Regulation of Gene Expression in Steroid Hormone Biosynthesis 
In a related effort, we are trying to define the 
potential role of the steroidogenic enzymes in hy- 
pertension. Extremely prevalent, hypertension 
aff^ects approximately 20 percent of the adult 
population. As such, it is a major risk factor for 
heart attacks and strokes, the leading causes of 
-death in developed nations. Although the under- 
lying defect is unknown in most cases, family 
studies indicate a significant genetic component. 
Furthermore, in certain animal models with a 
more carefully defined genetic basis, the inheri- 
tance of hypertension has been clearly linked to 
differences in activity of 11/3-OHase, one of the 
steroidogenic enzymes described above. We are 
investigating the function of this protein in more 
detail. 
Initial studies implicated a single lljS-OHase 
protein in the biosynthesis of both mineralocorti- 
coids and glucocorticoids. We now have defini- 
tive evidence that the mouse has two 1 1 i8-OHase 
genes, one of which is expressed at significantly 
higher levels than the other. By analogy to the rat, 
for which biochemical characterization has been 
more extensive, it is likely that the gene ex- 
pressed at higher levels participates in the forma- 
tion of glucocorticoids in the inner zone, 
whereas the other gene, encoding aldosterone 
synthetase, produces mineralocorticoids in the 
outer zone. 
Although the two genes are very similar in their 
coding regions, which specify the proteins' com- 
position, they differ markedly in their 5'-flanking 
regions, which regulate the proteins' production. 
We are now seeking to define the precise role of 
these two genes in the production of steroid hor- 
mones. In particular, we will compare and con- 
trast the promoter regions of the two genes to 
identify both shared elements and unique ele- 
ments responsible for zone-specific expression. 
Based on our preliminary results, we plan to 
use these promoter regions in transgenic mice to 
target gene expression specifically to either the 
outer or inner cortical zones. Initially we are us- 
ing the two promoters to direct the expression of 
renin, a gene previously shown to cause genetic 
hypertension when expressed in multiple tissues 
of transgenic animals. If successful, these experi- 
ments will validate the zone-specific expression 
of the two promoter regions and will establish 
that adrenal expression of renin is relevant to the 
hypertensive state. 
Next, we want to express the aldosterone syn- 
thetase gene in the inner, glucocorticoid-produc- 
ing zone. As discussed above, this gene normally 
produces mineralocorticoids in the outer zone. 
We have prepared a hybrid gene with the inner- 
zone-specific promoter driving expression of the 
aldosterone synthetase gene. We anticipate that 
this hybrid gene will synthesize large amounts of 
mineralocorticoids, thus creating a genetic form 
of hypertension. Moreover, treatment with glu- 
cocorticoids, which will suppress expression of 
the hybrid gene in the inner zone, should allevi- 
ate the hypertension. This model may therefore 
mimic a subset of human patients with glucocor- 
ticoid-responsive hypertension. 
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