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.
Rahman
Nafis A
NA
Department of Physiology, University of Turku, 20520 Turku, Finland.
Kiiveri
Sanne
S
Rivero-Müller
Adolfo
A
Levallet
Jérôme
J
Vierre
Susanna
S
Kero
Jukka
J
Wilson
David B
DB
Heikinheimo
Markku
M
Huhtaniemi
Ilpo
I
D000306:Adrenal Cortex Neoplasms / Q000235:genetics*; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics*; D001483:Base Sequence; D015152:Blotting, Northern; D045744:Cell Line, Tumor; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000235:genetics*; D050991:GATA4 Transcription Factor; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D017403:In Situ Hybridization; D007265:Inhibins / Q000235:genetics*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009919:Orchiectomy; D011974:Receptors, LH / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013539:Simian virus 40 / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics*
D000952:Antigens, Polyomavirus Transforming; D017931:DNA Primers; D004268:DNA-Binding Proteins; D050991:GATA4 Transcription Factor; D011974:Receptors, LH; D014157:Transcription Factors; C094377:inhibin-alpha subunit; D007265:Inhibins