Cell free translation of rat adrenal messenger RNA coding for an ACTH-induced protein

Protein markers induced by hormones are the necessary probes to study hormone regulation of gene expression. We have previously shown that ACTH was able to induce one of these markers in the cytosol of the rat adrenal: protein E (Dazord et al, Biochem. J., 176, 233-239, 1978). In this paper by using adrenal mRNA from control and in vivo ACTH treated rats as well as protein E antibodies, we show that: 1) ACTH affects both the amount of adrenal mRNA and its translational activity; 2) the translation of protein E is increased by the hormone; 3) protein E is the major translational product following ACTH treatment.

Effects of FSH on acidic nuclear protein synthesis in cultured pig Sertoli cells

We studied the effect of FHS on nuclear protein synthesis by a primary culture of immature porcine Sertoli cells. The cells were cultured in a chemically defined medium and treated with FSH (50 ng/ml) for various periods (4, 8, 25 and 64 h). About 65 spots (pHi less than 8) were identified by two-dimensional polyacrylamide gel electrophoresis of the radiolabelled nuclear proteins. After 25 h of FSH treatment, we observed an increase of 5 proteins, a slight decrease of two and a disappearance of one. For the short periods of FSH treatment (4 and 8 h), no effect of FHS on nuclear protein synthesis was observed. After 64 h of FSH treatment (4 and 8 h), no effect of FHS on nuclear protein synthesis was observed. After 64 h of FSH treatment, the synthesis of all nuclear proteins appears to be decreased.

hCG-Increased phosphorylation of proteins in primary culture of Leydig cells: further characterization

Previous studies using monodimensional gel electrophoresis of total cell proteins have shown that hCG was able to increase the phosphorylation of at least 6 proteins in cultured porcine Leydig cells. By using subcellular fractionation and 2D gel electrophoresis, we now show that most of these proteins, whose phosphorylation was increased by hCG, are basic nuclear proteins. In addition, hCG also increases the phosphorylation of microsomal proteins in particular ribosomal protein S6. Moreover no phosphoproteins were detected in the cytosol.

Effects of ACTH on protein synthesis in rat adrenal analyzed by two dimensional gel electrophoresis

The effect of in vivo ACTH injection on adrenal cytosolic protein synthesis has been studied by two dimensional polyacrylamide gel electrophoresis. Using this sensible technique about 70 proteins were identified and the pattern found was much more complex than previously thought using monodimensional gel electrophoresis. These proteins were analyzed. and fell into 4 categories: the first group is composed of two proteins which are dramatically increased after 4 h of ACTH in vivo treatment. The second group is composed of 10 proteins whose stimulation by the hormone, although less dramatic, is still very important. In the third group (8 proteins) the stimulation is more discrete but constant and significant. The rest of the proteins are not affected by the hormonal treatment.

Immunocytochemical visualization of luteinizing hormone-human chorionic gonadotropin (LH-hCG) receptors in Leydig cells in primary culture

Visualization of human chorionic gonadotropin (hCG) binding sites was obtained by immunocytochemical reaction on Leydig cells cultured in chemically defined medium. After a short in vitro incubation with hCG or luteinizing hormone (LH), the cells were fixed and the bound molecules were revealed using anti-hCG or anti-LH antisera. In both cases the immunocytochemical reaction appeared as granulations at the cell surface. After prolonged (48 hr) culture in the presence of 0.5, 5, or 50 ng/ml of hCG, the hormone receptor complex is still visible. Similarly, following short exposure to hCG (0.5 or 50 ng/ml) and one or two days of culture without hCG, the immunocytochemical reaction is still present. These observations suggest that the half-life of the bound hormone is very long. This in vitro system in which the amount and time of hormone exposure are precisely defined provides arguments in favor of a long-term maintenance of the receptor complexes at the cell surface.

[Mechanism of action of ACTH]

The intent in writing this chapter has been to review selected areas in which several observations by one or more workers have led to the emergence of new concepts in the mechanisms of action of ACTH. Therefore, the involvement of the lipid metabolism and of the cytoskeleton on the steroidogenic action of ACTH were studied in the two initial sections. The two other sections concern ACTH control of the protein synthesis and of the replicative capacity of the adrenal gland.

Maturation of adrenocorticotropin-sensitive adenylate cyclase of ovine fetal adrenal during late pregnancy

The number of ACTH-(1-24) receptors and the adenylate cyclase (AC) responsiveness to several stimuli have been measured in crude adrenal membranes from fetal and newborn lambs. At 124 days of gestation, the number of ACTH-(1-24)-binding sites was 51 +/- 9 (SE) pmol/microgram DNA, and AC was stimulated by 2 x 10(-2) M NaF (195 +/- 5%) and 10(-5) M guanosine (beta, gamma-imido) triphosphate [Gpp(NH)p]; (168 +/- 8%) but not by 10(-6) M ACTH-(1-24). However, when Gpp(NH)p was added to ACTH-(1-24), the response was significantly higher than with Gpp(NH)p alone. On the contrary, at 140 days, despite no increase in the number of ACTH-(1-24) receptors, AC was stimulated by ACTH-(1-24) (135 +/- 6%), and Gpp(NH)p enhanced this response. In addition, the response to NaF and to Gpp(NH)p alone was higher at 140 than at 124 days. Between day 140 of gestation and birth, the stimulation of AC by ACTH-(1-24) and ACTH-(1-24) plus Gpp(NH)p increased, but the response to NaF and to Gpp(NH)p alone did not. During the same time, the number of ACTH-(1-24) receptors was increased by a factor of 3. No change in the Kd and Km of ACTH-(1-24) was observed during the period studied. Neither prostaglandin E2 (10(-5) M) nor alpha MSH (10(-6) M) stimulated AC at any stage. The relative insensitivity of AC before 140 days can thus be related to 1) a defect of availability of GTP, and 2) a low activity of the catalytic subunit of AC (subunit C) or, alternatively, a defect in the GTP-binding component (subunit N). The increased sensitivity to ACTH-(1-24) of the enzyme just before parturition correlates closely with an increase in the number of ACTH-(1-24) receptors.

Mechanism of corticotropin action on adrenal protein synthesis. The effects of inhibitors of protein synthesis and calcium chelators

We have recently shown that beside a general stimulation of most adrenal proteins, corticotropin induces a marked increase in a specific adrenal cytosolic protein, protein E, in intact and hypophysectomized rats. To further clarify the mechanisms by which corticotropin exerts its trophic action we have investigated the effects of cycloheximide, calcium and calcium chelator administration on intact and hypophysectomized animals. These substances were injected in rats with or without corticotropin, and slices of adrenal glands from control and treated animals were removed 5 h later, incubated with [14C]- or [3H]-leucine for 2 h, and cytosolic proteins analyzed by polyacrylamide gel electrophoresis using a dual labelling technique. When high doses of cycloheximide (higher than 500 micrograms) were injected in rats, incorporation of labelled leucine in adrenal slices of control and corticotropin-treated animals was inhibited. With 500 micrograms cycloheximide per rat, incorporation of labelled leucine in adrenal slices of control animals was normal, but the corticotropin stimulation of both protein E and total protein synthesis was inhibited. Lower doses of cycloheximide (100 micrograms per rat) completely inhibited the stimulatory effect of corticotropin on total protein synthesis but did not affect protein E synthesis, while after 50 micrograms per rat both stimulatory effects were preserved. The two higher doses of cycloheximide (500 and 100 micrograms per rat) could not completely block the steroidogenic effect of the hormone. The effects of calcium and calcium chelators were studied in 1-day hypophysectomized rats. Calcium alone or injected simultaneously with corticotropin has no effect. Calcium chelators injected simultaneously with corticotropin partially inhibited the stimulatory effects of corticotropin on steroidogenesis but totally inhibited stimulation of total protein synthesis, while the stimulation of protein E persisted. Our results show that after corticotropin, stimulation of protein E synthesis correlates better with steroidogenesis than with total protein synthesis.

Corticotropin regulation of the synthesis of a specific rat adrenal cytosolic protein. Effects of hypophysectomy and actinomycin D

The mechanism of corticotropin stimulation of the synthesis of a specific rat adrenal cytosolic protein was investigated. This protein (protein E) has a mol.wt. of approx. 30000. It is detected by polyacrylamide-gel electrophoresis of cytosol prepared from adrenal slices from rats treated with corticotropin in vivo and control rats, the slices being incubated with [(3)H]- and [(14)C]-leucine respectively. In rats 1-15 days after hypophysectomy, corticotropin, like dibutyryl cyclic AMP, induces an increase in protein E similar to that induced in control rats, even though both compounds no longer stimulate total protein synthesis. Corticotropin stimulation of protein E synthesis is mediated by cyclic AMP but not by corticosterone, since aminoglutethimide, a steroidogenic inhibitor, does not affect corticotropin stimulation, and dexamethasone alone has no effect. Actinomycin D, when injected in vivo 1h before or after corticotropin injection, prevents the effect of corticotropin on protein E synthesis, which is interpreted as evidence that mRNA synthesis is necessary for the stimulation of protein E synthesis. When injected more than 2h after corticotropin, actinomycin D does not prevent corticotropin stimulation of protein E synthesis, but completely blocks corticotropin stimulation of total protein synthesis. This is interpreted as meaning that, after stimulation of mRNA coding for protein E, corticotropin has no effect on the synthesis of protein E. On the other hand, corticotropin stimulation of protein E synthesis persists after hypophysectomy even though it no longer stimulates total protein synthesis. These data suggest that the factor(s) involved in the synthesis of protein E are more stable than those involved in total protein synthesis.

Effect of corticotropin treatment in vivo on the synthesis of a specific adrenal cytosolic protein. Characterization by dual-labelling technique and polyacrylamide-gel electrophoresis

The effect of corticotropin in vivo on total and specific protein synthesis in the adrenal was studied. Adrenal slices from control and corticotropin-treated animals were incubated with [14C]- and [3H]-leucine respectively, followed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis of subcellular components. With this sensitive dual-labelling technique the following results were obtained. There was a general trophic effect on most adrenal proteins, but corticotropin produced a marked stimulation of a specific adrenal cytosolic protein. This protein has mol.wt. approx. 30 000 and pI 5.5. Corticotropin increased the incorporation of labelled leucine into proteins within 4 h, but no effect was observed before 2 h and after 16 h there was no further increase. These data suggest that this protein is not involved in the corticosteroidogenic action of corticotropin, but rather in the trophic action of this hormone.

[Stimulation by ACTH of protein synthesis in cultured adrenal cells. Absence of an effect by cyclin AMP]

ACTH stimulates the incorporation of 14C-leucine into proteins of adrenal tumor cells in culture. This stimulation though about 20% over controls is statistically significant. Cyclic AMP did not reproduce the stimulation observed with ACTH.

Artificial hybrid protein containing a toxic protein fragment and a cell membrane receptor-binding moiety in a disulfide conjugate. II. Biochemical and biologic properties of diphtheria toxin fragment A-S-S-human placental lactogen

The biochemical and biologic properties of a purified disulfide conjugate of diphtheria toxin fragment A and human placental lactogen (toxin A-hPL) have been studied by (a) assaying the ADP-ribosyltransferase activity of the intact conjugate, (b) assaying the binding of the intact conjugate to mammary gland plasma membrane lactogenic receptors, and (c) assaying the effect of the conjugate on the rate of protein synthesis in rabbit mammary gland explants maintained in organ culture. The toxin A-hPL conjugate retains one-third of the NAD+:EF-2 ADP-ribosyltransferase activity of toxin A, and 26% of the hPL-binding activity to lactogenic receptors. Binding activity was demonstrated by radioreceptor assay and by assaying toxin A activity bound to membranes which was competitively displaced by excess hPL. Since the toxin A-hPL conjugate retained activities of its separate subunits, it could be regarded as a structural analogue of nicked diphtheria toxin with replacement of the original membrane-binding chain by another binding chain that is specific for lactogenic receptor. However, the conjugate failed to inhibit protein synthesis in organ-cultured mammary gland explants, although these were sensitive to native diphtheria toxin and could bind hPL. It is concluded from these results that the toxin A-hPL conjugate does not act as a functional analogue of diphtheria toxin with altered receptor specificity, and that the hPL receptor cannot mediate the entry of toxin A or toxin A-hPL from membrane-bound conjugate into the cytosol site of action of toxin A.

ACTH and prostaglandin receptors in human adrenocortical tumors. Apparent modification of a specific component of the ACTH-binding site

The failure of certain adrenal tumors to respond to ACTH was investigated in vivo be administration of corticotropin-(1-24)-tetracosapeptide (ACTH1-24) and dexamethasone and in vitro by studying the binding properties of ACTH1-24 and prostaglandin E1 (PGE1) and their effect on adenylate cyclase activity of the tumors' crude membranes; in addition, in five cases the stimulation of cortisol production in isolated adrenal cells by both hormones and dibuttyryl cyclic adenosine 3',5'-monophosphate (cAMP) was also studied. The results obtained in 13 hormone-producing tumors of the human adrenal cortex, i.e. 10 carcinomas and 3 adenomas, were compared with those found in normal human adrenal glands. According to the adenylate cyclase responses to ACTH1-24 and PGE1, the tumors fall into different categories. In the first group are six rumors in which the adenylate cyclase was stimulated by both ACTH1-24 and PGE; in addition specific binding could be demonstrated for the two hormones in all six. The binding affinity for 125I-ACTH1-24 was found to be about 10 times higher than that for 125I-ACTH11-24. In the one tumor in which the experiment was performed, bound 125I-ACTH1-24 was displaced by ACTH1-10. These results are similar to the ones found in normal human adrenal preparations. For two rumors of the group in which ACTH did not increase steroidogenesis in vivo, the biochemical abnormality might be located beyond cAMP formation. A second group encompasses six tumors in which the steroidogenesis in vivo and the adenylate cyclase activity were insensitive to ACTH1-24 but in which the enzyme was stimulated by PGE1 and NaF. However, these preparations bound 125I-ACTH1-24 and 125I-ACTH11-24, the binding affinity being similar for both peptides but 10 times lower than the one found in normal adrenal cortex for 125I-ACTH1-24. In the only case of this group where it was tested, ACTH1-10 did not displace bound 125I-ACTH1-24. This result strongly suggests the possibility of a modification or a loss of the receptor site that binds the N-terminal sequency (1-10) of ACTH, the biologically active part of the molecule. In the last tumor, both PGE1 and ACTH were unable to stimulate adenylate cyclase activity and steroid production in a preparation of isolated adrenal cells, although steroidogenesis was stimulated by dibutyryl though steroidogenesis was stimulated by dibutyryl cAMP. No specific binding for PGE1 could be demonstrated. However, 125I-ACTH1-24 and 125I-ACTH11-24 were found to be bound to the tumor with the same affinity.

Interactions of adrenocorticotropic hormone with its adrenal receptors. Degradation of ACTH-1-24 and ACTH-11-24

Crude membranes (20,000 times g pellet) prepared from human, rat, and ovine adrenals bind 125-I-corticotropin-(1-24)-tetracosapeptide (125-I-ACTH-1-24) and degrade unbound hormone. The degradation is dependent on temperature and the concentration of membrane proteins. The degradation of 125-I-[9-tryptophan(o-nitrophenylsulfenyl)]-corticotropin-(1-24)-tetracosapeptide (125-I-NPS-ACTH-1-24) is similar to 125-I-ACTH-1-24, but that of 125-I-corticotropin-(11-24)-tetradecapeptide (125-I-ACTH-1-24 is inhibited by ACTH-1-24 and corticotropin-(1-10)-decapeptide (ACTH-1-10), but ACTH-11-24 at the same molar concentration has no effect. On the other hand, the degradation of 125-I-ACTH-11-24 is protected by ACTH-11-24 and ACTH-1-24, but not by ACTH-1-10. This suggests two systems of degradation, one will have the NH-2-terminal sequence of ACTH-1-24 as substrate, and the other the 11-24 COOH-terminal sequence. The main label product from the degradation of the 125-I-ACTH-1-24 and 125-I-ACTH-11-24 behaves as [125-I]monoiodotyrosine on Sephadex G-50 and paper chromatography. The independence of ACTH binding to its receptor and degradation is demonstrated by the following facts. (a) Calcium and pancreatic trypsin inhibitor completely inhibit the binding at concentrations when the degradation is not altered; (b) the sequences of peptides of ACTH which inhibit the binding and degradation of 125-I-ACTH-1-24 are different.

Adrenal and testicular contribution to plasma oestrogens

The concentration of oestrone (E1) and oestradiol (E2) in plasma was measured by a radioimmunological method. In five premenopausal women, ovariectomy provoked a significant fall in the concentrations of E1 and E2. In 11 subjects of both sexes with cancer, dexamethasone (20 μg/kg/day) caused a significant fall in the levels of cortisol (84 ± 9·5%) and E1 (55 ± 16%), but not in E2 (2 ± 18%). Ninety minutes after administration of tetracosactrin, the increase in concentration of cortisol (80 ± 30%) and of E1 (70 ± 49%) was highly significant: that of E2 (5 ± 12%) was not. Similar results were observed in four subjects during infusion of corticotrophin. In six subjects, plasma concentration of E1, androstenedione and dehydroepiandrosterone was higher in the adrenal vein than in a peripheral vein, but the concentration of E2 and of testosterone was similar in the two samples. In two men, the concentration of androgens and oestrogens was measured in plasma from a peripheral vein and in plasma of mixed origin from the renal and the spermatic vein. The level of E2 was higher in plasma from the renal—spermatic mixture than in that from the peripheral vein, but the concentration of E1 was similar. All these results suggest that: (1) the adrenal secretes only 17-oxo androgens and oestrogens whereas in the testicular secretion, 17β-hydroxylated compounds predominate; (2) in men, nearly all of the E2 is secreted directly or indirectly by the testes, but the main source of E1 is the adrenal; (3) in postmenopausal women, most of the E1 also derives from the adrenal gland.