In situ estrogen biosynthesis is considered to play pivotal roles in the development and progression of human endometrial carcinoma. However, the biological roles of androgen have remained virtually unknown. Various epidemiological studies have revealed that elevated serum androgen levels are generally associated with an increased risk of developing endometrial carcinoma; however, studies directly examining androgens in carcinoma tissues are relatively rare and reviews summarizing this information are scarce. Therefore, we summarized recent studies on androgens in endometrial carcinoma, especially focusing androgen actions and in situ androgen biosynthesis. Among the enzymes required for local biosynthesis of androgen, 17β-hydroxysteroid dehydrogenase type 5 (conversion from androstenedione to testosterone) and 5α-reductase (reduction of testosterone to dihydrotestosterone (DHT)) are the principal enzymes involved in the formation of biologically most potent androgen, DHT. Both enzymes and androgen receptor were expressed in endometrial carcinoma tissues, and in situ production of DHT has been reported to exist in endometrial carcinoma tissues. However, testosterone is not only a precursor of DHT production, but also a precursor of estradiol synthesis, as a substrate of the aromatase enzyme. Therefore, aromatase could be another key enzyme serving as a negative regulator for in situ production of DHT by reducing amounts of the precursor. In an in vitro study, DHT was reported to exert antiproliferative effects on endometrial carcinoma cells. Intracrine mechanisms of androgens, the downstream signals of AR, which are directly related to anticancer progression, and the clinical significance of DHT-AR pathway in the patients with endometrial carcinoma have, however, not been fully elucidated.

It is well known that sex steroids are involved in the growth of breast cancers, and the great majority of breast carcinomas express estrogen (ER), progesterone (PR), and androgen (AR) receptors. In particular, recent studies have demonstrated that estrogens and androgens are locally produced in breast carcinoma tissues, and total blockade of in situ estrogen production potentially leads to an improvement in prognosis of breast cancer patients. Therefore, it is important to obtain a better understanding of sex steroid-producing enzymes in breast carcinoma tissues. In this review, we summarize recent studies on the expression and regulation of enzymes related to intratumoral production of estrogens (aromatase, 17β-hydroxysteroid dehydrogenase type 1 (17βHSD1), and steroid sulfatase (STS) etc) and androgens (17βHSD5 and 5α-reductase) in human breast carcinoma tissues, and discuss the biological and/or clinical significance of these enzymes. The cellular localization of aromatase in breast carcinoma tissues still remains controversial. Therefore, we examined localization of aromatase mRNA in breast carcinoma tissues by laser capture microdissection/real time-polymerase chain reaction. Aromatase mRNA expression was detected in both carcinoma and intratumoral stromal cells, and the expression level of aromatase mRNA was higher in intratumoral stromal cells than in carcinoma cells in the cases examined. We also examined an association among the immunoreactivity of enzymes related to intratumoral estrogen production and ERs in breast carcinoma tissues, but no significant association was detected. Therefore, the enzymes responsible for the intratumoral production of estrogen may not always be the same among breast cancer patients, and not only aromatase but also other enzymes such as STS and 17βHSD1 may have important therapeutic potential as targets for endocrine therapy in breast cancer patients.

It is well known that sex steroids play important roles in the development of invasive ductal carcinoma (IDC) of the human breast. However, biological significance of sex steroids remains largely unclear in ductal carcinoma in situ (DCIS), regarded as a precursor lesion of IDC, which is partly due to the fact that the intratumoral concentration of sex steroids has not been examined in DCIS. Therefore, in this study, we first examined the intratumoral concentrations of estradiol and 5α-dihydrotestosterone (DHT) using liquid chromatography/electrospray tandem mass spectrometry in DCIS. Intratumoral concentrations of both estradiol and DHT were threefold higher in DCIS than non-neoplastic breast tissues and estrogen-producing enzymes (aromatase, steroid sulfatase, and 17β-hydroxysteroid dehydrogenase type 1 (17βHSD1)), and androgen-producing enzymes (17βHSD5 and 5α-reductase type 1 (5αRed1)) were abundantly expressed in DCIS by real-time PCR and immunohistochemical analyses. The intratumoral concentration of DHT was significantly lower in IDC than DCIS, while the expression of aromatase mRNA in carcinoma cells and intratumoral stromal cells was significantly higher in IDC than those in DCIS. Immunohistochemistry for sex steroid-producing enzymes in DCIS demonstrated that 5αRed1 immunoreactivity was positively correlated with Ki-67 labeling index and histological grade and was also associated with an increased risk of recurrence in patients with DCIS examined. Results of our study suggest that intratumoral concentrations of estradiol and DHT are increased in DCIS, which is possibly due to intratumoral production of these steroids. Therefore, estradiol and DHT may play important roles in the development of DCIS of the human breast.

Early growth responsive gene 3 (EGR3) is a zinc-finger transcription factor and plays important roles in cellular growth and differentiation. We recently demonstrated estrogen-mediated induction of EGR3 in breast carcinoma cells. However, EGR3 has not yet been examined in breast carcinoma tissues and its significance remains unknown. Therefore, in this study, we examined biological functions of EGR3 in the breast carcinoma by immunohistochemistry, in vitro study, and nude mouse xenograft model. EGR3 immunoreactivity was detected in carcinoma cells in 99 (52%) out of 190 breast carcinoma tissues and was associated with the mRNA level. EGR3 immunoreactivity was positively associated with lymph node status, distant metastasis into other organs, estrogen receptor α, or EGR3 immunoreactivity in asynchronous recurrent lesions in the same patients, and was negatively correlated with tubule formation. EGR3 immunoreactivity was significantly associated with an increased risk of recurrence and adverse clinical outcome by both uni- and multivariate analyses. Egr3-expressing transformant cell lines derived from MCF-7 Tet-Off cells (Eg-10 and Eg-11) significantly enhanced the migration and invasion properties according to the treatment of doxycyclin, but did not significantly change the cell proliferation. Moreover, Eg-11 cells injected into athymic mice irregularly invaded into the adjacent peritumoral tissues, although Clt-7, which was stably transfected with empty vector as a control, demonstrated a well-circumscribed tumor. Eg-11 cells were significantly associated with invasive components and less tubule formation in the xenograft model. These results suggest that EGR3 plays an important role in estrogen-meditated invasion and is an independent prognostic factor in breast carcinoma.

Androgens have been proposed to be actively produced in situ in human prostate cancer. These locally produced androgens have also been considered to play important roles in the pathogenesis and development of prostate cancer. Therefore, it is important to examine the status of this in situ androgen metabolism and/or synthesis in detail in order to improve the clinical response to hormonal therapy in patients diagnosed with prostate cancer. Several studies have previously demonstrated the expression of androgen-producing enzymes such as 5α-reductase types 1 and 2, and 17β-hydroxysteroid dehydrogenase type 5 (17β-HSD5), in human prostate carcinoma cells. However, their biological significance has remained largely unknown. In this study, we evaluated the immunoreactivities of these steroidogenic enzymes in human prostate cancer obtained from surgery (n=70), and correlated the findings with clinicopathological features of the patients. 17β-HSD5 immunoreactivity was detected in 54 cases (77%), 5α-reductase type 1 in 51 cases (73%) and 5α-reductase type 2 in 39 cases (56%). 5α-reductase type 2 immunoreactivity was significantly correlated with that of androgen receptor (AR), and 17β-HSD5 positive cases were significantly associated with clinical stage (TNM stage pT3 vs pT2). These data all suggest that androgen-producing enzymes, such as 5α-reductase type 1 and type 2, and 17β-HSD5 are expressed in a majority of prostate cancers, and are involved in the local production and actions of androgens in prostate cancers.

Nuclear factor erythroid 2-related factor 2 (NRF2 (NFE2L2)) is an important transcriptional activator involved in the cellular defense mechanisms against electrophilic and oxidative stress. Recent studies have demonstrated that the expression of NRF2 protein is upregulated in several human malignancies and is associated with worse prognosis in these patients. However, the pathological and clinical significance of NRF2 has remained largely unknown in breast cancer patients. Therefore, in this study, we immunolocalized NRF2 in 106 breast carcinoma cases. NRF2 immunoreactivity was mainly detected in the nucleus of the breast carcinoma cells and it was positive in 44% of the cases. NRF2 status was significantly associated with histological grade, Ki-67 labeling index, p62 immunoreactivity, and NAD(P)H:quinone oxidoreductase 1 (NQO1) immunoreactivity, and the results of multivariate analyses revealed that NRF2 status was an independent adverse prognostic factor for both recurrence and disease-free survival of the patients. Subsequent in vitro studies demonstrated that the expression of NRF2 significantly increased the proliferation activity of MCF7 and SK-BR-3 breast carcinoma cells. These results indicate that nuclear NRF2 protein plays important roles in the proliferation and/or progression of breast carcinoma, and nuclear NRF2 immunoreactivity is therefore considered a potent prognostic factor in breast cancer patients.

Krüppel-like factor 5 (intestinal) or Krüppel-like factor 5 (KLF5) is a zinc finger-containing transcription factor and involved in important biological processes including cell proliferation and differentiation. However, clinical significance of KLF5 protein has remained largely unknown in breast cancer. Therefore, in this study, we immunolocalized KLF5 in 113 human breast carcinoma cases. KLF5 immunoreactivity was frequently detected in the nuclei of breast carcinoma cells, and median value of the ratio of KLF5-positive carcinoma cells was 30% and was positively associated with the status of androgen receptor. KLF5 immunoreactivity was also significantly associated with increased risk of recurrence and worse clinical outcome in breast cancer patients by univariate analyses, and subsequent multivariate analyses demonstrated that KLF5 immunoreactivity was an independent prognostic factor for both disease-free and breast cancer-specific survival of the patients. We then examined possible regulation of KLF5 by androgen using MCF-7 breast carcinoma cells. KLF5 mRNA was induced by biologically active androgen 5α-dihydrotestosterone in a dose- and time-dependent manner in MCF-7 cells. In addition, results of transfection experiments demonstrated that proliferation activity of MCF-7 cells was significantly associated with the KLF5 expression level. These findings suggest that KLF5 is an androgen-responsive gene in human breast carcinomas and play important roles in the progression of breast carcinomas. KLF5 immunoreactivity is therefore considered a potent prognostic factor in human breast cancers.

The estrogen pathway plays an important role in the etiology of human endometrial carcinoma (EC). We examined whether estrogen biosynthesis in the tumor microenvironment promotes endometrial cancer. To examine the contribution of stromal cells to estrogen signaling in EC, we used reporter cells stably transfected with the estrogen response element (ERE) fused to the destabilized green fluorescent protein (GFP) gene. In this system, the endometrial cancer stromal cells from several patients activated the ERE of cancer cells to a variable extent. The GFP expression level increased when testosterone, a substrate for aromatase, was added. The effect was variably inhibited by aromatase inhibitors (AIs), although the response to AIs varied among patients. These results suggest that GFP expression is driven by estrogen synthesized by aromatase in the endometrial cancer stromal cells. In a second experiment, we constructed an adenovirus reporter vector containing the same construct as the reporter cells described above, and visualized endogenous ERE activity in primary culture cancer cells from 15 EC specimens. The GFP expression levels varied among the cases, and in most primary tissues, ERE activities were strongly inhibited by a pure anti-estrogen, fulvestrant. Interestingly, a minority of primary tissues in endometrial cancer showed ERE activity independent of the estrogen-ER pathway. These results suggest that AI may have some therapeutic value in EC; however, the hormonal microenvironment must be assessed prior to initiating therapy.

It is well known that oestrogens play important roles in both the pathogenesis and development of invasive ductal carcinoma (IDC) of human breast. However, molecular features of oestrogen actions have remained largely unclear in pure ductal carcinoma in situ (pDCIS), regarded as a precursor lesion of many IDCs. This is partly due to the fact that gene expression profiles of oestrogen-responsive genes have not been examined in pDCIS. Therefore, we first examined the profiles of oestrogen-induced genes in oestrogen receptor (ER)-positive pDCIS and DCIS (DCIS component (DCIS-c)) and IDC (IDC component (IDC-c)) components of IDC cases (n=4 respectively) by microarray analysis. Oestrogen-induced genes identified in this study were tentatively classified into three different groups in the hierarchical clustering analysis, and 33% of the genes were predominantly expressed in pDCIS rather than DCIS-c or IDC-c cases. Among these genes, the status of MYB (C-MYB), RBBP7 (RBAP46) and BIRC5 (survivin) expressions in carcinoma cells was significantly higher in ER-positive pDCIS (n=53) than that in ER-positive DCIS-c (n=27) or IDC-c (n=27) by subsequent immunohistochemical analysis of the corresponding genes (P<0.0001, P=0.03 and P=0.0003 respectively). In particular, the status of C-MYB immunoreactivity was inversely (P=0.006) correlated with Ki67 in the pDCIS cases. These results suggest that expression profiles of oestrogen-induced genes in pDCIS may be different from those in IDC; and C-MYB, RBAP46 and survivin may play important roles particularly among oestrogen-induced genes in ER-positive pDCIS.

Sex steroids play important roles in the development of many human breast carcinomas, and aromatase inhibitors are used for the anti-estrogen therapy. Recent studies have demonstrated that aromatase suppressed 5α-dihydrotestosterone (DHT) synthesis in breast carcinoma cells, but intratumoral concentration of androgens and its significance have not been reported in the breast carcinoma patients treated with aromatase inhibitors. Therefore, we examined androgen concentrations in breast carcinoma tissues treated with exemestane, and further performed in vitro studies to characterize the significance of androgen actions. Intratumoral DHT concentration was significantly higher in breast carcinoma tissues following exemestane treatment (n=9) than those without the therapy (n=7), and 17β-hydroxysteroid dehydrogenase type 2 (17βHSD2) status was significantly altered to be positive after the treatment. Following in vitro studies showed that 17βHSD2 expression was dose dependently induced by both DHT and exemestane in T-47D breast carcinoma cells, but these inductions were not additive. DHT-mediated induction of 17βHSD2 expression was markedly suppressed by estradiol (E₂) in T-47D cells. E₂-mediated cell proliferation was significantly inhibited by DHT in T-47D cells, associated with an increment of 17βHSD2 expression level. These findings suggest that intratumoral androgen actions are increased during exemestane treatment. 17 β HSD2 is a potent DHT-induced gene in human breast carcinoma, and may not only be involved in anti-proliferative effects of DHT on breast carcinoma cells but also serve as a potential marker for response to aromatase inhibitor in the breast carcinoma patients.