Retinoid receptors in human breast carcinoma: possible modulators of in situ estrogen metabolism

Identification of significantly mutated subnetworks in the breast cancer genome

Recent studies showed that somatic cancer mutations target genes that are in specific signaling and cellular pathways. However, in each patient only a few of the pathway genes are mutated. Current approaches consider only existing pathways and ignore the topology of the pathways. For this reason, new efforts have been focused on identifying significantly mutated subnetworks and associating them with cancer characteristics. We applied two well-established network analysis approaches to identify significantly mutated subnetworks in the breast cancer genome. We took network topology into account for measuring the mutation similarity of a gene-pair to allow us to infer the significantly mutated subnetworks. Our goals are to evaluate whether the identified subnetworks can be used as biomarkers for predicting breast cancer patient survival and provide the potential mechanisms of the pathways enriched in the subnetworks, with the aim of improving breast cancer treatment. Using the copy number alteration (CNA) datasets from the METABRIC (Molecular Taxonomy of Breast Cancer International Consortium) study, we identified a significantly mutated yet clinically and functionally relevant subnetwork using two graph-based clustering algorithms. The mutational pattern of the subnetwork is significantly associated with breast cancer survival. The genes in the subnetwork are significantly enriched in retinol metabolism KEGG pathway. Our results show that breast cancer treatment with retinoids may be a potential personalized therapy for breast cancer patients since the CNA patterns of the breast cancer patients can imply whether the retinoids pathway is altered. We also showed that applying multiple bioinformatics algorithms at the same time has the potential to identify new network-based biomarkers, which may be useful for stratifying cancer patients for choosing optimal treatments.

High Expression of RARβ Is a Favorable Factor in Colorectal Cancer

RARβ plays a critical role in cancer progression and is associated with several types of human cancer. It remains unclear, however, whether it is linked to the clinicopathological parameters of colorectal cancer (CRC). We therefore determined the expression of RARβ protein in patients with primary CRC and examined its relationship with clinical outcomes. RARβ expression in 234 samples of CRC patients and matched benign noncancerous tumors was detected by immunohistochemistry. RARβ mRNA expression was confirmed using the TCGA and Oncomine databases. COX regression analysis and Kaplan–Meier survival analysis were performed to determine the relationship between RARβ expression and CRC prognosis. Our results show that high expression of RARβ correlated with better prognosis in CRC patients. RARβ expression in CRC specimens was clearly lower than in peritumoral specimens (30.8% vs 58.8%, p < 0.001) and significantly correlated with gender (χ² = 3.926, p = 0.048), tumor differentiation (χ² = 5.978, p = 0.014), and tumor stage (χ² = 6.642, p = 0.036). Multivariate analyses further revealed that low RARβ expression (p = 0.001), distant metastasis (p = 0.001), tissue differentiation (p = 0.006), and tumor stage (p = 0.002) were associated with overall survival in CRC patients. In addition, Kaplan–Meier analysis indicated that increased RARβ expression in cytoplasm (p = 0.001) and early tumor TNM stage (p = 0.030) was associated with a more favorable outcome in patients with CRC. In conclusion, RARβ expression was strongly correlated with several clinicopathological factors of CRC and may represent a favorable prognostic marker in patients with CRC.

Retinoic Acid Receptor β: A Potential Therapeutic Target in Retinoic Acid Treatment of Endometrial Cancer

OBJECTIVE

Several studies have reported that retinoic acid (RA) might be used to treat malignancies. The effects of RA are mediated by the RA receptor (RAR), and RARα/RARβ especially acts as a tumor suppressor. However, little is known about its role in human endometrial cancer.

MATERIALS AND METHODS

In this study, we examined the effects of all-trans RA (ATRA) on progression of human endometrial cancer cell line, RL95-2 and Hec1A. We then examined the expression of RARα and RARβ in 50 endometrial cancer tissues by using immunohistochemistry.

RESULTS

We found inhibitory effects of ATRA on cell proliferation, apoptosis, and migration in RL95-2 cells, but not in Hec1A cells. RARα or RARβ knockdown individually could not cancel out the inhibition of cell proliferation by ATRA in RL95-2 cells, but simultaneous knockdown of RARα and RARβ could block its effect on proliferation. RARα and RARβ knockdown dose dependently reduced the inhibition of migration by ATRA, but the effect was more pronounced with RARβ knockdown than with RARα knockdown. We confirmed that RARβ gene was directly regulated by ATRA in microarray and real-time reverse transcription polymerase chain reaction. Furthermore, the RARβ agonist (BMS453) significantly suppressed proliferation of RL95-2 cells. In immunohistochemical analysis, RARα expression was positively correlated with tumor grade, and RARβ showed the opposite tendency in endometrial cancer.

CONCLUSIONS

Retinoic acid might have multiple antitumor effects, and RARβ may be a potent therapeutic target in RA treatment for endometrial cancers.

Interplay between estrogen and retinoid signaling in breast cancer--current and future perspectives

All-trans-retinoic acid (RA) is a promising agent for breast cancer treatment, but it induces several adverse effects and the few clinical trials performed up to now in breast cancer patients have provided disappointing results. The combination of RA and antiestrogenic compounds, such as tamoxifen, synergistically decreases the proliferation of breast cancer cells and an interplay between retinoid and estrogen signaling has begun to be unraveled, turning these combinations into an appealing strategy for breast cancer treatment. This review focus on the current knowledge regarding the interplay between retinoid and estrogen signaling in breast cancer and the combinations of RA with antiestrogens, aiming their future utilization in cancer therapy.

Expression of steroid and xenobiotic receptor in uterine carcinosarcoma, leiomyosarcoma and endometrial stromal sarcoma

We analyzed the expression of the steroid and xenobiotic receptor (SXR) in human uterine sarcomas and evaluated its clinical significance. Forty-seven cases with archival specimens were examined for SXR expression using immunohistochemistry. All cases were scored using a semi-quantitative histological scoring (HSCORE) method. Specimens with a HSCORE >40 were regarded as SXR-positive. Various clinicopathological variables, including the expression status of estrogen receptor (ER)-α, progesterone receptor (PR) and Ki67 (MIB-1) were examined. The mean SXR HSCOREs of carcinosarcoma (CS) and leiomyosarcoma (LMS) were 9.13 and 23.6, respectively, and SXR-positive rates were 3 out of 24 (12.5%) and 4 out of 17 (23.5%), respectively. SXR was not detected in endometrial stromal sarcoma (ESS). In CS cases, significant differences were detected between the expression of SXR and age and disease stages. There was no significant correlation between SXR-positive status and either disease-free survival or overall survival. Our results support an association between SXR and malignant behavior. Our results show that overexpression of SXR may represent a useful marker to identify patients with advanced-stage CS. In addition, our results showed that SXR may aid in the diagnosis of uterine sarcomas.

Intratumoral estrogen concentration and expression of estrogen-induced genes in male breast carcinoma: comparison with female breast carcinoma

It is speculated that estrogens play important roles in the male breast carcinoma (MBC) as well as the female breast carcinoma (FBC). However, estrogen concentrations or molecular features of estrogen actions have not been reported in MBC, and biological significance of estrogens remains largely unclear in MBC. Therefore, we examined intratumoral estrogen concentrations, estrogen receptor (ER) α/ERβ status, and expression profiles of estrogen-induced genes in MBC tissues, and compared these with FBC. 17β-Estradiol concentration in MBC (n = 4) was significantly (14-fold) higher than that in non-neoplastic male breast (n = 3) and tended to be higher than that in FBC (n = 7). Results of microarray analysis clearly demonstrated that expression profiles of the two gene lists, which were previously reported as estrogen-induced genes in MCF-7 breast carcinoma cell line, were markedly different between MBC and FBC. In the immunohistochemistry, MBC tissues were frequently positive for aromatase (63 %) and 17β-hydroxysteroid dehydrogenase type 1 (67 %), but not for steroid sulfatase (6.7 %). A great majority (77 %) of MBC showed positive for both ERα and ERβ, and its frequency was significantly higher than FBC cases. These results suggest that estradiol is locally produced in MBC tissue by aromatase. Different expression profiles of the estrogen-induced genes may associate with different estrogen functions in MBC from FBC, which may be partly due to their ERα/ERβ status.

The effect of retinoic acid receptor agonist acitretin on the production of bile and concentrations of some serum components in ovariectomized rats

OBJECTIVE

Acitretin is an oral retinoid that is approved for the treatment of psoriasis and in the chemoprevention of nonmelanoma skin cancer. The metabolism of acitretin occurs in the liver and may affect other metabolic processes in the liver, such as metabolism of bilirubin, bile acids, and lipids. These processes may be also affected by physiologic loss of estrogens in postmenopausal women. Therefore, the aim of this study was to examine the effect of acitretin on the secretion and composition of bile and the turnover of cholesterol in a model of estrogen deficiency in ovariectomized rats.

METHODS

The study was carried out on female Wistar rats divided into three groups: sham-operated control, ovariectomized control, and ovariectomized rats receiving acitretin. The studied group was administered acitretin (Neotigason capsules 25 mg, Roche; 7.1 mg/kg body weight per 24 h) for 28 days. Bile fractions and blood were collected for determinations of concentration of bile acids, total cholesterol, calcium ions, chloride ions, and direct bilirubin. In addition, low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol were assayed.

RESULTS

It was found that ovariectomy produced alterations in the process of secretion of bile and its principal components: cholesterol, bile acids, chloride ions, and bilirubin. The administration of acitretin decreased the secretion of bile and bile cholesterol, as well as serum levels of total, LDL, and HDL cholesterol, and moreover increased the proportion of bile acids to total cholesterol.

CONCLUSIONS

Acitretin may influence the hepatic metabolism of bile, bile acids, and lipids. This action is associated with a decrease in factors influencing the lithogenicity of bile, with reductions in the serum levels of total, LDL, and HDL cholesterol.

Retinoid receptors in human esophageal squamous cell carcinoma: retinoid X receptor as a potent prognostic factor

Retinoids regulate cell proliferation and differentiation in normal and neoplastic tissue. These effects are mainly mediated by two types of nuclear retinoid receptors, retinoic acid receptors (RAR) and retinoid X receptors (RXR). RXR have been demonstrated to play important roles in esophageal carcinoma, but the expression of RXRβ and RXRγ has not been examined in esophagus. Therefore, we examined the immunoreactivity of all subtypes of RAR and RXR in 53 non-neoplastic esophageal epithelium and 74 esophageal squamous cell carcinoma tissues. In non-neoplastic epithelium RARβ immunoreactivity was marked in the basal layer and weak in the suprabasal layer, but immunoreactivity of other retinoid receptors was detected in both of layers. In addition, the status of RARβ and RXRβ immunoreactivity inversely correlated with that of lymph node metastasis (P= 0.0477 and P= 0.0034, respectively); decreased RXRβ immunoreactivity of carcinoma cells was positively associated with adverse clinical outcome of the patients (P= 0.0187). These findings all indicate the important roles of retinoid receptors, especially, RXR in the esophageal squamous cell carcinoma.

Steroid and Xenobiotic Receptor (SXR) as a possible prognostic marker in epithelial ovarian cancer

We examined the expression of the steroid and xenobiotic receptor (SXR) and evaluated its clinical significance in human epithelial ovarian carcinoma. One hundred forty-one cases were examined using immunohistochemistry for SXR with archival specimens. All cases were scored using a semi-quantitative histological scoring (HSCORE) method. Specimens with an HSCORE > 60 were regarded as SXR-positive. Various clinicopathologic variables were examined. SXR showed significant differences in age, histology, grade, ER alpha and PR. SXR was detected in 35 of 141 (24.8%) ovarian cancer tissues. There was a statistically significant negative correlation between SXR-positive status and both disease-free survival and overall survival (P= 0.0415 and 0.0316, respectively), independent of stage (P= 0.0167 and 0.021, respectively). In multivariate analysis, SXR was a statistically independent risk factor for both disease-free survival and overall survival (P= 0.049 and 0.0354). Our results support an association of SXR between ER alpha and PR in epithelial ovarian cancers. Our data suggest that SXR is a prognostic factor in epithelial ovarian cancer and may represent a useful marker to identify patients at risk of recurrence or death.

17beta-hydroxysteroid dehydrogenases in human breast cancer

Estrogen plays a pivotal role in development and progression of human breast carcinoma. Before menopause the main source of estrogen in women is circulating estrogen secreted from the ovary, but following menopause the source changes to the hormone that is converted from circulating adrenal androgens in peripheral tissues. Therefore, adrenal androgens have to be converted to estrogen to stimulate breast carcinoma cells. In these steps, several enzymes such as aromatase, steroid sulfatase, and 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) are involved in the production of estrogens. The reaction related to 17beta-HSDs activity is one of the last steps of estradiol biosynthesis, and 14 isozymes of 17beta-HSD have been identified at this juncture. The balance of the relative expression levels of 17beta-HSD isozymes in human breast carcinomas is thought to play a pivotal role in supply of estradiol to estrogen receptor positive carcinoma cells. Understanding the character of 17beta-HSD isozymes in human breast carcinoma thus provides important information on the mechanisms of biosynthesis of estradiol in breast carcinoma and for development of a therapeutic agent targeted for inhibition of local estradiol synthesis in breast carcinoma cells. In the present review we summarize the roles played by 17beta-HSDs in human breast carcinoma to obtain a better understanding of the properties of 17beta-HSDs in human breast carcinoma.

Human pregnane X receptor is expressed in breast carcinomas, potential heterodimers formation between hPXR and RXR-alpha

Background

The human pregnane X receptor (hPXR) is an orphan nuclear receptor that induces transcription of response elements present in steroid-inducible cytochrome P-450 gene promoters. This activation requires the participation of retinoid X receptors (RXRs), needed partners of hPXR to form heterodimers. We have investigated the expression of hPXR and RXRs in normal, premalignant, and malignant breast tissues, in order to determine whether their expression profile in localized infiltrative breast cancer is associated with an increased risk of recurrent disease.

Methods

Breast samples from 99 patients including benign breast diseases, in situ and infiltrative carcinomas were processed for immunohistochemistry and Western-blot analysis.

Results

Cancer cells from patients that developed recurrent disease showed a high cytoplasmic location of both hPXR isoforms. Only the infiltrative carcinomas that relapsed before 48 months showed nuclear location of hPXR isoform 2. This location was associated with the nuclear immunoexpression of RXR-alpha.

Conclusion

Breast cancer cells can express both variants 1 and 2 of hPXR. Infiltrative carcinomas that recurred showed a nuclear location of both hPXR and RXR-alpha; therefore, the overexpression and the subcellular location changes of hPXR could be considered as a potential new prognostic indicator.

Biological roles of estrogen and progesterone in human endometrial carcinoma--new developments in potential endocrine therapy for endometrial cancer

Endometrial carcinoma is one of the most common female pelvic malignancies. It is well known that uterine endometrial cell proliferation is under the control of both estrogen and progesterone. In this review, results of the recent studies on the biosynthesis and action of estrogen and progestin in normal endometrium and its disorders will be summarized and the new aspects of hormonal therapies in the patients with endometrial carcinoma will be discussed including its future prospectives. We reported that the enzymes responsible for intratumoral estrogen metabolism and biosynthesis are markedly different between human breast and endometrial carcinoma, although both of them are considered "estrogen-dependent malignancies". In addition, the biological significance of Progesterone receptor (PR) isoforms is considered to differ between endometrial and breast carcinomas. Clinical data concerning Hormone replacement therapy (HRT) and estrogen-dependent cancer risk also support these findings. These basic and clinical findings help to understand the biology and provide the new knowledge for prevention, diagnosis and treatment of human endomerial carcinoma. Specific endocrine treatment of endometrial carcinoma should be explored in future, although aromatase inhibitors are the most effective endocrine treatments of estrogen-responsive breast carcinoma. Retinoid, metabolities of vitamin A, and synthetic peroxisome proliferator-activated receptor (PPAR) gamma ligands, which have been used for the treatment of insulin resistance in type II diabetes mellitus, may be the important candidates as drugs not only for prevention but also for possible endocrine treatment of endometrial carcinoma.

Prognostic Significance of Vitamin D Receptor and Retinoid X Receptor Expression in Renal Cell Carcinoma

PURPOSE

The active form of vitamin D3, that is 1alpha,25-dihydroxyvitamin D3, binds with vitamin D receptor, which forms a complex with retinoid X receptors alpha, beta and gamma to manifest antitumor effects. We examined the expression of vitamin D receptor and retinoid X receptors in renal cell carcinoma and elucidated the prognostic significance of these receptors.

MATERIALS AND METHODS

We performed immunohistochemical examination of vitamin D receptor, and retinoid X receptors alpha, beta and gamma in nephrectomized specimens of 68 patients with renal cell carcinoma. We analyzed the correlation between the expression of these receptors and clinicopathological parameters or patient survival. Mean followup was 68.2 months.

RESULTS

No significant correlation was found between the expression of vitamin D receptor, retinoid X receptor alpha or beta and clinicopathological parameters. In contrast, retinoid X receptor gamma expression correlated significantly with tumor stage (p = 0.009) and distant metastasis (p = 0.005). The 5-year cancer specific survival rate was higher in patients with retinoid X receptor gamma positive renal cell carcinoma than those with retinoid X receptor gamma negative renal cell carcinoma (79.3% vs 40.0%, p <0.05). Cox regression analysis revealed that retinoid X receptor gamma expression, tumor status and lymph node status were significant independent prognostic factors in patients with renal cell carcinoma (p <0.05). A significant correlation was observed between the expression of retinoid X receptor gamma and tumor stage, distant metastasis or the 5-year cancer specific survival rate. Furthermore, retinoid X receptor gamma expression was an independent prognostic factor in patients with renal cell carcinoma.

CONCLUSIONS

Our observations suggest that alterations of vitamin D receptor and retinoid X receptor expression may be involved in renal carcinogenesis and retinoid X receptor gamma expression may be a useful prognostic marker in patients with renal cell carcinoma.

In situ production of sex steroids in human breast carcinoma

It is well known that sex steroids are closely involved in the growth of human breast carcinomas, and the great majority of breast carcinomas express sex steroid receptors. In particular, recent studies have demonstrated that estrogens and androgens are locally produced and act in breast carcinoma tissues without release into plasma. Blockade of intratumoral estrogen production potentially leads to an improvement in the prognosis of invasive breast carcinoma patients, and, therefore, it is important to obtain a better understanding of sex steroid-producing enzymes in breast carcinoma. In this review, we summarize recent studies on tissue concentration of sex steroids and expression of enzymes related to intratumoral production of estrogens [aromatase, steroid sulfatase (STS), and 17beta-hydroxysteroid dehydrogenase type 1 (17betaHSD1)], and androgens (17betaHSD5 and 5alpha-reductase) in invasive and in situ (noninvasive) breast carcinomas, and discuss the significance of intratumoral production of sex steroids in breast carcinoma.

Controversies of aromatase localization in human breast cancer--stromal versus parenchymal cells

Aromatase is a key enzyme of estrogen production through conversion from serum androgens in estrogen-dependent postmenopausal breast cancer. Aromatase has been reported to be predominantly located in intratumoral stromal cells and adipocytes but not in parenchymal or carcinoma cells in breast cancer tissue. It is, however, true that there have been controversies regarding intratumoral localization of aromatase in human breast carcinoma, especially whether intratumoral production of estrogens through aromatase occurs in parenchymal or stromal cells. Results of several studies suggested that aromatase present in parenchymal carcinoma cells plays more important roles in the growth and invasion of breast carcinomas than that in stromal cells through providing higher levels of estrogens to carcinoma cells. Aromatase inhibitors are increasingly being used in place of tamoxifen after results of various clinical trials demonstrated that aromatase inhibitors are more effective in increasing survival and recurrence of estrogen-dependent breast cancer patients. Therefore, it is important to clarify the estrogen supplying pathway by aromatase inside of breast carcinoma tissues in order to evaluate the possible efficacy of aromatase inhibitor treatment. In this review, the controversies regarding these intratumoral localization patterns in human breast carcinoma will be briefly summarized.

Expression of the steroid and xenobiotic receptor and its possible target gene, organic anion transporting polypeptide-A, in human breast carcinoma

Steroid and xenobiotic receptor (SXR) or human pregnane X receptor (hPXR) has been shown to play an important role in the regulation of genes related to xenobiotic detoxification, such as cytochrome P450 3A4 and multidrug resistance gene 1. Cytochrome P450 enzymes, conjugation enzymes, and transporters are all considered to be involved in the resistance of breast carcinoma to chemotherapeutic or endocrine agents. However, the expression of SXR/hPXR proteins and that of its target genes and their biological or clinical significance have not been examined in human breast carcinomas. Therefore, we first examined SXR/hPXR expression in 60 breast carcinomas using immunohistochemistry and quantitative reverse transcription-PCR. We then searched for possible SXR/hPXR target genes using microarray analysis of carcinoma cells captured by laser microscissors. SXR/hPXR was detected in carcinoma tissues but not in nonneoplastic and stromal cells of breast tumors. A significant positive correlation was detected between the SXR/hPXR labeling index and both the histologic grade and the lymph node status of the carcinoma cases. Furthermore, in estrogen receptor-positive cases, SXR/hPXR expression was also positively correlated with expression of the cell proliferation marker, Ki-67. Microarray analysis showed that organic anion transporting polypeptide-A (OATP-A) was most closely correlated with SXR/hPXR gene expression, and both OATP-A mRNA and protein were significantly associated with SXR/hPXR in both breast carcinoma tissues and its cell lines. These results suggest that SXR/hPXR and its target gene, such as OATP-A, may play important roles in the biology of human breast cancers.

Induction of PDCD4 tumor suppressor gene expression by RAR agonists, antiestrogen and HER-2/neu antagonist in breast cancer cells. Evidence for a role in apoptosis

The growth of human breast tumor cells is regulated through signaling involving cell surface growth factor receptors and nuclear receptors of the steroid/thyroid/retinoid receptor gene family. Retinoic acid receptors (RARs), members of the steroid/thyroid hormone receptor gene family, are ligand-dependent transcription factors, which have in vitro and in vivo growth inhibitory activity against breast cancer cells. RAR-agonists inhibit the proliferation of many human breast cancer cell lines, particularly those whose growth is stimulated by estradiol (E2) or growth factors. Additionally, RAR-agonists and synthetic retinoids such as Ferentinide have been shown to induce apoptosis in malignant breast cells but not normal breast cells. To better define the genes involved in RAR-mediated growth inhibition of breast cancer cells, we used oligonucleotide microarray analysis to create a database of genes that are potentially regulated by RAR-agonists in breast cancer cells. We found that PDCD4 (programmed cell death 4), a tumor suppressor gene presently being evaluated as a target for chemoprevention, was induced about three-fold by the RARalpha-selective agonist Am580, in T-47D breast cancer cells. RAR pan-agonists and Am580, but not retinoid X receptors (RXR)-agonists, stimulate the expression of PDCD4 in a wide variety of retinoid-inhibited breast cancer cell lines. RAR-agonists did not induce PDCD4 expression in breast cancer cell lines, which were not growth inhibited by retinoids. We also observed that antiestrogen and the HER-2/neu antagonist, Herceptin (Trastuzumab), also induced PDCD4 expression in T-47D cells, suggesting that PDCD4 may play a central role in growth inhibition in breast cancer cells. Transient overexpression of PDCD4 in T-47D (ER+, RAR+) and MDA-MB-231 (ER-, RAR-) cells resulted in apoptotic death, suggesting a role for PDCD4 in mediating apoptosis in breast cancer cells. PDCD4 protein expression has previously been reported in small ductal epithelium of normal breast. To date, there has been no report of induction of PDCD4 expression by RAR-agonists, antiestrogen or HER2/neu antagonist in breast cancer cells and its potential role in apoptosis in these cells.

About GATA3, HNF3A, and XBP1, three genes co-expressed with the oestrogen receptor-alpha gene (ESR1) in breast cancer

In breast tumours and breast cancer cell (BCC) lines, microarray analyses have revealed that a series of genes are expressed in close association with the oestrogen receptor-alpha (ER-alpha) gene, ESR1. Three of them, GATA3, HNF3A (also known as FOXA1), and XBP1 encode transcription factors. Here, we present these factors and we discuss their potential involvement in the ER-alpha-mediated actions in BCC. We notably show the relations that exist, or that might exist, between these factors and the oestrogen-inducible trefoil factor TFF1.

Intracrine mechanism of estrogen synthesis in breast cancer

It has been demonstrated that biologically active estrogens are locally produced from circulating inactive steroids in an intracrine mechanism in the breast carcinoma. The in situ production of estrogens is considered to play an important role in the proliferation of breast cancer cells, especially in the postmenopausal women. Therefore, the total blockade of this pathway may lead to an improvement in the prognosis in breast cancer patients due to the inhibition of estrogenic actions. In this review, we describe the recent studies of enzymes related to intracrine mechanism of estrogen synthesis, including aromatase, steroid sulfatase (STS), and 17beta-hydroxysteroid dehydrogenase, in human breast carcinoma tissues, and discuss the biological significance of local production of estrogens in human breast cancer.

Retinoids, retinoic acid receptors, and breast cancer

Retinoids comprise both naturally and synthetically occurring compounds that have been proven to be differentiation agents for a variety of neoplasias, including breast cancer and promyelocytic leukemia in animal models and humans. They offer a unique panoply of therapeutics for the prevention or treatment of breast cancer. Nonetheless, considerable controversy remains as to the efficacy and potential toxic side-effects and as to which group of patients may most benefit. In this article, we review evidence of retinoid efficacy in breast cancer in humans and in animal models and provide possible mechanisms of retinoid action in breast cancer treatment, focusing on the roles of the different retinoic acid receptors and the metabolic pathways necessary for gene activation and cellular homeostasis.

In situ production of estrogens in human breast carcinoma

Recent studies have demonstrated that biologically active estrogens are locally produced from circulating inactive steroids in the estrogen-dependent breast carcinoma. The in situ production of estrogens in the breast carcinoma is considered to play an important role in the proliferation of breast cancer cells, especially in the postmenopausal women. Therefore, the total blockade of this pathway may inhibit estrogenic actions in breast cancer tissues and lead to an improvement in the prognosis in these patients. In this review, we describe the recent studies concerning the expression of enzymes related to intratumoral estrogen production, including aromatase, 17beta-hydroxysteroid dehydrogenase, steroid sulfatase, and estrogen sulfotransferase in human breast carcinoma tissues, and discuss the biological significance of local production of estrogens in human breast cancer.

Transcription Suppression of Thromboxane Receptor Gene Expression by Retinoids in Vascular Smooth Muscle Cells

Thromboxane (TX) A2 induces contraction and proliferation of vascular smooth muscle cells (VSMCs) via its specific membrane TX receptor (TXR), possibly leading to the progression of atherosclerosis. Retinoids, derivatives of vitamin A, have recently been shown to be anti-atherosclerotic in VSMCs. We therefore examined the effects of retinoids on TX-induced cell growth and TXR expression in VSMCs. TX-induced VSMC proliferation assessed by 3H-thymidine incorporation was completely abrogated by all-trans retinoic acid (ATRA) treatment. The expression of TXR mRNA was significantly decreased by treatment either with ATRA or its stereoisomer 9-cis retinoic acid (RA). Transcription activity of the TXR gene promoter was suppressed by treatment with these retinoids, and a study using retinoid receptor-selective agonists demonstrated that retinoic acid receptors (RARs), rather than retinoid X receptors (RXRs), were mainly involved in the transcription suppression. Deletion analyses demonstrated that the suppression was mediated via the -22/-7 GC-box related sequence. Electrophoretic mobility shift assays showed that Sp1, but not RAR and/or RXR, could bind to the element. The formation of the Sp1-DNA complex was inhibited by co-incubation with RAR, but not by RXR. Taken together, these findings suggest that TXR gene transcription suppression may be mediated by the inhibition of Sp1 binding to the -22/-7 GC-box related sequence by activated RAR, which may result in the inhibition of TX-induced VSMC proliferation. Our study indicates a novel anti-atherosclerotic action of retinoids in VSMCs.

Analysis of vitamin D-receptor (VDR) and retinoid X-receptor alpha in breast cancer

The expression of vitamin D-receptor (VDR) and retinoid X-receptor alpha (RXR-alpha) has been analysed immunohistochemically in benign (n = 62 and n = 5 respectively) and malignant (n = 228 and n = 15 respectively) breast tissue samples using a monoclonal antibody 9A7gamma against VDR and a polyclonal antibody against RXR-alpha. A recently developed immunoreactive scoring method (IRS) was employed. The expression of VDR was detected at the RNA-level using the reverse transcriptase-polymerase chain reaction. A statistically significant higher expression of VDR at the protein level was seen in breast cancer compared with benign breast tissue, whereas at the mRNA level no visible differences in the expression of VDR were found. A higher expression of RXR-alpha was seen in breast cancer compared with benign breast tissue. Our findings indicate that breast tissue may be a new target organ for therapeutically applied vitamin D and retinoid analogues. VDR and RXR-alpha are upregulated at the protein level in breast carcinomas as compared to normal breast tissue, indicating a possibly increased sensitivity to therapeutically applied vitamin D analogues. New vitamin D analogues exerting less calcemic side effects may be promising new drugs for the treatment or chemoprevention of breast carcinomas as well as of precancerous breast lesions. Combination therapies of vitamin D and retinoid analogues with fewer side effects seen promising for the treatment of breast cancer.