Overlapping cis-acting elements located in the first intron of the gene for type I 3 beta-hydroxysteroid dehydrogenase modulate its transcriptional activity.

Abstract

High levels of expression for the gene encoding human type I 3 beta-hydroxysteroid dehydrogenase (3 beta-HSDI) have been detected in placenta and skin but not in adrenals, which, however, express high levels of type II 3 beta-HSD. In this study, we addressed the issue of whether the differential pattern of cell-specific expression for type I 3 beta-HSD can be explained by the differential utilization of cis-acting regulatory elements present in the 3 beta-HSDI gene regulatory sequences. Deletion analyses indicated that removal of intron 1 strongly impaired the transcriptional activity directed by the 3 beta-HSDI basal promoter. Consequently, we focused our attention to the characterization of the 128 base pair first intronic sequence from the 3 beta-HSDI gene. A single protected region, designated the 3 beta I-A element, was identified by DNase I footprinting. Gel mobility shift assays indicated that at least four nuclear proteins with distinct biochemical and binding properties possess the ability to bind the 3 beta I-A element to produce four DNA-protein complexes (R1 to R4). However, the one producing R1, a 37-kilodalton protein that has been found in both human choriocarcinoma JEG-3 and adrenal cortex adenocarcinoma SW13 cells, as well as in all tested tissue culture cells, clearly accounts for the major 3 beta I-A-binding species. Site-directed mutagenesis provided the evidence that the 3 beta I-A element acts positively on the 3 beta-HSD-I gene promoter-mediated transcriptional activity upon transient transfection of both JEG-3 and SW13 cells. No homology has been found between the 3 beta I-A element and target sequences for other known transcription factors. In addition, of the four proteins binding the 3 beta I-A element, that producing R2 was identified as the positive transcription factor Sp1, whereas the identity of the remaining factors is still unknown. This is consistent with the presence of an Sp1 motif overlapping the 3 beta I-A element in intron 1, therefore pointing toward an important function played by this particular region in 3 beta-HSDI basal, but not cell-specific, gene expression.

New 19 bp deletion polymorphism in intron‐1 of dihydrofolate reductase (DHFR): A risk factor for spina bifida acting in mothers during pregnancy?

“…Expression of the TIMP‐1 gene involves cis ‐elements in intron‐1 [Clark et al, 1997]. Cis ‐elements in the first intron of type‐I 3‐beta‐hydroxysteroid dehydrogenase modulate the transcriptional activity [Guerin et al, 1995].…”

“…We recently discovered a polymorphic 19 bp deletion within intron‐1 of DHFR. Since, (1) intron‐1 is well known to be a site of regulatory sequences for some genes [Guerin et al, 1995; Clark et al, 1997], (2) an intron‐1 regulatory sequence has been documented for human [Kaneda et al, 1992; Takayanagi et al, 1992] and mouse [Ke et al, 1996] thymidylate synthase ( TYMS ), a gene closely related to DHFR, (3) the mouse dhfr gene contains an intron‐1 regulatory sequence [Farnham and Means, 1990], and (4) the 19 bp deletion of human DHFR removes a potential Sp1 transcription factor binding site, we hypothesized that this new polymorphism might function as a teratogenic allele in SB mothers, acting to decrease the supply of reduced folate to the fetus. We, therefore, tested the possibility that the fraction of deletion allele homozygotes might be increased in SB mothers compared with controls.…”

AP-2γ and the Homeodomain Protein Distal-less 3 Are Required for Placental-specific Expression of the Murine 3β-Hydroxysteroid Dehydrogenase VI Gene, Hsd3b6

“…3␤-HSD I is the major or only isoform expressed in gonads and adrenal glands, whereas 3␤-HSD VI is the only isoform expressed in giant trophoblast cells during mid-pregnancy (3). The orthologous isoforms in human are human 3␤-HSD II, the isoform expressed in the gonads and adrenal glands (6), and human 3␤-HSD I (7,8), the only isoform expressed in placenta throughout pregnancy. The expression of human 3␤-HSD I in placenta is essential for placental progesterone biosynthesis and, thus, is vital for maintenance of pregnancy (9).…”

“…This latter step is brought about by distinct tissue-specific isoforms of 3␤-HSD. Previous studies designed to identify placental-specific regulatory elements in the human placental-specific 3␤-HSD promoter were unsuccessful (8). Moreover, identity of transcription factors essential for placental-specific expression of P450scc remains to be resolved (11).…”

The effect of non-coding DNA variations on P53 and cMYC competitive inhibition at cis-overlapping motifs

“…Cis-overlapping motifs (COMs) are overlapping conserved binding sequences of multiple TFs that are located on the same DNA strand (7)(8)(9). This feature suggests a mechanism of gene regulation by competitive binding and inhibition, where binding of one factor occurs at the cost of another factor.…”