Adrenocortical Tumorigenesis in Transgenic Mice Expressing the Inhibin α-Subunit Promoter/Simian Virus 40 T-Antigen Transgene: Relationship between Ectopic Expression of Luteinizing Hormone Receptor and Transcription Factor GATA-4

Abstract

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.

Targeted therapy for adrenocortical tumors in transgenic mice through their LH receptor by Hecate-human chorionic gonadotropin conjugate

“…As these mice have earlier been extensively characterized (Kananen et al 1996a, Rahman et al 2001, the discernible adrenocortical tumors appear at the age of 6 months with 100% penetrance. We started all the treatments at the age of 6.5 months, in order to make sure that any treatment effect will be only due to the anti-tumoral effect, but not by prevention of the tumor development.…”

Transgenic GATA-4 expression induces adrenocortical tumorigenesis in C57Bl/6 mice

“…In previous studies, we showed an apparent positive and reciprocal feed-forward amplification link between GATA-4 and luteinizing hormone/human chorionic gonadotropin receptor (LHCGR/LHR) expression during adrenocortical tumorigenesis in humans and mice (Kananen et al, 1996;Bielinska et al, 2003;Rahman et al, 2004). However, it remains unknown how GATA-4 and LHCGR convene their activities in this process.…”

“…Wild-type (WT) murine adrenal glands do not express detectable levels of LHCGR, whereas exceptional conditions such as chronically elevated serum LH levels (e.g. GDX) can induce its expression (Rilianawati et al, 1998;Kero et al, 2000;Rahman et al, 2004). Aberrant LHCGR expression in the adrenal cortex has been reported in women with transient Cushing syndrome during pregnancy and persistent Cushing syndrome after menopause, both associated with elevated serum levels of hCG or LH (Guilhaume et al, 1992;Pabon et al, 1996;Lacroix et al, 1999;Mijnhout et al, 2004).…”

GATA-4 is a granulosa cell factor employed in inhibin-α activation by the TGF-β pathway

“…Transcription factor GATA-4 has emerged as a potent activator of several genes expressed in endocrine tissues, including anti-Müllerian hormone, aromatase, luteinizing hormone receptor, inhibin-B and inhibin- (Ketola et al 1999, Tremblay & Viger 1999, Feng et al 2000, Rahman et al 2004. GATA-4 belongs to a family of zinc-finger transcription factors, termed the GATAbinding proteins, primarily recognizing a consensus GATA motif in the promoters and enhancers of their target.…”