title: Connecdenn 3/DENND1C binds actin linking Rab35 activation to the actin cytoskeleton.
abstract: The small GTPase Rab35 regulates endosomal membrane trafficking but also recruits effectors that modulate actin assembly and organization. Differentially expressed in normal and neoplastic cells (DENN)-domain proteins are a newly identified class of Rab guanine-nucleotide exchange factors (GEFs) that are grouped into eight families, each activating a common Rab. The members of one family, connecdenn 1-3/DENND1A-C, are all GEFs for Rab35. Why Rab35 requires multiple GEFs is unknown. We demonstrate that connecdenn 3 uses a unique C-terminal motif, a feature not found in connecdenn 1 or 2, to directly bind actin. This interaction couples Rab35 activation to the actin cytoskeleton, resulting in dramatic changes in cell shape, notably the formation of protrusive membrane extensions. These alterations are specific to Rab35 activated by connecdenn 3 and require both the actin-binding motif and N-terminal DENN domain, which harbors the GEF activity. It was previously demonstrated that activated Rab35 recruits the actin-bundling protein fascin to actin, but the relevant GEF for this activity was unknown. We demonstrate that connecdenn 3 and Rab35 colocalize with fascin and actin filaments, suggesting that connecdenn 3 is the relevant GEF. Thus, whereas connecdenn 1 and 2 activate Rab35 for endosomal trafficking, connecdenn 3 uniquely activates Rab35 for its role in actin regulation.
authors.affiliation: Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Canada.
authors.forename: Andrea L
authors.initials: AL
authors.lastname: Marat
authors.forename: Maria S
authors.initials: MS
authors.lastname: Ioannou
authors.forename: Peter S
authors.initials: PS
authors.lastname: McPherson
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D048430:Cell Shape; D017124:Conserved Sequence; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry / Q000378:metabolism*; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008840:Microfilament Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D051381:Rats; D020691:rab GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; C571411:DENND1C protein, human; D020662:Guanine Nucleotide Exchange Factors; D008840:Microfilament Proteins; D021382:Protein Sorting Signals; C020324:fascin; C511183:RAB35 protein, human; D020691:rab GTP-Binding Proteins
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