Transcriptional regulatory elements for basal expression of cytochrome P450IIC genes

J Biol Chem. 1992 Aug 25;267(24):17333-8.

Abstract

To analyze the transcriptional regulatory elements in rabbit cytochrome P450IIC genes, varying lengths of the 5'-flanking regions of CYP2C1 and CYP2C2 were fused to a luciferase reporter gene. Promoter activity was assayed by transfection into HepG2 cells, a hepatic cell line, and monkey kidney COS-1 cells, a nonhepatic cell line. Activity of the CYP2C1 promoter in HepG2 cells increased slightly with progressive 5' deletions of the 5'-flanking region from nucleotide -3600 to -1500 relative to the transcription start site. Additional deletions to -900, -358, and -116 each reduced activity by about 50%, and deletion of the sequence from -116 to -67 reduced activity by a factor of 12. Activity of the CYP2C2 promoter increased about 3-fold with progressive 5' deletions of sequence from nucleotide -3500 to -410. In contrast, deletions of sequences from -251 to -193 and from -133 to -64 reduced promoter activity by factors of 2 and 8, respectively. In COS-1 cells, the maximum activities of the CYP2C1 and CYP2C2 promoters normalized to a Rous sarcoma viral promoter were about 10-20% of that in the HepG2 cells. The changes in activity between different constructions in COS-1 cells largely paralleled those in the HepG2 cells except for deletions of the sequences -133 to -64 and -116 to -67 for CYP2C1 and CYP2C2, respectively, which produced the largest reduction of promoter activity in HepG2 cells but had little effect in COS-1 cells. These results show that HepG2-specific regulatory elements are present in the regions between -120 and -65 in both genes. Nuclear proteins from HepG2 cells, but not from COS-1 cells, bound to sequences within these regions, and the binding was inhibited by an oligonucleotide containing a sequence conserved in rabbit P450IIC genes which has been designated the HepG2-specific P450 2C factor-1 (HPF1) motif. Mutation of this sequence eliminated the binding of nuclear proteins and reduced transcriptional activity 25-fold. The HPF1 binding sequence is conserved in CYP2A, CYP2C, and CYP2D genes and resembles the binding motif for hepatic nuclear factor-4. These results demonstrate that CYP2C1 and CYP2C2 contain several potential regulatory elements for basal expression, including one HepG2-specific sequence that may be important for liver expression.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Avian Sarcoma Viruses / genetics
  • Base Sequence
  • Cell Line
  • Cell Nucleus / metabolism
  • Chromosome Deletion
  • Cytochrome P-450 Enzyme System / biosynthesis
  • Cytochrome P-450 Enzyme System / genetics*
  • Gene Expression Regulation, Enzymologic*
  • Humans
  • Luciferases / genetics
  • Luciferases / metabolism
  • Molecular Sequence Data
  • Oligodeoxyribonucleotides
  • Promoter Regions, Genetic
  • Rabbits
  • Recombinant Fusion Proteins / metabolism
  • Regulatory Sequences, Nucleic Acid*
  • Restriction Mapping
  • Sequence Homology, Nucleic Acid
  • Transcription, Genetic*
  • Transfection

Substances

  • Oligodeoxyribonucleotides
  • Recombinant Fusion Proteins
  • Cytochrome P-450 Enzyme System
  • Luciferases