Golgi localized Arl15 regulates cargo transport, cell adhesion and motility

Arf-like GTPases (Arls) regulate membrane trafficking and cytoskeletal organization. Genetic studies predicted a role for Arl15 in type-2 diabetes, insulin resistance, adiposity, and rheumatoid arthritis. Recent studies indicate a possible role for Arl15 in multiple physiological processes, including magnesium homeostasis. However, the molecular function of Arl15 is poorly defined. We evaluated the role of Arl15 in vesicular transport using techniques to quantify cargo trafficking, to mechanobiology. Fluorescence microscopy of stably expressing Arl15-GFP HeLa cells showed its localization to the Golgi and cell surface, including filopodia, and a cohort to recycling endosomes. The dissociation of Golgi, using small molecular inhibitors or the expression of Arf1 dominant-negative mutant, completely mislocalized Arl15 to the cytosol. Interestingly, site-directed mutagenesis analysis identified a novel V80A mutation in the GTP-binding domain that turns Arl15 into a dominant-negative form with reduced number of filopodia. Depletion of Arl15 in HeLa cells caused mislocalization of cargo, such as caveolin-2 and STX6, from the Golgi. Arl15 knockdown cells displayed reduced filopodial number, altered focal adhesion kinase organization, and enhanced soluble and receptor-mediated cargo uptake without affecting the TfR recycling. Arl15 knockdown decreased cell migration and enhanced cell spreading and adhesion strength. Traction force microscopy experiments revealed that Arl15 depleted cells exert higher tractions and generate multiple focal adhesion points during the initial phase of cell adhesion as compared to control cells. Collectively, these studies demonstrated a functional role for Arl15 in the Golgi, which includes regulating cargo transport to organize membrane domains at the cell surface.