We have developed a transgenic (TG) mouse model for gonadal tumorigenesis expressing the Simian virus 40 T-antigen (Tag) under the mouse inhibin alpha-subunit promoter. Gonadal tumors appear with 100% penetrance by the age of 5-8 months in the TG mice. When 1-month-old TG mice were gonadectomized, adrenal gland tumors were observed in each animal (12 females, 11 males) at the age of 6-8 months. No adrenal tumors were detected in gonadectomized non-TG mice (nine females, nine males) or in the intact TG mice (n > 100). The tumors appeared to originate from the X zone of the adrenal cortex. The TG mice with adrenocortical tumors had elevated serum levels of progesterone, estradiol, and immunoreactive inhibin (including dimeric forms), but corticosterone secretion was reduced. The lack of adrenal tumors in intact TG mice suggested that the tumorous gonads secrete factor(s) inhibiting adrenal tumorigenesis. As a candidate molecule, we studied the effects of inhibin, which was high in the serum of control females and TG females with ovarian tumors, as well as in TG males with testicular tumors. The DNA synthesis, as well as the levels of inhibin-alpha and Tag mRNA expression, were significantly reduced by recombinant human inhibin A in cell cultures derived from the adrenal tumors. In accordance, the expression level of inhibin-alpha mRNA in the normal adrenal gland was elevated 2 weeks after gonadectomy. These findings suggest that gonadal inhibin can down-regulate the expression of the inhibin alpha-subunit gene in the adrenal gland. When circulating inhibin is eliminated by gonadectomy, Tag expression and tumorigenesis are stimulated in the adrenal glands of the TG mice. The results demonstrate a novel mechanism of autoregulation in inhibin alpha-subunit gene expression.

Transgenic (TG) mice expressing the Simian virus 40 T-antigen under the control of the murine inhibin-a promoter (Inha/Tag) develop granulosa and Leydig cell tumors at the age of 5-6 months, with 100% penetrance. When these mice are gonadectomized, they develop adrenocortical tumors. Suppression of gonadotropin secretion inhibits the tumorigenesis in the gonads of intact animals and in the adrenals after gonadectomy. To study further the role of luteinizing hormone (LH) in gonadal and adrenal tumorigenesis, a double TG mouse model was generated by crossing the Inha/Tag mice with mice producing constitutively elevated levels of LH (bLHb-CTP mice). Our results show that in double TG mice (bLHb-CTP/Inha/Tag), gonadal tumorigenesis starts earlier and progresses faster than in Inha/Tag mice. Both ovarian and testicular tumors were histologically comparable with the tumors found in Inha/Tag mice. In addition, adrenal tumorigenesis was found in intact double TG females, but not in Inha/Tag females. Inhibin-a and LH receptor (LHR) were highly expressed in tumorigenic gonadal tissues, and the elevated LH levels were shown to be associated with ectopic LHR and high inhibin-a expression in the female adrenals. We conclude that in the Inha/Tag tumor mouse model, elevated LH levels act as a tumor promoter, advancing gonadal and adrenal tumorigenesis.

Transgenic (TG) female mice, expressing a chimeric bovine luteinizing hormone (LH) β-subunit/human chorionic gonadotropin β-subunit COOH-terminal extension (bLHβ-CTP) gene, produce high levels of circulating LH and serve as a model for functional ovarian hyperandrogenism and follicular cysts. We report here that obesity is a typical feature of these female mice. The mean body weight of the bLHβ-CTP females was significantly higher than in controls at, and beyond 5 wk of age, and at 5 mo, it was 32% increased. At this age, the amount of white adipose tissue in the bLHβ-CTP females was significantly increased, as reflected by the weight difference of the retroperitoneal fat pad. In addition, the expression of leptin mRNA in white adipose tissue of the TG females was elevated about twofold. Serum leptin and insulin levels, and food intake, were also increased significantly in the TG females. Brown adipose tissue (BAT) thermogenic activity, as measured by GDP binding to BAT mitochondria, was reduced ( P < 0.05). Ovariectomy at the age of 3 wk totally prevented the development of obesity. In summary, the present results show that intact female bLHβ-CTP mice are obese, have increased food consumption, and reduced BAT thermogenic activity. The weight gain can be explained partly by elevated androgens but is probably also contributed to the increased adrenal steroidogeneisis. Hence, the bLHβ-CTP mice provide a useful model for studying obesity related to elevated LH secretion, with consequent alterations in ovarian and adrenal function.

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We have previously produced transgenic (TG) mice expressing the mouse inhibin -subunit promoter/Simian virus 40 T-antigen (Inh /Tag) fusion gene. The mice develop gonadal somatic cell tumors at the age of 5-7 months; the ovarian tumors originate from granulosa cells, and those of the testes from Leydig cells. In the present study another TG mouse line was produced, expressing under the same inh-promoter the herpes simplex virus thymidine kinase gene (Inh /TK). Crossbreeding of the two TG mouse lines resulted in double TG mice (Inh / TK-Inh /Tag), which also developed gonadal tumors. The single (Inh /Tag) and double TG (Inh /TK-Inh / Tag) mice, both bearing gonadal tumors, were treated at the age of 5·5-6·5 months with ganciclovir (GCV, 150 mg/kg body weight twice daily i.p.) for 14 days, or with aciclovir (ACV, 300-400 mg/kg body weight per day perorally) for 2 months. During GCV treatment, the total gonadal volume including the tumor, decreased in double TG mice by an average of 40% (P<0·05), while in single TG mice, there was a concomitant increase of 60% in gonadal size (P<0·05). GCV was also found to increase apoptosis in gonads of the double TG mice. Peroral treatment with ACV was less effective, it did not reduce significantly the gonadal volume. We also analyzed the in vitro efficacy of ACV and GCV treatments in transiently HSV-TK-transfected KK-1 murine granulosa tumor cells, originating from a single-positive Inh /Tag mouse. GCV proved to be more effective and more specific than ACV in action. These results prove the principle that targeted expression of the HSV-TK gene in gonadal somatic cell tumors is potentially useful for tumor ablation by antiherpes treatment. The findings provide a lead for further development of somatic gene therapy for gonadal tumors.