Transcriptional regulatory elements for basal expression of cytochrome P450IIC genes.

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.

• Authors: P Venepally, D Chen, B Kemper
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 267 Issue 24 Pg. 17333-8 (Aug 25 1992) ISSN: 0021-9258 [Print] United States
• PMID: 1324931 (Publication Type: Comparative Study, Journal Article, Research Support, U.S. Gov't, P.H.S.)

Chemical References

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

Topics

• Animals
• Avian Sarcoma Viruses (genetics)
• Base Sequence
• Cell Line
• Cell Nucleus (metabolism)
• Chromosome Deletion
• Cytochrome P-450 Enzyme System (biosynthesis, genetics)
• Gene Expression Regulation, Enzymologic
• Humans
• Luciferases (genetics, 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