The Golgin Tether Giantin Regulates the Secretory Pathway by Controlling Stack Organization within Golgi Apparatus

The Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
PLoS ONE (Impact Factor: 3.23). 03/2013; 8(3):e59821. DOI: 10.1371/journal.pone.0059821
Source: PubMed


Golgins are coiled-coil proteins that play a key role in the regulation of Golgi architecture and function. Giantin, the largest golgin in mammals, forms a complex with p115, rab1, GM130, and soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs), thereby facilitating vesicle tethering and fusion processes around the Golgi apparatus. Treatment with the microtubule destabilizing drug nocodazole transforms the Golgi ribbon into individual Golgi stacks. Here we show that siRNA-mediated depletion of giantin resulted in more dispersed Golgi stacks after nocodazole treatment than by control treatment, without changing the average cisternal length. Furthermore, depletion of giantin caused an increase in cargo transport that was associated with altered cell surface protein glycosylation. Drosophila S2 cells are known to have dispersed Golgi stacks and no giantin homolog. The exogenous expression of mammalian giantin cDNA in S2 cells resulted in clustered Golgi stacks, similar to the Golgi ribbon in mammalian cells. These results suggest that the spatial organization of the Golgi ribbon is mediated by giantin, which also plays a role in cargo transport and sugar modifications.

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    • "Several studies have shown defective trafficking upon loss of individual golgins (Brémond et al., 2009; Diao et al., 2008; Diao et al., 2003; Hicks et al., 2006; Koreishi et al., 2013; Lieu et al., 2008; Yamane et al., 2007), although the effects are usually subtle, whereas others have failed to observe any consequences upon secretory trafficking (Friggi-Grelin et al., 2006; Puthenveedu et al., 2006; Vasile et al., 2003; Yadav et al., 2009). These findings have led to the proposal that golgins function in a redundant manner, acting collectively on the surface of Golgi membranes to tether vesicles and Golgi membranes (Munro, 2011; Sinka et al., 2008). "
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    ABSTRACT: Golgins are coiled-coil proteins that participate in membrane tethering events at the Golgi apparatus. Golgin-mediated tethering is thought to be important for vesicular trafficking and Golgi organization. However, the degree to which individual golgins contribute to these processes is poorly defined, and it has been proposed that golgins act in a largely redundant manner. Previous studies on the golgin GMAP-210, which is mutated in the rare skeletal disorder achondrogenesis type 1A, have yielded conflicting results regarding its involvement in trafficking. Here, we re-investigated the trafficking role of GMAP-210, and find that it is indeed required for efficient trafficking in the secretory pathway. GMAP-210 acts at both the ERGIC and Golgi apparatus during anterograde trafficking, and is also required for retrograde trafficking to the endoplasmic reticulum. Using co-depletion experiments, we also find that GMAP-210 acts in a partially redundant manner with the golgin GM130 to ensure efficient anterograde cargo delivery to the cis-Golgi. In summary, our results indicate a role for GMAP-210 in several trafficking steps at the ER/Golgi interface, some of which are partially redundant with another golgin, namely GM130.
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