The Contribution of 17beta-Hydroxysteroid Dehydrogenase Type 1 to the Estradiol-Estrone Ratio in Estrogen-Sensitive Breast Cancer Cells

Abstract

Estrone and estradiol are both estrogens with estrone being the less potent form and estradiol being the most potent estrogen. The binding of the latter to cellular regulatory elements stimulates the proliferation of breast cancer cells. A high ratio of estradiol/estrone is related to increased cell proliferation, and is of great importance to understanding of breast cancer mechanisms. 17beta-hydroxysteroid dehydrogenase type 1 and type 2 play important roles in the activation of estrone and inactivation of estradiol. Breast cancer cells T47D, MCF-7, BT 20, and JEG 3 as control cells, were chosen to evaluate the contribution of these two enzymes to the ratio. Twenty four hours after addition of different concentrations of estrone and estradiol, the ratio stabilized to around 9/1 in breast cancer cell lines with high expression of type 1 (T47D, BT 20, and JEG 3), whereas it approached 1/5 in cells with low expression of type 1 (MCF-7). The estradiol/estrone concentration ratio was modified to 9/1 in MCF-7 and HEK-293 cells over-expressing type 1. In T47D and BT 20, this ratio was decreased from 9/1 to nearly 1/5 (19/81 and 17/83 respectively) after type 1 knockdown by specific siRNAs. Type 2 is mainly involved in the conversion of estradiol into estrone. This ratio was decreased from 9/1 to 7/3 after over-expression of type 2 in MCF-7 cells already over-expressing type 1. The ratio was further decreased by the addition of the oxidative cofactor, NAD, to the cell culture to facilitate the estradiol to estrone conversion catalyzed by type 2. These results demonstrate that the estradiol/estrone ratio is controlled by both type 1 and type 2 with an additional contribution by NAD, although type 1 is the first determining factor in the cellular environment compared with type 2 and cofactors. Moreover, kinetic studies were carried out in intact cells as a new approach, using HEK-293 cells over-expressing type 1 and T47D breast cancer cells.

Increased 17ß-hydroxysteroid dehydrogenase type 1 levels in primary cervical cancer

“…In addition, the presence of HSD17B1, which converts E1 to E2, has been reported in breast, colon, endometrial, gastric and prostate carcinomas, as well as in haematopoietic malignancies [37][38][39][40][41][42][43]. Our results are in agreement with previous studies that showed that cervical cancer cells are able to convert E1 to E2 in vitro [44].…”

HSD17B1 expression enhances estrogen signaling stimulated by the low active estrone, evidenced by an estrogen responsive element-driven reporter gene in vivo

“…Based on these studies, human HSD17B1 is considered to be highly estrogen-specific with markedly higher K m values and lower catalytic activity for androgenic substrates [7][8][9]11,76]. Our recent studies have further provided evidence for the predominantly reductive estrogenic activity of human HSD17B1 in vivo [15,17,18,65].…”

“…In line with this, http structural studies have indicated that the narrow substrate-binding tunnel is highly complementary to estrogens [5,6]. In cultured cells, HSD17B1 has been shown to catalyze predominantly the reductive reaction: the expression of HSD17B1 was shown to decrease the oxidative activity (converting E2 to E1), while the reductive activity converting E1 to E2 was increased 23-fold [7][8][9][10][11]. The K m value measured for the purified human enzyme was shown to be between 0.36-0.9 lM, and 0.03-0.07 lM, in the presence of NADH and NADPH, respectively [12][13][14].…”

“…These enzymes have a variable sequence homology, unique expression patterns, differential cofactor and substrate preference, and differential subcellular localization patterns. Functionally, the family can be divided into steroid-inactivating, oxidative enzymes preferring NAD + as a cofactor (types 2,4,6,8,9,10,11,14), and into reductive, steroid-activating enzymes preferring NADPH as cofactor (types 1, 3,5,7,12). Furthermore, recent studies have indicated that these enzymes also possess other metabolic roles, and for example, HSD17B7 and HSD17B12 are involved in cholesterol biosynthesis and fatty acid metabolism, respectively [2][3][4].…”

“…Until now, most of the development has been focused on steroidal inhibitors, in particular E1-and E2-derived inhibitors, but also non-steroidal inhibitors such as phytoestrogens and thiophenepyrimidinone derivatives have been studied [57][58][59][60][61][62]. Interestingly, several preclinical studies indicate that HSD17B1 inhibitors are, indeed, capable of modulating estrogen responses in different preclinical models in vitro and in vivo [7][8][9][10][11][15][16][17][62][63][64][65][66][67][68].…”