GMAP-210 Recruits γ-Tubulin Complexes to cis-Golgi Membranes and Is Required for Golgi Ribbon Formation

Mammalian cells concentrate Golgi membranes around the centrosome in a microtubule-dependent manner. The mechanisms involved in generating a single Golgi ribbon in the periphery of the centrosome remain unknown. Here we show that GMAP-210, a cis-Golgi microtubule binding protein, recruits gamma-tubulin-containing complexes to Golgi membranes even in conditions where microtubule polymerization is prevented and independently of Golgi apparatus localization within the cell. Under overexpression conditions, very short microtubules, or tubulin oligomers, are stabilized on Golgi membranes. GMAP-210 depletion by RNA interference results in extensive fragmentation of the Golgi apparatus, supporting a role for GMAP-210 in Golgi ribbon formation. Targeting of GMAP-210 or its C terminus to mitochondria induces the recruitment of gamma-tubulin to their surface and redistribution of mitochondria to a pericentrosomal location. All our experiments suggest that GMAP-210 displays microtubule anchoring and membrane fusion activities, thus contributing to the assembly and maintenance of the Golgi ribbon around the centrosome.