title: Rab7b, a novel lysosome-associated small GTPase, is involved in monocytic differentiation of human acute promyelocytic leukemia cells.
abstract: Rab7 is a small Rab GTPase that regulates vesicular traffic from early to late endosomal stages of the endocytic pathway. Here we report the cloning and characterization of a novel Rab7-like GTPase, which shares highest homology with Rab7 and thus is designated as Rab7b. Northern blot analysis shows that Rab7b mRNA is expressed in human heart, placenta, lung, skeletal muscle, and peripheral blood leukocyte. RT-PCR or Western blot analysis of Rab7b expression shows that Rab7b is selectively expressed in monocytes, monocyte-derived immature dendritic cells (DCs), and promyeloid or monocytic leukemia cell lines. In the peripheral blood, Rab7b is specifically detected in CD14(+) cells, but not in CD4(+), CD8(+), CD19(+) or CD56(+) cells. When immature DCs are matured with lipopolysaccharide (LPS), Rab7b expression is gradually downregulated, while Rab7b is upregulated when monocytes are activated by LPS treatments. In acute promyelocytic leukemia (APL) HL-60 and NB4 cell lines, Rab7b expression is upregulated after phorbol myristate acetate (PMA)-induced monocytic differentiation. By immunofluorescence confocal microscopy, we demonstrate that Rab7b is associated with lysosomal organelles. Our data suggest that Rab7b is a lysosome-localized monocytic cell-specific small GTPase, and is involved in PMA-induced APL cell differentiation and possibly in regulation of monocyte functions.
authors.affiliation: Institute of Immunology, Zhejiang University, 353 Yanan Road, Hangzhou 310031, PR China.
authors.forename: Mingjin
authors.initials: M
authors.lastname: Yang
authors.forename: Taoyong
authors.initials: T
authors.lastname: Chen
authors.forename: Chaofeng
authors.initials: C
authors.lastname: Han
authors.forename: Nan
authors.initials: N
authors.lastname: Li
authors.forename: Tao
authors.initials: T
authors.lastname: Wan
authors.forename: Xuetao
authors.initials: X
authors.lastname: Cao
mesh_terms: D000595:Amino Acid Sequence; D002454:Cell Differentiation; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D003713:Dendritic Cells / Q000166:cytology; D015870:Gene Expression; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism*; D008969:Molecular Sequence Data; D009000:Monocytes / Q000166:cytology* / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013347:Subcellular Fractions / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014018:Tissue Distribution; D015854:Up-Regulation; D020691:rab GTP-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*
chemical_list: D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D020691:rab GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate