Nokelainen P, Peltoketo H, Vihko R, Vihko P
Biocenter Oulu, Finland.
Mol Endocrinol. 1998 Jul;12(7):1048-59. doi: 10.1210/mend.12.7.0134.
17 beta-Hydroxysteroid dehydrogenases/17-ketosteroid reductases (17HSDs) modulate the biological activity of certain estrogens and androgens by catalyzing reductase or dehydrogenase reactions between 17-keto- and 17 beta-hydroxysteroids. In the present study, we demonstrate expression cloning of a novel type of 17HSD, chronologically named 17HSD type 7, from the HC11 cell line derived from mouse mammary gland. The cloned cDNA, 1.7 kb in size, encodes a protein of 334 amino acids with a calculated molecular mass of 37,317 Da. The primary structure contains segments characteristic of enzymes belonging to the short-chain dehydrogenase/reductase superfamily. Strikingly, mouse 17HSD type 7 (m17HSD7) shows 89% identity with a recently cloned rat protein called PRL receptor-associated protein (PRAP). The function of PRAP has not yet been demonstrated. The enzymatic characteristics of m17HSD7 and RT-PCR-cloned rat PRAP (rPRAP) were analyzed in cultured HEK-293 cells, where both of the enzymes efficiently catalyzed conversion of estrone (E1) to estradiol (E2). With other substrates tested no detectable 17HSD or 20 alpha-hydroxysteroid dehydrogenase activities were found. Kinetic parameters for m17HSD7 further indicate that E1 is a preferred substrate for this enzyme. Relative catalytic efficiencies (Vmax/K(m) values) for E1 and E2 are 244 and 48, respectively. As it is the case with rPRAP, m17HSD7 is most abundantly expressed in the ovaries of pregnant animals. Further studies show that the rat enzyme is primarily expressed in the middle and second half of pregnancy, in parallel with E2 secretion from the corpus luteum. The mRNA for m17HSD7 is also apparent in the placenta, and a slight signal for m17HSD7 is found in the ovaries of adult nonpregnant mice, in the mammary gland, liver, kidney, and testis. Altogether, because of their similar primary structures, enzymatic characteristics, and the tissue distribution of m17HSD7 and rPRAP, we suggest that rPRAP is rat 17HSD type 7. Furthermore, the results indicate that 17HSD7 is an enzyme of E2 biosynthesis, which is predominantly expressed in the corpus luteum of the pregnant animal.
17β-羟基类固醇脱氢酶/17-酮类固醇还原酶（17HSDs）通过催化17-酮类固醇和17β-羟基类固醇之间的还原酶或脱氢酶反应来调节某些雌激素和雄激素的生物活性。在本研究中，我们从源自小鼠乳腺的HC11细胞系中展示了一种新型17HSD（按时间顺序命名为17HSD 7型）的表达克隆。克隆的cDNA大小为1.7 kb，编码一个334个氨基酸的蛋白质，计算分子量为37317 Da。其一级结构包含属于短链脱氢酶/还原酶超家族的酶的特征性片段。引人注目的是，小鼠17HSD 7型（m17HSD7）与最近克隆的一种名为催乳素受体相关蛋白（PRAP）的大鼠蛋白具有89%的同一性。PRAP的功能尚未得到证实。在培养的HEK-293细胞中分析了m17HSD7和RT-PCR克隆的大鼠PRAP（rPRAP）的酶学特性，这两种酶都能有效地催化雌酮（E1）向雌二醇（E2）的转化。对于其他测试的底物，未发现可检测到的17HSD或20α-羟基类固醇脱氢酶活性。m17HSD7的动力学参数进一步表明E1是该酶的首选底物。E1和E2的相对催化效率（Vmax/K(m)值）分别为244和48。与rPRAP情况相同，m17HSD7在怀孕动物的卵巢中表达最为丰富。进一步的研究表明，大鼠的这种酶主要在妊娠中期和后半期表达，与黄体分泌E2同步。m17HSD7的mRNA在胎盘中也很明显，在成年未孕小鼠的卵巢、乳腺、肝脏、肾脏和睾丸中发现了m17HSD7的微弱信号。总之，由于m17HSD7和rPRAP具有相似的一级结构、酶学特性和组织分布，我们认为rPRAP是大鼠17HSD 7型。此外，结果表明17HSD7是一种E2生物合成酶，主要在怀孕动物的黄体中表达。
