Transcriptional regulation of the human cystathionine beta-synthase -1b basal promoter: synergistic transactivation by transcription factors NF-Y and Sp1/Sp3

Biochem J. 2001 Jul 1;357(Pt 1):97-105. doi: 10.1042/0264-6021:3570097.


Cystathionine beta-synthase (CBS) catalyses the condensation of serine and homocysteine to form cystathionine, an intermediate step in the synthesis of cysteine. Human CBS encodes five distinct 5' non-coding exons, the most frequent termed CBS -1a and CBS -1b, each transcribed from its own unique GC-rich TATA-less promoter. The minimal transcriptional region (-3792 to -3667) of the CBS -1b promoter was defined by 5'- and 3'-deletions, and transient transfections of reporter gene constructs in HepG2 cells, characterized by CBS transcription exclusively from the -1b promoter. Included in this 125 bp region are 3 GC-boxes (termed GC-a, GC-b and GC-c), an inverted CAAT-box and an E-box. By gel-shift and supershift assays, binding of specificity protein (Sp)1 and Sp3 to the GC-box elements, upstream stimulatory factor 1 (USF-1) to the E-box, and both nuclear factor (NF)-Y and an NF-1-like factor to the CAAT box could be demonstrated. By transient trans fections and reporter gene assays in HepG2 and Drosophila SL2 cells, a functional interplay was indicated between NF-Y binding to the CAAT-box, or between USF-1 binding to the E-box, and Sp1/Sp3 binding to the GC-box elements. In SL2 cells, NF-Y and Sp1/Sp3 were synergistic. Furthermore, both Sp1 and the long Sp3 isoform transactivated the CBS -1b minimal promoter; however, the short Sp3 isoforms were potent repressors. These results may explain the cell- or tissue-specific regulation of CBS transcription, and clarify the bases for alterations in CBS gene expression in human disease and Down's syndrome.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Binding Sites
  • CCAAT-Binding Factor / metabolism*
  • Cystathionine beta-Synthase / genetics*
  • Exons
  • Gene Expression Regulation, Enzymologic
  • Humans
  • Introns
  • Molecular Sequence Data
  • Oligodeoxyribonucleotides / chemistry
  • Promoter Regions, Genetic*
  • Recombinant Proteins / biosynthesis
  • Regulatory Sequences, Nucleic Acid
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sp1 Transcription Factor / metabolism*
  • Transcription, Genetic*
  • Transcriptional Activation*
  • Transfection
  • Tumor Cells, Cultured


  • CCAAT-Binding Factor
  • Oligodeoxyribonucleotides
  • Recombinant Proteins
  • Sp1 Transcription Factor
  • Cystathionine beta-Synthase