GBF1-Arf-COPI-ArfGAP-mediated Golgi-to-ER transport involved in regulation of lipid homeostasis

Cell Struct Funct. 2011;36(2):223-35. doi: 10.1247/csf.11035.

Abstract

Eukaryotic cells store neutral lipids and cholesteryl esters in cytoplasmic lipid droplets (LDs), which are generated from the endoplasmic reticulum (ER). Accumulating lines of evidence have indicated that Golgi-to-ER-retrograde transport mediated by COPI-coated vesicles under the control of Arf small GTPases is implicated in LD formation and utilization. However, the detailed mechanism underlying the regulation of lipid homeostasis by COPI-dependent transport has been poorly understood. Here we show that LD deposition and the cellular triacylglycerol content are significantly increased by siRNA-mediated depletion of not only β-COP (a subunit of the COPI coat complex) but also GBF1 (a guanine nucleotide exchange factor for Arfs), Arf4 and Arf5 (class II Arfs), and ArfGAP1-ArfGAP3 (GTPase-activating proteins for Arfs). Although a previous proteomic study suggested the presence of COPI subunits and Arfs on LDs, we have failed to show that components of the GBF1-Arf-COPI-ArfGAP retrograde transport machinery are directly associated with and closely apposed to LDs. Furthermore, although recent studies suggested that COPI-mediated transport and GBF1 participated in delivery of adipose triglyceride lipase (ATGL) onto the LD surface, we have found that depletion of β-COP or GBF1 does not affect association of ATGL with LDs or ATGL-mediated lipolysis. On the basis of these results, we propose other mechanisms how the GBF1-Arf-COPI-ArfGAP transport machinery is implicated in the regulation of lipid homeostasis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ADP-Ribosylation Factors / metabolism*
  • Animals
  • Biological Transport
  • Cells, Cultured
  • Coat Protein Complex I / metabolism*
  • Dogs
  • Endoplasmic Reticulum / metabolism*
  • GTPase-Activating Proteins / metabolism*
  • Golgi Apparatus / metabolism*
  • Guanine Nucleotide Exchange Factors / metabolism*
  • HeLa Cells
  • Homeostasis
  • Humans
  • Lipid Metabolism*
  • Lipids

Substances

  • Coat Protein Complex I
  • GBF1 protein, human
  • GTPase-Activating Proteins
  • Guanine Nucleotide Exchange Factors
  • Lipids
  • ADP-Ribosylation Factors