Ovarian stimulation and granulosa-cell tumour

Ovarian pathology and high incidence of sex cord tumors in follitropin receptor knockout (FORKO) mice

In this investigation we describe our observations of the status of the aging ovary in mice with disruption of the receptor for FSH. Knockout mice at 3-5 months of age are acyclic and sterile, with very small, underdeveloped ovaries. Thus, they exhibit hypergonadotropic-hypogonadism with high levels of circulating FSH similar to the postmenopausal state in women. By 12 months more than 92% of these animals developed various kinds of ovarian pathology, including neoplasms of sex cord-stromal type as well as cysts. Interestingly, the majority of tumors were located in the right ovary, with the contralateral ovary remaining unaffected but atrophic. The ovary from heterozygotes also showed pathology after 15 months. None of the age-matched wild-type mice that remained fertile developed any sign of ovarian tumors. Circulating LH and FSH levels were increased in follitropin receptor knockout mice and remained severalfold higher in tumor-bearing animals. The histological appearances of ovarian tumors were similar to the pathology observed in some types of sex cord-stromal neoplasms in women. The tumor burden caused weight loss and cachexia in follitropin receptor knockout mice. Based on these characteristics as well as the high incidence of ovarian pathology in the aging mutant, we propose that the loss of the FSH receptor signaling mechanisms predispose the ovary to molecular and structural changes leading to tumor formation. Hence, in the intact and fertile animal, FSH receptor signaling offers a protective mechanism that is lost upon reproductive senescence (menopause in women). Further studies are warranted in this genetic model to explore the molecular changes underlying the development of ovarian neoplasia.

Loss of alternately spliced messenger RNA of the luteinizing hormone receptor and stability of the follicle-stimulating hormone receptor messenger RNA in granulosa cell tumors of the human ovary

OBJECTIVES

The expression of messenger RNA (mRNA) for the LH (LHR) and FSH receptors (FSHR) was examined in normal human corpora lutea and granulosa cell tumors.

METHODS

Expression was examined by RT/PCR and DNA sequencing techniques.

RESULTS

The full-length (FL) coding region and seven additional isoforms were identified for normal LHR mRNA. Isoform 1 had portions of exons II and III deleted, and isoform 2 had exon IX omitted. Isoform 3 also had portions of exons II and III deleted and all of exon IX deleted. Exons III through VI were missing in isoforms 4-7. Isoform 5 also had exon IX omitted, and isoform 6 also had part of exon XI missing. Isoform 7 also had exon IX and part of exon XI deleted. An aberrant migration pattern of the LHR mRNA isoforms was observed for granulosa cell tumors with FIGO Stage I-IV. Five tumor samples of Stage III-IV had many isoforms absent. Seven Stage I samples had aberrant migration patterns that depended on the size of the tumor. As the size of the tumor increased the aberrant migration pattern of the LHR mRNA isoforms was more pronounced and some isoforms were not detected. The FL and at least one additional isoform were identified for FSHR mRNA. Isoform 1 had regions of exons IV and V deleted. The FSHR mRNA isoforms had a similar migration pattern for the normal ovary and the granulosa cell tumors.

CONCLUSIONS

Alternately spliced forms of mRNA for the LHR and FSHR exist for normal human ovary and granulosa cell tumors. The aberrant migration and missing LHR mRNA isoforms in granulosa cell tumors do not appear to result from general genomic instability associated with tumor progression. These findings are important to understand the role of alternate splicing in the regulation of LHR and FSHR expression in different pathological states.

A mutation in the follicle-stimulating hormone receptor occurs frequently in human ovarian sex cord tumors

A subset of ovarian tumors, referred to as sex cord-stromal tumors, produce endocrine manifestations due to the secretion of estrogens or androgens. Because gonadotropins induce the growth, differentiation, and function of the steroid-producing cells of the ovary, we hypothesized that mutations in the FSH receptor (FSH-R) might occur in this group of tumors. Ovarian sex cord tumors (n = 13), small cell carcinomas of the ovary (n = 3), and control DNA specimens (n = 116) were screened for mutations in the transmembrane domains of the FSH-R. A heterozygous T-->C mutation was found at nucleotide 1777 that converts codon 591 from phenylalanine to serine (F591S). This sixth transmembrane domain mutation was found in 9 of 13 (69%) sex cord tumors and 2 of 3 ovarian small cell carcinomas, but it was not present in control specimens, including 5 normal ovaries, 5 nonsex cord ovarian tumors, 16 thyroid tumors, or 90 specimens of peripheral blood leukocyte DNA, suggesting that this nucleotide change is not a polymorphism. The functional effects of identified mutations were assessed by expression of the wild-type or the F591S mutant FSH-R in COS-7 cells. The F591S mutation eliminated FSH-stimulated cAMP production, and a similar effect was observed when this mutation was introduced into the homologous location of the LH receptor. The high prevalence of the F591S mutation in the FSH-R suggests that it plays a role in the development of ovarian sex cord tumors.