Lupashin, V. | bioRxiv Science

bioRxiv2020

The Golgi-associated retrograde protein (GARP) complex plays an essential role in the maintenance of the Golgi glycosylation machinery

The Golgi apparatus is a central hub for intracellular protein trafficking and glycosylation. Steady-state localization of glycosylation enzymes is achieved by a combination of mechanisms involving retention and vesicle recycling, but the machinery governing these mechanisms is poorly understood. Herein we show that the Golgi-associated retrograde protein (GARP) complex is a critical component of this machinery. Using multiple human cell lines, we show that depletion of GARP subunits is detrimental to N- and O-glycosylation, and reduces the stability of glycoproteins and Golgi enzymes. Moreover, GARP-KO cells exhibit impaired retention of glycosylation enzymes in the Golgi. Indeed, a RUSH assay shows that, in GARP-KO cells, the enzyme beta-1,4-galactosyltransferase 1 is not retained at the Golgi but instead is missorted to the endolysosomal compartment. We propose that the endosomal compartment is part of the trafficking itinerary of Golgi enzymes and that the GARP complex is essential for recycling and stabilization of the Golgi glycosylation machinery.

cell biology↗

bioRxiv2020

Golgi-Dependent Copper Homeostasis Sustains Synaptic Development and Mitochondrial Content

Rare genetic diseases preponderantly affect the nervous system with phenotypes spanning from neurodegeneration to neurodevelopmental disorders. This is the case for both Menkes and Wilson disease, arising from mutations in ATP7A and ATP7B, respectively. The ATP7A and ATP7B proteins localize to the Golgi and regulate copper homeostasis. We demonstrate conserved interactions between ATP7 paralogs with the COG complex, a Golgi complex tether. Disruption of Drosophila copper homeostasis by ATP7 tissue-specific transgenic expression caused alterations in epidermis, catecholaminergic, sensory, and motor neurons. Prominent among neuronal phenotypes was a decreased mitochondrial content at synapses, a phenotype that paralleled with alterations of synaptic morphology, transmission, and plasticity. These neuronal and synaptic phenotypes caused by transgenic expression of ATP7 were rescued by downregulation or haploinsufficiency of COG complex subunits. We conclude that the integrity of Golgi-dependent copper homeostasis mechanisms, requiring ATP7 and COG, are necessary to maintain mitochondria functional integrity and localization to synapses. Significance StatementMenkes and Wilson disease affect copper homeostasis and characteristically afflict the nervous system. However, their molecular neuropathology mechanisms remain mostly unexplored. We demonstrate that copper homeostasis in neurons is maintained by two factors that localize to the Golgi apparatus, ATP7 and the COG complex. Disruption of these mechanisms affect mitochondrial function and localization to synapses as well as neurotransmission and synaptic plasticity. These findings suggest a new principle of interorganelle communication whereby the Golgi apparatus and mitochondria are functionally coupled through homeostatically controlled cellular copper levels.

neuroscience↗