Inhibin Alpha mRNA Levels Research Articles

Expression of inhibin alpha in adrenocortical tumours reflects the hormonal status of the neoplasm.

Inhibins are gonadal glycoprotein hormones whose main endocrine function is to inhibit pituitary FSH secretion. In addition to testes and ovaries, other steroid-producing organs are sites of inhibin alpha subunit expression. To study the role of inhibins in human adrenal gland, we screened a panel of 150 adrenals (10 normal adrenals, 25 adrenocortical hyperplasias, 65 adrenocortical adenomas, 30 adrenocortical carcinomas and 20 phaeochromocytomas) for inhibin alpha expression. mRNA levels of inhibin alpha subunit were studied in 57 samples and all tissues were stained immunohistochemically with an inhibin alpha subunit-specific antibody. Inhibin alpha mRNA was detected in all adrenocortical tissues. Virilizing adenomas possessed a 10-fold higher median inhibin alpha mRNA expression than did normal adrenals. Bilaterally and nodularly hyperplastic adrenals and other than virilizing adrenocortical tumours had their median inhibin alpha mRNA levels close to those of normal adrenals. Immunohistochemically, inhibin alpha subunit was detectable in all normal and hyperplastic adrenals, as well as in 73% of the adrenocortical tumours. However, the percentage of inhibin alpha-positive cells varied greatly in different tumour types. The median percentage of positive cells was 10 in non-functional and Conn's adenomas, 30 in Cushing's adenomas and 75 in virilizing adenomas. In malignant adrenocortical tumours the median percentage of inhibin alpha-immunopositive cells was 20 in non-functional carcinomas, 30 in Conn's carcinomas, 65 in Cushing's carcinomas and 75 in virilizing carcinomas. All phaeochromocytomas were negative for inhibin alpha subunit both at the mRNA level and immunohistochemically. Our data show that inhibin alpha subunit is highly expressed in both normal and neoplastic androgen-producing adrenocortical cells, with less expression in cortisol-producing and hardly any in aldosterone-producing cells. This suggests a specific role for inhibins in the regulation of adrenal androgen production. We did not find any significant difference in inhibin alpha expression between benign and malignant adrenocortical tumours. Thus inhibin alpha gene does not seem to have a tumour suppressor role in human adrenal cortex.

The pattern of inhibin/activin alpha- and betaB-subunit messenger ribonucleic acid expression in rat testis after selective Leydig cell destruction by ethylene dimethane sulfonate.

To further investigate the regulatory mechanisms responsible for the control of testicular inhibin/activin subunit gene expression, inhibin-alpha, -betaA, and -betaB messenger RNA (mRNA) levels were assessed after ethylene dimethane sulfonate (EDS)-induced destruction of Leydig cells (LC) in different animal models: the intact rat, the rat treated with high doses of testosterone, and the unilaterally cryptorchid rat. In intact rats, EDS selectively eliminates the mature adult-type LCs, activating the proliferation and differentiation of preexisting LC precursors into a new population of functionally active LCs. In this model, a single dose of EDS (75 mg/kg BW, ip) induced a significant increase in testicular inhibin-alpha and -betaB mRNA levels 5 days after treatment (5.0- and 5.5-fold increases, respectively), whereas inhibin-betaA mRNA remained undetectable upon Northern hybridization in control and EDS-treated testes. Moreover, in situ hybridization analysis demonstrated that the increased expression of inhibin-alpha and -betaB mRNAs observed 5 days after EDS takes place mainly in Sertoli cells. Along with LC repopulation, the expression level of inhibin-alpha and -betaB messages declined, and inhibin-alpha mRNA returned to control values on day 40 after EDS. This treatment, however, failed to alter the pattern of testicular expression of FSH receptor and androgen-binding protein mRNAs, thus suggesting selectivity for the above effects. In EDS-treated rats supplemented with high doses of testosterone, the preexisting mature LCs are destroyed, but, due to elevated testosterone concentrations, disruption of spermatogenesis is attenuated, and the post-EDS rise in serum gonadotropins is blocked; the latter prevents LC regeneration. In this model, a 5.0-fold increase in inhibin-alpha mRNA levels, similar to that found in intact animals, was detected 5 days after EDS administration, but the rise in inhibin-betaB levels was partially delayed. In addition, the blockade of LC repopulation resulted in permanent elevation of inhibin-alpha and -betaB messages throughout the study period. In unilaterally cryptorchid rats, the abdominal testis shows disrupted spermatogenesis and altered paracrine environment that expedites LC repopulation after EDS treatment. In this model, the abdominal testes showed a significant 2.5-fold increase in inhibin-alpha mRNA levels 5 days after EDS, but no effect was found in those of inhibin-betaB. Further, the faster rate of LC repopulation resulted in precocious decline of inhibin-alpha mRNA levels. Finally, the expression of inhibin/activin subunit mRNAs was monitored during postnatal testicular development, specifically at the time of regression of fetal-type LCs and appearance of those of the adult type. High levels of expression of inhibin-alpha and -betaB mRNAs were detected in neonatal and infantile testes. A sharp decline in both messages took place between days 15-20, i.e. at the time when fetal-type Leydig cells are replaced by adult-type cells. From this time point onward, inhibin-alpha and -betaB mRNA levels remained low, ranging between 15-30% of the maximum. In conclusion, our results suggest that the adult-type LCs differentially modulate the expression of inhibin/activin subunit genes and point to a major inhibitory role in this cell type on expression of the inhibin-alpha gene.

Transcriptional and posttranscriptional regulation of inhibin alpha-subunit gene expression in rat Sertoli cells by 8-bromo-3',5'-cyclic-adenosine monophosphate.

FSH is a major regulator of inhibin production in the testis. FSH effects on Sertoli cell inhibin production are believed to be mediated, at least in part, via the cAMP second messenger system. Previously, it has been shown that 8-bromo-cAMP (8-Br-cAMP) stimulates inhibin-alpha mRNA levels. This study examines whether the cAMP-induced increase in inhibin-alpha mRNA levels results from increased alpha mRNA synthesis, decreased degradation of mRNA, or both. The effects of cAMP on inhibin-alpha gene transcription were examined using nuclear run-on assays. Furthermore, the ability of 8-Br-cAMP to drive the transcription of chimeric constructs containing a 2.2-kilobase (kb) segment of the 5'-regulatory region of the alpha gene placed upstream of the coding region of the luciferase reporter gene was also examined. Data from nuclear run-on assays demonstrated rapid induction of alpha gene transcription by cAMP within 2 h and maximal 4- to 5-fold increase within 4-8 h in primary Sertoli cells. Transfection of TM.4 and JEG.3 cells with an alpha (2.2 kb):luciferase chimeric construct (containing 2.2 kb of the alpha gene 5'-flanking DNA) revealed rapid time-dependent induction of luciferase activity by 8-Br-cAMP in these cell types. To examine the effects of 8-Br-cAMP on alpha mRNA stability, cells were pretreated with medium or 50 micrograms/ml 8-Br-cAMP for 24 h before addition of 5 microM actinomycin D to arrest new RNA synthesis, and the decay of alpha mRNA transcripts was assessed over 24 h by Northern analysis and nonlinear regression.(ABSTRACT TRUNCATED AT 250 WORDS)

The biphasic modulation of inhibin mRNA levels and secretion by PMSG in rat granulosa cells in vitro

Granulosa cell cultures derived from diethylstilboestrol-treated immature rats were used to study the in vitro effect of pregnant mare serum gonadotrophin (PMSG) on steady state mRNA levels for the inhibin alpha and beta A subunits and the secretion of immunoreactive inhibin and progesterone. After 48 h treatment the dose-response curve of PMSG revealed a maximum stimulation (2.5-3.5 fold) of cytosolic alpha and beta A mRNAs over the range of 1 to 10 mU PMSG mL-1, with corresponding stimulation of inhibin secretion. A high dose of PMSG (160-500 mU mL-1) clearly suppressed inhibin alpha mRNA levels as well as inhibin secretion, whereas progesterone (P) was maximally stimulated (up to 600 fold). Although the level of cytosolic inhibin beta A subunit mRNA was also down-regulated by a high concentration of PMSG in the culture medium, the doses required to suppress its mRNA level to less than those of the control varied. These data demonstrate that low doses of follicle stimulating hormone/luteinizing hormone (FSH/LH)-like (PMSG) activity enhances and high doses decrease the steady-state mRNA levels of inhibin in rat granulosa cells in vitro; this biphasic regulation in vitro reflects the differential regulation of inhibin secretion observed during the rat oestrous cycle.