17 beta-Hydroxysteroid dehydrogenases (17HSDs) are enzymes catalyzing the conversion between 17 beta-hydroxy- and 17-ketosteroids. Both estrogens and androgens possess their highest activity in the 17 beta-hydroxy form, and the enzymes, therefore, regulate the biological activity of sex hormones. In this study, we have characterized the complementary DNA (cDNA) for rat 17HSD type 2. The cDNA encodes a protein with a predicted mol wt of 42,010 Da. The protein has 77% similarity and 62% identity with the human 17HSD type 2 enzyme. Furthermore, the hydropathicity profiles of the enzymes are very similar. The two isozymes contain a putative transmembrane region close to the N-terminus. However, the rat isozyme lacks the two lysine-rich amino acid cluster present at the N- and C-terminals of human 17HSD type 2. The tissue distribution of the rat 17HSD type 1 and type 2 enzymes is very similar to that of the human enzymes. The highest expression of 17HSD type 2 was detected in the placenta. In addition, a 1.5-kilobase messenger RNA for the enzyme was detected in the small intestine, liver, and kidney of both sexes. The two messenger RNAs for rat 17HSD type 1 (1.4 and 1.7 kilobases) were highly expressed only in the ovary, and at very low concentrations in the kidney of both sexes. Transiently expressed rat 17HSD type 2 showed oxidative activity almost exclusively in cultured human embryonic kidney 293 cells, converting estradiol into estrone and testosterone into androstenedione, whereas the opposite was observed for the rat type 1 enzyme. The data suggest that similarly to the corresponding human isoforms, rat 17HSD type 2 is mostly involved in the oxidation of 17 beta-hydroxysteroids into their relatively inactive keto derivative in peripheral tissues, whereas rat 17HSD type 1 is mainly involved in the glandular biosynthesis of estradiol.

In the present study, expressions of 17beta-hydroxysteroid dehydrogenase (17HSD) types 1, 2, and 3, 5alpha-reductase type 2 and human androgen receptor mRNAs were determined in 12 benign prostatic hyperplasia and 17 prostatic carcinoma specimens. 17HSD type 2 was found to be the principle isoenzyme expressed in the prostate. Significantly higher expressions of 17HSD type 2 and 5alpha-reductase type 2 were detected in benign prostatic hyperplasia compared with the carcinoma specimens. Expression of the androgen receptor in the 2 groups was not significantly different. 17HSD type 3 mRNA was not detected in any of the specimens investigated. Only low constructive expression of the 2.3 kb mRNA of 17HSD type 1 was seen. Immunohistochemical analysis indicated that this did not lead to significant enzyme expression, only faint staining for the enzyme protein being detected, mainly in uroepithelial cells. No significant correlation was found between any of the mRNAs analysed, but the data on 5alpha-reductase type 2 mRNA support the presence of an increased proportion of 5alpha-dihydrotesterone in the hyperplastic prostate. In cultured PC-3 prostatic cancer cells and in the transiently transfected human embryonic kidney 293 cells, 17HSD type 2 was found exclusively to convert 5alpha-dihydrotestosterone and testosterone into the less potent 17-keto compounds 5alpha-androstanedione and 4-androstenedione, respectively. We suggest that the 17HSD type 2 isoenzyme plays a part in the metabolic pathway, resulting in the inactivation of testosterone and 5alpha-dihydrotestosterone locally in the prostate. The enzyme expressed in the prostate could, therefore, protect cells from excessive androgen action.

In the present study, expressions of 17fj-hydroxysteroid dehydrogenase (I 7HSD) types I, 2 and 3, 5a-reductase type 2 and human androgen receptor mRNAs were determined in 12 benign prostatic hyperplasia and I 7 prostatic carcinoma specimens. I7HSD type 2 was found to be the principal isoenzyme expressed in the prostate. Significantly higher expressions of I7HSD type 2 and 5a-reductase type 2 were detected in benign prostatic hyperplasia compared with the carcinoma specimens. Expression of the androgen receptor in the 2 groups was not significantly different. I7HSD type 3 mRNA was not detected in any of the specimens investigated. Only low constitutive expression of the 2.3 kb mRNA of I7HSD type I was seen. Immunohistochemical analyses indicated that this did not lead to significant enzyme expression, only faint staining for the enzyme protein being detected, mainly in uroepithelial cells. No significant correlation was found between any of the mRNAs analyzed, but the data on Sa-reductase type 2 mRNA support the presence of an increased proportion of Sa-dihydrotesterone in the hyperplastic prostate. In cultured PC-3 prostatic cancer cells and in transiently transfected human embryonic kidney 293 cells, I7HSD type 2 was found exclusively to convert 5a-dihydrotestosterone and testosterone into the less potent 17-keto compounds Sa-androstanedione and 4-androstenedione, respectively. We suggest that the I7HSD type 2 isoenzyme plays a part in the metabolic pathway, resulting in the inactivation of testosterone and 5a-dihydrotestosterone locally in the prostate. The enzyme expressed in the prostate could, therefore, protect cells from excessive androgen action.b 1996 Wiley-Liss. Inc.Local androgen metabolism has been suggested to play a central role in regulating androgen action in the human prostate. Detailed understanding of the intra-prostatic metabolism of androgens in prostatic growth disorders (benign prostatic hyperplasia and carcinoma) is therefore important. In the prostate, testosterone (T) is convertcd into a more potent form, Sa-dihydrotestosterone (DHT), by 5a-reductase, and this is thought to be a crucial feature of androgen action in the prostate (Enderle-Schmitt et al., 1986). In addition to Sareductase, the activities of several other steroid-metabolizing enzymes are evident in the prostate, including those of 17P-hydroxysteroid dehydrogenase (17HSD) (Abalain et al., 1989). 17HSDs catalyze interconversion between the active 17P-hydroxysteroids, T and DHT, and the less activc 17-ketosteroids, Sa-androstanedione (SaA-dione) and 4-androstenedione (A-dione). The 17HSD enzymcs may, thercfore, play a significant role in regulating biological androgenic activity in the prostate.The primary structures of 3 human 17HSD isoenzymes have been characterized (Peltoketo er al., 1988; Wu et al., Geissler et ul., 1994). However, there is only fragmentary information on the 17HSD isoenzymes expressed in the human prostate (Pylkkiincn et al., 1994). It is not clear whether 17p-oxidation or -reduction of androgens is pr...

In the present study, we evaluated the expression and regulation of 17beta-hydroxysteroid dehydrogenase (17HSD) type 1 and type 2, cytochrome P450 aromatase (P450arom), and 20alpha-hydroxysteroid dehydrogenase (20HSD) in mature and pregnant rats. Immunohistochemical analysis of rat 17HSD type 1 showed that the enzyme is exclusively expressed in the granulosa cells of developing, healthy, primary, secondary, and tertiary follicles at all stages of the estrous cycle and pregnancy, and is not detected in the corpora lutea. The data showed that the amount of the enzyme expressed in the follicle increases as follicular maturation progresses and is highest in tertiary and Graafian follicles. However, Northern blot analysis of total RNA from whole ovaries showed a rather constitutive expression of the 17HSD type 1 enzyme. It is evident that compared with P450arom, 17HSD type 1 is more widely expressed in the follicles during the various maturational stages of folliculogenesis. Hence, the data indicate distinct localization, expression, and regulation patterns for 17HSD type 1 and P450arom during the rat estrous cycle and pregnancy. Furthermore, compared with the two estradiol biosynthetic enzymes, a different expression pattern was detected for 20HSD messenger RNA. During the estrous cycle the enzyme was detected in the ovaries throughout the cycle, and in the ovaries of pregnant animals the enzyme showed an expression pattern the opposite of that observed for P450arom. Rat 17HSD type 2, not detected in the ovaries, was constitutively expressed in both female and male liver and small intestine in 21-day-old fetuses up to 6-week-old mature animals. Similarly, in these tissues the enzyme was constitutively expressed in normal cycling and pregnant animals, but it showed increasing expression in the placenta as pregnancy advanced. The relatively constitutive expression of the enzyme at all physiological stages of the animals suggests a general role for the enzyme in the inactivation of circulating sex steroids.

In the present study, we evaluated the expression and regulation of 17beta-hydroxysteroid dehydrogenase (17HSD) type 1 and type 2, cytochrome P450 aromatase (P450arom), and 20alpha-hydroxysteroid dehydrogenase (20HSD) in mature and pregnant rats. Immunohistochemical analysis of rat 17HSD type 1 showed that the enzyme is exclusively expressed in the granulosa cells of developing, healthy, primary, secondary, and tertiary follicles at all stages of the estrous cycle and pregnancy, and is not detected in the corpora lutea. The data showed that the amount of the enzyme expressed in the follicle increases as follicular maturation progresses and is highest in tertiary and Graafian follicles. However, Northern blot analysis of total RNA from whole ovaries showed a rather constitutive expression of the 17HSD type 1 enzyme. It is evident that compared with P450arom, 17HSD type 1 is more widely expressed in the follicles during the various maturational stages of folliculogenesis. Hence, the data indicate distinct localization, expression, and regulation patterns for 17HSD type 1 and P450arom during the rat estrous cycle and pregnancy. Furthermore, compared with the two estradiol biosynthetic enzymes, a different expression pattern was detected for 20HSD messenger RNA. During the estrous cycle the enzyme was detected in the ovaries throughout the cycle, and in the ovaries of pregnant animals the enzyme showed an expression pattern the opposite of that observed for P450arom. Rat 17HSD type 2, not detected in the ovaries, was constitutively expressed in both female and male liver and small intestine in 21-day-old fetuses up to 6-week-old mature animals. Similarly, in these tissues the enzyme was constitutively expressed in normal cycling and pregnant animals, but it showed increasing expression in the placenta as pregnancy advanced. The relatively constitutive expression of the enzyme at all physiological stages of the animals suggests a general role for the enzyme in the inactivation of circulating sex steroids.

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17 beta-Hydroxysteroid dehydrogenases (17HSDs) are enzymes catalyzing the conversion between 17 beta-hydroxy- and 17-ketosteroids. Both estrogens and androgens possess their highest activity in the 17 beta-hydroxy form, and the enzymes, therefore, regulate the biological activity of sex hormones. In this study, we have characterized the complementary DNA (cDNA) for rat 17HSD type 2. The cDNA encodes a protein with a predicted mol wt of 42,010 Da. The protein has 77% similarity and 62% identity with the human 17HSD type 2 enzyme. Furthermore, the hydropathicity profiles of the enzymes are very similar. The two isozymes contain a putative transmembrane region close to the N-terminus. However, the rat isozyme lacks the two lysine-rich amino acid cluster present at the N- and C-terminals of human 17HSD type 2. The tissue distribution of the rat 17HSD type 1 and type 2 enzymes is very similar to that of the human enzymes. The highest expression of 17HSD type 2 was detected in the placenta. In addition, a 1.5-kilobase messenger RNA for the enzyme was detected in the small intestine, liver, and kidney of both sexes. The two messenger RNAs for rat 17HSD type 1 (1.4 and 1.7 kilobases) were highly expressed only in the ovary, and at very low concentrations in the kidney of both sexes. Transiently expressed rat 17HSD type 2 showed oxidative activity almost exclusively in cultured human embryonic kidney 293 cells, converting estradiol into estrone and testosterone into androstenedione, whereas the opposite was observed for the rat type 1 enzyme. The data suggest that similarly to the corresponding human isoforms, rat 17HSD type 2 is mostly involved in the oxidation of 17 beta-hydroxysteroids into their relatively inactive keto derivative in peripheral tissues, whereas rat 17HSD type 1 is mainly involved in the glandular biosynthesis of estradiol.

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