Mouse strain susceptibility to gonadectomy-induced adrenocortical tumor formation correlates with the expression of GATA-4 and luteinizing hormone receptor

Adrenocortical tumorigenesis in transgenic mice expressing the inhibin alpha-subunit promoter/simian virus 40 T-antigen transgene: relationship between ectopic expression of luteinizing hormone receptor and transcription factor GATA-4

We have analyzed the ontogeny and putative mechanisms of transregulation of LH receptor (LHR) and transcription factor GATA-4, coexpressed during the adrenocortical tumorigenesis of prepubertally gonadectomized transgenic (TG) mice expressing the inhibin alpha-subunit promoter/simian virus 40 T-antigen (inhalpha/Tag) transgene. The onset of adrenal LHR mRNA and protein expression coincided with that of GATA-4 at the age of 4 months and preceded the appearance of discernible adrenal tumors at about 6 months. In situ hybridization and double-immunohistochemistry demonstrated colocalization of the LHR and GATA-4 messages and proteins in the adrenal cortex. A GATA-4 expression plasmid cotransfected with a murine LHR promoter-driven luciferase reporter plasmid, containing a consensus GATA-binding site, induced a dose-dependent significant transactivation of the LHR promoter in nonsteroidogenic human embryonic kidney 293, steroidogenic murine mLTC-1 Leydig cells and in murine adrenal Y-1 cells. The Calpha1 cells derived from an Inhalpha/Tag adrenal tumor did not show this response, apparently due to their high endogenous GATA-4 expression. However, an additional link between GATA-4 and LHR in Calpha1 cells was provided upon the LH/human chorionic gonadotropin stimulation of LHR promoter activity; mutations or deletion of the consensus GATA-4 binding site of the LHR promoter abolished this transactivation. EMSAs further proved GATA-4 binding to the putative consensus GATA recognition site. Our results demonstrate direct interrelationship between LHR and GATA-4 expression during adrenocortical tumorigenesis of the inhalpha/Tag mice. There is apparently a positive and reciprocal feed-forward amplification link between LHR and GATA-4 expression. This mechanism gradually and in synergy with Tag expression leads to formation of the LH-dependent adrenocortical tumors.

Characterization of blood pressure and morphological traits in cardiovascular-related organs in 13 different inbred mouse strains

To better understand the contributions of various genetic backgrounds to complex quantitative phenotypes, we have measured several quantitative traits of cardiovascular interest [i.e., systolic blood pressure, weight (corrected by body weight) of several cardiac compartments and adrenals and kidneys, and histological correlates for kidneys and adrenals] in male and female mice from 13 different inbred strains. We selected strains so that each major genealogical group would be represented and to conform to priorities set by the Mouse Phenome Database project. Interstrain comparisons of phenotypes made it possible to identify strains that displayed values that belonged to either the low or the high end of the interstrain variance for quantitative traits, such as systolic blood pressure, body weight, left ventricular weight, and/or adrenocortical structure. For instance, both male and female C3H/HeJ and A/J mice displayed either low systolic blood pressure or low cardiac ventricular mass, respectively, and male C57BL6/J displayed low adrenal weight. Likewise, intersex comparisons made it possible to identify phenotypic values that were sexually dimorphic for some of the same traits. For instance, female AKR/J mice had relatively higher body weight and systolic blood pressure values than their male counterparts, perhaps constituting an animal model of the metabolic X syndrome. These strain- and sex-specific features will be of value both for future genetic and/or developmental studies and for the development of new animal models that will help in the generation of mechanistic hypotheses. All data have been deposited to the Mouse Phenome Database for future integration with the Mouse Genome Database and can be further analyzed and compared with tools available on the site.

GATA-4 and GATA-6 modulate tissue-specific transcription of the human gene for P450c17 by direct interaction with Sp1

Cytochrome P450c17 catalyzes steroidogenic 17alpha-hydroxylase and 17,20 lyase activities. Expression of the gene for P450c17 is cAMP dependent, tissue specific, developmentally programmed, and varies among species. Binding of Sp1, Sp3, and NF1-C (nuclear factor 1-C) to the first 227 bp of 5'flanking DNA (-227/LUC) is crucial for basal transcription in human NCI-H295A adrenal cells. Human placental JEG-3 cells contain Sp1, Sp3, and NF1, but do not express -227/LUC, even when transfected with a vector expressing steroidogenic factor 1 (SF-1). Therefore, other factors are essential for basal expression of P450c17. Deoxyribonuclease I footprinting and EMSAs identified a GATA consensus site at -64/-58 and an SF-1 site at -58/-50. RT-PCR identified GATA-4, GATA-6, and SF-1 in NCI-H295A cells and GATA-2 and GATA-3, but not GATA-4, GATA-6, or SF-1 in JEG-3 cells. Cotransfection of either GATA-4 or GATA-6 without SF-1 activated -227/LUC in JEG-3 cells, but cotransfection of GATA-2 or GATA-3 with or without SF-1 did not. Surprisingly, mutation of the GATA binding site in -227/LUC increased GATA-4 or GATA-6 induced activity, whereas mutation of the Sp1/Sp3 site decreased it. Furthermore, promoter constructs including the GATA site, but excluding the Sp1/Sp3 site at -196/-188, were not activated by GATA-4 or GATA-6, suggesting an interaction between Sp1/Sp3 and GATA-4 or GATA-6. Glutathione-S-transferase pull-down experiments and coimmunoprecipitation demonstrated interaction between GATA-4 or GATA-6 and Sp1, but not Sp3. Chromatin immunoprecipitation assays confirmed that this GATA-4/6 interaction with Sp1 occurred at the Sp site in the P450c17 promoter in NCI-H295A cells. Demethylation with 5-aza-2-deoxycytidine permitted JEG-3 cells to express endogenous P450c17, SF-1, GATA-4, GATA-6, and transfected -227/LUC. Thus, GATA-4 or GATA-6 and Sp1 together regulate expression of P450c17 in adrenal NCI-H295A cells and methylation of P450c17, GATA-4 and GATA-6 silence the expression of P450c17 in placental JEG-3 cells.