2. Academic Validation
  3. The activity of Sac1 across ER-TGN contact sites requires the four-phosphate-adaptor-protein-1

The activity of Sac1 across ER-TGN contact sites requires the four-phosphate-adaptor-protein-1

  • J Cell Biol. 2019 Mar 4;218(3):783-797. doi: 10.1083/jcb.201812021.
Rossella Venditti 1 2,  Maria Chiara Masone 1,  Laura Rita Rega 1,  Giuseppe Di Tullio 1,  Michele Santoro 1,  Elena Polishchuk 1,  Ivan Castello Serrano 1,  Vesa M Olkkonen 3 4,  Akihiro Harada 5,  Diego L Medina 1,  Raffaele La Montagna 1,  Maria Antonietta De Matteis 6 2
Affiliations

Affiliations

  • 1 Telethon Institute of Genetics and Medicine, Pozzuoli, Italy.
  • 2 Department of Molecular Medicine and Medical Biotechnology, University of Napoli Federico II, Medical School, Naples, Italy.
  • 3 Minerva Foundation Institute for Medical Research, Biomedicum 2U, Helsinki, Finland.
  • 4 Department of Anatomy, Faculty of Medicine, University of Helsinki, Helsinki, Finland.
  • 5 Osaka University, Osaka, Japan.
  • 6 Telethon Institute of Genetics and Medicine, Pozzuoli, Italy dematteis@tigem.it.
PMID: 30659099 DOI: 10.1083/jcb.201812021
Abstract

Phosphatidylinositol-4-phosphate (PI4P), a phosphoinositide with key roles in the Golgi complex, is made by Golgi-associated phosphatidylinositol-4 kinases and consumed by the 4-phosphatase Sac1 that, instead, is an ER membrane protein. Here, we show that the contact sites between the ER and the TGN (ERTGoCS) provide a spatial setting suitable for Sac1 to dephosphorylate PI4P at the TGN. The ERTGoCS, though necessary, are not sufficient for the Phosphatase activity of Sac1 on TGN PI4P, since this needs the phosphatidyl-four-phosphate-adaptor-protein-1 (FAPP1). FAPP1 localizes at ERTGoCS, interacts with Sac1, and promotes its in-trans Phosphatase activity in vitro. We envision that FAPP1, acting as a PI4P detector and adaptor, positions Sac1 close to TGN domains with elevated PI4P concentrations allowing PI4P consumption. Indeed, FAPP1 depletion induces an increase in TGN PI4P that leads to increased secretion of selected cargoes (e.g., ApoB100), indicating that FAPP1, by controlling PI4P levels, acts as a gatekeeper of Golgi exit.

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