Charbonneau A, The V L
Oncology and Molecular Endocrinology Research Center, Laval University Medical Center (CHUL), 2705 Laurier Boulevard, Quebec, G1V 4G2, Canada.
Biochim Biophys Acta. 2001 Jan 26;1517(2):228-35. doi: 10.1016/s0167-4781(00)00278-5.
The enzyme 5beta-reductase catalyzes the reduction of the 4-ene of 3-ketosteroids, converting them into 5beta-dihydro-3-ketosteroids and, thus, could be involved in the metabolism of 4-cholestene-3-one, progesterone, 17-hydroxyprogesterone, aldosterone, corticosterone, cortisol, 4-androstenedione, and testosterone. In this study, we report the genomic structure of a human 5beta-reductase gene, its tissue distribution, the characterization of an intronless pseudogene and the substrate selectivity of the enzyme. The gene coding for the active 5beta-reductase contains nine exons like most members of the aldo-keto reductase family, but the sequence covered by the gene, more than 42 kb, is much longer than the sequence of other members of this family. There are many large introns, especially introns 3, 4 and 7 that span approx. 7 kb, and intron 1 that contains more than 10 kb. Northern blot analysis showed three band sizes of 1.3, 2.2 and 2.7 kb. The 1.3 and 2.7 kb bands are highly expressed in the liver while weaker 2.2 and 1.3 kb bands have been observed in the testis and colon, respectively. We also identified an intronless gene having 86% homology with the 5beta-reductase cDNA sequence. Since its sequence contains many stop codons, this gene is most probably a pseudogene. To determine more precisely the substrate selectivity of the enzyme, we established a stable cell line expressing human 5beta-reductase in transformed embryonic kidney (HEK-293) cells. The transfected cells efficiently catalyze the transformation of progesterone, androstenedione, 17alpha-hydroxyprogesterone and testosterone. However, they catalyze much less efficiently the transformation of compounds containing an 11beta-hydroxy group, such as aldosterone, corticosterone and cortisol. In addition to its role in cholesterol catabolism, it is well recognized that 5beta-reductase inactivates active androgens. Indeed, 5beta-dihydrotestosterone (5beta-DHT), the product of the reduction of testosterone by 5beta-reductase, is not active while its 5-isomer (DHT) is the most potent natural androgen. Recent findings show that 5beta-pregnanes are active ligands in the induction of CYP3A through the orphan receptor hPAR. Our results thus open an opportunity for studying the new role of 5beta-reductase in the formation of a new type of active steroids.
5β-还原酶可催化3-酮甾体4-烯的还原反应，将其转化为5β-二氢-3-酮甾体，因此可能参与4-胆甾烯-3-酮、孕酮、17α-羟孕酮、醛固酮、皮质酮、皮质醇、4-雄烯二酮和睾酮的代谢。在本研究中，我们报道了人类5β-还原酶基因的基因组结构、其组织分布、一个无内含子假基因的特征以及该酶的底物选择性。编码活性5β-还原酶的基因与醛糖酮还原酶家族的大多数成员一样含有9个外显子，但该基因覆盖的序列超过42 kb，比该家族其他成员的序列长得多。有许多大的内含子，特别是跨越约7 kb的内含子3、4和7，以及包含超过10 kb的内含子1。Northern印迹分析显示有1.3、2.2和2.7 kb三种条带大小。1.3和2.7 kb的条带在肝脏中高度表达，而在睾丸和结肠中分别观察到较弱的2.2和1.3 kb条带。我们还鉴定出一个与5β-还原酶cDNA序列有86%同源性的无内含子基因。由于其序列包含许多终止密码子，该基因很可能是一个假基因。为了更精确地确定该酶的底物选择性，我们在转化的胚胎肾（HEK-293）细胞中建立了一个表达人类5β-还原酶的稳定细胞系。转染的细胞能有效地催化孕酮、雄烯二酮、17α-羟孕酮和睾酮的转化。然而，它们对含有11β-羟基的化合物，如醛固酮、皮质酮和皮质醇的转化效率要低得多。除了在胆固醇分解代谢中的作用外，人们还充分认识到5β-还原酶可使活性雄激素失活。实际上，5β-还原酶还原睾酮产生的产物5β-双氢睾酮（5β-DHT）无活性，而其5α-异构体（DHT）是最有效的天然雄激素。最近的研究发现表明，5β-孕烷是通过孤儿受体hPAR诱导CYP3A的活性配体。因此，我们的结果为研究5β-还原酶在新型活性甾体形成中的新作用提供了机会。
