New factors for protein transport identified by a genome-wide CRISPRi screen in mammalian cells
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.