Negative control of the rat inhibin alpha subunit promoter in MA-10 Leydig tumour cells

A tissue-specific knockout reveals that Gata1 is not essential for Sertoli cell function in the mouse

The transcription factor Gata1 is essential for the development of erythroid cells. Consequently, Gata1 null mutants die in utero due to severe anaemia. Outside the haematopoietic system, Gata1 is only expressed in the Sertoli cells of the testis. To elucidate the function of Gata1 in the testis, we made a Sertoli cell-specific knockout of the Gata1 gene in the mouse. We deleted a normally functioning 'floxed' Gata1 gene in pre-Sertoli cells in vivo through the expression of Cre from a transgene driven by the Desert Hedgehog promoter. Surprisingly, Gata1 null testes developed to be morphologically normal, spermatogenesis was not obviously affected and expression levels of putative Gata1 target genes, and other Gata factors, were not altered. We conclude that expression of Gata1 in Sertoli cells is not essential for testis development or spermatogenesis in the mouse.

Gonadotropins, via cAMP, negatively regulate GATA-1 gene expression in testicular cells

We and others demonstrated that the mRNAs encoding GATA-binding proteins, GATA-1 and GATA-4, were detected in mouse and rat testis, and in isolated rat Sertoli cells and testicular tumor cell lines derived from Leydig and Sertoli cells. In this study, we investigated the possible effects of gonadotropins and cAMP on the expression of GATA-binding protein genes in testicular cells. Unexpectedly, FSH negatively regulated GATA-1 (but not GATA-4) mRNA in a dose-dependent manner in primary cultures of rat Sertoli cells isolated from 21-d-old animals. GATA-1 mRNA was also negatively regulated by cAMP in a dose- and time-dependent manner in MA-10, a mouse Leydig tumor cell line. When 0.3 mM cAMP was administered to MA-10 cell cultures for 4 h, more than 95% of the GATA-1 mRNA and protein was abolished. The reduction of GATA-1 mRNA by cAMP can be mimicked by treatment with forskolin, which elevates intracellular cAMP levels. The inhibitory effect of cAMP was specific to the GATA-1 gene, given that GATA-4 and alpha-tubulin mRNA levels were not changed by any of the cAMP treatments. Inhibin alpha-subunit mRNA, on the other hand, was evidently increased by cAMP treatment in both MA-10 and Sertoli cells. However, inhibin alpha-subunit mRNA levels were elevated at 60-90 min before the suppression of GATA-1 mRNA detected. The inhibitory effect of cAMP on GATA-1 mRNA and protein was shown to be specific to testicular cells. The GATA-1 mRNA expressed in MEL, a mouse erythroid leukemia cell line, was not affected by cAMP. The reduction of GATA-1 mRNA by cAMP can be prevented when a translational inhibitor, cycloheximide, is added. In summary, we demonstrated that gonadotropins via cAMP negatively regulate the mRNA and protein levels of GATA-1, but not GATA-4, in testicular cells. The inhibitory effect on GATA-1 gene expression was specific to testicular cells and was not observed in erythroid cells.

Testicular GATA-1 factor up-regulates the promoter activity of rat inhibin alpha-subunit gene in MA-10 Leydig tumor cells

We have previously demonstrated that the basal transcription of rat inhibin alpha-subunit gene in a mouse testicular Leydig tumor cell line, MA-10, depends upon a 67-bp DNA fragment at the position of -163 to -97. Within this promoter region two GATA motifs were observed. In this study, we investigated the possible role of GATA-binding proteins in the regulation of inhibin alpha-subunit gene transcription in testicular cells. Northern blot and RT-PCR analyses showed that mRNAs encoding GATA-binding proteins, GATA-1 and GATA-4, were detected in mouse and rat testis and in MA-10 and rat Sertoli cells. Testis-specific GATA-1 mRNA, which is transcribed from a promoter 8 kb upstream to the erythroid exon I of mouse GATA-1 gene, was also identified in MA-10 cells. Mutations of GATA sequences in alpha-subunit promoter markedly decreased the transcriptional activity of alpha-subunit gene when measured by their ability of transient expression of a bacterial reporter gene, chloramphenicol acetyltransferase (CAT), in MA-10 cells. Cotransfection of alphaCAT chimeric construct with cDNA expression plasmid coding for mouse GATA-1 or GATA-4 protein revealed that GATA-1 but not GATA-4 can transactivate alpha-subunit promoter in a dose-dependent manner. The transactivation by GATA-1 was inhibited if GATA sequences in alpha-subunit promoter were mutated. Furthermore, electrophoretic mobility shift assay demonstrated that GATA-binding proteins present in nuclear extracts of MA-10 cells and rat testis interacted with the GATA motifs in alpha-subunit promoter, and the GATA-1 in these nuclear extracts formed a supershifted immunocomplex with antibody raised against mouse GATA-1 protein. We therefore concluded that the basal transcription of inhibin alpha-subunit gene in testicular MA-10 cells is up-regulated by testicular GATA-1 but not GATA-4 through its interaction with the GATA motifs in alpha-subunit promoter. In summary, we have provided the first evidence of the functional role of a GATA-binding protein in the regulation of testicular gene expression.

The mouse inhibin alpha-subunit promoter directs SV40 T-antigen to Leydig cells in transgenic mice

Testicular tumorigenesis was observed in transgenic mice expressing the 6-kb mouse inhibin alpha-subunit promoter/Simian virus 40 T-antigen (SV40 Tag) fusion gene. The tumors were confined to Leydig cells using immunohistochemistry with anti-Tag antibody, specific binding of biotinylated hCG and histochemistry for 3 beta-hydroxysteroid dehydrogenase. Leydig cell hyperplasia and presence of Tag protein in the testicular interstitial tissue were already evident at 5 and 6.5 days of age, respectively. An immortalized cell line, BLT-1, was established from one testicular tumor. These cells expressed the LH receptor and P450scc mRNAs, and displayed LH-responsive cAMP and progesterone production, and low testosterone production. The cells also specifically bound 125I-labeled recombinant human LH with high affinity (36000 binding sites/cell), and the binding was regulated by 8Br-cAMP and hCG. This gonadal tumor model is valuable for further studies on endocrine functions of Leydig cells and their tumorigenesis in vivo and in vitro.