Diacylglycerol Is Required for the Formation of COPI Vesicles in the Golgi-to-ER Transport Pathway

TLDR

Diacylglycerol is required for trans‑Golgi network to cell‑surface transport, yet its role in early secretory steps remains unknown. Diacylglycerol depletion blocks Golgi‑to‑ER retrograde transport by preventing COPI vesicle fission, evidenced by KDEL receptor mislocalization, COPI coat accumulation, and rescue with DAG analogues, underscoring its essential role in late COPI vesicle formation.

Abstract

Diacylglycerol is necessary for trans-Golgi network (TGN) to cell surface transport, but its functional relevance in the early secretory pathway is unclear. Although depletion of diacylglycerol did not affect ER-to-Golgi transport, it led to a redistribution of the KDEL receptor to the Golgi, indicating that Golgi-to-ER transport was perturbed. Electron microscopy revealed an accumulation of COPI-coated membrane profiles close to the Golgi cisternae. Electron tomography showed that the majority of these membrane profiles originate from coated buds, indicating a block in membrane fission. Under these conditions the Golgi-associated pool of ARFGAP1 was reduced, but there was no effect on the binding of coatomer or the membrane fission protein CtBP3/BARS to the Golgi. The addition of 1,2-dioctanoyl-sn-glycerol or the diacylglycerol analogue phorbol 12,13-dibutyrate reversed the effects of endogenous diacylglycerol depletion. Our findings implicate diacylglycerol in the retrograde transport of proteins from Golgi to the ER and suggest that it plays a critical role at a late stage of COPI vesicle formation.