title: Mitochondria-localized glutamic acid-rich protein (MGARP) gene transcription is regulated by Sp1.
abstract: BACKGROUND
  Mitochondria-localized glutamic acid-rich protein (MGARP) is a novel mitochondrial transmembrane protein expressed mainly in steroidogenic tissues and in the visual system. Previous studies showed that MGARP functions in hormone biosynthesis and its expression is modulated by the HPG axis.
  
  
  RESULTS
  By bioinformatics, we identified two characteristic GC-rich motifs that are located proximal to the transcription start site (TSS) of MGARP, and each contains two Specificity protein 1 (Sp1) binding elements. We then determined that the -3 kb proximal MGARP promoter is activated in a Sp1-dependent manner using reporter assays and knockdown of Sp1 led to decreased expression of endogenous MGARP messages. We also demonstrated that one of the two GC-rich motifs, GC-Box1, harbors prominent promoter activity mediated by Sp1, and that it requires both GC boxes for full transcriptional activation. These findings suggest a dominant role for these GC boxes and Sp1 in activating the MGARP promoter through a synergistic mechanism. Consistently, the results of an Electrophoretic Mobility Gel Shift Assay (EMSA) and Chromatin Immunoprecipitation (ChIP) confirmed that Sp1 specifically interacts with the GC-rich region. We further found that estrogen receptor α (ERα), a known Sp1 co-activator, could potentiate GC-boxes containing MGARP promoter activity and this effect is mediated by Sp1. Knockdown of Sp1 significantly diminished the MGARP promoter transactivation and the expression of endogenous MGARP mediated by both Sp1 and ERα.
  
  
  CONCLUSIONS
  The present study identified a proximal core sequence in the MGARP promoter that is composed of two enriched Sp1 binding motifs and established Sp1 as one major MGARP transactivator whose functions are synergistic with ERα, providing a novel understanding of the mechanisms of MGARP gene transcriptional regulation.
authors.affiliation: State Key Laboratory of Biomembrane and Membrane Biotechnology, School of Life Sciences, Tsinghua University, Beijing, China.
authors.forename: Da
authors.initials: D
authors.lastname: Jin
authors.forename: Rui
authors.initials: R
authors.lastname: Li
authors.forename: Dongxue
authors.initials: D
authors.lastname: Mao
authors.forename: Nan
authors.initials: N
authors.lastname: Luo
authors.forename: Yifeng
authors.initials: Y
authors.lastname: Wang
authors.forename: Shaoyong
authors.initials: S
authors.lastname: Chen
authors.forename: Shuping
authors.initials: S
authors.lastname: Zhang
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D020862:GC Rich Sequence; D005786:Gene Expression Regulation; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D024101:Mitochondrial Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D059372:Nucleotide Motifs; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011960:Receptors, Estrogen / Q000378:metabolism; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation
chemical_list: C485853:MGARP protein, human; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D011960:Receptors, Estrogen; D016329:Sp1 Transcription Factor