title: COPI-TRAPPII activates Rab18 and regulates its lipid droplet association.
abstract: The transport protein particle (TRAPP) was initially identified as a vesicle tethering factor in yeast and as a guanine nucleotide exchange factor (GEF) for Ypt1/Rab1. In mammals, structures and functions of various TRAPP complexes are beginning to be understood. We found that mammalian TRAPPII was a GEF for both Rab18 and Rab1. Inactivation of TRAPPII-specific subunits by various methods including siRNA depletion and CRISPR-Cas9-mediated deletion reduced lipolysis and resulted in aberrantly large lipid droplets. Recruitment of Rab18 onto lipid droplet (LD) surface was defective in TRAPPII-deleted cells, but the localization of Rab1 on Golgi was not affected. COPI regulates LD homeostasis. We found that the previously documented interaction between TRAPPII and COPI was also required for the recruitment of Rab18 to the LD We hypothesize that the interaction between COPI and TRAPPII helps bring TRAPPII onto LD surface, and TRAPPII, in turn, activates Rab18 and recruits it on the LD surface to facilitate its functions in LD homeostasis.
authors.affiliation: Department of Anatomy, Histology and Developmental Biology, School of Basic Medical Sciences, Health Science Centre, Shenzhen University, Shenzhen, China.|School of Biomedical Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, China.
authors.forename: Chunman
authors.identifier: 0000-0003-1674-7136
authors.initials: C
authors.lastname: Li
authors.affiliation: School of Biomedical Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, China.
authors.forename: Xiaomin
authors.initials: X
authors.lastname: Luo
authors.affiliation: School of Biomedical Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, China.
authors.forename: Shan
authors.initials: S
authors.lastname: Zhao
authors.affiliation: School of Biomedical Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, China.
authors.forename: Gavin Ky
authors.initials: GK
authors.lastname: Siu
authors.affiliation: Key Laboratory of Agricultural Environmental Microbiology of MOA, College of Life Sciences, Nanjing Agricultural University, Nanjing, China.
authors.forename: Yongheng
authors.initials: Y
authors.lastname: Liang
authors.affiliation: School of Biomedical Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, China.|Epithelial Cell Biology Research Centre, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, China.
authors.forename: Hsiao Chang
authors.initials: HC
authors.lastname: Chan
authors.affiliation: The Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
authors.forename: Ayano
authors.initials: A
authors.lastname: Satoh
authors.affiliation: School of Biomedical Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, China sidney.yu@cuhk.edu.hk.|Epithelial Cell Biology Research Centre, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, China.
authors.forename: Sidney Sb
authors.identifier: 0000-0001-9643-2729
authors.initials: SS
authors.lastname: Yu
mesh_terms: D002460:Cell Line; D020755:Coat Protein Complex I / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D055786:Gene Knockout Techniques; D006801:Humans; D066292:Lipid Droplets / Q000378:metabolism*; D008066:Lipolysis; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000378:metabolism*; D020761:rab1 GTP-Binding Proteins / Q000378:metabolism
chemical_list: D020755:Coat Protein Complex I; C484168:RAB18 protein, human; D033921:Vesicular Transport Proteins; C406327:transport protein particle, TRAPP; D020691:rab GTP-Binding Proteins; D020761:rab1 GTP-Binding Proteins
keywords: 
  COPI
  ; 
  TRAPPII
  ; Rab18; TRAPPC10; TRAPPC9; lipid droplets