Abstract
The subcellular location and cell biological function of small GTPase Rab40c in mammalian cells have not been investigated in detail. In this study, we demonstrated that the exogenously expressed GFP-Rab40c associates with lipid droplets marked by neutral lipid specific dye Oil red or Nile red, but not with the Golgi or endosomal markers. Further examination demonstrated that Rab40c is also associated with ERGIC-53 containing structures, especially under the serum starvation condition. Rab40c is increasingly recruited to the surface of lipid droplets during lipid droplets formation and maturation in HepG2 cells. Rab40c knockdown moderately decreases the size of lipid droplets, suggesting that Rab40c is involved in the biogenesis of lipid droplets. Stimulation for adipocyte differentiation increases the expression of Rab40c in 3T3-L1 cells. Rab40c interacts with TIP47, and is appositionally associated with TIP47-labeled lipid droplets. In addition, over-expression of Rab40c causes the clustering of lipid droplets independent of its GTPase activity, but completely dependent of the intact SOCS box domain of Rab40c. In addition, Rab40c displayed self-interaction as well as interaction with TIP47 and the SOCS box is essential for its ability to induce clustering of lipid droplets. Our results suggest that Rab40c is a novel Rab protein associated with lipid droplets, and is likely involved in modulating the biogenesis of lipid droplets.
Highlights
Lipid droplets (LDs, referred to as adiposome) are the unique organelle for the storage of neutral lipids, mostly triacylglycerols (TG) and cholesterol esters
The monoclonal antibodies against GM130 and EEA1 were from BD (BD Biosciences, PaloAlto, CA), mAbs against rat Lamp2 was obtained from the Developmental Studies Hybridoma Bank maintained by the University of Iowa (Department of Biological Science, Iowa City, IA). mAb against Myc-tag (9E10) and mAb against Flag tag were obtained from American Type Culture Collection (ATCC, Manassas, VA). mAb against lysobisphosphatidicacid (LBPA) was a generous gift from Dr Jean Gruenberg(University of Geneva, Switzerland). mAb against KDEL receptor was from BD (BD Biosciences, PaloAlto, CA)
Proteomics studies revealed that many Rab GTPases are likely associated with LDs, but the members of the associated Rab proteins may vary in different experiments or cell types [26,27,28], suggesting that different Rab proteins will be recruited onto the LDs under different conditions, giving the reason that Rab40c was not previously reported to be found on LDs
Summary
Lipid droplets (LDs, referred to as adiposome) are the unique organelle for the storage of neutral lipids, mostly triacylglycerols (TG) and cholesterol esters. Lipid droplet has a lipid core surrounded by a monolayer of phospholipids membrane, and is produced by many types of cells in animals, plants and even microorganisms (comprehensively reviewed in [1,2,3]). Recent studies revealed that LD is not a static structure for the storage of lipid, but a dynamic organelle to maintain lipid homeostasis, generate energy and regulate cell signaling [4,5,6,7,8]. Excessive lipids in LDs can be metabolized through lipolysis and oxidation to generate ATP, and be transported to other organelle as the components of membrane biogenesis. Characterization of proteins associated with LDs will be helpful for understanding the biogenesis and dynamic interaction of LDs with other cellular structures
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
