title: Molecular characterization of seipin and its mutants: implications for seipin in triacylglycerol synthesis.
abstract: The human lipodystrophy gene product Berardinelli-Seip congenital lipodystrophy 2/seipin has been implicated in adipocyte differentiation, lipid droplet (LD) formation, and motor neuron development. However, the molecular function of seipin and its disease-causing mutants remains to be elucidated. Here, we characterize seipin and its mis-sense mutants: N88S/S90L (both linked to motoneuron disorders) and A212P (linked to lipodystrophy) in cultured mammalian cells. Knocking down seipin significantly increases oleate incorporation into triacylglycerol (TAG) and the steady state level of TAG, and induces the proliferation and clustering of small LDs. By contrast, overexpression of seipin reduces TAG synthesis, leading to decreased formation of LDs. Expression of the A212P mutant, however, had little effect on LD biogenesis. Surprisingly, expression of N88S or S90L causes the formation of many small LDs reminiscent of seipin deficient cells. This dominant-negative effect may be due to the N88S/S90L-induced formation of inclusions where wild-type seipin can be trapped. Importantly, coexpression of wild-type seipin and the N88S or S90L mutant can significantly reduce the formation of inclusions. Finally, we demonstrate that seipin can interact with itself and its mutant forms. Our results provide important insights into the biochemical characteristics of seipin and its mis-sense mutants, and suggest that seipin may function to inhibit lipogenesis.
authors.affiliation: School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia.
authors.forename: Weihua
authors.initials: W
authors.lastname: Fei
authors.affiliation: School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: Department of Biochemistry, National University of Singapore, Singapore, 117597 Republic of Singapore.
authors.forename: Guanghou
authors.initials: G
authors.lastname: Shui
authors.affiliation: School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia.
authors.forename: Tamar S
authors.initials: TS
authors.lastname: Kapterian
authors.affiliation: School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia.
authors.forename: Christopher
authors.initials: C
authors.lastname: Bielby
authors.affiliation: School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia.
authors.forename: Ximing
authors.initials: X
authors.lastname: Du
authors.affiliation: School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Brown
authors.affiliation: School of Life Sciences, Tsing-Hua University, Beijing, People's Republic of China; and.
authors.forename: Peng
authors.initials: P
authors.lastname: Li
authors.affiliation: Department of Biochemistry, National University of Singapore, Singapore, 117597 Republic of Singapore; Department of Biological Sciences, National University of Singapore, Singapore, 117597 Republic of Singapore.
authors.forename: Markus R
authors.initials: MR
authors.lastname: Wenk
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Beijing, People's Republic of China.
authors.forename: Pingsheng
authors.initials: P
authors.lastname: Liu
authors.affiliation: School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia;. Electronic address: h.rob.yang@unsw.edu.au.
authors.forename: Hongyuan
authors.initials: H
authors.lastname: Yang
mesh_terms: D050156:Adipogenesis / Q000235:genetics; D000818:Animals; D002460:Cell Line; D019143:Evolution, Molecular; D044388:GTP-Binding Protein gamma Subunits / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D006367:HeLa Cells; D006801:Humans; D008055:Lipids / Q000737:chemistry; D008066:Lipolysis / Q000235:genetics; D051379:Mice; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D041681:NIH 3T3 Cells; D014280:Triglycerides / Q000096:biosynthesis*
chemical_list: C432679:BSCL2 protein, human; D044388:GTP-Binding Protein gamma Subunits; D008055:Lipids; D050505:Mutant Proteins; D014280:Triglycerides