Human 3alpha-hydroxysteroid dehydrogenase isoforms (AKR1C1-AKR1C4) of the aldo-keto reductase superfamily: functional plasticity and tissue distribution reveals roles in the inactivation and formation of male and female sex hormones.
Human 3alpha-hydroxysteroid dehydrogenase isoforms (AKR1C1-AKR1C4) of the aldo-keto reductase superfamily: functional plasticity and tissue distribution reveals roles in the inactivation and formation of male and female sex hormones.
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发表时间：
2000
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通讯作者：
T. Penning;M. Burczynski;J. Jez;C. Hung;H. K. Lin;H. Ma;M. Moore;N. Palackal;K. Ratnam
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作者：
T. Penning;M. Burczynski;J. Jez;C. Hung;H. K. Lin;H. Ma;M. Moore;N. Palackal;K. Ratnam
测定了4种均质重组人3 α -羟基类固醇脱氢酶（3α - hsd）醛酮还原酶（AKR）超家族同工异构体的动力学参数、类固醇底物特异性和反应产物的特性。这些酶分别对应于1 3alpha-HSD型（AKR1C4）、2 3alpha(17beta)-HSD型（AKR1C3）、3 3alpha-HSD型（AKR1C2）和20alpha(3alpha)-HSD型（AKR1C1），并且具有至少84%的氨基酸序列一致性。所有酶均作为NAD(P)(H)依赖的3-、17-和20-酮类固醇还原酶以及3-、17-和20-羟类固醇氧化酶起作用。这些异构体的功能可塑性突出了它们调节活性雄激素、雌激素和黄体酮水平的能力。其中，AKR1C4的催化效率最高，其对底物的k(cat)/ k(m)值是其他同工异构体的10-30倍。在还原方向上，所有同工型均失活5 α -二氢睾酮（17 β -羟基-5 α -雄酮-3-one； 5 α - dht），生成5 α -雄酮-3 α，17 β -二醇（3 α -雄烷二醇）。然而，只有AKR1C3降低了δ(4)-雄烯-3,17-二酮以产生大量的睾酮。所有同种异构体将雌酮还原为17 -雌二醇，孕酮还原为20-羟基孕酮-4-烯-3,20-二酮（20 -羟基孕酮）。在氧化方向上，只有AKR1C2将3 α -雄甾二醇转化为活性激素5 α - dht。AKR1C3和AKR1C4氧化睾酮生成Delta(4)-雄烯-3,17-二酮。所有同种异构体都将17 -雌二醇氧化为雌二醇，将20 -羟孕酮氧化为孕酮。这些AKR1C酶的离散组织分布使用异构体特异性逆转录- pcr观察。AKR1C4实际上是肝脏特异性的，它的高k(cat)/ k(m)允许这种酶强有力地形成5 α /5 β -四氢类固醇。AKR1C3在前列腺和乳腺中最为突出。AKR1C3能够将睾酮与δ(4)-雄烯-3,17-二酮相互转化，但使5 - dht失活，这与该酶从前列腺中清除活性雄激素的能力是一致的。在乳腺中，AKR1C3将δ(4)-雄烯-3,17-二酮转化为睾酮（一种可芳香化为17-雌二醇的底物），雌酮转化为17-雌二醇，孕酮转化为20 -羟孕酮，这种协同还原活性可能产生促雌激素状态。AKR1C3也是子宫中的主要形式，负责3 - α -雄甾二醇的合成，后者被认为是一种分娩激素。大脑中能够合成抗焦虑类固醇的主要亚型是AKR1C1和AKR1C2。这些研究与大鼠的研究形成鲜明对比，在大鼠中，只有一个具有3 α -羟基类固醇定位和立体特异性的AKR存在。
The kinetic parameters, steroid substrate specificity and identities of reaction products were determined for four homogeneous recombinant human 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) isoforms of the aldo-keto reductase (AKR) superfamily. The enzymes correspond to type 1 3alpha-HSD (AKR1C4), type 2 3alpha(17beta)-HSD (AKR1C3), type 3 3alpha-HSD (AKR1C2) and 20alpha(3alpha)-HSD (AKR1C1), and share at least 84% amino acid sequence identity. All enzymes acted as NAD(P)(H)-dependent 3-, 17- and 20-ketosteroid reductases and as 3alpha-, 17beta- and 20alpha-hydroxysteroid oxidases. The functional plasticity of these isoforms highlights their ability to modulate the levels of active androgens, oestrogens and progestins. Salient features were that AKR1C4 was the most catalytically efficient, with k(cat)/K(m) values for substrates that exceeded those obtained with other isoforms by 10-30-fold. In the reduction direction, all isoforms inactivated 5alpha-dihydrotestosterone (17beta-hydroxy-5alpha-androstan-3-one; 5alpha-DHT) to yield 5alpha-androstane-3alpha,17beta-diol (3alpha-androstanediol). However, only AKR1C3 reduced Delta(4)-androstene-3,17-dione to produce significant amounts of testosterone. All isoforms reduced oestrone to 17beta-oestradiol, and progesterone to 20alpha-hydroxy-pregn-4-ene-3,20-dione (20alpha-hydroxyprogesterone). In the oxidation direction, only AKR1C2 converted 3alpha-androstanediol to the active hormone 5alpha-DHT. AKR1C3 and AKR1C4 oxidized testosterone to Delta(4)-androstene-3,17-dione. All isoforms oxidized 17beta-oestradiol to oestrone, and 20alpha-hydroxyprogesterone to progesterone. Discrete tissue distribution of these AKR1C enzymes was observed using isoform-specific reverse transcriptase-PCR. AKR1C4 was virtually liver-specific and its high k(cat)/K(m) allows this enzyme to form 5alpha/5beta-tetrahydrosteroids robustly. AKR1C3 was most prominent in the prostate and mammary glands. The ability of AKR1C3 to interconvert testosterone with Delta(4)-androstene-3,17-dione, but to inactivate 5alpha-DHT, is consistent with this enzyme eliminating active androgens from the prostate. In the mammary gland, AKR1C3 will convert Delta(4)-androstene-3,17-dione to testosterone (a substrate aromatizable to 17beta-oestradiol), oestrone to 17beta-oestradiol, and progesterone to 20alpha-hydroxyprogesterone, and this concerted reductive activity may yield a pro-oesterogenic state. AKR1C3 is also the dominant form in the uterus and is responsible for the synthesis of 3alpha-androstanediol which has been implicated as a parturition hormone. The major isoforms in the brain, capable of synthesizing anxiolytic steroids, are AKR1C1 and AKR1C2. These studies are in stark contrast with those in rat where only a single AKR with positional- and stereo-specificity for 3alpha-hydroxysteroids exists.