Characterization of the desensitized state of Leydig tumor cells

Arsenic compounds induce apoptosis through caspase pathway activation in MA-10 Leydig tumor cells

The incidence of testicular cancer is increasing worldwide. Leydig cell tumors represent one type of sex cord-stromal testis malignancy, which tend to respond unfavorably to chemotherapies. Identifying more efficient treatment strategies is therefore crucial for patients. The present study aimed to investigate the apoptotic effects of arsenic compounds and their underlying mechanisms. The results indicated that sodium arsenite and dimethylarsenic acid induced apoptosis of the murine Leydig tumor cell line, MA-10. These apoptotic effects were characterized morphologically by membrane blebbing and cell detachment assays, biochemically using a cell viability assay, and cytologically by flow cytometry analysis. Western blotting demonstrated that caspases-3, -8 and -9, and poly(ADP-ribose) polymerase protein levels were increased compared with untreated MA-10 cells; however, the caspase inhibitor, Z-VAD-fmk, reversed these effects. In conclusion, the present study has shown that sodium arsenite and dimethylarsenic acid may activate the intrinsic and extrinsic caspase pathways, and induce MA-10 cell apoptosis. These results suggest that sodium arsenite and dimethylarsenic acid may represent novel approaches to treat clinically unmanageable forms of testicular cancer.

Effect of human chorionic gonadotropin and estradiol in vivo on estradiol binder and cytochrome P-450 concentrations in rat testis

The effects of single administration to adult male rats in vivo of various amounts of human chorionic gonadotropin (HCG) and of single or repeated injections of estradiol on testicular cytoplasmic estradiol binder concentrations and on microsomal progesterone-binding cytochrome P-450 were compared. Half-life periods of HCG-induced loss of estradiol binder and cytochrome P-450 concentrations are identical (6 h) whereas a strong dissociation of these half-life periods are evident after chronic estradiol treatment (less than 2 h for the estradiol binder, about 35 h for cytochrome P-450). Depletion of cytoplasmic estradiol binder is not a sufficient condition for mediation of effects on cytochrome P-450 content. Rate of replenishment of microsomal cytochrome P-450 is similar after HCG or estradiol treatment. Both HCG- and estradiol-induced loss of cytochrome P-450 occur not only in Leydig cells but also in microsomes prepared from seminiferous tubules. Additional information is presented contradicting the hypothesis that loss of cytochrome P-450-dependent steroidogenic enzymes caused by HCG could be mediated by estrogens.

Desensitization of the cAMP system in mouse Leydig cells by hCG, cholera toxin, dibutyryl cAMP and cAMP: localization of the 'lesion' to the guanine nucleotide regulatory protein-adenylate cyclase complex

The mechanism of hCG-induced desensitization of the cAMP system was studied in Percoll-purified mouse Leydig cells. Pretreatment of Leydig cells with hCG resulted in a time- and dose-dependent decrease in the capacity of hCG-induced cAMP formation. Maximal desensitization (approximately 90%) was induced by only partial prior stimulation. Desensitization, however, was not observed without a prior increase in cAMP or testosterone production. Pretreatment of the cells with N6,O2'-dibutyryl cAMP (DBcAMP) also induced a dose- and time-dependent densensitization. cAMP was only effective in the presence of the phosphodiesterase inhibitor 1-methyl-3-isobutylxanthine (MIX). Cholera toxin desensitized the hormone-induced cAMP response as drastically as hCG. Cholera toxin was unable to reverse the refractory state induced by one of the agonists. hCG-induced desensitization was not associated with a loss in [125I]hCG binding or an increase in maximal phosphodiesterase activity, and appeared not to be dependent on protein synthesis. Membranes from hCG, cholera toxin of DBcAMP-desensitized cells showed an impaired adenylate cyclase activity in response to hCG, hCG plus beta-gamma-imidoguanosine 5'-triphosphate (GPPNP) and NaF. In conclusion, hCG-induced desensitization of the adenylate cyclase system in mouse Leydig cells can be mimicked by cholera toxin, DBcAMP and cAMP, indicating a cAMP-mediated process. The site of the 'lesion' has to be localized to the guanine nucleotide regulatory protein-adenylate cyclase complex rather than to its uncoupling from the hormone receptor.

Desensitization of steroidogenesis in cultured Leydig tumor cells: role of cholesterol

We have reported previously that the human choriogonadotropin (hCG) receptors of cultured Leydig tumor cells can be down-regulated with hCG or mouse epidermal growth factor (mEGF) and that such down-regulation results in a loss of the steroidogenic response of the cells to hCG. Exposure of the cells to hCG, but not to mEGF, also resulted in a decrease in steroidogenic responses to cholera toxin and cAMP. The results presented herein show that the hCG-induced loss of steroidogenic response to cAMP is due to the depletion of intracellular cholesterol and that this depletion can be prevented by the addition of low density lipoprotein. Our results also show that after exposure of the cells to mEGF or hCG their steroidogenic response to hCG is limited by the number of hCG receptors, regardless of the presence of low density lipoprotein.

Desensitization to gonadotropins in cultured Leydig tumor cells involves loss of gonadotropin receptors and decreased capacity for steroidogenesis

The ability of human choriogonadotropin (hCG) to regulate its receptors and target cell responses has been studied in a clonal strain of cultured Leydig tumor cells (MA-10). Exposure of the MA-10 cells to hCG results in decrease in hCG binding activity which is dependent on time and the concentration of hCG. This decrease is due to a change in the number of receptors rather than in the affinity of the receptors, and it is accompanied by a corresponding reduction in the ability of hCG to stimulate steroidogenesis. Exposure of the MA-10 cells to hCG also resulted in a reduction of the steroidogenic responses to cholera toxin and 8-Br-adenosine cyclic 3',5'-monophosphate. The hCG-induced loss of steroidogenic responses to these stimuli seems to be due to the stimulation of steroidogenesis rather than to the decrease in hCG receptors because it also can be induced when steroidogenesis is stimulated with cholera toxin or 8-Br-adenosine 3',5'-monophosphate under conditions such that the number of hCG receptors is not reduced.