title: Rab27a and MyRIP regulate the amount and multimeric state of VWF released from endothelial cells.
abstract: Endothelial cells contain cigar-shaped secretory organelles called Weibel-Palade bodies (WPBs) that play a crucial role in both hemostasis and the initiation of inflammation. The major cargo protein of WPBs is von Willebrand factor (VWF). In unstimulated cells, this protein is stored in a highly multimerized state coiled into protein tubules, but after secretagogue stimulation and exocytosis it unfurls, under shear force, as long platelet-binding strings. Small GTPases of the Rab family play a key role in organelle function. Using siRNA depletion in primary endothelial cells, we have identified a role for the WPB-associated Rab27a and its effector MyRIP. Both these proteins are present on only mature WPBs, and this rab/effector complex appears to anchor these WPBs to peripheral actin. Depletion of either the Rab or its effector results in a loss of peripheral WPB localization, and this destabilization is coupled with an increase in both basal and stimulated secretion. The VWF released from Rab27a-depleted cells is less multimerized, and the VWF strings seen under flow are shorter. Our results indicate that this Rab/effector complex controls peripheral distribution and prevents release of incompletely processed WPB content.
authors.affiliation: Medical Research Council Laboratory of Molecular Cell Biology, Cell Biology Unit, Department of Cell and Developmental Biology, University College London, London, United Kingdom. [corrected]
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Nightingale
authors.forename: Krupa
authors.initials: K
authors.lastname: Pattni
authors.forename: Alistair N
authors.initials: AN
authors.lastname: Hume
authors.forename: Miguel C
authors.initials: MC
authors.lastname: Seabra
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Cutler
mesh_terms: D002478:Cells, Cultured; D042783:Endothelial Cells / Q000378:metabolism*; D005089:Exocytosis / Q000235:genetics; D055785:Gene Knockdown Techniques; D006801:Humans; D008970:Molecular Weight; D055503:Protein Multimerization / Q000235:genetics; D021381:Protein Transport / Q000235:genetics; D014018:Tissue Distribution; D033921:Vesicular Transport Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D020302:Weibel-Palade Bodies / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D000075745:rab27 GTP-Binding Proteins; D014841:von Willebrand Factor / Q000378:metabolism*
chemical_list: C501262:MYRIP protein, human; D033921:Vesicular Transport Proteins; D000075745:rab27 GTP-Binding Proteins; D014841:von Willebrand Factor; C066694:RAB27A protein, human; D020691:rab GTP-Binding Proteins