Nameer B. Kirma

Overexpression of Aromatase Leads to Development of Testicular Leydig Cell Tumors : An in Vivo Model for Hormone-Mediated Testicular Cancer

Despite recent advances in diagnosis and treatment of testicular cancer, its causes remain unknown. The most common conditions known to be associated with testicular cancer are cryptorchidism, infertility, and overexposure to pesticides or radiation. Recent studies also indicate hormones may play a crucial role in testicular tumorigenesis. Our studies show that about half of the male transgenic mice overexpressing aromatase in testis were infertile and/or had larger than normal testicles. Gross pathology and histological analysis showed the mice to have Leydig cell tumors, unilaterally or bilaterally. Serum estradiol levels for transgenic mice were at least twice as high as those for nontransgenic mice. Expression of aromatase and estrogen receptor were also very high in testicular tissue of transgenic mice compared to nontransgenic mice. Consistent with increased estrogenic activity in the testicular tissue, we also saw an increase in the levels of genes involved in cell cycle that are regulated by the estrogen. To obtain a better understanding of the biological significance of testicular tumorigenesis, a reliable animal model is necessary to clarify the mechanisms and correlations associated with human cancers. Here we describe such a model, which shows that overexpression of aromatase results in increased estrogen production and a changed hormone milieu, leading to the induction of testicular cancer (Leydig cell tumors). This predictable and useful model is a potential tool for the study of testicular tumorigenesis, hormonal carcinogenesis, synergistic action of other carcinogens on hormone-induced tumors, and tumor dependency on endocrine factors.

Induction of Aromatase Expression in Cervical Carcinomas: Effects of Endogenous Estrogen on Cervical Cancer Cell Proliferation

Epidemiologic studies have implicated estrogenic exposure as well as human papilloma virus (HPV) infection in cervical carcinogenesis, and some studies have suggested that estrogen and HPV may play synergistic roles in cervical tumorigenesis. In this study, we report a novel finding that approximately 35% of cervical carcinomas tested (n = 19) express aromatase, the enzyme responsible for converting androgen to estrogen, the rate-limiting and final step in estrogen biosynthesis. On the other hand, no aromatase expression was detected in precancerous (n = 42) or normal cervical (n = 17) tissue samples. Increased aromatase was associated with increases in estrogen receptors (ER-alpha and ER-beta) and a decrease in progesterone receptor levels, suggesting that in situ estrogen signaling via ER may be involved in tumor growth. Stable overexpression of aromatase in HPV+ cervical cancer cells resulted in increased cellular proliferation, anchorage-independent growth, and ER expression and activity. In contrast, little change in ER was observed in HPV- cells. Steroid hormone receptor expression observed in vitro paralleled that seen in cervical carcinomas expressing aromatase. Aromatase overexpression also induced the expression of cyclin D1, proliferating cell nuclear antigen, and the HPV oncogenes, E6 and E7. Furthermore, the data underscores the importance of steroid receptor (estrogen and progesterone receptors) regulation in cervical carcinogenesis. To our knowledge, this is the first report demonstrating the induction of aromatase expression in cervical carcinomas, and opens the possibility that aromatase inhibitors may be potential therapeutic agents in cervical carcinomas expressing aromatase.

Elevated Expression of the Oncogene c-fms and Its Ligand, the Macrophage Colony-Stimulating Factor-1, in Cervical Cancer and the Role of Transforming Growth Factor-β1 in Inducing c-fms Expression

Cervical cancer is the third most common gynecologic cancer in the United States. The presence and possible involvement of several cytokines have been studied in cervical cancer; however, very little data, if any, are available on whether cervical tumors are responsive to stimulation by the macrophage colony-stimulating factor-1 (CSF-1). Given the involvement of c-fms and its ligand CSF-1 in gynecologic cancers, such as that of the uterus and the ovaries, we have examined the expression of c-fms and CSF-1 in cervical tumor (n = 17) and normal cervix (n = 8) samples. The data show that c-fms and its ligand are significantly higher in cervical carcinomas compared with normal samples. Immunohistochemistry not only showed that tumor cells expressed significantly higher levels of c-fms but also c-fms levels were markedly higher in tumor cells than tumor-associated stromal cells. Blocking c-fms activity in cervical cancer cells, which express CSF-1 and c-fms, resulted in increased apoptosis and decreased motility compared with control, suggesting that CSF-1/c-fms signaling may be involved in enhanced survival and possibly invasion by cervical cancer cells via an autocrine mechanism. Combined, the data show for the first time the induction of CSF-1 and c-fms in cervical carcinomas and suggest that c-fms activation may play a role in cervical carcinogenesis. Additionally, our data suggest that transforming growth factor-beta1 may be a factor in inducing the expression of c-fms in cervical cancer cells. The data suggest that c-fms may be a valuable therapeutic target in cervical cancer.

Up-regulation of VEGF, c-fms and COX-2 expression correlates with severity of cervical cancer precursor (CIN) lesions and invasive disease

OBJECTIVES To describe the expression of vascular endothelial growth factor (VEGF), proto-oncogene macrophage colony-stimulating factor receptor (c-fms) and cyclooxygenase-2 (COX-2) in cervical carcinogenesis and to analyze the correlation of VEGF with c-fms and COX-2 expression. METHODS In this study, 26 cases of benign cervix, 28 low-grade cervical intraepithelial neoplasia (CIN; CIN 1), 30 high-grade CIN (CIN 2/3) and 28 squamous cervical carcinomas (SCC) were examined by immunohistochemistry (IHC) and analysis was performed separately for epithelium and stroma. RESULTS Positive epithelial expressions in normal cervix, low-grade CIN, high-grade CIN and SCC were, respectively: VEGF - 11.5%, 39.3%, 53.3% and 75% (P<0.001); c-fms - 0%, 10.7%, 40% and 67.9% (P<0.001); COX-2 - 7.7%, 39.3%, 80% and 100% (P<0.001). Stromal VEGF expression was higher than epithelial expression in all CIN grades and was also associated with the lesion grade, while c-fms and COX-2 stromal expression was weak. VEGF expression was statistically correlated to c-fms and COX-2 expression in high-grade CIN (P=0.020 and P=0.027, respectively) and SCC (P=0.015 and P=0.005, respectively). CONCLUSIONS On the basis of our findings, these factors may participate in the development and progression of CIN lesions, with possible interaction of c-fms and COX-2 on VEGF expression, and may be potential molecular targets for studies of cervical cancer prevention and treatment.

Overexpression of the Colony-Stimulating Factor (CSF-1) and/or Its Receptor c-fms in Mammary Glands of Transgenic Mice Results in Hyperplasia and Tumor Formation

A number of recent studies have suggested that the colony-stimulating factor (CSF-1) and its receptor c-fms may be involved in the development of mammary glands during lactation and breast cancer. To study the role of CSF-1 or its receptor in initiation of mammary tumorigenesis, we have generated two independent lines of transgenic mice that overexpress either CSF-1 or c-fms under the control of the mouse mammary tumor virus promoter. Mammary glands of the virgin CSF-1 transgenic mice show increased ductal branching, hyperplasia, dysplasia, and other preneoplastic changes, which are indicative of increased cellular proliferation. Similar changes were also evident in the mammary glands of the c-fms transgenic mice. These changes became more prominent with age and resulted in mammary tumor formation. Moreover, secondary events like dimethylbenz(a)anthracene treatment accelerated mammary tumor formation in these mice. Although the expression of estrogen receptor α was not significantly changed in either of the transgenic mouse strains, progesterone receptor levels was higher in both transgenic lines as compared with the nontransgenic littermates. Expression of G1 cyclins was prominently increased in the mammary glands of both the CSF-1 and c-fms transgenic lines, suggesting increased cell cycle progression in these strains. In addition, the proliferation marker proliferating cell nuclear antigen (PCNA) and the mitogen-responsive transcription factor c-jun were also increased as compared with the nontransgenic controls. These findings, along with the histological data, support the hypothesis that CSF-1 and its receptor are involved in the etiology of breast cancer.

Comprehensive methylome analysis of ovarian tumors reveals hedgehog signaling pathway regulators as prognostic DNA methylation biomarkers.

Women with advanced stage ovarian cancer (OC) have a five-year survival rate of less than 25%. OC progression is associated with accumulation of epigenetic alterations and aberrant DNA methylation in gene promoters acts as an inactivating “hit” during OC initiation and progression. Abnormal DNA methylation in OC has been used to predict disease outcome and therapy response. To globally examine DNA methylation in OC, we used next-generation sequencing technology, MethylCap-sequencing, to screen 75 malignant and 26 normal or benign ovarian tissues. Differential DNA methylation regions (DMRs) were identified, and the Kaplan–Meier method and Cox proportional hazard model were used to correlate methylation with clinical endpoints. Functional role of specific genes identified by MethylCap-sequencing was examined in in vitro assays. We identified 577 DMRs that distinguished (p < 0.001) malignant from non-malignant ovarian tissues; of these, 63 DMRs correlated (p < 0.001) with poor progression free survival (PFS). Concordant hypermethylation and corresponding gene silencing of sonic hedgehog pathway members ZIC1 and ZIC4 in OC tumors was confirmed in a panel of OC cell lines, and ZIC1 and ZIC4 repression correlated with increased proliferation, migration and invasion. ZIC1 promoter hypermethylation correlated (p < 0.01) with poor PFS. In summary, we identified functional DNA methylation biomarkers significantly associated with clinical outcome in OC and suggest our comprehensive methylome analysis has significant translational potential for guiding the design of future clinical investigations targeting the OC epigenome. Methylation of ZIC1, a putative tumor suppressor, may be a novel determinant of OC outcome.

Activin A increases invasiveness of endometrial cells in an in-vitro model of human peritoneum

The aim of this study was to investigate whether activin A has an effect on the attachment and/or invasion of endometrial cells in a modeled peritoneum in vitro. Cultured endometrial stromal cells (ESCs) and endometrial epithelial cells (EECs) were treated with activin A (6.25-50 ng/ml) and with activin A (25 ng/ml) with and without inhibin A or follistatin. Fluorescent labeled cells were added to confluent peritoneal mesothelial cells (PMCs) and to a monolayer of confluent PMCs grown in a Matrigel invasion assay. The rate of endometrial cell attachment and invasion through PMCs was assessed. The expression of cell adhesion proteins N- and E-cadherin was evaluated with real-time RT-PCR. Activin A (25 ng/ml) promoted invasion of the endometrial cells through the modeled peritoneum (>2-fold versus control) and this effect was partially reversed by inhibin A and follistatin. Activin A had no effect on the rate of attachment of the endometrial cells to the PMCs or in the rate of proliferation. In addition, activin A induced a decreased mRNA expression of E-cadherin in cultured EECs. In conclusion, activin A increases invasion of EECs and ESCs into modeled peritoneum. In EECs, this effect may be related to down-regulation of E-cadherin expression. Further studies are warranted to evaluate the role of activin-A in the genesis of the endometriotic lesion.

Amplification of Distant Estrogen Response Elements Deregulates Target Genes Associated with Tamoxifen Resistance in Breast Cancer

A causal role of gene amplification in tumorigenesis is well known, whereas amplification of DNA regulatory elements as an oncogenic driver remains unclear. In this study, we integrated next-generation sequencing approaches to map distant estrogen response elements (DEREs) that remotely control the transcription of target genes through chromatin proximity. Two densely mapped DERE regions located on chromosomes 17q23 and 20q13 were frequently amplified in estrogen receptor-α-positive luminal breast cancer. These aberrantly amplified DEREs deregulated target gene expression potentially linked to cancer development and tamoxifen resistance. Progressive accumulation of DERE copies was observed in normal breast progenitor cells chronically exposed to estrogenic chemicals. These findings may extend to other DNA regulatory elements, the amplification of which can profoundly alter target transcriptome during tumorigenesis.

Overexpression of aromatase in transgenic male mice results in the induction of gynecomastia and other biochemical changes in mammary glands.

Our previous studies have shown that overexpression of aromatase in mammary glands results in the induction of hyperplastic and dysplastic changes in female transgenic mice. In this study we show that overexpression of aromatase in male transgenic mice results in increased mammary growth and histopathological changes similar to gynecomastia. Increased estrogenic activity also results in an increase in estrogen and progesterone receptor expression in the mammary glands of transgenic males as compared to the nontransgenic males, as well as an increase in the expression of various genes involved in cell cycle and cell proliferation. We have also observed an increase in certain growth factors, such as bFGF and TGFbeta, as a result of aromatase overexpression in the male transgenic mammary glands. In order to obtain a better understanding of the biological significance of gynecomastia, a reliable model is necessary to explain the mechanisms and correlations associated with human cancers. This model, can potentially serve as a predictable and useful tool for studying gynecomastia, hormonal carcinogenesis and action of other carcinogens on hormone induced cancers.

Estrogen receptor alpha is required for mammary development and the induction of mammary hyperplasia and epigenetic alterations in the aromatase transgenic mice.

Aromatase transgenic mice exhibit hyperplastic and dysplastic changes, attesting to the importance of local estrogen in breast carcinogenesis. These mice also show increased levels of the estrogen receptor alpha and beta (ERalpha, ERbeta) suggesting that this receptor may play an important role in the initiation of estrogen-mediated mammary hyperplasia observed in these mice. To address the specific role of ERalpha in the mammary development and in the induction of estrogen-mediated hyperplasia in aromatase transgenic mice, we have generated MMTV-aromatase x ERalpha knockout cross (referred as aromatase/ERKO). Even though ERbeta is expressed in aromatase/ERKO mice, lack of ERalpha leads to impaired mammary growth in these mice. The data suggest that ERalpha plays an important role in the mammary gland development as well as in the induction of mammary hyperplasia in aromatase transgenic mice. Lack of ERalpha expression in the aromatase/ERKO mice resulted in a decrease in the expression of Cyclin D1, PCNA and TGFbeta relative to the aromatase parental strain. The studies involving aromatase/ERKO mice show that lack of ERalpha results in impaired mammary development even in the presence of continuous tissue estrogen, suggesting estrogen/ERalpha-mediated actions are critical for mammary development and carcinogenesis.