title: A role for Rab27b in NF-E2-dependent pathways of platelet formation.
abstract: Megakaryocytes release platelets by reorganizing the cytoplasm into proplatelet extensions. Fundamental to this process is the need to coordinate transport of products and organelles in the appropriate abundance to nascent platelets. The importance of the Rab family of small GTPases (guanosine 5'-triphosphatases) in platelet biogenesis is revealed in gunmetal (gm/gm) mice, which show deficient Rab isoprenylation and macrothrombocytopenia with few granules and abnormal megakaryocyte morphology. Although some Rab proteins are implicated in vesicle and organelle transport along microtubules or actin, the role of any Rab protein in platelet biogenesis is unknown. The limited number of Rab proteins with defective membrane association in gm/gm megakaryocytes prominently includes Rab27a and Rab27b. Normal expression of Rab27b is especially increased with terminal megakaryocyte differentiation and dependent on nuclear factor-erythroid 2 (NF-E2), a transcription factor required for thrombopoiesis. Chromatin immunoprecipitation demonstrates recruitment of NF-E2 to the putative Rab27B promoter. Inhibition of endogenous Rab27 function in primary megakaryocytes causes severe quantitative and qualitative defects in proplatelet formation that mimic findings in gm/gm cells. Rab27b localizes to alpha and dense granules in megakaryocytes. These results establish a role for Rab27 in platelet synthesis and suggest that Rab27b in particular may coordinate proplatelet formation with granule transport, possibly by recruiting specific effector pathways.
authors.affiliation: Dana-Farber Cancer Institute, One Jimmy Fund Way, Boston, MA 02115, USA.
authors.forename: Sanjay
authors.initials: S
authors.lastname: Tiwari
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Italiano
authors.forename: Duarte C
authors.initials: DC
authors.lastname: Barral
authors.forename: Emilie H
authors.initials: EH
authors.lastname: Mules
authors.forename: Edward K
authors.initials: EK
authors.lastname: Novak
authors.forename: Richard T
authors.initials: RT
authors.lastname: Swank
authors.forename: Miguel C
authors.initials: MC
authors.lastname: Seabra
authors.forename: Ramesh A
authors.initials: RA
authors.lastname: Shivdasani
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000166:cytology* / Q000378:metabolism / Q000648:ultrastructure; D002454:Cell Differentiation; D003594:Cytoplasmic Granules; D004268:DNA-Binding Proteins / Q000378:metabolism*; D050981:Erythroid-Specific DNA-Binding Factors; D005786:Gene Expression Regulation; D008533:Megakaryocytes / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D051379:Mice; D009154:Mutation; D050983:NF-E2 Transcription Factor; D050984:NF-E2 Transcription Factor, p45 Subunit; D011401:Promoter Regions, Genetic; D017368:Protein Prenylation; D034061:Thrombopoiesis; D014157:Transcription Factors / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000075745:rab27 GTP-Binding Proteins
chemical_list: D004268:DNA-Binding Proteins; D050981:Erythroid-Specific DNA-Binding Factors; D050983:NF-E2 Transcription Factor; D050984:NF-E2 Transcription Factor, p45 Subunit; C494693:Nfe2 protein, mouse; D014157:Transcription Factors; D000075745:rab27 GTP-Binding Proteins; C512958:Rab27b protein, mouse; C512962:Rab27a protein, mouse; D020691:rab GTP-Binding Proteins