title: Expression, regulation and functional assessment of the 80 amino acid Small Adipocyte Factor 1 (Smaf1) protein in adipocytes.
abstract: The gene for Small Adipocyte Factor 1, Smaf1 (also known as adipogenin, ADIG), encodes a ∼600 base transcript that is highly upregulated during 3T3-L1 in vitro adipogenesis and markedly enriched in adipose tissues. Based on the lack of an obvious open reading frame in the Smaf1 transcript, it is not known if the Smaf1 gene is protein coding or non-coding RNA. Using a peptide from a putative open reading frame of Smaf1 as antigen, we generated antibodies for western analysis. Our studies prove that Smaf1 encodes an adipose-enriched protein which in western blot analysis migrates at ∼10 kDa. Rapid induction of Smaf1 protein occurs during in vitro adipogenesis and its expression in 3T3-L1 adipocytes is positively regulated by insulin and glucose. Moreover, siRNA studies reveal that expression of Smaf1 in adipocytes is wholly dependent on PPARγ. On the other hand, use of siRNA for Smaf1 to nearly abolish its protein expression in adipocytes revealed that Smaf1 does not have a major role in adipocyte triglyceride accumulation, lipolysis or insulin-stimulated pAkt induction. However, immunolocalization studies using HA-tagged Smaf1 reveal enrichment at adipocyte lipid droplets. Together our findings show that Smaf1 is a novel small protein endogenous to adipocytes and that Smaf1 expression is closely tied to PPARγ-mediated signals and the adipocyte phenotype.
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.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: Parisa
authors.initials: P
authors.lastname: Eskandari
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; Department of Nursing, Shangqiu Medical College, Shangqiu City, China.
authors.forename: Siqian
authors.initials: S
authors.lastname: Wang
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. Electronic address: cynthia.smas@utoledo.edu.
authors.forename: Cynthia M
authors.initials: CM
authors.lastname: Smas
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D050156:Adipogenesis / Q000502:physiology*; D000273:Adipose Tissue / Q000166:cytology* / Q000378:metabolism*; D000818:Animals; D005786:Gene Expression Regulation / Q000502:physiology; D066292:Lipid Droplets / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008970:Molecular Weight; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D047495:PPAR gamma / Q000378:metabolism
chemical_list: D009687:Nuclear Proteins; D047495:PPAR gamma; C495823:SMAF1 protein, mouse
keywords: Adipocyte; Adipogenesis; Adipogenin; Differentiation; Lipid metabolism; PPARγ; Smaf1