Identification of essential subelements in the hHSD17B1 enhancer: Difference in function of the enhancer and that of the hHSD17BP1 analog is due to-480C and-486G

The function of the gene encoding human 17 beta-hydroxysteroid dehydrogenas e (17HSD) type 1, the hHSD17B1 gene, is regulated by a cell-specific enhanc er at position -662 to -392. The adjacent hHSD17BP1 gene, whose function is not known, contains an analogous region in its 5'-flanking region. The ide ntity between the hHSD17B1 enhancer and the hHSD17BP1 equivalent is as high as 98%, i.e. they differ by only five nucleotides. Results from reporter g ene analyses showed that the hHSD17BP1 analog, a pseudoenhancer, has only 1 0% the activity of the hHSD17B1 enhancer. Furthermore, the results indicate that the reduced function of the pseudoenhancer is a consequence of the pr esence of G and A at positions -480 and -486, whereas the hHSD17B1 enhancer contains -480C and -486G. In addition, three protected areas were localize d to regions -495/-485 (FP1), -544/-528 (FP2), and -589/-571 (FP3) in deoxy ribonuclease I footprinting analysis of the hHSD17B1 enhancer. Replacement of the footprinted regions with a nonsense sequence demonstrated that the F P2 region is the most critical for enhancer activity. Mutations of FP2 or a short palindromic region within it led to almost complete abolishment of e nhancer activity. We have identified several subelements that are essential for appropriate function of the hHSD17B1 enhancer. The results also show t hat the hHSD17B1 and hHSD17BP1 genes operate differently despite the high h omology between them.