Ovarian tumorigenesis in mice transgenic for murine inhibin alpha subunit promoter-driven Simian Virus 40 T-antigen: ontogeny, functional characteristics, and endocrine effects

We previously reported formation of ovarian granulosa cell tumors with 100% penetration in a transgenic mouse model with murine inhibin alpha subunit promoter-driven (inhalpha)/Simian Virus 40 T-antigen (Tag). The tumor-bearing inhalpha/Tag mice showed highly elevated serum levels of immunoreactive inhibin. To investigate the onset of tumorigenesis and related endocrine consequences, 6-8 female mice of two inhalpha/Tag lines and their mating control littermates were killed monthly between 1 and 6 mo of age. We also investigated tumorigenesis-related fertility aspects of these two mouse lines. The ontogeny and progression of tumors could be monitored in both inhalpha/Tag lines by alterations of ovarian weights and serum hormone levels. Serum progesterone levels increased in both inhalpha/Tag lines in an age-dependent manner as ovarian tumorigenesis progressed, and a reciprocal decrease occurred in serum LH and FSH. Neither serum estradiol (E(2)) nor uterine weights were significantly altered during tumorigenesis, suggesting that the ovarian tumors represented late stages of granulosa cell differentiation. In conclusion, the present findings show in the inhalpha/Tag TG mice a relation between endocrine consequences of granulosa cell tumorigenesis, and a connection of onset of tumor formation with aberrant steroidogenesis and gonadotropin secretion. These findings indicate that tumors are endocrinologically active and able to exert enhanced negative feedback effects on pituitary function. The tumors provide a good model for endocrinologically active hormone-dependent tumors.     

Role of the inhibin/activin system and luteinizing hormone in adrenocortical tumorigenesis.

Adrenal masses are one of the most common endocrine tumors diagnosed. Although most adrenal tumors are inactive adenomas, a considerable proportion is associated with hormonal hyperfunction and/or malignancy. The adrenocortical carcinoma (ACC) is a rare but highly malignant tumor. Most ACCs in adults are diagnosed in an advanced tumor stage limiting therapeutic options. Accordingly, despite some progress in diagnostic and therapeutic approaches, the overall survival rate of patients with ACC remains poor. However, the prerequisite for the development of new diagnostic tools and therapeutic options in the management of patients with ACC is the elucidation of the molecular pathogenesis of adrenal tumorigenesis. Although our understanding of adrenal tumor biology has increased substantially over the last decades, the regulation of many molecular pathways involved in adrenocortical growth and differentiation awaits further elucidation. Luteinizing hormone (LH) and activin have only recently emerged as hormones likely to play opposite roles in adrenocortical hormone secretion and cellular proliferation. Recent evidence from studies on human surgical tumor sample expression and detailed characterization of murine adrenal tumor models suggests stimulatory effects of LH on adrenocortical growth and function. On the contrary, activin, which plays a critical role as a paracrine and autocrine factor regulating cellular growth and differentiation, has been demonstrated to induce apoptosis and suppress proliferation in the human and murine adrenal cortex. In this review, we will summarize molecular and functional aspects of adrenal tumorigenesis and highlight some prospects for future clinical applications.     

The cohesin SMC3 is a target the for beta-catenin/TCF4 transactivation pathway

The structural maintenance of chromosome protein SMC3 is a component of the cohesin complex that mediates sister chromatid cohesion and segregation in prokaryotes and eukaryotes. It is also present extracellularly in the form of a chondroitin sulfate proteoglycan known as bamacan. We have found previously that SMC3 expression is elevated in a large fraction of human colon carcinomas. The additional finding that the protein is significantly increased in the intestinal polyps of ApcMin/+ mice has led us to hypothesize that SMC3 expression is linked to activation of the APC/beta-catenin/TCF4 pathway. The immunohistochemical analysis of colon adenocarcinomas from clinical specimens revealed that beta-catenin and SMC3 antigens co-localize with maximal stain intensity within the transformed areas. Cloning and sequencing of 1578 bp of the human SMC3 promoter unveiled the presence of seven putative consensus sequences for beta-catenin/TCF4 binding, two of which are conserved in the mouse Smc3 promoter. Transient transfection experiments in HCT116 and SW480 human colon carcinoma cells using deletion and mutated promoter constructs in luciferase reporter vectors confirmed that the putative sites, the first located at -48 bp and the second located at -701 bp, are susceptible to beta-catenin/TCF4 transactivation. Co-transfection with a beta-catenin expression vector enhanced the promoter activity whereas E-cadherin had the opposite effect. Binding of beta-catenin/TCF4 complexes from SW480 nuclear extracts to these sequences was confirmed by electrophoretic shift and supershift mobility assays. Altogether these results are consistent with the idea that the beta-catenin/TCF4 transactivation pathway contributes to SMC3 overexpression in intestinal tumorigenesis.