Current concepts in ovarian epithelial tumorigenesis: correlation between morphological and molecular data

Ovarian carcinoma is the most lethal gynaecological malignancy, most tumours being advanced at presentation. However, little is known about precursor lesions and the cell of origin of epithelial ovarian malignancy. In this review, the proposed cell of origin is discussed as well as recent molecular data relating to ovarian cancers of different morphological types. It is stressed that ovarian carcinoma is a heterogeneous group of neoplasms with several different morphological types, each with their own underlying molecular genetic events. Recent data suggest that mucinous ovarian cancers and a small subset of serous cancers (low grade ovarian serous carcinoma) develop through a well-defined adenoma-carcinoma sequence while the much more common high grade ovarian serous carcinoma develops de novo from the ovarian surface epithelium or the epithelium of cortical inclusion cysts. The realisation that various morphological types of epithelial ovarian cancer are associated with different molecular genetic events is a major advance in the study of ovarian cancer. It can be anticipated that this will lead to the development of specific therapeutic agents of value against a specific tumour type.     

Vasohibin-1基因在上皮性卵巢癌中的表达和临床病理意义

目的:探讨卵巢癌中Vasohibin-1的表达情况及临床病理学意义。方法:采用实时定量PCR和免疫组化方法检测在60例上皮性卵巢癌和12例正常卵巢组织中Vasohibin-1的表达情况,ELISA法检测卵巢癌组织中VEGF蛋白表达,分析vasohibin-1表达与VEGF之间的关系及其与卵巢癌分期,分级和预后之间的关系。结果:卵巢癌中vasohibin-1表达明显高于正常卵巢(P0.05)。Vasohibin-1表达水平与卵巢癌分期相关(P0.05),而与卵巢癌分级和淋巴转移无关。Vasohibin-1表达与VEGF蛋白水平呈正相关(P0.01)。高vasohibin-1表达卵巢癌患者三年生存率(50%)低于低vasohibin-1表达的患者(83%)。结论:vasohibin-1可以反映卵巢癌的血管生成潜能,是卵巢癌的不良预后因素。     

NuMA overexpression in epithelial ovarian cancer

Highly aneuploid tumours are common in epithelial ovarian cancers (EOC). We investigated whether NuMA expression was associated with this phenomenon.NuMA protein levels in normal and tumour tissues, ovarian cell lines and primary cultures of malignant cells derived from ovarian ascitic fluids were analysed by Affymetrix microarray analysis, immunoblotting, immunohistochemistry (IHC) and immunofluorescence (IF), with results correlated to associated clinical data. Aneuploidy status in primary cultures was determined by FACS analysis.Affymetrix microarray data indicated that NuMA was overexpressed in tumour tissue, primary cultures and cell lines compared to normal ovarian tissue. IHC revealed low to weak NuMA expression in normal tissues. Expression was upregulated in tumours, with a significant association with disease stage in mucinous EOC subtypes (p = 0.009), lymph node involvement (p = 0.03) and patient age (p = 0.04). Additional discontinuous data analysis revealed that high NuMA levels in tumours decreased with grade (p = 0.02) but increased with disease stage (p = 0.04) in serous EOC. NuMA expression decreased in late disease stage 4 endometrioid EOCs. High NuMA levels decreased with increased tumour invasion in all subtypes (p = 0.03). IF of primary cultures revealed that high NuMA levels at mitotic spindle poles were significantly associated with a decreased proportion of cells in cytokinesis (p = 0.05), increased binucleation (p = 0.021) and multinucleation (p = 0.007), and aneuploidy (p = 0.008).NuMA is highly expressed in EOC tumours and high NuMA levels correlate with increases in mitotic defects and aneuploidy in primary cultures.     

Formation of E-cadherin-mediated cell-cell adhesion activates AKT and mitogen activated protein kinase via phosphatidylinositol 3 kinase and ligand-independent activation of epidermal growth factor receptor in ovarian cancer cells

E-cadherin is a well characterized adhesion molecule that plays a major role in epithelial cell adhesion. Based on findings that expression of E-cadherin is frequently lost in human epithelial cancers, it has been implicated as a tumor suppressor in carcinogenesis of most human epithelial cancers. However, in ovarian cancer development, our data from the current study showed that E-cadherin expression is uniquely elevated in 86.5% of benign, borderline, and malignant ovarian carcinomas irrespective of the degree of differentiation, whereas normal ovarian samples do not express E-cadherin. Thus, we hypothesize that E-cadherin may play a distinct role in the development of ovarian epithelial cancers. Using an E-cadherin-expressing ovarian cancer cell line OVCAR-3, we have demonstrated for the first time that the establishment of E-cadherin mediated cell-cell adhesions leads to the activation of Akt and MAPK. Akt activation is mediated through the activation of phosphatidylinositol 3 kinase, and both Akt and MAPK activation are mediated by an E-cadherin adhesion-induced ligand-independent activation of epidermal growth factor receptor. We have also demonstrated that suppression of E-cadherin function leads to retarded cell proliferation and reduced viability. We therefore suggest that the concurrent formation of E-cadherin adhesion and activation of downstream proliferation signals may enhance the proliferation and survival of ovarian cancer cells. Our data partly explain why E-cadherin is always expressed during ovarian tumor development and progression.     

Localisation and expression of aquaporin subtypes in epithelial ovarian tumours

To characterise AQP subtype localisation and expression in epithelial ovarian tumours, immunohistochemistry was used to assess the localisation and expression of AQP1-9 in 30 benign tumour cases, 30 borderline tumour cases, 50 malignant tumour cases and 20 normal ovarian tissue cases. Multiple AQP subtypes were expressed in epithelial ovarian tumours, with each AQP subtype displaying a different pattern of localisation and expression. AQP1 was mainly expressed in the microvascular endothelium, and AQP 2-9 were mainly expressed in tumour cells. Most AQP subtypes co-localised in the basolateral membranes of the epithelia of benign tumours and plasma membranes of malignant tumour cells. The positive rates for AQP1, 5, 6, 7, 8, and 9 were over 50%, but those for AQP2, 3 and 4 were only 10-40%. The expression of AQP1, 5 and 9 in malignant and borderline tumours was significantly higher than that in benign tumours (P<0.05) and normal ovarian tissue (P<0.05). However, AQP6 expression in ovarian malignant and borderline tumours was significantly lower than that in benign tumours (P<0.01) or normal ovarian tissue (P<0.01). AQP1 expression was increased in cases with ascites volumes greater than 1000 mL (P<0.05), AQP5 expression was greater in cases with lymph node metastasis (P<0.05), and more AQP9 expression was observed in G3 cases versus G1 and G2 cases (P<0.01). These results suggest that changes in the distribution and expression of AQP subtypes may be involved in ovarian carcinogenesis. This study presents a novel avenue of research that could illuminate the mechanism of ovarian carcinogenesis and treatment.     

Epidermal growth factor modulates claudins and tight junctional functions in ovarian cancer cell lines

Ovarian adenocarcinomas, like human ovarian surface epithelial cells, form functional tight junctions. Tight junction molecules claudin-3 and claudin-4, which are the receptors of Clostridium perfringens enterotoxin (CPE), are abnormally upregulated in epithelial ovarian cancers of all subtypes including, mucinous cystadenocarcinoma and serous cystadenocarcinoma. Clostridium perfringens enterotoxin may be a novel tumor-targeted therapy for ovarian cancers. In epithelial ovarian cancers, overexpression of epidermal growth factor receptor has been observed and the exogenous ligand EGF induces epithelial-mesenchymal transition in ovarian surface epithelium. Epidermal growth factor (EGF) signaling modulates expression of claudins with changes of fence and barrier functions in various cell types. However, the regulation of tight junctions by EGF in ovarian cancers remains unclear. In the present study, to investigate the mechanisms of the regulation of tight junctions in ovarian cancers, ovarian cancer cell lines mucinous cystadenocarcinoma (MCAS) and serous cystadenocarcinoma (HUOA) were treated with EGF. Epidermal growth factor downregulated claudin-3 in MCAS and claudin-4 in HUOA by inducing degradation of the proteins with changes in structures and functions of tight junctions via the MEK/ERK or PI3K/Akt signaling pathway. In addition, in HUOA but not MCAS, EGF downregulated the cytotoxic effect of CPE via claudin-4. Thus, there were different mechanisms for regulation of claudins by EGF between subtypes of epithelial ovarian cancer cells in vitro. These results indicate that EGF may affect claudins and tight junctional functions in ovarian cancer cells during cancer progression.     

Lineage infidelity of epithelial ovarian cancers is controlled by HOX genes that specify regional identity in the reproductive tract

Although epithelial ovarian cancers (EOCs) have been thought to arise from the simple epithelium lining the ovarian surface or inclusion cysts, the major subtypes of EOCs show morphologic features that resemble those of the müllerian duct-derived epithelia of the reproductive tract. We found that HOX genes, which normally regulate mullerian duct differentiation, are not expressed in normal ovarian surface epithelium (OSE), but are expressed in different EOC subtypes according to the pattern of mullerian-like differentiation of these cancers. Ectopic expression of Hoxa9 in tumorigenic mouse OSE cells gave rise to papillary tumors resembling serous EOCs. In contrast, Hoxa10 and Hoxa11 induced morphogenesis of endometrioid-like and mucinous-like EOCs, respectively. Hoxa7 showed no lineage specificity, but promoted the abilities of Hoxa9, Hoxa10 and Hoxa11 to induce differentiation along their respective pathways. Therefore, inappropriate activation of a molecular program that controls patterning of the reproductive tract could explain the morphologic heterogeneity of EOCs and their assumption of müllerian-like features.     

Aromatase expression in ovarian epithelial cancers

Our study focused on aromatase cytochrome P450 (CYP19) expression in ovarian epithelial normal and cancer cells and tissues. Aromatase mRNA expression was analyzed by real-time PCR in ovarian epithelial cancer cell lines, in human ovarian surface epithelial (HOSE) cell primary cultures, and in ovarian tissue specimens (n=94), including normal ovaries, ovarian cysts and cancers. Aromatase mRNA was found to be expressed in HOSE cells, in BG1, PEO4 and PEO14, but not in SKOV3 and NIH:OVCAR-3 ovarian cancer cell lines. Correlation analysis of aromatase expression was performed according to clinical, histological and biological parameters. Aromatase expression in ovarian tissue specimens was higher in normal ovaries and cysts than in cancers (P<0.0001). Using laser capture microdissection in normal postmenopausal ovaries, aromatase was found to be predominantly expressed in epithelial cells as compared to stromal component. Using immunohistochemistry (IHC), aromatase was also detected in the epithelium component. There was an inverse correlation between aromatase and ERalpha expression in ovarian tissues (P<0.001, r=-0.34). In the cancer group, no significant differences in aromatase expression were observed according to tumor histotype, grade, stage and survival. Aromatase activity was evaluated in ovarian epithelial cancer (OEC) cell lines by the tritiated water assay and the effects of third-generation aromatase inhibitors (AIs) on aromatase activity and growth were studied. Letrozole and exemestane were able to completely inhibit aromatase activity in BG1 and PEO14 cell lines. Interestingly, both AI showed an antiproliferative effect on the estrogen responsive BG1 cell line co-expressing aromatase and ERalpha. Aromatase expression was found in ovarian epithelial normal tissues and in some ovarian epithelial cancer cells and tissues. This finding raises the possibility that some tumors may respond to estrogen and provides a basis for ascertaining an antimitogenic effect of AI in a subgroup of ovarian epithelial cancers.     

Gene expression patterns in ovarian carcinomas

We used DNA microarrays to characterize the global gene expression patterns in surface epithelial cancers of the ovary. We identified groups of genes that distinguished the clear cell subtype from other ovarian carcinomas, grade I and II from grade III serous papillary carcinomas, and ovarian from breast carcinomas. Six clear cell carcinomas were distinguished from 36 other ovarian carcinomas (predominantly serous papillary) based on their gene expression patterns. The differences may yield insights into the worse prognosis and therapeutic resistance associated with clear cell carcinomas. A comparison of the gene expression patterns in the ovarian cancers to published data of gene expression in breast cancers revealed a large number of differentially expressed genes. We identified a group of 62 genes that correctly classified all 125 breast and ovarian cancer specimens. Among the best discriminators more highly expressed in the ovarian carcinomas were PAX8 (paired box gene 8), mesothelin, and ephrin-B1 (EFNB1). Although estrogen receptor was expressed in both the ovarian and breast cancers, genes that are coregulated with the estrogen receptor in breast cancers, including GATA-3, LIV-1, and X-box binding protein 1, did not show a similar pattern of coexpression in the ovarian cancers.     

Cell-nonautonomous induction of ovarian and uterine serous cystadenomas in mice lacking a functional Brca1 in ovarian granulosa cells

Women with germline mutations in BRCA1 have a 40% risk of developing ovarian cancer by age 70 and are also predisposed to cancers of the fallopian tubes. Given that ovulatory activity is a strong risk factor for sporadic ovarian cancer, we hypothesized that reduced BRCA1 expression might predispose to gynecological cancers indirectly, by influencing ovarian granulosa cells. These cells secrete sex steroids that control the ovulatory cycle and influence the growth of ovarian epithelial tumors. Granulosa cells also secrete mullerian inhibiting substance (MIS), a hormone that inhibits both the formation of female reproductive organs in male embryos and the proliferation of ovarian epithelial tumor cells. We tested this hypothesis by using the Cre-lox system to inactivate the Brca1 gene in mouse ovarian granulosa cells. A truncated form of the Fsh receptor promoter served as the Cre driver. Here, we show that indeed, inactivation of the Brca1 gene in granulosa cells led to the development of cystic tumors in the ovaries and uterine horns. These tumors carried normal Brca1 alleles, supporting the view that Brca1 may influence tumor development indirectly, possibly through an effector secreted by granulosa cells.     

MMP-2、MMP-7在卵巢癌中的表达及其临床意义

目的 探讨MMP-2、MMP-7的表达与卵巢癌临床病理生物学行为的关系以及对患者预后的影响.方法 应用核酸原位杂交和免疫组化对97例卵巢上皮性癌和23例卵巢上皮性良性肿瘤组织进行MMP-2、MMP-7mRNA及蛋白的检测.结果 MMP-2、MMP-7 mRNA及蛋白的表达阳性率在卵巢癌组均显著高于良性肿瘤组(P<0.05).多因素分析,PTNM分期、MMP-2及MMP-7的表达是影响卵巢癌根治术后患者预后的独立因素(P<0.05);MMP-2阳性组与阴性组5年生存率分别为30.6%和76.0%,MMP-7阳性组与阴性组5年生存率分别为19.7%和80.6%,差异均有统计学意义(P<0.05).结论 MMP-2、MMP-7的过表达促进卵巢癌的浸润和转移,联合检测MMP-2和MMP-7可能作为预测和评价患者预后的生物学指标.     

Decreased expression of autophagy-related proteins in malignant epithelial ovarian cancer

Some studies have shown that the change of autophagic capacity may correlate with malignant transformation. Our study was designed to investigate the expression and significance of two autophagy-related proteins, microtubule-associated protein 1 light chain 3 (LC3) and Beclin 1 in the tumorigenesis and development of epithelial ovarian carcinoma. We observed that the positive expression of LC3 and Beclin 1 was significantly higher in the samples of benign and borderline ovarian tumors than those in malignant epithelial ovarian cancers. The expression of LC3 and Beclin 1 was associated with FIGO stage and histological grade. No significant relationship was observed between age and histological grade. However, we observed that the expression of LC3 was not related to Beclin 1. Therefore, the decrease of autophagic capacity may be related to tumorigenesis and development of epithelial ovarian cancer.     

The RAB25 small GTPase determines aggressiveness of ovarian and breast cancers

High-density array comparative genomic hybridization (CGH) showed amplification of chromosome 1q22 centered on the RAB25 small GTPase, which is implicated in apical vesicle trafficking, in approximately half of ovarian and breast cancers. RAB25 mRNA levels were selectively increased in stage III and IV serous epithelial ovarian cancers compared to other genes within the amplified region, implicating RAB25 as a driving event in the development of the amplicon. Increased DNA copy number or RNA level of RAB25 was associated with markedly decreased disease-free survival or overall survival in ovarian and breast cancers, respectively. Forced expression of RAB25 markedly increased anchorage-dependent and anchorage-independent cell proliferation, prevented apoptosis and anoikis, including that induced by chemotherapy, and increased aggressiveness of cancer cells in vivo. The inhibition of apoptosis was associated with a decrease in expression of the proapoptotic molecules, BAK and BAX, and activation of the antiapoptotic phosphatidylinositol 3 kinase (PI3K) and AKT pathway, providing potential mechanisms for the effects of RAB25 on tumor aggressiveness. Overall, these studies implicate RAB25, and thus the RAB family of small G proteins, in aggressiveness of epithelial cancers.     

Animal models of ovarian cancer

Ovarian cancer is the most lethal of all of the gynecological cancers and can arise from any cell type of the ovary, including germ cells, granulosa or stromal cells. However, the majority of ovarian cancers arise from the surface epithelium, a single layer of cells that covers the surface of the ovary. The lack of a reliable and specific method for the early detection of epithelial ovarian cancer results in diagnosis occurring most commonly at late clinical stages, when treatment is less effective. In part, the deficiency in diagnostic tools is due to the lack of markers for the detection of preneoplastic or early neoplastic changes in the epithelial cells, which reflects our rather poor understanding of this process. Animal models which accurately represent the cellular and molecular changes associated with the initiation and progression of human ovarian cancer have significant potential to facilitate the development of better methods for the early detection and treatment of ovarian cancer. This review describes some of the experimental animal models of ovarian tumorigenesis that have been reported, including those involving specific reproductive factors and environmental toxins. Consideration has also been given to the recent progress in modeling ovarian cancer using genetically engineered mice.     

Constitutive Production of Macrophage Colony-Stimulating Factor and Interleukin-6 by Human Ovarian Surface Epithelial Cells

Normal and neoplastic epithelial cells produce growth factors that can affect cells from different lineages. Epithelial ovarian cancers produce M-CSF and IL-6. In the present study, production of these cytokines has been measured in the apparently normal epithelial cells from which epithelial ovarian neoplasms are thought to arise. Epithelial cells from the surface of premenopausal human ovaries were established in short-term cultures. The cells bound anti-cytokeratin antibodies and exhibited characteristic epithelial morphology by light and transmission electron microscopy. M-CSF and IL-6 were detected in supernatants from cultures of these cells, using assays specific for each factor. Cytokine levels were comparable to those in supernatants from ovarian and breast cancer cell lines. M-CSF expression could also be demonstrated by immunohistochemical analysis with specific rabbit heteroantiserum. Thus, M-CSF and IL-6 are produced constitutively by normal as well as by neoplastic ovarian epithelium.