Palade's corpus placed small vesicles as the sole means to transport proteins across stable distinct compartments of the secretory pathway. We suggest that cargo, spatial organization of secretory compartments, and the timing of fission of cargo-filled containers dictate the design of transport intermediates that can be vesicles and transient direct tunnels. ; We acknowledge support from the Spanish Ministry of Economy and Competitiveness through the Program "Centro de Excelencia Severo Ochoa 2013-2017" (SEV-2012-0208), support from the CERCA Program/Generalitat de Catalunya and fellowship IJCI-2017-34751 (to I. Raote). V. Malhotra is an Institució Catalana de Recerca i Estudis Avançats professor at the Centre for Genomic Regulation and the work in his laboratory is funded by grants from MINECO's Plan Nacional (BFU2013-44188-P) and Consolider (CSD2009-00016). The project has received research funding from the European Union. This paper reflects only the authors' views. The European Union is not liable for any use that may be made of the information contained therein.
The mechanism of cargo sorting at the trans-Golgi network (TGN) for secretion is poorly understood. We previously reported the involvement of the actin-severing protein cofilin and the Ca(2+) ATPase secretory pathway calcium ATPase 1 (SPCA1) in the sorting of soluble secretory cargo at the TGN in mammalian cells. Now we report that cofilin in yeast is required for export of selective secretory cargo at the late Golgi membranes. In cofilin mutant (cof1-8) cells, the cell wall protein Bgl2 was secreted at a reduced rate and retained in a late Golgi compartment, whereas the plasma membrane H(+) ATPase Pma1, which is transported in the same class of carriers, reached the cell surface. In addition, sorting of carboxypeptidase Y (CPY) to the vacuole was delayed, and CPY was secreted from cof1-8 cells. Loss of the yeast orthologue of SPCA1 (Pmr1) exhibited similar sorting defects and displayed synthetic sickness with cof1-8. In addition, overexpression of PMR1 restored Bgl2 secretion in cof1-8 cells. These findings highlight the conserved role of cofilin and SPCA1/Pmr1 in sorting of the soluble secretory proteins at the TGN/late Golgi membranes in eukaryotes. ; This work was supported by grants from the Plan Nacional (BFU2008-00414), Consolider (CSD2009-00016), AGAUR SGR2009-1488 Grups de Recerca Emergents (AGAUR-Catalan Government), and European Research Council (268692)
Procollagens, pre-chylomicrons, and pre–very low-density lipoproteins (pre-VLDLs) are too big to fit into conventional COPII-coated vesicles, so how are these bulky cargoes exported from the endoplasmic reticulum (ER)? We have shown that TANGO1 located at the ER exit site is necessary for procollagen export. We report a role for TANGO1 and TANGO1-like (TALI), a chimeric protein resulting from fusion of MIA2 and cTAGE5 gene products, in the export of pre-chylomicrons and pre-VLDLs from the ER. TANGO1 binds TALI, and both interact with apolipoprotein B (ApoB) and are necessary for the recruitment of ApoB-containing lipid particles to ER exit sites for their subsequent export. Although export of ApoB requires the function of both TANGO1 and TALI, the export of procollagen XII by the same cells requires only TANGO1. These findings reveal a general role for TANGO1 in the export of bulky cargoes from the ER and identify a specific requirement for TALI in assisting TANGO1 to export bulky lipid particles. ; We acknowledge support of the Ministerio de Economía y Competitividad, "Centro de Excelencia Severo Ochoa 2013-2017," SEV-2012-0208. The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement 625149 to A.J.M. Santos and European Research Council grant agreement 268692 to V. Malhotra. This work reflects only the author's views, and the community is not liable for any use that may be made of the information contained therein. V. Malhotra is an Institució Catalana de Recerca i Estudis Avançats professor at the Center for Genomic Regulation, and the work in his laboratory is funded by grants from Ministerio de Economía y Competitividad's Plan Nacional (ref. BFU2013-44188-P) and Consolider (CSD2009-00016).
TANGO1 (transport and Golgi organization 1) interacts with CTAGE5 and COPII components Sec23/Sec24 and recruits ERGIC-53 (endoplasmic reticulum [ER]–Golgi intermediate compartment 53)–containing membranes to generate a mega-transport carrier for export of collagens and apolipoproteins from the ER. We now show that TANGO1, at the ER, assembles in a ring that encircles COPII components. The C-terminal, proline-rich domains of TANGO1 molecules in the ring are initially tilted onto COPII coats but appear to be pushed apart as the carrier grows. These findings lend support to our suggestion that growth of transport carriers for exporting bulky cargoes requires addition of membranes and not simply COPII-mediated accretion of a larger surface of ER. TANGO1 remains at the neck of the newly forming transport carrier, which grows in size by addition of ERGIC-53–containing membranes to generate a transport intermediate for the export of bulky collagens. ; V. Malhotra is an Institució Catalana de Recerca i Estudis Avançats professor at the Centre for Genomic Regulation, and the work in his laboratory is funded by grants from the Ministerio de Economía, Industria y Competitividad Plan Nacional (ref. BFU2013-44188-P) and Consolider (CSD2009-00016). We acknowledge support of the Spanish Ministry of Economy and Competitiveness, through the Programmes "Centro de Excelencia Severo Ochoa 2013-2017" (SEV-2012-0208) and Maria de Maeztu Units of Excellence in R&D (MDM-2015-0502). The research leading to these results has received funding from the European Union Seventh Framework Program (FP7/2007-2013) under European Research Council grant agreement no. 268692 to V. Malhotra.
Ca(2+) import into the lumen of the trans-Golgi network (TGN) by the secretory pathway calcium ATPase1 (SPCA1) is required for the sorting of secretory cargo. How is Ca(2+) retained in the lumen of the Golgi, and what is its role in cargo sorting? We show here that a soluble, lumenal Golgi resident protein, Cab45, is required for SPCA1-dependent Ca(2+) import into the TGN; it binds secretory cargo in a Ca(2+)-dependent reaction and is required for its sorting at the TGN. ; V. Malhotra is an Institució Catalana de Recerca i Estudis Avançats (ICREA) professor at the Center for Genomic Regulation, and the work in his laboratory is funded by grants from Plan Nacional (BFU2008-00414), Consolider (CSD2009-00016), Agència de Gestió d'Ajuts Universitaris i de Recerca (AGAUR) Grups de Recerca Emergents (SGR2009-1488; AGAUR-Catalan Government), and the European Research Council (268692). The group of J. von Blume is funded by an Emmy Noether fellowship (project BL 1186/1-1) of the Deutsche Forschungsgemeinschaft (DFG). M.A. Valverde is the recipient of an ICREA Academia Award and the work in his laboratory is supported by the Spanish ministry of Science and Innovation (SAF2012-38140), Fondo de Investigación Sanitaria (RD12/0042/0014), FEDER Funds, and Generalitat de Catalunya (SGR05-266)
Protein and membrane trafficking pathways are critical for cell and tissue homeostasis. Traditional genetic and biochemical approaches have shed light on basic principles underlying these processes. However, the list of factors required for secretory pathway function remains incomplete, and mechanisms involved in their adaptation poorly understood. Here, we present a powerful strategy based on a pooled genome-wide CRISPRi screen that allowed the identification of new factors involved in protein transport. Two newly identified factors, TTC17 and CCDC157, localized along the secretory pathway and were found to interact with resident proteins of ER-Golgi membranes. In addition, we uncovered that upon TTC17 knockdown, the polarized organization of Golgi cisternae was altered, creating glycosylation defects, and that CCDC157 is an important factor for the fusion of transport carriers to Golgi membranes. In conclusion, our work identified and characterized new actors in the mechanisms of protein transport and secretion and opens stimulating perspectives for the use of our platform in physiological and pathological contexts. ; S.J. Popa acknowledges support from a Wellcome Trust PhD studentship (109152/z/15/z). S.E. Stewart acknowledges support from a Biotechnology and Biological Sciences Research Council Future Leader Fellowship (BB/P010911/1). F. Campelo acknowledges financial support from the Spanish Ministry of Economy and Competitiveness ("Severo Ochoa" program for Centres of Excellence in RD [SEV-2015-0522], FIS2015-63550-R, FIS2017-89560-R, and BFU2015-73288-JIN, AEI/FEDER/UE), Fundació Privada Cellex, and the Generalitat de Catalunya through the CERCA program. A. Ashok acknowledges support from a La Caixa Foundation fellowship. J. Villeneuve acknowledges support from a Marie Curie fellowship within the the European Union's Horizon 2020 research and innovation program (842919). D.C. Rubinsztein is grateful for support from the UK Dementia Research Institute (funded by the Medical Research Council, Alzheimer's Research UK, and the Alzheimer's Society) and the Roger de Spoelberch Foundation.
