title: Identification of RIFL, a novel adipocyte-enriched insulin target gene with a role in lipid metabolism.
abstract: To identify new genes that are important in fat metabolism, we utilized the Lexicon-Genentech knockout database of genes encoding transmembrane and secreted factors and whole murine genome transcriptional profiling data that we generated for 3T3-L1 in vitro adipogenesis. Cross-referencing null models evidencing metabolic phenotypes with genes induced in adipogenesis led to identification of a new gene, which we named RIFL (refeeding induced fat and liver). RIFL-null mice have serum triglyceride levels approximately one-third of wild type. RIFL transcript is induced >100-fold during 3T3-L1 adipogenesis and is also increased markedly during adipogenesis of murine and human primary preadipocytes. siRNA-mediated knockdown of RIFL during 3T3-L1 adipogenesis results in an ~35% decrease in adipocyte triglyceride content. Murine RIFL transcript is highly enriched in white and brown adipose tissue and liver. Fractionation of WAT reveals that RIFL transcript is exclusive to adipocytes with a lack of expression in stromal-vascular cells. Nutritional and hormonal studies are consistent with a prolipogenic function for RIFL. There is evidence of an approximately eightfold increase in RIFL transcript level in WAT in ob/ob mice compared with wild-type mice. RIFL transcript level in WAT and liver is increased ~80- and 12-fold, respectively, following refeeding of fasted mice. Treatment of 3T3-L1 adipocytes with insulin increases RIFL transcript ≤35-fold, whereas agents that stimulate lipolysis downregulate RIFL. Interestingly, the 198-amino acid RIFL protein is predicted to be secreted and shows ~30% overall conservation with the NH(2)-terminal half of angiopoietin-like 3, a liver-secreted protein that impacts lipid metabolism. In summary, our data suggest that RIFL is an important new regulator of lipid metabolism.
authors.affiliation: Department of Biochemistry and Cancer Biology and Center for Diabetes and Endocrine Research, University of Toledo College of Medicine, Toledo, OH 43614, USA.
authors.forename: Gang
authors.initials: G
authors.lastname: Ren
authors.forename: Ji Young
authors.initials: JY
authors.lastname: Kim
authors.forename: Cynthia M
authors.initials: CM
authors.lastname: Smas
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D050156:Adipogenesis / Q000187:drug effects / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D003001:Cloning, Molecular; D005786:Gene Expression Regulation / Q000187:drug effects; D055785:Gene Knockdown Techniques; D005796:Genes / Q000502:physiology; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D050356:Lipid Metabolism / Q000187:drug effects* / Q000235:genetics*; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D034741:RNA, Small Interfering / Q000494:pharmacology
chemical_list: D007328:Insulin; D034741:RNA, Small Interfering