Takayuki, Tohyama, Kaoru, Yamamura, Hirohei, Nishio, Hisahide, Tohyama, Yumi
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 09.03.2012
• Subjects: Autocrine Communication; c-Kit; Cell Line, Tumor; Cell Membrane - metabolism; Gene Knockdown Techniques; Humans; Lysosome; Lysosomes - metabolism; Proteolysis; Proto-Oncogene Proteins c-kit - biosynthesis; Proto-Oncogene Proteins c-kit - metabolism; rab GTP-Binding Proteins - genetics; rab GTP-Binding Proteins - metabolism; Rab27b; SCF; Stem Cell Factor - metabolism; Up-Regulation; Rab27b; c-Kit; Lysosome; SCF
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2012.02.030

► Rab27b negatively regulates c-kit expression in megakaryocytic lineage cells. ► c-kit is degraded by SCF-induced endolysosomal pathway. ► Rab27b regulates autocrine secretion of SCF and leads to c-kit degradation. 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.