Microtubule nucleation at the cis-side of the Golgi apparatus requires AKAP450 and GM130

Abstract

We report that microtubule (MT) nucleation at the Golgi apparatus requires AKAP450, a centrosomal c-TuRC-interacting protein that also forms a distinct network associated with the Golgi. Depletion of AKAP450 abolished MT nucleation at the Golgi, whereas depletion of the cis-Golgi protein GM130 led to the disorganisation of AKAP450 network and impairment of MT nucleation. Brefeldin-A treatment induced relocalisation of AKAP450 to ER exit sites and concomitant redistribution of MT nucleation capacity to the ER. AKAP450 specifically binds the cisside of the Golgi in an MT-independent, GM130-dependent manner. Short AKAP450-dependent growing MTs are covered by CLASP2. Like for centrosome, dynein/dynactin complexes are necessary to anchor MTs growing from the Golgi. We further show that Golgi-associated AKAP450 has a role in cell migration rather than in cell polarisation of the centrosome-Golgi apparatus. We propose that the recruitment of AKAP450 on the Golgi membranes through GM130 allows centrosome-associated nucleating activity to extend to the Golgi, to control the assembly of subsets of MTs ensuring specific functions within the Golgi or for transporting specific cargos to the cell periphery.

MTCL1 crosslinks and stabilizes non-centrosomal microtubules on the Golgi membrane

“…7). These results indicate that MTCL1 plays essential roles in the stable growing of MTs from the Golgi membrane, as has been demonstrated for CLASPs and AKAP450/ CG-NAP 8,9 .…”

“…However, the underlying mechanism for maintaining this specific Golgi arrangement as well as its physiological significance had been unclear until the above-mentioned studies. They have demonstrated that specific disruption of the Golgi-derived MTs by knockdown of CLASPs or AKAP450/CG-NAP converted the Golgi ribbon into a cluster of Golgi stacks gathering around the centrosome 7,9 . Together with data from live imaging analyses 7 , these results have indicated that the formation of the Golgi ribbon proceeds in two distinct steps, in which the Golgi-derived MTs first draw the Golgi ministacks together in a tangential manner, whereas the centrosomal MTs subsequently drag the laterally clustered Golgi stacks towards the centrosome 7 .…”

“…Recent studies have demonstrated that these perinuclear acetylated MTs correspond to the Golgi-derived MTs, which play essential roles in the lateral connection of the Golgi stacks and inhibit their complete clustering around the centrosome 7,9 . Consistent with these reports, MTCL1 knockdown also significantly affected the Golgi apparatus morphology (Fig.…”

“…One of the machineries is composed of the MT plus-end tracking proteins, CLASPs, which are anchored to the trans-Golgi membrane via GCC185 (refs 7,8), and the other is the g-TuRC (g-tubulin ring complex)-interacting protein, A-kinase anchoring protein 450 (AKAP450)/centrosome and Golgi localized protein kinase N-associated protein (CG-NAP), which is recruited to the cis-Golgi membrane via GM130 (ref. 9). Both machineries have been shown to play critical roles in the development of the Golgi-derived MTs, and thus regulate the formation of the vertebrate-specific higher order structures of the Golgi apparatus.…”

Microtubule nucleation and organization in dendrites

“…57 In addition to this outpost fusion function, GM130 may also recruit AKAP450/Plp to outposts, as it has been shown to link AKAP450/Plp to somatic Golgi for microtubule nucleation. 58 The role of alternative nucleation sites in orienting microtubule nucleation in the dendrite…”