Novel Components of the Stress Assembly Sec Body Identified by Proximity Labeling.

Sec bodies are membraneless stress-induced assemblies that form by the coalescence of endoplasmic reticulum exit sites (ERES). Through APEX2 tagging of Sec24AB, we biotinylated and identified the full complement of Sec body proteins. In the presence of biotin-phenol and HO (APEX on), APEX2 facilitates the transfer of a biotin moiety to nearby interactors of chimeric Sec24AB.

Pathways of Unconventional Protein Secretion.

Secretory proteins are conventionally transported through the endoplasmic reticulum to the Golgi and then to the plasma membrane where they are released into the extracellular space. However, numerous substrates also reach these destinations using unconventional pathways. Unconventional protein secretion (UPS) is complex and comprises cargos without a signal peptide or a transmembrane domain that can translocate across the plasma membrane, and cargos that reach the plasma membrane by bypassing the Golgi despite entering the endoplasmic reticulum (ER).

TORC2 mediates the heat stress response in Drosophila by promoting the formation of stress granules.

The kinase TOR is found in two complexes, TORC1, which is involved in growth control, and TORC2, whose roles are less well defined. Here, we asked whether TORC2 has a role in sustaining cellular stress. We show that TORC2 inhibition in Drosophila melanogaster leads to a reduced tolerance to heat stress, whereas sensitivity to other stresses is not affected.

SEC16 in COPII coat dynamics at ER exit sites.

Protein export from the endoplasmic reticulum (ER), the first step in protein transport through the secretory pathway, is mediated by coatomer protein II (COPII)-coated vesicles at ER exit sites. COPII coat assembly on the ER is well understood and the conserved large hydrophilic protein Sec16 clearly has a role to play in COPII coat dynamics. Sec16 localizes to ER exit sites, its loss of function impairs their functional organization in all species where it has been studied, and it interacts with COPII coat subunits.

Old dog, new tricks: Arf1 required for mitochondria homeostasis.

The small GTPase Arf1 that is classically required for the budding of COPI-coated vesicles from the Golgi membrane is now proposed to have novel and conserved roles in the morphological and functional maintenance of mitochondria: It functionally localizes to ER/mitochondria contact sites; it allows for the recruitment of a degradation machinery to mitochondria to remove toxic mitofusin/Fzo1 clusters; and it allows the extension of autophagy sequestration membranes needed for mitophagy to clear damaged mitochondria.