Foxa1 and Foxa2 are essential for sexual dimorphism in liver cancer

Hepatocellular carcinoma (HCC) is sexually dimorphic in both rodents and humans, with significantly higher incidence in males, an effect that is dependent on sex hormones. The molecular mechanisms by which estrogens prevent and androgens promote liver cancer remain unclear. Here, we discover that sexually dimorphic HCC is completely reversed in Foxa1- and Foxa2-deficient mice after diethylnitrosamine-induced hepatocarcinogenesis. Coregulation of target genes by Foxa1/a2 and either the estrogen receptor (ERα) or the androgen receptor (AR) was increased during hepatocarcinogenesis in normal female or male mice, respectively, but was lost in Foxa1/2-deficient mice. Thus, both estrogen-dependent resistance to and androgen-mediated facilitation of HCC depend on Foxa1/2. Strikingly, single nucleotide polymorphisms at FOXA2 binding sites reduce binding of both FOXA2 and ERα to their targets in human liver and correlate with HCC development in women. Thus, Foxa factors and their targets are central for the sexual dimorphism of HCC.     

Diabetes insipidus in mice with a mutation in aquaporin-2

Congenital nephrogenic diabetes insipidus (NDI) is a disease characterized by failure of the kidney to concentrate urine in response to vasopressin. Human kindreds with nephrogenic diabetes insipidus have been found to harbor mutations in the vasopressin receptor 2 (Avpr2) gene or the vasopressin-sensitive water channel aquaporin-2 (Aqp2) gene. Development of a treatment is rendered difficult due to the lack of a viable animal model. Through forward genetic screening of ethylnitrosourea-mutagenized mice, we report the identification and characterization of a mouse model of NDI, with an F204V mutation in the Aqp2 gene. Unlike previously attempted murine models of NDI, our mice survive to adulthood and more exactly recapitulate the human disorder. Previous in vitro experiments using renal cell lines suggest recessive Aqp2 mutations result in improper trafficking of the mutant water pore. Using these animals, we have directly proven this hypothesis of improper AQP2 translocation as the molecular defect in nephrogenic diabetes insipidus in the intact organism. Additionally, using a renal cell line we show that the mutated protein, AQP2-F204V, is retained in the endoplasmic reticulum and that this abnormal localization can be rescued by wild-type protein. This novel mouse model allows for further mechanistic studies as well as testing of pharmacological and gene therapies for NDI.     

Causes of the urinary concentrating defect in mice with nephrogenic diabetes insipidus

In a strain of mice called DI +/+ Severe, nephrogenic (or vasopressin-resistant) diabetes insipidus is caused by an inability of the antidiuretic hormone (ADH, or vasopressin) to increase the water permeability of the renal collecting system. That inability, in turn, arises from abnormally high activity of the enzyme cAMP-phosphodiesterase, specifically of the isozyme type III (PDE-III), which hydrolyzes cAMP and prevents the intracellular buildup of this second messenger. Two rather specific inhibitors of PDE-III, rolipram and cilostamide, used either in vitro or in vivo, reverse the deficiencies in DI +/+ Severe mice by increasing intracellular cAMP and water permeability toward or to their normal values. These results have implications for the treatment of nephrogenic diabetes insipidus in human patients.     

A urine-concentrating defect in 11β-hydroxysteroid dehydrogenase type 2 null mice

In aldosterone target tissues, 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) is coexpressed with mineralocorticoid receptors (MR) and protects the receptor from activation by glucocorticoids. Null mutations in the encoding gene, HSD11B2, cause apparent mineralocorticoid excess, in which hypertension is thought to reflect volume expansion secondary to sodium retention. Hsd11b2(-/-) mice are indeed hypertensive, but impaired natriuretic capacity is associated with significant volume contraction, suggestive of a urine concentrating defect. Water turnover and the urine concentrating response to a 24-h water deprivation challenge were therefore assessed in Hsd11b2(-/-) mice and controls. Hsd11b2(-/-) mice have a severe and progressive polyuric/polydipsic phenotype. In younger mice (～2 mo of age), polyuria was associated with decreased abundance of aqp2 and aqp3 mRNA. The expression of other genes involved in water transport (aqp4, slc14a2, and slc12a2) was not changed. The kidney was structurally normal, and the concentrating response to water deprivation was intact. In older Hsd11b2(-/-) mice (>6 mo), polyuria was associated with a severe atrophy of the renal medulla and downregulation of aqp2, aqp3, aqp4, slc14a2, and slc12a2. The concentrating response to water deprivation was impaired, and the natriuretic effect of the loop diuretic bumetanide was lost. In older Hsd11b2(-/-) mice, the V2 receptor agonist desmopressin did not restore full urine concentrating capacity. We find that Hsd11b2(-/-) mice develop nephrogenic diabetes insipidus. Gross changes to renal structure are observed, but these were probably secondary to sustained polyuria, rather than of developmental origin.     

Colocalization of the gene for nephrogenic diabetes insipidus (DIR) and the vasopressin type 2 receptor gene (AVPR2) in the Xq28 region

The gene for nephrogenic diabetes insipidus (DIR) and the vasopressin type 2 receptor gene (AVPR2) have both been localized in the Xqter region by genetic mapping and functional expression studies, respectively. In this paper genetic evidence that the DIR locus is localized distal to the DXS305 locus and that the functional gene for the V2 receptor is localized between the markers DXS269 and F8 is presented. These further refinements in the localization of both genes strengthen the assumption that both genes are identical and provide a rationale for cloning the gene by reversed genetics strategies.     

A Low Affinity Vasopressin V2-Receptor in Inherited Nephrogenic Diabetes Insipidus

Abstract

Congenital nephrogenic diabetes insipidus (NDI) is an X-linked inherited disorder characterized by renal resistance to the antidiuretic hormonal action of vasopressin. This study describes the molecular basis of nephrogenic diabetes insipidus in a dog family. Kidney membranes prepared from NDI-affected male huskies were examined for vasopressin binding and response. Compared to membranes from unaffected canines, those from the kidney inner medulla of NDI-dogs possessed normal V₂-receptor numbers, but with 10–fold lower affinity for [Arg⁸] vasopressin (AVP). Adenylate cyclase stimulation by AVP in contrast to that by forskolin or GTP-analogues was similarly reduced in a dose responsive manner. The NDI-affected dogs showed antidiuretic responses to very high doses of V₂–specific agonists, consistent with their possessing V₂–receptors of lower affinity. Prolonged treatment with V₂–agonists, 1–deamino [D-Arg⁸] VP (dDAVP) and 1–deamino [Va]⁴, Sar⁷] AVP (dVSAVP), rendered the NDI-affected dogs near normal in terms of water intake and urine osmolality.