FUNCTIONAL-CHARACTERIZATION OF THE HUMAN CYP1A1 NEGATIVE REGULATORY ELEMENT - MODULATION OF AH RECEPTOR-MEDIATED TRANSCRIPTIONAL ACTIVITY

The mechanisms that underly the regulation of human CYP1A1 have merite d considerable attention because of their association both with toxic outcomes and the etiology of several cancers. Previous work conducted in this laboratory has identified a negative regulatory element (NRE) in the 5' region of this gene that appeared to modulate CYP1A1 transcr iptional activity, This NRE is present in two functional copies, a hig h affinity 21-bp palindrome centered at position -784, and an addition al element found within a GC-rich region between position -728 and -55 8. In this report, the regulatory function of the NREs in the context of the CYP1A1 promoter was evaluated. This was accomplished by substit uting mutated elements for the corresponding wild-type element in a ve ctor that contained human CYP1A1 sequences positions -1140 to + 59 dir ecting the transcription of the chloramphenicol acetyltransferase repo rter gene. Expression vectors containing specific mutations in each or both NREs were characterized. We show that eliminating the binding of the CYP1A1 repressor protein to one or both repressor motifs results in a significant 2- to 3-fold increase in the inducibility of CYP1A1 p romoter activity. Although mutation of both sites appeared to result i n an increase in inducibility over that observed with only one site mu tated, the effect was not additive. Such aberrant transcriptional acti vity correlates with the highly inducible aryl hydrocarbon hydroxylase phenotype that is a reported marker for individuals predisposed to lu ng cancer. Mutation of the NRE, or more likely, the cognate repressor protein(s), may provide a genetic basis for this phenotype.