Gc. Ibeanu et Ja. Goldstein, TRANSCRIPTIONAL REGULATION OF HUMAN CYP2C GENES - FUNCTIONAL COMPARISON OF CYP2C9 AND CYP2C18 PROMOTER REGIONS, Biochemistry, 34(25), 1995, pp. 8028-8036
The cytochrome P4502C subfamily comprises a group of constitutive micr
osomal hemoproteins which are expressed primarily in liver. In humans,
this subfamily is responsible for metabolism of a variety of therapeu
tic drugs such as warfarin, mephenytoin, omeprazole, and antiinflammat
ory drugs. In the present study, we analyzed the promotor activity of
the 5'-flanking region of two human CYP2C genes, CYP2C9 and CYP2C18. T
he ability of the 2.2-kb 5'-flanking region of the CYP2C9 gene to dire
ct expression of a luciferase reporter gene in HepG2 cells was 25 time
s greater than that of the 1.3-kb 5'-flanking region of CYP2C18. Delet
ional analysis of CYP2C9 indicated that the minimal promotor was locat
ed between the translation start site and nucleotide -155, and an HPF-
1 domain consensus sequence was identified in this region. Gel shift a
nalysis demonstrated that nuclear proteins from HepG2 cells had a high
binding affinity for a 20-bp oligonucleotide containing the HPF-1 sit
e of CYP2C9. Antiserum to rat HNF-4 supershifted this DNA-protein comp
lex, and an oligonucleotide derived from an HNF-4 motif present in the
human apolipoprotein CIII promotor competed for the supershifted comp
lex, Cotransfection with an HNF-4 expression plasmid increased transcr
iptional activity of the CYP2C9 minimal promotor (similar to 2-fold) i
n HepG2 cells and elevated activity more substantially in nonhepatic N
IH3T3 cells (26-fold) and Cos 1 cells (9-fold). A possible HPF-1 motif
was identified 661 to 641 bases upstream of the translational start s
ite of CYP2C18 which differed from the HPF-1 consensus sequence by the
substitution of three cytosines for purines at positions 4-6 and one
adenine residue at position 15. An oligonucleotide containing the CYP2
C18 HPF-1 motif bound nuclear proteins from HepG2 cells only weakly in
gel shift assays, but replacement of the three tandem cytosine residu
es in the HPF-1 site by guanines using site-directed mutagenesis cause
d the formation of a complex whose mobility was supershifted by anti-H
NF4. Similarly, mutation of the three guanines in the CYP2C9 HPF-1 sit
e to cytosines prevented the formation of the specific DNA-protein com
plex seen with this motif. However, cotransfection with an HNF-4 expre
ssion plasmid did not increase transcriptional activity of CYP2C18 pro
motor constructs containing the original CYP2C18 HPF-1 motif or the mu
tated motif containing guanine residues in any of the cell lines teste
d. We conclude that the HPF-1 site is an important cis-acting element
directing hepatic expression of the CYP2C9 promoter but does not contr
ibute to the weak transcriptional activity of the 1.3-kb upstream regi
on of CYP2C18.