Immunohistochemical localization of inhibin and activin subunits in human epithelial ovarian tumors

Inhibin subunit beta B (INHBB): an emerging role in tumor progression

The gene inhibin subunit beta B (INHBB) encodes the inhibin βB subunit, which is involved in forming protein members of the transforming growth factor-β (TGF-β) superfamily. The TGF-β superfamily is extensively involved in cell proliferation, differentiation, adhesion, movement, metabolism, communication, and death. Activins and inhibins, which belong to the TGF-β superfamily, were first discovered in ovarian follicular fluid. They were initially described as regulators of pituitary follicle-stimulating hormone (FSH) secretion both in vivo and in vitro. Later studies found that INHBB is expressed not only in reproductive organs such as the ovary, uterus, and testis but also in numerous other organs, including the brain, spinal cord, liver, kidneys, and adrenal glands. This wide distribution implies its involvement in the normal physiological functions of various organs; however, the mechanisms underlying these functions have not yet been fully elucidated. Recent studies suggest that INHBB plays a significant, yet complex role in tumorigenesis. It appears to have dual effects, promoting tumor progression in some contexts while inhibiting it in others, although these roles are not yet fully understood. In this paper, we review the different expression patterns, functions, and mechanisms of INHBB in normal and tumor tissues to illustrate the research prospects of INHBB in tumor progression.

Inhibin Alpha Expression in Human Tumors: A Tissue Microarray Study on 12,212 Tumors

As a result of its expression in corresponding normal cell types, inhibin alpha (INHA) is used as an immunohistochemical marker for adrenocortical neoplasms and testicular or ovarian sex cord stromal tumors. However, other tumors can also express INHA. To comprehensively determine INHA expression in cancer, a tissue microarray containing 15,012 samples from 134 different tumor types and subtypes was analyzed by immunohistochemistry. INHA positivity was found in 72 of 134 tumor categories, including 26 categories with ≥1 strongly positive case. A moderate to strong INHA positivity was found in 100% of 37 granulosa cell tumors of the ovary, 100% of 43 other sex cord stromal tumors of the ovary/testis, 100% of 31 granular cell tumors, 78.5% of 28 adenomas, 44% of 25 carcinomas of the adrenal cortex, and 46.7% of 15 pancreatic acinar cell carcinomas. At least a weak INHA positivity was seen in <33% of cases of 46 additional tumor entities. In summary, these data support the use of INHA antibodies for detecting sex cord stromal tumors, granular cell tumors, and adrenocortical neoplasms. Since INHA can also be found in other tumor entities, INHA immunohistochemistry should only be considered as a part of any panel for the distinction of tumor entities.

High Concentrations of Activin A in the Peritoneal Fluid of Women With Epithelial Ovarian Cancer

OBJECTIVE

The aim of the present study was to evaluate the concentrations of activin A in the peritoneal fluid of women with epithelial (serous) ovarian cancer.

METHODS

A group of 160 women was studied and divided in four subgroups as follows: 1) serous ovarian carcinoma (n = 32); 2) serous ovarian cystadenoma (n = 20); 3) endometriosis (n = 53); and 4) healthy controls (n = 55), including both fertile (n = 32) and postmenopausal women (n = 23). Specimens of peritoneal fluid were collected during surgical interventions, and activin A was quantified using a specific two-site enzyme immunoassay.

RESULTS

Peritoneal fluid activin A concentrations in women with ovarian carcinoma were about five-fold higher than those found in the control group (median [interquartile range] = 7.60 [2.85-10.15] and 1.50 [1.00-2.50] ng/mL, respectively, P <.001). In contrast, the women with benign serous cystadenoma had peritoneal fluid activin A concentrations (1.50 [1.0-2.70] ng/mL) similar to those of the control group. High peritoneal fluid activin A levels (>2 multiples of the mean) distinguished carcinoma from cystadenoma with a sensitivity of 72% and a specificity of 80%. The follow-up of nine patients with stage IIIc ovarian cancer showed no apparent relationship between the peritoneal fluid activin A levels and overall survival. No significant difference in peritoneal fluid activin A concentrations between patients with endometriosis and control women was observed.

CONCLUSION

Most women with serous ovarian carcinoma had high concentrations of activin A in the peritoneal fluid, supporting a possible role of this growth factor in ovarian cancer.

Endocrine signaling in ovarian surface epithelium and cancer

Ovarian cancer is the sixth most common cancer and the fifth leading cause of cancer-related death among women in developed countries. Greater than 85% of human ovarian cancer arises within the ovarian surface epithelium (OSE), with the remainder derived from granulosa cells or, rarely, stroma or germ cells. The pathophysiology of ovarian cancer is the least understood among all major human malignancies because of a poor understanding of the aetiological factors and mechanisms of ovarian cancer progression. There is increasing evidence suggesting that several key reproductive hormones, such as GnRH, gonadotrophins and sex steroids, regulate the growth of normal OSE and ovarian cancer cells. The objective of this review was to highlight the effects of these endocrine factors on ovarian cancer cell growth and to summarize the signalling mechanisms involved in normal human OSE and its neoplastic counterparts.

Inhibin Resistance Is Associated with Aggressive Tumorigenicity of Ovarian Cancer Cells

Malignant ovarian epithelial tumors have been shown to have decreased inhibin production relative to activin production compared with normal ovarian surface epithelial (OSE) cells and nonmalignant ovarian tumors. Activin stimulates proliferation of many ovarian cancer cell lines. Inhibin antagonizes the action of activin, and inhibin-deficient mice develop gonadal tumors, suggesting that inhibin may be a tumor suppressor. However, its effects on OSE and ovarian cancer cells are unknown. We hypothesize that activin and inhibin are important regulators of biological activity in ovarian cancers. We found that inhibin A decreased murine OSE proliferation, whereas activin A had no effect. Activin A increased the proliferation of four of eight ovarian cancer cell lines (SKOV3, OCC1, OVCAR3, and A2780-s). Inhibin A decreased the proliferation of SKOV3, A2780-s, and OVCAR3 but had no effect on OCC1, ES-2, HEY, A2780-cp, and OVCA429 cells. When injected into nude mice, the inhibin-resistant cancer cell lines resulted in shorter survival time compared with the inhibin-responsive cells. Further investigations on SKOV3 and OCC1 cells showed that activin A increased invasion through Matrigel. Inhibin A decreased both basal and activin-induced proliferation and invasion of SKOV3 but had no effect on OCC1 cells. Reverse transcription-PCR analyses showed that the SKOV3 and OCC1 cells produced activin, but only SKOV3 produced inhibin. Analysis of the activin/inhibin signaling pathways indicated that Smad anchor for receptor activation was elevated in SKOV3 and OCC1 cells and that an up-regulation of the activin receptor expression may explain the inhibin resistance of OCC1 cells. Our results suggest that activin responsiveness may be gained during transformation of OSE cells and that inhibin resistance may contribute to the aggressive behavior of ovarian cancer cells.

Inhibins and ovarian cancer

The inhibins are produced and secreted by several ovarian cancers. Monitoring serum levels by immunoassay may be a useful diagnostic aid in the initial assessment of this disease and in monitoring its potential recurrence following surgery. The assays are applicable to women after menopause when the majority of ovarian cancers are detected, and when the normal ovarian production of inhibin is low to negligible. A new inhibin immunoassay (total inhibin ELISA) has been developed with the intention of widespread clinical application. The assay readily detects granulosa cell and mucinous tumours. CA125, a widely used ovarian cancer marker, detects the other main ovarian cancer types (serous, endometrioid, undifferentiated) with high sensitivity. The combination of the two tests detects the majority of ovarian cancers with high specificity (95%) and sensitivity (95%). Studies have been undertaken to assess its application to women in the perimenopausal stage and to younger women during normal reproductive life. These studies are providing a platform for the introduction of the test into clinical practice.

Inhibin alpha and beta expression in ovarian stromal tumors and their histological equivalences

Inhibin is a heterodimeric protein hormone that appears to be a sensitive immunohistochemical marker of sex cord-stromal tumors. Although sex cord-stromal tumors can usually be distinguished from ovarian epithelial tumors or their metastases by morphology or by using antibodies against intermediate filaments, the diagnosis remains difficult in rare situations in such cases as sarcomatoid granulosa-theca cell tumors, ovarian small cell carcinomas, or soft-tissue sarcomas. The purposes of this study were to examine inhibin alpha and beta immunoreactivity in a wide range of gonadal stromal neoplasms and to assess its value in the differential diagnosis of problematic tumors. A total of 108 paraffin-embedded ovarian and extraovarian tumors were examined immunohistochemically by using anti-alpha inhibin and anti-beta inhibin. Inhibin alpha immunostaining was identified in 46 (81%) of 57 gonadal stromal tumors, one (14%) of seven endometrial stromal tumors, and one (50%) of two primary ovarian carcinoid tumors. Inhibin beta immunostaining was detected in 55 (96%) of 57 gonadal stromal tumors, two (29%) of seven endometrial stromal tumors, one (50%) of two dysgerminomas, and in all of two (100%) primary ovarian carcinoid tumors. Inhibin alpha expression was not detected in any ovarian surface epithelial tumor cells. Some surface epithelial tumors showed stromal inhibin alpha (15% of cases) and inhibin beta (48% of cases) positivity. Weak immunoreactivity for inhibin beta was found in most (83% of cases) ovarian surface epithelial tumors. Two ovarian Burkitt lymphomas were negative for inhibin alpha and beta. Inhibin alpha is a sensitive immunohistochemical marker of gonadal stromal tumors and is of value in the differential diagnosis of ovarian neoplasia. Inhibin beta is a nonspecific marker for ovarian neoplasms, showing expression on tumor and stromal cells of different epithelial or stromal tumors.

Establishment and Characterization of a Human Ovarian Granulosa Tumor Cell line (HSOGT)

We successfully established a novel ovarian granulosa tumor cell line (HSOGT). The tumor tissue of the ovary was derived from a 25 year-old Japanese woman under her consent. The cell line was maintained for over 14 months, subcultured more than 73 times, and had a population doubling time of 18.9 hours. Phase contrast microscopy displayed a pavement-like arrangement without contact inhibition. The chromosome number showed a wide distribution of aneuploidy and the mode was 83; many marker chromosomes were observed. The HSOGT was also successfully xenotransplanted into nude mice. The cell line produced estradiol and has preserved some characters of granulosa cells with stable growth in vitro. We firmly believe that this cell line will be a most useful tool for endocrinological investigation of human granulosa cells.

The role of calretinin, inhibin, melan-A, BCL-2, and C-kit in differentiating adrenal cortical and medullary tumors: an immunohistochemical study

Morphologic distinction between adrenal cortical and medullary tumors can be difficult. Previous studies have shown inhibin, melan-A, and BCL-2 to be useful markers for adrenal cortical tumors. We have recently observed a high level of calretinin expression in normal adrenal cortex but not the medulla and therefore evaluated its diagnostic application for adrenal tumors in comparison with inhibin, melan-A, and BCL-2. C-kit is a transmembrane tyrosine kinase receptor. Immunodetection of c-kit expression has been recently used for tumor diagnosis, and c-kit-positive tumors can potentially benefit from kit kinase inhibitor treatment. Although c-kit expression was reported in adrenal medulla and pheochromocytoma, it has not been evaluated in adrenal cortical tumors. In this study, 28 adrenal cortical tumors (12 carcinomas, 16 adenomas), 20 pheochromocytomas, and 20 extraadrenal paragangliomas were evaluated for calretinin, inhibin, melan-A, BCL-2, and c-kit expression by standard immunohistochemical assays on paraffin sections. The percentage of immunoreactivity in adrenal cortical tumors was as follows: calretinin, 96%; melan-A, 89%; inhibin, 92%; BCL-2, 20%; and c-kit, 5%. Normal adrenal medulla did not stain for c-kit but was positive for BCL-2. Eighty-six percent of pheochromocytomas stained for BCL-2 and none for calretinin, with the exception of the ganglioneuromatous areas in composite pheochromocytomas (n = 5). Extraadrenal paragangliomas showed reactivity with calretinin in 25%, melan-A in 5%, inhibin in 16%, BCL-2 in 38%, and c-kit in 8% of the cases. Our results indicate that calretinin is the most sensitive among all the adrenal markers tested. Like melan-A and inhibin, calretinin is also a very specific marker in differentiating cortical from medullary adrenal tumors. In addition, calretinin can be used to confirm a composite pheochromocytoma. BCL-2 does not appear to be useful in differentiating adrenal cortical from medullary tumors. C-kit is not useful in the diagnosis of adrenal tumors, and kit kinase inhibitor might have a limited role in the treatment of adrenal tumors and paraganglioma because of the low frequency of c-kit expression in these tumors.

Activin betaB expression in rat experimental goiter and human thyroid tumors

Activins are dimeric proteins of the transforming growth factor beta superfamily, which exhibit multiple functions in gonadal and extragonadal tissues. Expression of activin A, composed of two betaA subunits, has been shown in the thyroid, whereas there has been no study regarding activin B (betaBbetaB) in this gland. In other tissues, such as the gonads, pancreas, and adrenal cortex, expression of both activin betaA and activin betaB has been described. In this study, we detected activin betaB mRNA and protein expression using reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry in rat experimental goiter and in human thyroid, including multinodular goiter, follicular adenoma, papillary carcinoma, and follicular carcinoma. Activin betaA mRNA and protein expression was also investigated in rat and human thyroid tissue. The expression of both activin betaB and activin betaA was highest in rat methimazole-induced goiter and in human follicular adenoma, and papillary and follicular carcinomas when compared with multinodular goiter and normal thyroid tissue. The increased expression of activin betaB as well as activin betaA, observed in this study, suggests that activin B and activin A may be involved in the proliferative and neoplastic processes of the thyroid.

Gonadoblastoma and dysgerminoma associated with XY gonadal dysgenesis in an adolescent with chronic renal failure: a case of Frasier syndrome

STUDY OBJECTIVES

To report a rare reason for primary amenorrhea, a Frasier syndrome, XY gonadal dysgenesis associated with renal failure with eventual development of gonadoblastoma. To study immunohistochemical analysis of gonadoblastoma and dysgerminoma. To analyze the possibility of androgen receptor mutation in this rare syndrome.

METHODS

We report a case of a 16-yr-old female with this syndrome. She underwent a laparoscopic bilateral gonadectomy and salpingectomy. A histopathological examination revealed gonadoblastoma with focal malignant dysgerminoma in the left dysgenetic gonad and an immunohistochemical of these fairly rare, malignant tumors. An androgen receptor was coded. Analysis was done.

RESULTS

Immunohistochemical analysis showed that inhibin was strongly positive in gonadoblastoma but negative in dysgerminoma. No mutations of the androgen receptor gene were found.

CONCLUSIONS

Inhibin positivity in gonadal stroma and in gonadoblastoma may indicate hormonal activity causing advanced puberty in patients with XY gonadal dysgenesis.

Inhibins/activins as diagnostic markers for ovarian cancer

It is widely recognised that the early detection and subsequent assessment of recurrence of ovarian cancers are key steps for successful treatment. Available serum markers (e.g. CA125) are sensitive for some epithelial carcinomas (e.g. serous, endometrioid, clear cell), however, these markers are less sensitive for granulosa cell tumours and mucinous carcinomas. Serum inhibin is an ovarian product which decreases to non detectable levels after menopause, however, certain ovarian cancers (mucinous carcinomas and sex cord stromal tumours such as granulosa cell tumours) continue to produce inhibin which provides a basis for a serum diagnostic test. Studies from this and other laboratories have investigated the suitability of inhibin as a diagnostic marker by identifying which inhibin (inhibin A (alphabetaA), inhibin B (alphabetaB), free alpha subunit) or activin (betaAbetaA) form is associated with these cancers. Available data show that inhibin assays which detect all inhibin forms, i.e. assays which detect the alpha subunit both as the free form and as an alphabeta subunit dimer provide the highest sensitivity/specificity characteristics as an ovarian cancer diagnostic test. This review will discuss the data supporting these observations and show recent studies in which a new alpha subunit monoclonal antibody-based ELISA is used as a potential diagnostic test. Furthermore, based on the high sensitivity/specificity characteristics of the respective assays for the various types of ovarian cancer, the combination of the inhibin assay with CA125 detects the majority of all ovarian cancers.

Activins and inhibins in endocrine and other tumors

Inhibin and activin are members of the TGF beta superfamily of growth and differentiation factors. They were first identified as gonadal-derived regulators of pituitary FSH and were subsequently assigned multiple actions in a wide range of tissues. More recently, the inhibin alpha subunit was considered as a tumor suppressor based on functional studies employing transgenic mouse models. This review evaluates the functional and molecular evidence that the inhibin alpha subunit is a tumor suppressor in endocrine cancers. The evaluation highlights the discrepant results from the human and mouse studies, as well as the differences between endocrine tumor types. In addition, we examine the evidence that the activin-signaling pathway is tumor suppressive and identify organ-specific differences in the actions and putative roles of this pathway in endocrine tumors. In summary, there is a considerable body of evidence to support the role of inhibins and activins in endocrine-related tumors. Future studies will define the mechanisms by which inhibins and activins contribute to the process of initiation, promotion, or progression of endocrine-related cancers.

Production of activin A in hyperplasia and adenocarcinoma of the human endometrium

OBJECTIVES

To examine the possible localization and production of activin A in human normal endometrium, endometrial hyperplasia, and adenocarcinoma tissues.

METHODS

Human endometrial tissues were collected from 45 patients who were undergoing abdominal hysterectomy. Tissue sections were stained with monoclonal antibodies against the inhibin/activin alpha- and beta A-subunits and activin A using an avidin-biotin-peroxidase complex technique. Concentrations of activin A and inhibin A in tissue extracts of the endometrial tissues were measured using enzyme-linked immunosorbent assays (ELISAs). The expressions of the inhibin alpha-subunit and activin beta A-subunit messenger RNA (mRNA) in the endometrial tissues were demonstrated by reverse transcription-polymerase chain reaction (RT-PCR) analysis.

RESULTS

No immunostaining with an antibody against the inhibin alpha-subunit was observed in human normal endometrium, endometrial hyperplasia, and adenocarcinoma. By contrast, immunostaining for the activin beta A-subunit and activin A was observed in the cytoplasm of glandular cells in normal endometrium, endometrial hyperplasia, and tumor cells of endometrial adenocarcinoma. The percentages of stained cells in endometrial adenocarcinoma were higher than those in normal endometrium. Also, the percentages of stained tumor cells with poor differentiation were higher than those with good and moderate differentiation of the endometrium. The stromal cells in normal endometrium, endometrial hyperplasia, and adenocarcinoma were weakly immunoreactive with antibodies against the beta A-subunit and activin A. Immunoreactivity of activin A in tissue extracts from normal endometrium and endometrial adenocarcinoma was detected by the two-site ELISA. Immunoreactivity of activin A was significantly higher in adenocarcinoma than in normal endometrium. On the other hand, the immunoreactive inhibin A was not detected. The expression of the alpha-subunit mRNA in endometrial tissues was demonstrated as the RT-PCR products migrated at 905 bp and the PCR products of the beta A-subunit showed a band at 366 bp.

CONCLUSIONS

It is suggested that activin A, but not inhibins, are produced by endometrial tissues. The amounts of produced activin A were higher in adenocarcinoma tissues than in normal endometrium. Activin A might be involved in human endometrial tumorigenesis.