Preparation and properties of the o-nitrophenyl sulfenyl derivative of ACTH: an inhibitor of the lipolytic action of the hormone

Adrenocorticotropin. 48. Synthesis and biological activity of (15, 16-D-lysine, 17, 18-D-arginine)-adrenocorticotropin-(1-19) and an all-D-retropeptide related to the amino terminal octadecapeptide of adrenocorticotropin

The peptide [15, 16-D-lysine, 17, 18-D-arginine]-adrenocorticotropin-(1-19) and an all-D-retropeptide related to the amino terminal octadecapeptide of adrenocorticotropin have been synthesized by the solid-phase method. The nonadecapeptide was shown to possess 10-15% of the steroidogenic activity and 3% of the lipolytic activity of adrenocorticotropin-(1-19). The all-D-retropeptide showed no activity and exhibited no inhibitory activity in steroidogenesis and lipolysis.

Synthesis and charge-transfer properties of two acth analogues containing pentamethylphenylalanine in position 9

In order to investigate the possible role of the Trp residue in ACTH as a change-transfer donor in the activation of ACTH receptors, two ACTH analogues (beta-corticotrophins (I-24) with L-Ser1 and D-Ser1, respectively) containing pentamethylphenylalanine instead of Trp have been synthesized. In these syntheses a new, alkaline-labile, amino-protecting group, the methylsulphonylethyloxycarbonyl group, was employed. The association constants of ACTH (I-24) and (Pmp9)-ACTH (I-24) with the water-soluble acceptor paraquat, were nearly equal.

Ca2+ signal stimulates the expression of steroidogenic acute regulatory protein and steroidogenesis in bovine adrenal fasciculata–reticularis cells

Adrenal glucocorticoid synthesis is stimulated by ACTH or its nitrophenylsulphenyl derivative, NPS-ACTH. Acute stimulation of steroid hormone biosynthesis is highly dependent on the expression of steroidogenic acute regulatory (StAR) protein. To determine the regulatory mechanism of StAR expression in bovine fasciculata/reticularis cells, we analyzed the second messenger systems involved in StAR protein expression using cultured cells activated by ACTH and NPS-ACTH. We concluded that cAMP is not the essential second messenger for StAR protein expression, since NPS-ACTH activated StAR protein expression more than ACTH without increase in cellular cAMP. A 15-lipoxygenase metabolite(s) of arachidonic acid stimulated steroidogenesis without increase in StAR protein expression, since AA-861, a lipoxygenase inhibitor, inhibited steroidogenesis without affecting StAR protein expression. Stimulation of StAR protein expression and the corresponding increase in the steroidogenesis were inhibited by nicardipine in cells treated with ACTH or NPS-ACTH. These data indicate that the dominant second messenger for the stimulation of StAR protein expression is Ca2+. Calmodulin-dependent kinase II inhibitors KN-93 and KN-62 suppressed steroidogenic activity without affecting StAR expression. The protein kinase C inhibitor Ro 31-8220 did not show any effects on StAR expression and steroidogenesis. Calmodulin-dependent kinase II and protein kinase C can therefore be concluded not to be involved in StAR protein expression in bovine cells.

Calcium ion as a second messenger for o-nitrophenylsulfenyl-adrenocorticotropin (NPS-ACTH) and ACTH in bovine adrenal steroidogenesis

o-Nitrophenyl sulfenyl-modified ACTH (NPS-ACTH) stimulated steroidogenesis acutely in bovine fasciculata-reticularis cells without increase in cellular cAMP synthesis. Application of NPS-ACTH to the cultured cells induced Ca2+ signals in individual cells as detected by video-enhanced microscopic fluorescence measurements. The percentage of Ca2+ signaling cells corresponded well with the increase of steroidogenesis induced by NPS-ACTH below 1 nM. Treatment of the cells with nicardipine, a Ca2+ channel blocker, suppressed the Ca2+ signals except for the transient increase just after the addition of NPS-ACTH and also blocked completely the stimulative effect on the steroidogenesis of NPS-ACTH below 1 nM. At a dosage of NPS-ACTH higher than 10 nM, the stimulative effect of steroidogenesis was partly suppressed by nicardipine and also by AA-861, a lipoxygenase inhibitor. The action of NPS-ACTH might be mediated by both Ca2+ and lipoxygenase metabolite(s) of arachidonic acid as dual second messengers. The effect of ACTH in pM range on the steroidogenesis was suppressed completely by the treatment with nicardipine and AA-861 at the same time, indicating that the action was mediated by both Ca2+ and the lipoxygenase metabolite(s) but not by cAMP. cAMP plays a significant role as a second messenger for ACTH action only at ACTH concentrations greater than 10 pM.

The effects of synthetic locust adipokinetic hormone on dispersed locust fat body cell preparations: cAMP induction, lipid mobilization, and inhibition of protein synthesis

A procedure for the preparation of functional cells from adult locust fat bodies by collagenase treatment has been developed. The high variability of replicates encountered when whole fat bodies are incubated in vitro is greatly reduced in incubation of the dispersed cells. Synthetic locust adipokinetic hormone (AKH) (40 nM) stimulated release of lipids from the dispersed fat body cells at a rate comparable to that observed using whole fat bodies in vitro. Synthetic AKH elevated cAMP levels sixfold in dispersed cells. In addition, AKH inhibited protein synthesis to a maximum of 50-70% in a concentration-dependent manner. None of these actions of AKH required the presence of locust hemolymph components. These results demonstrate the utility of the isolated locust fat body cells for investigating hormonal action in vitro.

Adrenocorticotropin. 57. Synthesis and biological activity of ostrich and turkey hormones

Synthesis of ostrich and turkey corticotropin (ACTH) has been accomplished by the solid-phase method. Each was identical to the natural hormone in high performance liquid chromatography. Relative potencies in a lipolytic assay in isolated rabbit fat cells were: human ACTH, 100; ostrich ACTH, 53; turkey ACTH, 28. In isolated rat fat cells relative lipolytic potencies were: human ACTH, 100; ostrich ACTH, 2; turkey ACTH, 13. It was concluded that lipolytic potency is sensitive to alterations in structure throughout the entire length of the ACTH sequence in the rat fat cell assay.

Comparison of the structural features of corticotropin required for stimulation of steroidogenesis and cAMP production in rat and rabbit adrenocortical cells

The steroidogenic activities of ACTH, alpha-MSH, beta-MSH as well as analogs of the hormones have been compared in rat and rabbit adrenocortical cells. ACTH is equally active in both species and the melanotropins have very low steroidogenic potency in either species. The steroidogenic potencies of the peptide analogs are strikingly similar in the two species, suggesting that the structural requirements for eliciting steroidogenesis are the same in rat and rabbit adrenocortical cells. The analog NPS-ACTH has low, comparable steroidogenic activity in both species. NPS-ACTH is a potent antagonist of ACTH-induced cAMP production in rat adrenocortical cells but acts as a weak partial agonist in rabbit adrenocortical cells. These results suggest that steroidogenesis may be mediated by receptors different from those involved in the cAMP response observed at supraphysiological concentrations of ACTH.

Photoaffinity labeling of corticotropin receptors

A photoaffinity label for corticotropin (ACTH) receptors was prepared by selective chemical modification of the single tryptophan residue in the hormone by reaction with 2-nitro-5-azidophenylsulfenyl chloride. The photoreactive derivative, [(2-nitro-5-azidophenylsulfenyl)-Trp9]ACTH (2,5-NAPS-ACTH), stimulated corticosterone synthesis to 60% of the maximal rate induced by ACTH in isolated rat adrenocortical cells. 2.5-NAPS-ACTH caused only a marginal stimulation of cyclic AMP production compared to the unmodified hormone. Stimulation of corticosterone production and cyclic AMP accumulation induced by ACTH were both inhibited in a competitive manner by 2,5-NAPS-ACTH. Photolysis of adrenocortical cells in the presence of 2,5-NAPS-ACTH resulted in a 40% inactivation of ACTH receptors mediating steroidogenesis, as shown by the decrease in response to subsequent stimulation with ACTH. No loss of function was observed when photolysis was conducted in the presence of the photoresistant analog [(2,4-dinitrophenylsulfenyl)-Trp9]ACTH. Covalent attachment of the hormone to the receptors was also demonstrated by photolyzing adrenocortical cells in the presence of tritiated 2,5-NAPS-ACTH of high specific radioactivity (90 Ci/mmol) and analyzing the cell proteins by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. A protein with an approximate molecular weight of 100,000 was specifically labeled by this procedure. The unique labeling of an adrenocortical cell protein and the concomitant loss of ACTH responsiveness suggest that physiologically relevant receptors are photolabeled by this method.

Responses of Y1 adrenocortical tumor cells to o-nitrophenyl sulfenyl ACTH

NPS(o-nitrophenyl sulfenyl)-ACTH stimulated steroidogenesis in Y1 cells to the same maximum level as did ACTH, but with a 60-fold lower potency than the native hormone. NPS-ACTH also stimulated the extracellular accumulation of cAMP in Y1 cells with lower potency than the unmodified hormone. The amount of cAMP accumulated in the presence of NPS-ACTH approached 75% of the maximum with ACTH. In Y1 plasma membranes, NPS-ACTH was a partial agonist of adenylate cyclase activity, witn an efficacy dependent upon the type of guanyl nucleotide present. The steroidogenic responses of two Y1(Kin) mutants and two Y1(Cyc) mutants to NPS-ACTH paralleled their responses to ACTH and reflected closely their defects in cAMP-dependent protein kinase and ACTH-sensitive adenylate cyclase activity. These data imply an obligatory role for adenylate cyclase and cAMP-dependent protein kinase activities in stimulation of steroidogenesis in Y1 cells by NPA-ACTH.

Adrenocorticotropin. 52 Synthesis and biological activity of adrenocorticotropic peptides with cystine bridges

Three analogs of the amino terminal nonadecopeptide of adrenocorticotropin which incorporate cystine cystine bridges between positions (5, 10), (3, 10), or (2, 10) have been synthesized. All of the peptide analogs showed reduced biological activity; however, the peptide with the 5, 10 cystine bridge was shown to possess significantly higher lipolytic activity in rat fat cells than the peptides with a 3, 10 or 2, 10 cystine bridge.

Design and synthesis of parathyroid hormone analogues of enhanced biological activity

Three analogues of bovine parathyroid hormone (bPTH), [Tyr-34]bPTH-(1--34) amide, [Nle-8,Nle-18,Tyr-34]bPTH-(1--34)amide, and [Nle-8,Nle-18, o-NPS-Trp-23,Tyr-34]bPTH-(1--34)amide were synthesized by the solid-phase method. The synthetic peptides were found to be homogeneous in multiple analytical systems. These analogues represent the NH2-terminal one-third of the hormone, previously shown to contain all the structural requirements necessary for biological activity, but containing several structural modifications associated with enhancement and stabilization of biological activity. When tested in the in vitro renal adenylylcyclase assay, in which unsubstituted bPTH-(1--34) has a potency of 5400 MRC Units/mg, [Tyr-34]bPTH-(1--34)amide had a potency of 16,1000 MRC Units/mg, [Nle-8,Nle-18,Tyr-34]bPTH-(1--34)amide was 10,100 MRC Units/mg, and [Nle-8,Nle-18,o-NPS-Trp-23,Tyr-34]bPTH-(1--34)amide was 10,600 MRC Units/mg. The diverse structural features incorporated in these hormone analogues, resulting in a several-fold increase in biological activity in vitro, demonstrate additive effects on biological activity and should prove valuable in certain biological applications, as well as in the design of other parathyroid hormone analogues of enhanced potency.

Adrenal cortex adenylate cyclase. In vitro acitivity of ACTH fragments and analogues

The ability of ACTH fragments and of an ACTH analogue [9-tryptophan(o-nitrophenylsulfenyl)] corticotropin-(1-24)-tetracosapeptide[Trp-(Nps)9 ACTH1-24] to stimulate adenylate cyclase in bovine adrenal cortex membranes and a crude membrane fraction from rat adrenals has been determined. Partial agonists like Trp (Nps)9 ACTH1-24 displayed intrinsic activity in the rat adrenal preparation only if tested in the presence of 5'-guanylylimidodiphosphate [Gpp(NH)p]. On the other hand, no addition of Gpp(NH)p was necessary to demonstrate intrinsic activity of Trp(Nps)9 ACTH1-24 for bovine adrenal cortex adenylate cyclase. A large decrease (15-fold) of the apparent Km values for ACTH1-24, ACTH1-23 and ACTH1-17 was observed with the rat adrenal preparation when Gpp(NH)p was added. The shift in apparent Km values for ACTH1-24 and ACTH1-23 for the bovine adrenal cortex adenylate cyclase system was small or insignificant when Gpp(NH)p was added. The observations suggest that the hormone receptor facilitates the action of guanylnucleotide sites in the membrane. When guanylnucleotide sites are occupied by Gpp(NH)p even weak interactions of the hormone receptor with e.g. partial agonists are propagated to the catalytic subunits of the adenylate cyclase complex resulting in enhanced activity. The differences in adenylate cyclase activation with hormone fragments or analogues and different target tissues may rather reflect the state of the coupling process involving guanylnucleotide binding sites of the isolated membrane fraction than differences in the receptor itself.

Divergent effects of adrenocorticotropin and melanotropin on isolated rat and rabbit adipocytes

The stimulation of lipolysis in isolated rat and rabbit fat cells by adrenocorticotropin (ACTH) and alpha-melanotropin has been studied. The concentration of alpha-melanotropin required for half maximal stimulation is 0.23 times that of ACTH in rabbit adipocytes but as high as 1140 times that of ACTH in rat fat cells. Chemical modification of the tryptophan residue in ACTH and melanotropin resulted in a loss of lipolytic activity in rat adipocytes and an increase in lipolytic potency in rabbit fat cells. These differences between rat and rabbit fat cells were evident when stimulation of cyclic AMP synthesis was measured in isolated cells or ghosts. The results are discussed in terms of the difference in the hormone receptors of the fat cells of the two species.

Comparison of the steroidogenic and melanotropic activities of corticotropin, alpha-melanotropin and analogs with their lipolytic activities in rat and rabbit adipocytes

The ability of alpha-melanotropin and a series of synthetic peptides related to adrenocorticotropin (ACTH) to stimulate steroidogenesis in isolated rat adrenal cells, melanin dispersion in frog melanophores and lipolysis in rat and rabbit fat cells have been studied. It was found that the steroidogenic activity closely paralleled the lipolytic activity of these peptides in rat fat cells, whereas the melanocyte stimulating activity paralleled the lipolytic activity in rabbit fat cells. These results indicate that the structural requirements for stimulating steroidogenesis in isolated rat adrenal cells and lipolysis in isolated rat fat cells are quite similar. The structural features required for eliciting lipolysis in rabbit fat cells appear to be very similar to those necessary for stimulating frog melanophores. The possibility that regulation of lipid metabolism in the rabbit may be a new function acquired by melanotropin is discussed.