Use of ion-exchange Sep-Pak cartridges in the batch fractionation of pituitary peptides

The stimulation of mitogenic signaling pathways by N-POMC peptides

The N-terminal fragment of pro-opiomelancortin (POMC) has been shown previously to act as an adrenal mitogen. However, little is known about the molecular mechanisms by which mitogenesis is stimulated, although it has been shown that N-POMC(1-28) stimulates the ERK pathway in human H295R cells. We have investigated signaling stimulated by N-POMC(1-28) and N-POMC(1-49) in the mouse Y1 cell line and found that both peptides stimulate ERK phosphorylation with maximal stimulation being achieved within 5min. Similar results were observed for both MEK and c-Raf phosphorylation, although N-POMC(1-49) stimulated the phosphorylation of Akt more robustly than N-POMC(1-28). We also investigated the expression of tyrosine kinase receptors in adrenal cells. PCR utilizing degenerate primers was performed on cDNA from both Y1 cells and rat adrenal tissue. Sequencing of 114 clones from each cDNA population revealed the expression of a number of receptors, several of which have not been described previously in the adrenal.

Evidence of a possible role for Lys-gamma3-MSH in the regulation of adipocyte function

Lys-gamma3-MSH is a melanocortin peptide derived from the C-terminal of the 16 kDa fragment of POMC. The physiological role of Lys-gamma3-MSH is unclear, although it has previously been shown that, although not directly steroidogenic, it can act to potentiate the steroidogenic response of adrenal cortical cells to ACTH. This synergistic effect appears to be correlated with an ability to increase the activity of hormone sensitive lipase (HSL) and therefore the rate of cholesterol ester hydrolysis. Ligand binding studies have suggested that high-affinity binding sites for Lys-gamma3-MSH exist in the adrenal gland and a number of other rat tissues that express HSL, including adipose, skeletal muscle and testes. To investigate the hypothesis that Lys-gamma3-MSH may play a wider role in cholesterol and lipid metabolism, we tested the effect of Lys-gamma3-MSH on lipolysis, an HSL-mediated process, in 3T3-L1 adipocytes. In comparison with other melanocortin peptides, Lys-gamma3-MSH was found to be a potent stimulator of lipolysis. It was also able to phosphorylate HSL at key serine residues and stimulate the hyperphosphorylation of perilipin A. The receptor through which the lipolytic actions of Lys-gamma3-MSH are being mediated is not clear. Attempts to characterise this receptor suggest that either the pharmacology of the melanocortin receptor 5 in 3T3-L1 adipocytes is different from that described when expressed in heterologous systems or the possibility that a further, as yet uncharacterised, receptor exists.

Female sex pheromone suppression and the fate of sex-peptide-like peptides in mated moths of Helicoverpa armigera

Insect males produce accessory gland (MAG) factors that are transferred in the seminal fluid to females during copulation, and elicit changes in the mated female's behavior and physiology. Our previous studies showed that the injection of synthetic Drosophila melanogaster sex-peptide (DrmSP) into virgin females of the moth Helicoverpa armigera causes a significant inhibition of pheromone production. In this and other moth species, pheromone production, correlated with female receptivity, is under neuroendocrine control due to the circadian release of the neuropeptide PBAN. In this study, we show that PBAN, present in the hemolymph during the scotophase in females, is drastically reduced after mating. We also identify 4 DrmSP-like HPLC peaks (Peaks A, S1, S2, and B) in MAGs, with increasing levels of DrmSP immunoreactivity during the scotophase, when compared to their levels observed during the photophase. In H. armigera MAGs, a significant reduction in the pheromonostatic peak (Peak B) was already evident after 15 min of copulation, and depletion of an additional peak (Peak S2) was evident after complete mating. Peak A is also detected in female brains, increasing significantly 1 h after mating, at which time inhibition of pheromone biosynthesis also occurs. However, changes corresponding to the other MAG peaks were not detected in mated female tissues.

Regulation of progranulin expression in myeloid cells

Progranulin (pgrn; granulin-epithelin precursor, PC-cell-derived growth factor, or acrogranin) is a multifunctional secreted glycoprotein implicated in tumorigenesis, development, inflammation, and repair. It is highly expressed in macrophage and monocyte-derived dendritic cells. Here we investigate its regulation in myeloid cells. All-trans retinoic acid (ATRA) increased pgrn mRNA levels in myelomonocytic cells (CD34(+) progenitors; monoblastic U-937; monocytic THP-1; progranulocytic HL-60; macrophage RAW 264.7) but not in nonmyeloid cells tested. Interleukin-4 impaired basal expression of pgrn in U-937. Differentiation agents DMSO, and, in U-937 only, phorbol ester [phorbol 12-myristate,13-acetate (PMA)] elevated pgrn mRNA expression late in differentiation, suggestive of roles for pgrn in more mature terminally differentiated granulocyte/monocytes rather than during growth or differentiation. The response of pgrn mRNA to ATRA differs in U-937 and HL-60 lineages. In U-937, ATRA and chemical differentiation agents greatly increased pgrn mRNA stability, whereas, in HL-60, ATRA accelerated pgrn mRNA turnover. The initial upregulation of pgrn mRNA after stimulation with ATRA was independent of de novo protein synthesis in U-937 but not HL-60. Chemical blockade of nuclear factor-kappaB (NF-kappaB) activation impaired ATRA-stimulated pgrn expression in HL-60 but not U-937, whereas in U-937 it blocked PMA-induced pgrn mRNA expression, suggestive of cell-specific roles for NF-kappaB in determining pgrn mRNA levels. We propose that: 1) ATRA regulates pgrn mRNA levels in myelomonocytic cells; 2) ATRA acts in a cell-specific manner involving the differential control of mRNA stability and differential requirement for NF-kappaB signaling; and 3) elevated pgrn mRNA expression is characteristic of more mature cells and does not stimulate differentiation.

The role of the melanocortin 3 receptor in mediating the effects of gamma-MSH peptides on the adrenal

The pro-opiomelanocortin (POMC)-derived peptides, pro-gamma-MSH (16K fragment), and Lys-gamma3-MSH, have been shown to potentiate the steroidogenic action of corticotrophin (ACTH) on the adrenal cortex. Using a continuously perfused adrenal cell column system, we have tested the hypothesis that gamma-MSH peptides exert their effect through the Melanocortin 3 Receptor (MC3-R), since this is the only known receptor to have high affinity for gamma-MSH peptides and has been suggested to be expressed in the rat adrenal. To investigate this hypothesis we tested whether the MC3-R agonist MTII and antagonist SHU9119 could mimic or block the actions of pro-gamma-MSH. We found that MTII could not mimic, and SHU9119 could not block pro-gamma-MSH mediated potentiation of ACTH-induced steroidogenesis. These results suggest that the MC3-R is not involved in mediating the potentiation effect, adding further evidence to the argument that another melanocortin receptor exists.

The presence of Drosophila melanogaster sex peptide-like immunoreactivity in the accessory glands of male Helicoverpa armigera

In this study a highly specific polyclonal antibody to DrmSP was produced and used to develop and standardize a sensitive direct ELISA. Structure-activity studies revealed that the antiserum is specific to the N-terminal of DrmSP. This ELISA was used for the detection of DrmSP-like immunoreactivity in the reproductive tissues of male Helicoverpa armigera moths at femtomole levels. Two positive immunoreactive peaks were found in HPLC purified extracts of male accessory glands. The immunoreactive peak, which contained a higher amount of immunoreactivity, was also found to be pheromonostatic in PBAN-injected decapitated females as well as in intact female moths during their peak pheromone production. Lower levels of DrmSP-like immunoreactivity were found in younger males (1-2 day-old) when compared to older males (3-7 day-old).

Isolation and structure-bioactivity characterization of glycosylated N-pro-opiomelanocortin isoforms

The N-terminal fragment of mouse pro-opiomelanocortin (N-POMC) was isolated from AtT-20 cell-conditioned medium on the basis of immunoreactivity to an anti-POMC1-50 monoclonal antibody by a concentration step, a cation exchange step, reversed phase high-performance liquid chromatography (HPLC) and size exclusion HPLC. Two groups of N-POMC isoforms with a molecular weight (MW) of approximately 11 kDa and 13 kDa, respectively, were identified by mass spectrometry and N-terminal amino acid sequencing. C-terminal sequencing indicated that 11 kDa isoforms correspond to POMC1-74 and 13 kDa isoforms to POMC1-95. Isoforms from both groups enhanced the prolactin mRNA content (measured by means of TaqMan real-time reverse transcription-polymerase chain reaction) in cultured rat pituitary cell aggregates in a dose-dependent manner, but not all of them showed this activity. POMC1-74 compounds were significantly more potent than POMC1-95 isoforms. The observed effects were abolished by coincubation with the monoclonal anti-POMC1-50 antibody, showing the specificity of this biological action. Incorporation of bromodeoxyuridine into DNA of immunostained lactotrophs was enhanced by only a minor part of the isoforms. Some of these had no effect on prolactin mRNA expression. The N-POMC isoforms appeared to be N- and at least in part O-glycosylated. After enzymatic N-deglycosylation of selected N-POMC isoforms, the stimulatory effect on the prolactin mRNA level was depressed (in case of the POMC1-95 isoforms) or totally abolished (in case of the POMC1-74 isoforms). The present findings show that N-POMC is a mixture of differentially glycosylated isoforms, that the isoforms of POMC1-74 are the biologically more effective forms and that different isoforms induce different biological responses in the same cell population. The data also show the essential role of N-glycosylation in the biological response.

Male accessory gland derived factors can stimulate oogenesis and enhance oviposition in Helicoverpa armigera (Lepidoptera: Noctuidae)

In Helicoverpa armigera, female moths began to lay eggs on the third day after emergence. Mating stimulated earlier egg maturation/oogenesis (P = 0.002) and oviposition (P << 0.01). We established a suitable bioassay model for the influence of male accessory glands (MAG) on the physiology of virgin females: Crude extracts of MAG (2- to 3-day-old) were injected into 2-day-old virgin females, and the injected females were dissected 20 h after mating. It was shown that crude extracts of MAG stimulated earlier egg maturation (P < 0.001) and oviposition (the oviposition ratio was more than 2 times the ratio of the control). Proteinaceous components in crude extracts purified by fractionation and sub-fractionation in reverse phase high performance liquid chromatography also stimulated earlier egg maturation (P < 0.01) and ovipositon (more than 2 times the ratio of the control), and we called them the oogenesis and ovipostion factors (OOSF). With SDS-PAGE, the molecular mass of the bands from OOSF was estimated to be between 55-66 KD. Arch.

Beta-endorphin-containing proteins in the human pituitary

Two new proopiomelanocortin (POMC)-derived beta-endorphin (BE)-containing proteins were detected in the human pituitary, using HPLC, trypsin digestion, and a high sensitivity search with liquid secondary ion mass spectrometry (LSIMS) for the protonated molecule ion, (M + H)+, of tryptic peptides that are unique to BE. Proteins were extracted from pituitary tissues and were purified by solid phase extraction (SPE) chromatography and RP-HPLC. Each HPLC fraction was treated with trypsin, and each unseparated peptide mixture was analyzed by LSIMS to detect the two selected marker peptides (BE 20-24 and BE 10-19) that have excellent LSIMS desorption-ionization properties. The detection of both of those peptides indicated the presence of BE-containing proteins in two HPLC fractions (number 47 and 51). Tandem MS determined the amino acid sequence of the marker peptide BE 20-24 (NAIIK), and those sequence data optimized the specificity of the method. The two new BE-containing proteins derive from the C-terminal region of POMC, and were minor components in the two HPLC fractions. The major component in fraction 51 derived from the vasopressin-neurophysin 2-copeptin precursor.

Evaluation of solid-phase extraction procedures in peptide analysis

Solid-phase extraction (SPE) procedures for peptide isolation and fractionation, based on non-polar and ionic interactions, were evaluated using small synthetic peptides and casein enzymatic hydrolysates. SPE based on hydrophobic phases is a useful, efficient and rapid procedure for peptide extraction and concentration. It allows a successful peptide fractionation using eluents that contain an increasing content of acetonitrile in the presence of trifluoroacetic acid. Differences regarding selectivity are observed between sorbents. Non-polar interaction with C18 sorbents is adequate for the isolation of very polar and hydrophobic peptides. CN sorbents are only adequate for very hydrophobic peptides. PH, CH, C8 and C2 sorbents are useful for isolating and fractionating hydrophobic and very non-polar peptides, but generally not for very polar peptides. Ionic solid-phase extraction using Accell Plus cartridges of QMA (quaternary methylammonium) and CM (carboxymethyl) are very useful for the fractionation of peptide mixtures into basic, acidic and neutral pools of peptides. It can be concluded that SPE using these procedures is a useful tool for the isolation and fractionation of peptides from biological and food samples.

Isolation and characterization of corticostatic peptides from guinea pig bone marrow

Three corticostatic peptides (GP-CS1, GP-CS2 and GP-CS3) were purified from extracts of guinea pig bone marrow. Each was identified on the basis of their ability to inhibit the secretion of corticosterone by isolated rat adrenal cells stimulated by ACTH. GP-CS1 and GP-CS2 were found to be 31 residues in length, rich in arginine and to have six cysteines typical of the corticostatin/defensin family of peptides previously purified from phagocytic cells of the immune system. GP-CS1 was found to be identical to GP-CS2 except for having a leucine at position 21 instead of isoleucine. GP-CS3 was also found to be rich in arginine and cysteine but structurally distinct from the other peptides. A combination of endoprotease mapping, ion-spray mass spectrometry and gas-phase sequencing revealed that GP-CS3 was a novel homo-dimer consisting of two 13 amino acid residue subunits cross-linked through eight cysteines in an anti-parellel configuration.

Differential glycosylation of N-POMC1-77 regulates the production of gamma 3-MSH by purified pro-opiomelanocortin converting enzyme. A possible mechanism for tissue-specific processing

The amino terminus of bovine pro-opiomelanocortin (N-POMC1-77) is partially processed in the intermediate lobe of the pituitary to N-POMC1-49 and lys-gamma 3-melanotropin. Two pools of N-POMC1-77 were isolated which were differentially glycosylated at threonine45, while N-POMC1-49 isolated from bovine intermediate lobe extracts existed in a non-glycosylated form. This suggested that differential O-linked glycosylation of N-POMC1-77 may regulate cleavage at the Arg49-Lys50 processing site. We tested this hypothesis by incubating N-POMC1-77 glycoforms with purified proopiomelanocortin converting enzyme. Only non-O-glycosylated N-POMC1-77 and O-glycosylated N-POMC1-77 with truncated oligosaccharide sidechains were sensitive to cleavage and generated predominantly lys-gamma 3-melanotropin, identified by high-performance liquid chromatography. These data provide the first functional evidence to support a role for differential O-linked glycosylation in the regulation of the processing of the N-terminus of bovine POMC.

Analysis of methionine enkephalin in human pituitary by multi-dimensional reversed-phase high-performance liquid chromatography, radioreceptor assay, radioimmunoassay, fast atom bombardment mass spectrometry, and mass spectrometry-mass spectrometry

Methionine enkephalin (ME = YGGFM) was measured in five individual human post-mortem pituitaries using four different analytical methods, with the objective of comparing the molecular specificities of the methods. Radioreceptor assay (RRA) used a receptor-rich preparation from brain and [3H]etorphine as radioligand to determine ME-like receptoractivity (ME-LR). Radioimmunoassay (RIA) measured ME-like immunoreactivity (ME-LI). Pituitary samples analyzed by RRA and RIA were purified first with a high-performance liquid chromatography (HPLC) gradient on a polymer analytical column. Fast atom bombardment mass spectrometry (FAB-MS) in two different detection modes quantified ME using the protonated molecular ion MH+ of ME at 574 a.m.u. and B/E linked-field selected reaction monitoring (SRM) to monitor the specific unimolecular metastable transition that produced the unique amino acid sequence-determining tetrapeptide fragment ion YGGFA+ from the MH+ precursor ion. Both FAB-MS methods used the deuterated internal standard YGG[2H5-F]M. Samples analyzed with FAB-MS were purified first with multi-dimensional reversed-phase HPLC. The first dimension was an ODS gradient, and the second dimension was a polymer isocratic elution. The following ME amounts were measured (mean +/- standard error of the mean): ME-LR, 7.0 +/- 1.9 micrograms g-1 tissue; ME-LI, 1.8 +/- 0.7 micrograms g-1 tissue; MH+, 2.7 +/- 0.6 micrograms g-1 tissue; SRM, 3.0 +/- 0.8 micrograms g-1 tissue. The FAB SRM method provided the highest level of molecular specificity amount these four analytical methods used to measure picomole amounts of endogenous ME in a human pituitary.

Serum and prostatic growth-promoting factors for steroid-independent epithelial cells of adult dog prostate

A growth factor-like effect has been observed on canine prostatic epithelial cells when cultured in the presence of their homologous serum and prostatic extracts; the mitogenic activities of both preparations were dose-dependent and not altered by charcoal treatment. The effect of dog serum decreased when the density of the epithelial cell cultures increased and was minimal on canine prostatic fibroblasts. Trace amounts of intracellular sex steroids did not contribute to epithelial cell proliferation since the presence of sex steroid action inhibitors did not alter growth rate; in those conditions, cycloheximide completely prevented cell division. When various hormones and known mitogenic agents were tested alone or in combination with steroids, none elicited an increase in the number of epithelial cells cultured in serum-free medium or altered the proliferative effect of dog serum observed in parallel cultures. On gel filtration, dog serum or tissue cytosol showed a major mitogenic activity at an apparent molecular mass of 150 kDa and a minor one of 1.5 kDa as evaluated by gel filtration of dog serum ultrafiltrate. Acidic extraction of prostatic tissue followed by chromatography on a hydrophobic C-18 column and subsequent gel filtration also led to the detection of the low Mr component. Thus, humoral and/or tissular factors present in vivo and different from known mitogens may be of importance as direct modulators of the basal epithelial cell growth in the adult canine prostate.

A trace-enrichment technique for the loading of gel-permeation high-performance liquid chromatography columns

Gel-permeation high-performance liquid chromatography (GP-HPLC) columns provide rapid high-resolution separations but are frequently limited to analytical tasks because the injection volumes must be small. The reduction of volume required for the loading of solutes can often be impractical and lead to poor recoveries. We have developed a trace-enrichment technique to circumvent this problem. By placing a Waters Guard Pak within the loop of a Valco injector and connecting a pump to the injection port it is possible to concentrate proteins and peptides onto the guard column from relatively large volumes. Enrichment onto a reversed-phase guard column insert is achieved by loading solutes in an aqueous solution or one of low organic solvent concentration. Provided that the GP-HPLC is mean-while equilibrated with a solvent system of sufficiently high organic solvent concentration (i.e., 40% acetonitrile containing 0.1% trifluoroacetic acid) it is possible to elute material that has been loaded in this manner by simply placing the injection loop in line with the column. The solvent strength abruptly increases and the peptide or protein sample is loaded onto the column in a very small volume. We have applied this loading principle to both analytical and semipreparative problems. The amino-terminal fragment of pro-opiomelanocortin (POMC) has been extracted from a single human fetal pituitary (18 weeks gestation) and characterized in terms of its molecular weight. This study indicated that no proteolytic processing of the amino-terminal fragment of POMC takes place at this stage in development. In a larger scale application the amino-terminal fragment of POMC was purified from bovine anterior pituitaries.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and biological activity of corticostatic peptides (anti-ACTH)

Corticostatins (CS's) are a family of low molecular weight peptides, rich in arginine and cysteine with the ability to inhibit ACTH stimulated adrenocortical steroidogenesis. They show a high degree of specificity in that they do not inhibit the action of angiotensin II in the adrenal cortex. Four corticostatins have been isolated from rabbit lung extracts and peritoneal neutrophil extracts and one from human neutrophils. Among them corticostatin I, CSI, is the most potent with an I.D.50 of 25 nM. Corticostatin activity is different from other published inhibitory factors such as TGF-B and ANF, which inhibit basal and angiotensin II stimulated steroidogenesis. Other factors such as macrophage secreted products, and septic shock plasma factors which have not been fully characterized also have suppressive activity on ACTH induced adrenocortical steroidogenesis in vitro. It is not yet clear whether there is any relationship between corticostatins and these macrophage products and shock plasma factor. Corticostatins do not inhibit dbcAMP induced steroidogenesis, however they do inhibit the accumulation of cAMP in response to ACTH in rat adrenal cell suspensions. Binding studies show that CSI is a competitive inhibitor of ACTH, probably acting by blocking, the address recognition site of the receptor. There is wide variation in the potency of the corticostatins ranging from an ID50 of 100 ng/ml for CSI to a completely inactive analog, HP1. In this paper we will describe the purification of the corticostatins and some recent results obtained on their mechanism of action.

Localisation and identification of melanocyte-stimulating hormones in the fish brain

The existence of melanocyte-stimulating hormone (MSH) in fish brains was investigated by a range of techniques: radioimmunoassay, HPLC, bioassay, and immunocytochemistry. Immunoreactive alpha MSH (ir alpha MSH) was detected by radioimmunoassay in all regions of carp and trout brains, with the highest concentration in the basal hypothalamus. In trout, ir alpha MSH cell bodies were located by immunocytochemistry only periventricularly, in the medial basal hypothalamus near the third ventricle, whereas in the carp ir alpha MSH staining was seen both in periventricular cells and also in some of the magnocellular neurones in the lateral hypothalamus. When white-adapted fish were transferred to a black tank for 6 days, the melanin-concentrating hormone (MCH) content of the basal hypothalamus of both carp and trout increased 2- and 4.6-fold, respectively, but the alpha MSH content did not change in either species. Analysis by HPLC of pituitary gland, hypothalamic, and optic tectal extracts revealed that the pituitary contains desacetyl, monoacetyl, and diacetyl alpha MSH, although the ratio of these forms differed in the two species. The hypothalamus and optic tectum, however, contained predominantly the desacetyl form of alpha MSH. Bioassays for MSH in the HPLC fractions revealed the existence of presumptive beta MSH in both the pituitary and hypothalamus. An argument is advanced that the periventricular ir alpha MSH neurones are homologous with the proopiomelanocortin cells of the arcuate nucleus in mammals, and that the immunocytochemical alpha MSH-like activity in the MCH neurones may not be authentic alpha MSH.

Improvement in HPLC fractionation of thyroxine-containing thyroglobulin tryptic peptides by prior Accell ion-exchange column chromatography

The isolation and purification of the peptides containing the hormonogenic tyrosyl residues in thyroglobulin is of great interest to the understanding of structure-function relationships in this iodoprotein. This is usually performed in reduced alkylated selectively hydrolyzed thyroglobulin by subsequent HPLC fractionation. However, the main difficulty encountered when trying to isolate these peptides is their disproportion with respect to the total number of possible peptides (14 vs a total of 508). Several HPLC runs with different mobile phases are necessary and each run is accompanied with significant losses of the peptides to be purified. In an attempt to improve the separation of the T4-containing peptides in thyroglobulin tryptic digests from the much more abundant iodotyrosine-containing ones, which are present as contaminants, we have used a very simple and fast step prior to the HPLC fractionation as it is a self-packed ion-exchange column chromatography. This preliminary step results in an improvement in the separation of these peptides and leads to a relative enrichment of the hormonogenic peptides falling in different zones of the HPLC chromatogram, which facilitates their subsequent separation and purification by HPLC.

Reverse phase liquid chromatography of beta-endorphins and related peptides

Anomalous band broadening of beta-endorphin related polypeptides chromatographed on hydrophobic high performance stationary phases can be attributed to ligand induced conformational changes associated with polypeptide folding. In the presence of anionic lipids the size exclusion chromatographic behaviour of members of the beta-endorphin family also exhibits similar behaviour. These structure-retention and band broadening behaviour of these polypeptides were in accord with predictions made by hydropathy algorithms and amphipathic helix representations. These observations on surface accessibility of key amino acid residues and their interaction as a conformationally induced domains with stationary phase ligands are equally relevant to other peptidic solutes and neurotransmitters.

General strategies in the separation of proteins by high-performance liquid chromatographic methods

General fractionation strategies for the high-resolution purification of proteins are described. The impact of different separation parameters and resolution optimisation approaches with tandem-based systems on retention and recovery behaviour is reviewed. Procedures for the successful linkage of different chromatographic steps into a preferred sequence of operations are discussed in terms of the underlying principles and modus operandi of high-performance liquid chromatographic purification of proteins and related biomacromolecules.

Steroidogenesis-activator polypeptide isolated from a rat Leydig cell tumor

A cycloheximide-sensitive protein responsive to adenosine 3',5'-monophosphate has been postulated to participate in the regulation of cholesterol side-chain cleavage activity in steroidogenic tissues. Such a steroidogenesis activator polypeptide (SAP) had been isolated from rat adrenocortical tissue and partially characterized. Now a polypeptide with comparable chromatographic behavior and biological activity has been purified from the rat H-540 Leydig cell tumor in quantities sufficient for amino acid sequencing. The activator contains 30 amino acid residues and has a molecular weight of 3215. The synthetic construct based on this sequence is virtually equipotent with native H-540 tumor SAP in an adrenal mitochondrial cholesterol side-chain cleavage assay. Hormonal regulation of the intracellular concentration of this activator may control the rate of cholesterol metabolism in steroidogenic organs.

The corticostatic (anti-ACTH) and cytotoxic activity of peptides isolated from fetal, adult and tumor-bearing lung

The possibility that corticosteroids influence lung maturation was suggested in 1968 by Buckingham et al. and supported by studies mounted in humans and in rabbits by Liggins and Howie and by a collaborative study from the N.I.H. To our knowledge no reverse process, i.e. the regulation of adrenal function by the lung, has been postulated. In attempting to isolate ACTH from fetal lung we found peptides which depressed corticosterone production. Eventually, we isolated a group of peptides from rabbit fetal lung which showed potent inhibition of corticosterone production in rat adrenal cell suspensions. Using high-resolution reverse-phase HPLC and high-sensitivity gas-phase sequencing techniques the primary structure of one of these peptides has been determined and it was called corticostatin. The adult rabbit lung contains a large quantity of a very similar peptide, which elutes close to corticostatin but whose amino acid composition differs by a single glycine and possibly a serine. This peptide is also potently corticostatic. We have isolated homologous human peptides but these show no apparent corticostatic activity in rat adrenal cell suspensions. They do, however, show interesting effects on in vitro growth of lung cell lines.

Structure and bioactivity of the amino-terminal fragment of pro-opiomelanocortin

The primary sequence of the amino-terminal or 16 K fragment (16 K) of pro-opiomelanocortin (POMC) is highly conserved throughout the mammals. This suggests an important biological role for this peptide. We have performed studies to determine the structure, biosynthetic origin and bioactivity of this pituitary peptide. A comprehensive study of all the biosynthetic derivatives of POMC in the neurointermediate lobe of the rat and mouse pituitary was undertaken. Inspection of the amino acid composition of these peptides indicated that cleavage at all available dibasic processing sites within POMC is essentially complete except for Arg49-Lys50 within the 1-74 16 K fragment (16 K1-74). Only about 50% of 16 K1-74 was found to be processed to give rise to the extreme amino-terminal 1 to 49 sequence (16 K1-49) and the carboxyl-terminal 50 to 74 sequence (Lys1 gamma 3 melanotropin). Sufficient 16 K1-77 and 16 K1-49 was purified from bovine posterior pituitaries in order to determine if there are any structural features controlling the limited degree of processing of 16 K within the intermediate lobe. Both bovine 16 K1-77 and 16 K1-49 were found to have cystine bridges linking cystine residues 2 and 24 and linking cystine residues 8 and 20. While 16 K1-77 was found to be O-glycosylated at threonine45 and N-glycosylated as asparagine65, 16 K1-49 was found to have no carbohydrate content. Thus the presence of O-glycosylation at threonine45 apparently inhibits cleavage at -Arg49-Lys50-. Lys1 gamma 3 MSH 16 K1-74 and 16 K1-49 purified from rat neurointermediate pituitaries were tested for their ability to potentiate the action of corticotropin (ACTH) in an isolated rat adrenal cell bioassay. None of the 16 K-related peptides showed any intrinsic steroidogenic activity. Experiments were performed in which dispersed adrenal cells were incubated with serial dilutions of ACTH. Constant amounts of test peptides were added in concentrations ranging from 10 pM to 5 nM. Lys1 gamma 3 MSH potentiated the steroidogenic activity of ACTH by up to 2-fold with an ED50 of approx 0.5 nM. 16 K1-49 showed no ability to potentiate the action of ACTH. In contrast the most highly glycosylated form of 16 K1-74 potentiated the action of ACTH by up to 6-fold.