Androgen Responsiveness of the Murine β-Glucuronidase Gene Is Associated with Nuclease Hypersensitivity, Protein Binding, and Haplotype-Specific Sequence Diversity within Intron 9

Abstract

The tissue specificity and genetic variability of the murine β-glucuronidase (GUS) response to androgen provide useful markers for identifying elements which underlie this responsiveness. While GUS is expressed constitutively in all examined cell types, kidney epithelial cells uniquely exhibit a manyfold yet slow rise in GUS mRNA and enzyme levels when stimulated by androgens. Three major phenotypes of this androgen response have been described among inbred strains of mice: (i) a strong response in strains of the Gus^a haplotype, (ii) a reduced response in strains of the Gus^b and Gus^h haplotypes, and (iii) no response, as observed in Gus^or mice. These response variants define a cis-active element(s) which is tightly linked to the GUS structural gene. Nuclease hypersensitivity scans of kidney chromatin within and surrounding the structural gene revealed an androgen-inducible hypersensitive site in intron 9 of the gene in Gus^a but not in Gus^or mice. When a radiolabeled fragment of Gus^a DNA containing this hypersensitive site was incubated with kidney nuclear extracts and then subjected to gel electrophoresis, two shifted bands were observed whose levels were dramatically higher in extracts of androgen-treated than in those of untreated Gus^a mice. The shifted bands reflect binding of a kidney-specific factor(s) to a 57-bp region of complex dyad symmetry in Gus^a and Gus^or mice which is partially deleted in Gus^b and Gus^h mice. This binding site is located approximately 130 bp downstream of a glucocorticoid response element sequence motif which is totally deleted in [Gus]^or mice. Taken together, our results suggest that the androgen responsiveness of GUS in murine kidney epithelial cells is controlled by elements within the proximal end of intron 9 of the GUS structural gene. ^{* †}