CGI-58 facilitates mobilization of cytoplasmic triglyceride for lipoprotein secretion in hepatoma cells

Brown JM, Chung S, Das A, Shelness G, Rudel LL, Yu L
Source: J Lipid Res
Publication Date: (2007)
Issue: 48(10): 2295-305
Research Area:
Cancer Research/Cell Biology
Cells used in publication:
Species: hamster
Tissue Origin: ovarian
Species: rat
Tissue Origin:
Nucleofector® I/II/2b
2x10^6 cells were nucleofected with 5 micrograms pEGFP-N1 or pEGFP-hCGI-58 plasmids. For CHO-K1 cells, solution T and program O-017 were used. Stable clones were isolated by ring cloning. For COS-1, Hep-G2 and McA-RH777, solution V and program T-028 were applied.
Comparative Gene Identification-58 (CGI-58) is a member of the alpha/beta-hydrolase family of proteins. Mutations in the human CGI-58 gene are associated with Chanarin-Dorfman syndrome, a rare autosomal recessive genetic disease in which excessive triglyceride (TG) accumulation occurs in multiple tissues. In this study, we investigated the role of CGI-58 in cellular lipid metabolism in several cell models and discovered a role for CGI-58 in promoting the packaging of cytoplasmic TG into secreted lipoprotein particles in hepatoma cells. Using both gain-of-function and loss-of-function approaches, we demonstrate that CGI-58 facilitates the depletion of cellular TG stores without altering cellular cholesterol or phospholipid accumulation. This depletion of cellular TG is attributable solely to augmented hydrolysis, whereas TG synthesis was not affected by CGI-58. Furthermore, CGI-58-mediated TG hydrolysis can be completely inhibited by the known lipase inhibitors diethylumbelliferyl phosphate and diethyl-p-nitrophenyl phosphate, but not by p-chloro-mercuribenzoate. Intriguingly, CGI-58-driven TG hydrolysis was coupled to increases in both fatty acid oxidation and secretion of TG. Collectively, this study reveals a role for CGI-58 in coupling lipolytic degradation of cytoplasmic TG to oxidation and packaging into TG-rich lipoproteins for secretion in hepatoma cells.