Promiscuity of the catalytic Sec7 domain within the guanine nucleotide exchange factor GBF1 in ARF activation, Golgi homeostasis, and effector recruitment

Mol Biol Cell. 2019 Jun 1;30(12):1523-1535. doi: 10.1091/mbc.E18-11-0711. Epub 2019 Apr 3.

Abstract

The integrity of the Golgi and trans-Golgi network (TGN) is disrupted by brefeldin A (BFA), which inhibits the Golgi-localized BFA-sensitive factor (GBF1) and brefeldin A-inhibited guanine nucleotide-exchange factors (BIG1 and BIG2). Using a cellular replacement assay to assess GBF1 functionality without interference from the BIGs, we show that GBF1 alone maintains Golgi architecture; facilitates secretion; activates ADP-ribosylation factor (ARF)1, 3, 4, and 5; and recruits ARF effectors to Golgi membranes. Unexpectedly, GBF1 also supports TGN integrity and recruits numerous TGN-localized ARF effectors. The impact of the catalytic Sec7 domain (Sec7d) on GBF1 functionality was assessed by swapping it with the Sec7d from ARF nucleotide-binding site opener (ARNO)/cytohesin-2, a plasma membrane GEF reported to activate all ARFs. The resulting chimera (GBF1-ARNO-GBF1 [GARG]) targets like GBF1, supports Golgi/TGN architecture, and facilitates secretion. However, unlike GBF1, GARG activates all ARFs (including ARF6) at the Golgi/TGN and recruits additional ARF effectors to the Golgi/TGN. Our results have general implications: 1) GEF's targeting is independent of Sec7d, but Sec7d influence the GEF substrate specificity and downstream effector events; 2) all ARFs have access to all membranes, but are restricted in their distribution by the localization of their activating GEFs; and 3) effector association with membranes requires the coincidental presence of activated ARFs and specific membrane identifiers.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • ADP-Ribosylation Factors / metabolism*
  • Catalytic Domain*
  • GTPase-Activating Proteins / metabolism
  • Golgi Apparatus / metabolism*
  • Guanine Nucleotide Exchange Factors / chemistry*
  • Guanine Nucleotide Exchange Factors / metabolism*
  • HeLa Cells
  • Homeostasis*
  • Humans
  • trans-Golgi Network / metabolism

Substances

  • GBF1 protein, human
  • GTPase-Activating Proteins
  • Guanine Nucleotide Exchange Factors
  • Sec7 guanine nucleotide exchange factors
  • cytohesin-2
  • ADP-Ribosylation Factors