Aim: The Golgi apparatus is a dynamic organelle that, in vertebrates, is organized into a continuous ribbon-like structure known as the Golgi ribbon. The conversion of individual Golgi stacks into a ribbon structure is a highly regulated process which relies on a balance between the actin and microtubule network. While the involvement of the microtubule network has been well defined, the role of the actin network is poorly characterised. Our previous studies have shown that a membrane tether/golgin known as GCC88, located at the trans-Golgi network (TGN), modulates the architecture of the Golgi ribbon in a dose-dependent manner. Increased levels of GCC88 led to the loss of the Golgi ribbon whereas GCC88 depletion resulted in the formation of longer Golgi ribbons1. The aim of the current study was to identify the underlying mechanism for GCC88-mediated re-organization of the Golgi ribbon.
Methods: To delineate the role of GCC88 in the modulation of the Golgi ribbon, candidate interactors were identified through an in vivo enzymatic labelling approach known as BioID. We have also generated a HeLa cell line referred to as HeLa-B6 that stably expresses a GFP-GCC88 chimera at ~ 2-fold increase compared with endogenous GCC88. HeLa-B6 cells are characterised by the loss of the Golgi ribbon and dispersal of Golgi mini-stacks.
Results: We have shown that GCC88-mediated dispersal of the Golgi ribbon is an actin-dependent process and involves non-muscle myosin-IIA. We have identified the long isoform of Intersectin-1 (ITSN-1), which has GEF activity for the Rho GTPase Cdc42, as a novel interaction partner of GCC88 and demonstrated its localisation at the TGN and involvement in GCC88-mediated loss of the Golgi ribbon. We have also shown that the ITSN-1-GCC88 interaction is important in other models of Golgi fragmentation such as alterations to membrane flux and in a neurodegenerative model.
Conclusion: Our study shows that GCC88 is involved in linking the TGN to the actin cytoskeleton through the interaction with ITSN-1. This interaction regulates the balance between a compact Golgi ribbon and dispersed mini-stacks and is a relevant pathway to pathophysiological conditions.