title: OSBP-related protein 8 (ORP8) regulates plasma and liver tissue lipid levels and interacts with the nucleoporin Nup62.
abstract: We earlier identified OSBP-related protein 8 (ORP8) as an endoplasmic reticulum oxysterol-binding protein implicated in cellular lipid homeostasis. We now investigated its action in hepatic cells in vivo and in vitro. Adenoviral overexpression of ORP8 in mouse liver induced a decrease of cholesterol, phospholipids, and triglycerides in serum (-34%, -26%, -37%, respectively) and liver tissue (-40%, -12%, -24%), coinciding with reduction of nuclear (n)SREBP-1 and -2 and mRNA levels of their target genes. Consistently, excess ORP8 reduced nSREBPs in HuH7 cells, and ORP8 overexpression or silencing by RNA interference moderately suppressed or induced the expression of SREBP-1 and SREBP-2 target genes, respectively. In accordance, cholesterol biosynthesis was reduced by ORP8 overexpression and enhanced by ORP8 silencing in [(3)H]acetate pulse-labeling experiments. ORP8, previously shown to bind 25-hydroxycholesterol, was now shown to bind also cholesterol in vitro. Yeast two-hybrid, bimolecular fluorescence complementation (BiFC), and co-immunoprecipitation analyses revealed the nuclear pore component Nup62 as an interaction partner of ORP8. Co-localization of ORP8 and Nup62 at the nuclear envelope was demonstrated by BiFC and confocal immunofluorescence microscopy. Furthermore, the impact of overexpressed ORP8 on nSREBPs and their target mRNAs was inhibited in cells depleted of Nup62. Our results reveal that ORP8 has the capacity to modulate lipid homeostasis and SREBP activity, probably through an indirect mechanism, and provide clues of an entirely new mode of ORP action.
authors.affiliation: Department of Biology, Jinan University, Guangzhou, China.
authors.forename: Tianhong
authors.initials: T
authors.lastname: Zhou
authors.forename: Shiqian
authors.initials: S
authors.lastname: Li
authors.forename: Wenbin
authors.initials: W
authors.lastname: Zhong
authors.forename: Terhi
authors.initials: T
authors.lastname: Vihervaara
authors.forename: Olivier
authors.initials: O
authors.lastname: Béaslas
authors.forename: Julia
authors.initials: J
authors.lastname: Perttilä
authors.forename: Wei
authors.initials: W
authors.lastname: Luo
authors.forename: Yingliang
authors.initials: Y
authors.lastname: Jiang
authors.forename: Markku
authors.initials: M
authors.lastname: Lehto
authors.forename: Vesa M
authors.initials: VM
authors.lastname: Olkkonen
authors.forename: Daoguang
authors.initials: D
authors.lastname: Yan
mesh_terms: D000818:Animals; D001483:Base Sequence; D045744:Cell Line, Tumor; D017931:DNA Primers; D005260:Female; D006801:Humans; D050356:Lipid Metabolism; D008055:Lipids / Q000097:blood*; D008099:Liver / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D028861:Nuclear Pore Complex Proteins / Q000378:metabolism*; D011485:Protein Binding; D011987:Receptors, Steroid / Q000378:metabolism / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020798:Two-Hybrid System Techniques; D000098825:Oxysterol Binding Proteins
chemical_list: D017931:DNA Primers; D008055:Lipids; D008562:Membrane Glycoproteins; D028861:Nuclear Pore Complex Proteins; D011987:Receptors, Steroid; C049312:nuclear pore protein p62; D000098825:Oxysterol Binding Proteins