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Substrate specificity, gene structure, and tissue-specific distribution of multiple human 3 alpha-hydroxysteroid
1Department of Pediatrics, Cornell University Medical College, New York, New York 10021, USA.
The Journal of Biological Chemistry
|August 25, 1995
Summary
Researchers identified two human 3 alpha-hydroxysteroid dehydrogenase (HSD3B) enzymes, type I and type II, with distinct substrate affinities and tissue distributions. Their gene structures and regulatory elements were also elucidated.
Area of Science:
- Biochemistry
- Molecular Biology
- Genetics
Background:
- Human 3 alpha-hydroxysteroid dehydrogenases (HSD3B) play a role in steroid metabolism.
- Previous studies identified human cDNAs encoding HSD3B enzymes.
Purpose of the Study:
- To express and characterize two novel human HSD3B enzymes.
- To determine the tissue-specific expression and gene structure of these enzymes.
Main Methods:
- Functional expression of human cDNAs in Escherichia coli.
- Enzyme activity assays for substrate interconversion.
- Reverse transcription polymerase chain reaction (RT-PCR) for tissue distribution analysis.
- Genomic clone analysis to determine gene structure.
Main Results:
- Two functionally active HSD3B enzymes, type I and type II, were successfully expressed.
- Type I enzyme exhibits high affinity for dihydrotestosterone; type II shows low affinity.
- Type I HSD3B mRNA is liver-specific; type II mRNA is found in brain, kidney, liver, lung, placenta, and testis.
- Both genes consist of 9 exons with identical sizes and boundaries, spanning ~20 kbp (type I) and ~16 kbp (type II).
- Type I gene has a TATA box upstream of multiple transcription start sites; type II gene has tandem AP2 sequences near a single start site.
Conclusions:
- The characterization of type I and type II HSD3B enzymes provides insight into human steroid metabolism.
- Distinct expression patterns and gene regulation suggest specialized roles for each enzyme in different tissues.