title: ARF6-regulated shedding of tumor cell-derived plasma membrane microvesicles.
abstract: BACKGROUND
  Increased mitogen-activated protein kinase (MAPK) signaling, small GTPase activation, cytoskeletal rearrangements, and the directed targeting of proteases to sites of extracellular matrix degradation all accompany the process of tumor cell invasion. Several studies have implicated the small GTP-binding protein ARF6 in tumor cell invasion, although the molecular basis by which ARF6 facilitates this process is unclear.
  
  
  RESULTS
  We show that the ARF6 GTP/GDP cycle regulates the release of protease-loaded plasma membrane-derived microvesicles from tumor cells into the surrounding environment. To enable microvesicle shedding, ARF6-GTP-dependent activation of phospholipase D promotes the recruitment of the extracellular signal-regulated kinase (ERK) to the plasma membrane where, in turn, ERK phosphorylates and activates myosin light-chain kinase (MLCK). MLCK-mediated MLC phosphorylation is required for microvesicle release. Inhibition of ARF6 activation is accompanied by PKC-mediated phosphorylation of MLC, which blocks microvesicle shedding. Protein cargo appears to be selectively sorted into microvesicles, and adhesion to the extracellular matrix (ECM) is facilitated by microvesicle-associated integrin receptors.
  
  
  CONCLUSIONS
  Microvesicle shedding in tumor cells occurs via an actomyosin-based membrane abscission mechanism that is regulated by nucleotide cycling on ARF6. Microvesicle shedding appears to release selected cellular components, particularly those involved in cell adhesion and motility, into the surrounding environment. These findings suggest that ARF6 activation and the proteolytic activities of microvesicles, both of which are thought to correlate directly with tumor progression, could potentially serve as biomarkers for disease.
authors.affiliation: Department of Biological Sciences, University of Notre Dame, IN 46556, USA.
authors.forename: Vandhana
authors.initials: V
authors.lastname: Muralidharan-Chari
authors.forename: James
authors.initials: J
authors.lastname: Clancy
authors.forename: Carolyn
authors.initials: C
authors.lastname: Plou
authors.forename: Maryse
authors.initials: M
authors.lastname: Romao
authors.forename: Philippe
authors.initials: P
authors.lastname: Chavrier
authors.forename: Graca
authors.initials: G
authors.lastname: Raposo
authors.forename: Crislyn
authors.initials: C
authors.lastname: D'Souza-Schorey
mesh_terms: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D009361:Neoplasm Invasiveness
chemical_list: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors; C000715348:ARF6 protein, human