Genetic deciphering of the antagonistic activities of the melanin-concentrating hormone and melanocortin pathways in skin pigmentation

The genetic origin of human skin pigmentation remains an open question in biology. Several skin disorders and diseases originate from mutations in conserved pigmentation genes, including albinism, vitiligo, and melanoma. Teleosts possess the capacity to modify their pigmentation to adapt to their environmental background to avoid predators. This background adaptation occurs through melanosome aggregation (white background) or dispersion (black background) in melanocytes. These mechanisms are largely regulated by melanin-concentrating hormone (MCH) and α-melanocyte–stimulating hormone (α-MSH), two hypothalamic neuropeptides also involved in mammalian skin pigmentation. Despite evidence that the exogenous application of MCH peptides induces melanosome aggregation, it is not known if the MCH system is physiologically responsible for background adaptation. In zebrafish, we identify that MCH neurons target the pituitary gland-blood vessel portal and that endogenous MCH peptide expression regulates melanin concentration for background adaptation. We demonstrate that this effect is mediated by MCH receptor 2 (Mchr2) but not Mchr1a/b. mchr2 knock-out fish cannot adapt to a white background, providing the first genetic demonstration that MCH signaling is physiologically required to control skin pigmentation. mchr2 phenotype can be rescued in adult fish by knocking-out pomc, the gene coding for the precursor of α-MSH, demonstrating the relevance of the antagonistic activity between MCH and α-MSH in the control of melanosome organization. Interestingly, MCH receptor is also expressed in human melanocytes, thus a similar antagonistic activity regulating skin pigmentation may be conserved during evolution, and the dysregulation of these pathways is significant to our understanding of human skin disorders and cancers.

Melanocytes produce melanin, a natural skin pigment, for body coloration which helps to protect and camouflage an organism and to attract mates. Melanocytes are ubiquitous pigment cells in vertebrates and the genes underlying their development are well conserved, making fishes that possess the ability to modify their pigmentation, biologically relevant and successful models for human skin disorders. Many human skin diseases including albinism, vitiligo, and melanoma are derived from mutations in conserved pigmentation genes. However, much of the conserved molecular mechanisms behind these diseases and human pigmentation remain unknown. For instance, melanin concentrating hormone (MCH) was originally identified as a peptide that when injected, could make fish paler by promoting melanin aggregation but no mutants demonstrating an endogenous function for MCH in pigmentation have been reported. Here, we use zebrafish mutants of MCH and the MCH receptor to determine their specific genetic function in pigmentation. Additionally, we demonstrate that MCH has an antagonistic pigmentation function to the melanocortin system, where MCH expression promotes lighter pigmentation and melanocortin activity promotes darkening. Thus, we find that the balance between the MCH and melanocortin system activities are likely required for skin pigmentation and dysregulation of these pathways could underlie adverse human skin conditions.

Effects of tank color brightness on the body color, somatic growth, and endocrine systems of rainbow trout Oncorhynchus mykiss

We investigated the effects of tank brightness on body color, growth, and endocrine systems of rainbow trout (Oncorhynchus mykiss). Five different tank colors that produce varying levels of brightness were used, including black, dark gray [DG], light gray [LG], white, and blue. The fish were reared in these tanks for 59 days under natural photoperiod and water temperature. The body color was affected by tank brightness, such that body color brightness was correlated with tank brightness (white-housed ≥ LG-housed ≥ DG-housed ≥ blue-housed ≥ black-housed). No difference in somatic growth was observed among the fish reared in the five tanks. The mRNA levels of melanin-concentrating hormone (mch1) was higher in white-housed fish than those in the other tanks, and the mRNA levels of proopiomelanocortins (pomc-a and pomc-b) were higher in fish housed in a black tank than those in other tanks. mRNA level of somatolactin, a member of growth hormone family, was higher in black-housed fish than those in white-housed fish. The mRNA levels of mch1 and mch2 in blue-housed fish were similar to those in black-housed fish, while the mRNA levels of pomc-a and pomc-b in blue-housed fish were similar to those in white-housed fish. The current results suggest that tank color is not related to fish growth, therefore any color of conventional rearing tank can be used to grow fish. Moreover, the association between somatolactin with body color changes is suggested in addition to the role of classical MCH and melanophore stimulating hormone derived from POMC.

Expression of genes for melanotropic peptides and their receptors for morphological color change in goldfish Carassius auratus

To evaluate the association of the melanotropic peptides and their receptors for morphological color change, we investigated the effects of changes in background color, between white and black, on xanthophore density in the scales and expression levels of genes for hormonal peptides and corresponding receptors (MCH-R2, MC1R, and MC5R) in goldfish (Carassius auratus). The xanthophore density in both dorsal and ventral scales increased after transfer from a white to black background. However, xanthophore density in dorsal scales increased after transfer from a black to white background, and that of ventral scales decreased after transfer from a black to black background, which served as the control. In the white-reared fish, melanin-concentrating hormone (mch) mRNA content in the brain was higher than that in black-reared fish, whereas proopiomelanocortin a (pomc-a) mRNA content in the pituitary was lower than that in the black-reared fish. Agouti-signaling protein (asp) mRNA was detected in the ventral skin but not in the dorsal skin. No difference was observed in the asp mRNA content between fish reared in white or black background, suggesting that ASP might not be associated with background color adaptation. In situ hybridization revealed that both mc1r and mc5r were expressed in the xanthophores in scales. The mRNA content of mc1r in scales did not always follow the background color change, whereas those of mc5r decreased in the white background and increased in the black background, suggesting that mc5r might be a major factor reinforcing the function of MSH in morphological color changes. White backgrounds increased mch mRNA content in the brain, but decreased mch-r2 mRNA content in the scales. These altered expression levels of melanotropin receptors might affect reactivity to melanotropins through long-term adaptation to background color.

Effects of subchronic exposure to waterborne cadmium on H-P-I axis hormones and related genes in rare minnows (Gobiocypris rarus)

The H (hypothalamic)-P (pituitary)-I (interrenal) axis is critical in the stress response and other activities of fish. To further investigate cadmium (Cd) toxicity on the H-P-I axis and to identify its potential regulatory genes in fish, the adult female rare minnows (Gobiocypris rarus) were exposed to subchronic (5weeks) levels of waterborne Cd in the present study. This kind of treatment caused dose-dependent decline in fish growth, with significance in the high dose group (100μg/L). Correspondingly, low dose (5-50μg/L) waterborne Cd disrupted the endocrine system of H-P-I axis just at the secretion level, while high dose Cd disrupted both the secretion and synthesis of cortisol and its downstream signals in rare minnows, revealed by the significantly upregulation and positive correlation of corticosteroidogenic genes including MC2R, StAR, CYP11A1, and CYP11B1 in the kidney (including the interrenal tissue) (P<0.05), and the significant alteration of Glcci1, Hsp90AA and Hsp90AB in the hepatopancreas, gill and intestine as well (P<0.05). The expression of Glcci1 was significantly decreased in hepatopancreas, gill and intestine of tested fish following treatment, and its positive correlation with GR (Glucocorticoid receptor) suggested its potential regulation on the cortisol and/or H-P-I axis in fish. The expression of FKBP5 in the intestine was positively and significantly correlated with that of Hsp90AA (P<0.05), and the Hsp90AB transcript in the hepatopancreas was positively correlated with that of Hsp90AA (P<0.05), which indicated that Hsp90AA and Hsp90AB were more likely to serve as cofactors of GR and FKBP5 in response to Cd exposure.

60 YEARS OF POMC: Purification and biological characterisation of melanotrophins and corticotrophins

The remarkable conservation of the primary structures and anatomical location of dogfish α-melanocyte-stimulating hormone (MSH), corticotrophin-like intermediate lobe peptide (CLIP) and adrenocorticotrophic hormone (ACTH) compared with mammals reinforced the tissue-specific processing hypothesis of ACTH peptides in the pituitary gland. The cloning of dogfish pro-opiomelanocortin (POMC) led to the identification of δ-MSH and simultaneously revealed the high conservation of the γ-MSH sequence during evolution. These studies have also shown that β-MSH is much less conserved during evolution and in some species is not even processed from β-LPH. Human pro-γ-MSH potentiates the corticosteroidogenic activity of ACTH and peptides generated from its N-terminal, in particular big-γ-MSH, appear to have adrenal mitogenic activity. Human big-γ-MSH (from the zona intermedia) may also cause the adrenache. The review finishes with a cautionary note with regard to the misdiagnosis of the ectopic ACTH syndrome in which partial processing of ACTH can result in large concentrations of α-MSH and CLIP, which can interfere in the performance of two-site immunoassays, and the problem of the correct disulphide bridge arrangement in synthetic N-POMC peptides is also discussed.

Complex structural and regulatory evolution of the pro-opiomelanocortin gene family

The melanocortin system is a neuroendocrine machinery that has been associated with phenotypic diversification in a number of vertebrate lineages. Central to the highly pleiotropic melanocortin system is the pro-opiomelanocortin (pomc) gene family, a family of pre-prohormones that each give rise to melanocyte stimulating hormone (MSH), adrenocorticotropic releasing hormone (ACTH), β-lipotropin hormone, and β-endorphin. Here we examine the structure, tissue expression profile, and pattern of cis transcriptional regulation of the three pomc paralogs (α1, α2, and β) in the model cichlid fish Astatotilapia burtoni and other cichlids, teleosts, and mammals. We found that the hormone-encoding regions of pomc α1, pomc α2 and pomc β are highly conserved, with a few notable exceptions. Surprisingly, the pomc β gene of cichlids and pomacentrids (damselfish) encodes a novel melanocortin peptide, ε-MSH, as a result of a tandem duplication of the segment encoding ACTH. All three genes are expressed in the brain and peripheral tissues, but pomc α1 and α2 show a more spatially restricted expression profile than pomc β. In addition, the promoters of each pomc gene have diverged in nucleotide sequence, which may have facilitated the diverse tissue-specific expression profiles of these paralogs across species. Increased understanding of the mechanisms regulating pomc gene expression will be invaluable to the study of pomc in the context of phenotypic evolution.

Malignant melanoma and melanocortin 1 receptor

The conventional chemotherapeutic treatment of malignant melanoma still remains poorly efficient in most cases. Thus the use of specific features of these tumors for development of new therapeutic modalities is highly needed. Melanocortin 1 receptor (MC1R) overexpression on the cell surface of the vast majority of human melanomas, making MC1R a valuable marker of these tumors, is one of these features. Naturally, MC1R plays a key role in skin protection against damaging ultraviolet radiation by regulating eumelanin production. MC1R activation is involved in regulation of melanocyte cell division. This article reviews the peculiarities of regulation and expression of MC1R, melanocytes, and melanoma cells, along with the possible connection of MC1R with signaling pathways regulating proliferation of tumor cells. MC1R is a cell surface endocytic receptor, thus considered perspective for diagnostics and targeted drug delivery. A number of new therapeutic approaches that utilize MC1R, including endoradiotherapy with Auger electron and α- and β-particle emitters, photodynamic therapy, and gene therapy are now being developed.

Possible paracrine function of alpha-melanocyte-stimulating hormone and inhibition of its melanin-dispersing activity by N-terminal acetylation in the skin of the barfin flounder, Verasper moseri

Melanocyte-stimulating hormone (MSH) is generated from a precursor protein, proopiomelanocortin (POMC), mainly in the pituitary. The barfin flounder, Verasper moseri, expresses three different POMC genes (Pomc), among which Pomc-c is also expressed in the skin. Herein, we characterized the biological significance of POMC and MSH produced in barfin flounder skin. The reverse transcription polymerase chain reaction showed the expression of Pomc-c in isolated non-chromatophoric dermal cells. Mass spectrometry analyses of fractions of skin extract separated by high-performance liquid chromatography revealed the presence of a peptide with a molecular mass corresponding to Des-acetyl (Ac)-alpha-MSH-C derived from POMC-C. These results indicate that, in addition to endocrine functions, MSH in barfin flounder is associated with skin pigmentation via paracrine mechanisms. On the other hand, in vitro studies showed that Des-Ac-alpha-MSH-C dispersed pigments in both melanophores and xanthophores. These functions are similar to those of Des-Ac-alpha-MSH, which differs from Des-Ac-alpha-MSH-C only at the C-terminus, generated from POMC-A and -B. Alpha-MSH, which has an acetyl group at the N-terminus, led to pigment dispersion in xanthophores, but showed no effect in melanophores. A series of bioassays indicated that acetylation enhances MSH activity in xanthophores, but inhibits it in melanophores, suggesting that receptors for MSHs expressed in xanthophores and melanophores are different from each other.

Pro-opiomelanocortin (POMC)-derived peptides and the regulation of energy homeostasis

Human genetic data indicate impaired synthesis or processing of POMC results in obesity. We have used a mouse model of POMC deficiency (Pomc null) to explore the role of POMC-derived peptides in energy homeostasis. The phenotype of Pomc null mice recapitulates the clinical syndrome seen in humans congenitally lacking POMC. Loss of only one copy of the Pomc gene is sufficient to render mice susceptible to the effects of high fat feeding, emphasizing an important gene-environment interaction predisposing to obesity. Our studies indicate that POMC-derived peptides have influences on the response to a high fat diet, including a major influence on the dietary preference for fat. Pomc null mice are unusual in that obesity and hyperphagia develop in the absence of circulating glucocorticoid (GC). To investigate the interaction between GCs and the melanocortin system, we administered corticosterone to Pomc null mice. They appear hypersensitive to the adverse metabolic effects of GCs, developing hypertension, an exacerbation of both hyperphagia and obesity and a profound insulin resistance. GC treatment of Pomc null mice significantly increases the expression of the melanocortin antagonist agouti-related protein (AgRP). On-going studies in mice lacking both AgRP and Pomc will determine whether the metabolic phenotype seen with this GC therapy is due to a lack of melanocortin peptide, the unopposed action of AgRP or a combination of both.

[Research of cellular toxic effect to Hep-2 of recombinant toxin MSH-Ang]

OBJECTIVE

To study the cytotoxicity of recombinate toxin MSH-Ang to Hep-2.

METHOD

The depurated MSH-Ang were applied in cytotoxicity experiment, and the growth inhibiting action to laryngeal carcinoma cell Hep-2 were observed.

RESULT

Recombination protein inhibited the growth of laryngeal carcinoma cell Hep-2, and its inhibiting action enhanced and corpuscular mortality rate increased along with the concentration increasing.

CONCLUSION

Recombinant toxin MSH-Ang can not only take special effect in tumors with high MSHR, but also target to many other popular tumors.

RFamide peptides inhibit the expression of melanotropin and growth hormone genes in the pituitary of an Agnathan, the sea lamprey, Petromyzon marinus

Neuropeptides with the Arg-Phe-amide motif at their C termini (RFamide peptides) were identified in the brains of several vertebrates, and shown to have important physiological roles in neuroendocrine, behavioral, sensory, and autonomic functions. The present study identified RFamide peptides, which are teleost prolactin-releasing peptide (PrRP) homologs, in the sea lamprey, Petromyzon marinus and characterized their effect on the release of pituitary hormones in vitro. Two RFamide peptides (RFa-A and RFa-B) were isolated from an acid extract of sea lamprey brain, including hypothalamus by Sep-Pak C18 cartridge, affinity chromatography using anti-salmon PrRP serum, and reverse-phase HPLC on an ODS-120T column. Amino acid (aa) sequences and mass spectrometric analyses revealed that RFa-A and RFa-B consist of 25 and 20 aa, respectively, and have 75% sequence identity within the C-terminal 20 aa. The RFa-B cDNA encoding a preprohormone of 142 aa was cloned from the lamprey brain, and the deduced aa sequence from positions 48-67 was identical to the sequence of RFa-B. However, the preprohormone does not include an aa sequence similar to the RFa-A sequence. Cell bodies, which were immunoreactive to anti-salmon PrRP serum, were located in the periventricular arcuate nucleus, ventral part of the hypothalamus, and immunoreactive fibers were abundant from the hypothalamus to the brain. A small number of immunoreactive fibers were detected in the dorsal half of the rostral pars distalis of the pituitary, close to the GH-producing cells. In addition, anti-salmon PrRP immunoreactivities were observed in the pars intermedia, corresponding to melanotropin cells. Likewise, signal of RFa-B mRNA was detected not only in the brain but also in the pars intermedia. The synthetic RFa-A and -B inhibited GH mRNA expression in a dose-dependent fashion in vitro, which is comparable to the inhibitory effect of teleost PrRP on GH release. Both RFa-A and -B also inhibited the expression of proopiomelanotropin mRNA, but no effects were observed in the expression of proopiocortin and gonadotropin beta mRNAs. The results indicate that RFamide peptides, which are teleost PrRP homologs, are present in the hypothalamus and pituitary of sea lamprey, and may be physiologically involved in the inhibition of GH and melanotropin release in the sea lamprey pituitary.

Transgenic MSH overexpression attenuates the metabolic effects of a high-fat diet

To determine whether long-term melanocortinergic activation can attenuate the metabolic effects of a high fat diet, mice overexpressing an NH(2)-terminal POMC transgene that includes alpha- and gamma(3)-MSH were studied on either a 10% low-fat diet (LFD) or 45% high-fat diet (HFD). Weight gain was modestly reduced in transgenic (Tg-MSH) male and female mice vs. wild type (WT) on HFD (P < 0.05) but not LFD. Substantial reductions in body fat percentage were found in both male and female Tg-MSH mice on LFD (P < 0.05) and were more pronounced on HFD (P < 0.001). These changes occurred in the absence of significant feeding differences in most groups, consistent with effects of Tg-MSH on energy expenditure and partitioning. This is supported by indirect calorimetry studies demonstrating higher resting oxygen consumption and lower RQ in Tg-MSH mice on the HFD. Tg-MSH mice had lower fasting insulin levels and improved glucose tolerance on both diets. Histological and biochemical analyses revealed that hepatic fat accumulation was markedly reduced in Tg-MSH mice on the HFD. Tg-MSH also attenuated the increase in corticosterone induced by the HFD. Higher levels of Agrp mRNA, which might counteract effects of the transgene, were measured in Tg-MSH mice on LFD (P = 0.02) but not HFD. These data show that long-term melanocortin activation reduces body weight, adiposity, and hepatic fat accumulation and improves glucose metabolism, particularly in the setting of diet-induced obesity. Our results suggest that long-term melanocortinergic activation could serve as a potential strategy for the treatment of obesity and its deleterious metabolic consequences.

Evolution of melanocortin systems in fish

Proopiomelanocortin (POMC) is a common precursor of melanocortin (MC), the collective term for adrenocorticotropic hormone (ACTH) and melanophore-stimulating hormone (MSH), and of beta-endorphin (beta-END). Over the past decade, considerable progress has been made in the analysis of the POMC gene from a board taxonomic group of vertebrates and invertebrates. The results suggest that three MSHs (alpha-, beta-, and gamma-MSH) and a single END were established in ancestral invertebrates. Thereafter, unequal crossing over may have resulted in class-specific numbers of MSH segments during the radiation of fish. Moreover, duplication of the entire POMC gene may have led to the differentiation of POMC as shown in lampreys; one of the two subtypes is a precursor for ACTH and beta-END, the other is a precursor for two forms of MSH and the other form of beta-END. On the other hand, at least five subtypes of MC receptor (MCR) have been observed in fish. These are G-protein-coupled receptors with seven transmembrane domains. The ancestral MCR is suggested to have appeared before vertebrates, and then MCRs may have diverged by genome duplication and local duplication of each receptor gene during the evolution of vertebrates. They are distributed in many tissues in rather a subtype-specific manner and are responsible for a variety of biological functions. Thus, MC systems may have diverged by producing structurally different MC peptides from POMC and expressing MCR subtypes differing in ligand selectivity in a variety of tissues.

Structures for the proopiomelanocortin family genes proopiocortin and proopiomelanotropin in the sea lamprey Petromyzon marinus

Gnathostomes express a common proopiomelanocortin (POMC) gene in the pars distalis (PD) and the pars intermedia (PI) of the pituitary gland. In contrast, the sea lamprey Petromyzon marinus expresses one distinct gene in each lobe; proopiocortin (POC) encoding adrenocorticotropic hormone (ACTH) and beta-endorphin (END) is expressed in the PD and proopiomelanotropin (POM) encoding melanophore-stimulating hormone (MSH), and a different beta-END is expressed in the PI. We characterized the genomic structure of the sea lamprey POC and POM genes including their 5'-flanking regions. Both genes have two introns at positions similar to those of gnathostomes. Each exon encodes genetic information seen in the gnathostome POMC gene: exon 1 encodes an untranslated nucleotide sequence, exon 2 encodes a signal peptide and the N-terminal short part of POC or POM, and exon 3 encodes all other parts including ACTH, MSHs or beta-END. Intron-A of POM (2289 bp) is six times longer than that of POC (379 bp). The POM intron-A has three transposon-like sequences (TnL-1, -2, -3), the total length of which is 1781 bp, suggesting that it has expanded via the insertion of TnLs. The 5'-flanking region of the POC gene contains two TATA boxes, a CCAAT box, eight E boxes, STAT, RAIE, and one binding site each for Ptx1, Pit-1, and Tpit. The POM gene contains four TATA boxes, eight E boxes, three STATs, two RAIEs, two CRE-like elements, and one binding site for Pit1. However, there is virtually no similarity between the two genes in the distribution of the elements. The transcriptional regulation of POC and POM may have diverged with the functional differentiation of the two genes.

Promoter activity of sea lamprey proopiocortin and proopiomelanotropin genes in AtT-20/D16v cells

Adrenocorticotropic hormone (ACTH) and melanophore-stimulating hormone (MSH) are produced in the pars distalis and pars intermedia, respectively, throughout vertebrates. These hormones together with beta-endorphin are encoded on a single gene proopiomelanocortin (POMC) in gnathostomes, but in the sea lamprey, an agnathan, ACTH and MSH are encoded on two separate genes, proopiocortin (POC) and proopiomelanotropin (POM), respectively. Moreover, the nucleotide sequences of 5'-flanking regions of the POC and POM genes are significantly different from each other. To investigate the potential promoter activities of the POC and POM genes, we constructed promoter reporter plasmids by fusing the 5' flanking sequences (nucleotides -1151 to +31 and -2510 to +51, respectively) to a firefly luciferase gene. Transient transfection studies in AtT-20/D16v cells, which derived from a mouse pituitary tumor cell line, revealed that the 5'-flanking sequence of the POC gene did not exhibit promoter activity, whereas that of the POM gene showed the activity at high levels nearly equivalent to SV40 promoter. Analysis of a series of the 5'-deleted reporter for the POM gene in the AtT-20/D16v cells demonstrated that the 422 bp 5'-flanking sequence was sufficient for promoter activity, while the sequence from -853 to -574 may contain negatively acting regulatory elements. Because the POC and POM genes are supposed to have differentiated from a common ancestor, during evolution, the POC gene may lack essential element(s) for expression in the AtT-20/D16v cells.

Metabolic effects of transgenic melanocyte-stimulating hormone overexpression in lean and obese mice

The proopiomelanocortin-derived peptide, alpha-MSH, inhibits feeding via melanocortin receptors in the hypothalamus and genetic defects inactivating the melanocortin system have been shown to lead to obesity in experimental animals and humans. To determine whether long-term melanocortinergic activation has significant effects on body weight and composition and insulin sensitivity, transgenic mice overexpressing N-terminal proopiomelanocortin, including alpha- and gamma(3)-MSH, under the control of the cytomegalovirus-promoter were generated. The transgene was expressed in multiple tissues including the hypothalamus, in which both alpha-MSH and gamma(3)-MSH levels were increased approximately 2-fold, compared with wild-type controls. Transgene homozygous mice were also crossed with obese leptin receptor-deficient db(3J) and obese yellow A(y) mice. MSH overexpression led to uniform, dose- dependent darkening of coat color. MSH overexpression reduced weight gain and adiposity and improved glucose tolerance in lean male mice. In female transgenic mice, there was no significant effect on body weight, but there was a significant decrease in insulin levels. Obesity was attenuated in obese db(3J)/db(3J) male and female mice, but there was no improvement in glucose metabolism. In contrast, the MSH transgene improved glucose tolerance in male A(y) mice. These results support the hypothesis that long-term melanocortinergic activation could serve as a potential strategy for anti-obesity and/or antidiabetic therapy.

Mutational analysis of evolutionarily conserved ACTH residues

alpha-Melanocyte stimulating hormone (MSH) and adrenocorticotropin (ACTH)1-24, the minimal ACTH sequence required for full activity, differ only by the 10 C-terminal amino acids of ACTH1-24. Interestingly, these ten C-terminal residues have been highly conserved throughout vertebrate evolution. To understand the functional constraints of these 10 amino acids we analyzed the effects of mutating these residues on steroidogenic activity in vivo and in vitro. Alanine substitutions of some of the first four amino acid residues (the basic core residues KKRR, 15-18) greatly reduces ACTH activity in vitro and in vivo; replacement of mutant alanines at residues 15 and 17 with glutamine residues partially restores ACTH activity. Thus, for ACTH receptor binding and activation, the amino acid residues 15-18 are important for their side chains. Surprisingly, conversion of the five C-terminal residues (20-24) to alanines increases ACTH activity in vivo over that of native ACTH. With respect to receptor binding and activity, the last five amino acid residues are important only for the peptide length they contribute; however, with respect to serum stability, their side chains are significant.

Presence of the delta-MSH sequence in a proopiomelanocortin cDNA cloned from the pituitary of the galeoid shark, Heterodontus portusjacksoni

Since a fourth MSH sequence, delta-MSH, has been detected in the proopiomelanocortin (POMC) gene of a dogfish and a stingray, members of superorder Squalea (class Chondrichthyes), it is possible that this novel MSH sequence might be a feature common to the POMC genes of all modern sharks and rays. As an initial step towards addressing this question, a full-length POMC cDNA was cloned and sequenced from the pituitary of the Port Jackson shark, Heterodontus portusjacksoni. The Port Jackson shark represents one of the oldest lineages in superorder Galea, and this superorder together with superorder Squalea form infraclass Neoselachii (the extant sharks and rays). The Port Jackson shark POMC cDNA has an open reading frame that is 1032 nucleotides in length and encodes the deduced amino acids sequences for beta-endorphin, ACTH/alpha-MSH, beta-MSH, gamma-MSH, and delta-MSH. Port Jackson shark delta-MSH has 83% primary sequence identity with dogfish and stingray delta-MSH, and it appears that the delta-MSH sequence may have been the result of an internal domain duplication and reinsertion of the beta-MSH sequence. The presence of the delta-MSH sequence in the POMC genes of representatives of both superorders of infraclass Neoselachii would indicate that the delta-MSH sequence must have been present in the ancestral euselachian shark that gave rise to the neoselachian radiation.

Subtype selective binding properties of substituted linear melanocyte stimulating hormone analogues

The melanocortin receptors are peptide binding G-protein coupled receptors that play a role in important physiological functions such as energy balance, inflammatory processes and several aspects of reproduction. In this study, we synthesised 11 new linear MSH analogues and tested their binding to the human MC receptors (MC1, MC3, MC4 and MC5) expressed in COS cells. Our results show that introduction of Asp in position 4 similarly affects the binding to the MC1, MC4 and MC5 receptors, but drastically lowers the binding to the MC3 receptor. Arg(5) substitution shows relatively high affinity for the MC4 receptor, while the results also give further support for specific importance of His(6) for the MC1 receptor. Introduction of Asp in position 10, mimicking gamma-MSH, decreased the affinity for the MC3 receptor in similar manner as for the MC4 receptor, suggesting that there are important differences in the binding conformation of gamma-MSH and NPD-MSH. Our results provide further information about the ligand binding requirements for each of the MC receptor subtypes, and highlights differential influence of the core residues in the MSH peptides. The data set also provides useful information for further calculations and modeling of MC receptor binders.

The role of melanocortins in body weight regulation: opportunities for the treatment of obesity

Five G-protein-coupled melanocortin receptors (MC(1)-MC(5)) are expressed in mammalian tissues. The melanocortin receptors support diverse physiological functions, including the regulation of hair color, adrenal function, energy homeostasis, feed efficiency, sebaceous gland lipid production and immune and sexual function. The melanocortins (adrenocorticotropic hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), beta-MSH and gamma-MSH) are agonist peptide ligands for the melanocortin receptors and these peptides are processed from the pre-prohormone proopiomelanocortin (POMC). Peptide antagonists for the melanocortin MC(1), MC(3) and MC(4) receptors include agouti-related protein (AgRP) and agouti. Diverse lines of evidence, including genetic and pharmacological data obtained in rodents and humans, support a role for the melanocortin MC(3) and MC(4) receptors in the regulation of energy homeostasis. Recent advances in the development of potent and selective peptide and non-peptide melanocortin receptor ligands are anticipated to help unravel the roles for the melanocortin receptors in humans and to accelerate the clinical use of small molecule melanocortin mimetics.

The role of melanocortins in body weight regulation: opportunities for the treatment of obesity

Five G-protein-coupled melanocortin receptors (MC(1)-MC(5)) are expressed in mammalian tissues. The melanocortin receptors support diverse physiological functions, including the regulation of hair color, adrenal function, energy homeostasis, feed efficiency, sebaceous gland lipid production and immune and sexual function. The melanocortins (adrenocorticotropic hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), beta-MSH and gamma-MSH) are agonist peptide ligands for the melanocortin receptors and these peptides are processed from the pre-prohormone proopiomelanocortin (POMC). Peptide antagonists for the melanocortin MC(1), MC(3) and MC(4) receptors include agouti-related protein (AgRP) and agouti. Diverse lines of evidence, including genetic and pharmacological data obtained in rodents and humans, support a role for the melanocortin MC(3) and MC(4) receptors in the regulation of energy homeostasis. Recent advances in the development of potent and selective peptide and non-peptide melanocortin receptor ligands are anticipated to help unravel the roles for the melanocortin receptors in humans and to accelerate the clinical use of small molecule melanocortin mimetics.

Mutational analysis of melanocortin-4 receptor, agouti-related protein, and alpha-melanocyte-stimulating hormone genes in severely obese children

OBJECTIVE

To search for mutations in melanocortin pathway elements, that is, the melanocortin-4 receptor (MC4R ), agouti-related protein (AGRP ), and (alpha-melanocyte-stimulating hormone (alpha MSH ) genes in children with severe obesity.

STUDY DESIGN

Direct sequencing of the MC4R encoding sequence and single-strand polymorphism conformation analysis of AGRP and alpha MSH genes were performed in 63 severely obese children. Polymerase chain reaction (PCR) assays of restriction fragment length polymorphism were used to assess the frequency of each newly discovered mutation in 283 non-obese control subjects.

RESULTS

Four dominantly inherited, heterozygous, missense MC4R mutations (Val50Met, Ser58Cys, Ile102Ser, and Ile170Val) were identified in 4 unrelated children and none of the control subjects. Expression of the obese phenotype was variable in mutation-positive family members. Clinical and laboratory features were similar in the obese children with and without an MC4R mutation. Two polymorphisms were detected in the AGRP -encoding sequence (a silent mutation in exon 1 and Ala67Thr in exon 2), with similar frequencies in the obese and control groups. No mutations were found in the alpha MSH gene.

CONCLUSIONS

MC4R mutations may be a non-negligible cause of severe obesity in children with variable expression and penetrance. Mutations in AGRP and alpha MSH genes were not among the causes of obesity in our population.

Human dermal fibroblasts express prohormone convertases 1 and 2 and produce proopiomelanocortin-derived peptides

In the last few years it has become apparent that the skin is a locoregional source for several proopiomelanocortin-derived peptides including alpha-melanocyte-stimulating hormone, adrenocorticotropin, and beta-endorphin. The enzymes that regulate expression of these neuropeptides are the prohormone convertases 1 and 2. In this study we demonstrate, by reverse transcriptase polymerase chain reaction and Western immunoblotting, that cultured human dermal fibroblasts express prohormone convertases 1 and 2 as well as 7B2, which is an essential cofactor for enzymatic activity of prohormone convertase 2. Immunofluorescence studies revealed prohormone convertase 1 to be mainly expressed in the perinuclear region in vesicular structures resembling the trans-Golgi network, whereas prohormone convertase 2 was found in the trans-Golgi network as well as in vesicular structures diffusely distributed in the peripheral cytoplasm. Expression of both enzymes was also confirmed in fibroblasts of normal adult human skin by immunohistochemistry using antibodies against prohormone convertases 1 and 2 and vimentin. To assess the relevance of prohormone convertase 1 and 2 expression in human dermal fibroblasts, we studied the expression of proopiomelanocortin and proopiomelanocortin-derived peptides. Proopiomelanocortin expression was detected by reverse transcriptase polymerase chain reaction and Western immunoblotting. Alpha-melanocyte-stimulating hormone, adrenocorticotropin, and beta-endorphin were mainly located in vesicular structures as demonstrated by immunofluorescence. Production of these peptides was confirmed by radioimmunoassay, immunoradiometric assay, or enzyme immunoassay. Among several stimuli tested, interleukin-1 was found to upregulate production of alpha-melanocyte-stimulating hormone in human dermal fibroblasts. In summary, we have shown that human dermal fibroblasts express the enzymatic machinery for proopiomelanocortin processing and make proopiomelanocortin, alpha-melanocyte-stimulating hormone, adrenocorticotropin, and beta-endorphin. Production of proopiomelanocortin peptides by human dermal fibroblasts may be relevant for fibroblast functions such as collagen degradation and/or regulation of dermal immune responses.

Role of central melanocortin signaling in eating disorders

Melanocortins are derived from posttranslational processing of the precursor protein pro-opiomelanocortin (POMC). The central melanocortinergic system consists of endogenous agonist alpha-melanocyte-stimulating hormone, the naturally occurring antagonist Agouti-related protein (AGRP), and two melanocortin receptors (MC3R, MC4R). Activation of central melanocortin receptors inhibits feeding and leads to weight loss, whereas blockade of the central melanocortin signaling pathway increases food consumption and promotes weight gain. This review will focus on the role of central melanocortin signaling in eating behavior and will evaluate studies of the neural pathways of POMC and AGRP systems, the effects of the central melanocortinergic system on food intake and body weight, and the regulation of hypothalamic POMC and AGRP neurons in response to altered feeding state and energy balance. In addition, this review will explore what is known about the interplay between the central melanocortinergic system and peripheral signals of energy homeostasis, i.e., leptin and glucocorticoids. Furthermore, evidence will be presented that genetic defects within the melanocortin signaling system are involved in determining susceptibility to obesity and anorexia in humans, and the therapeutic potential of melanocortin agonists and antagonists in the treatment of these disorders will be discussed.

Pro-opiomelanocortin and weight regulation: from mice to men

Significant progress in our understanding of the mechanisms of weight homeostasis has been made by studying the many genetic mouse models of obesity. Positional cloning in the obese mouse led to the discovery of leptin as a feedback messenger indicating the adequacy of peripheral energy stores. This was the first in a series of important advances in this field. Shortly after this discovery, two research laboratories presented evidence for the role of hypothalamic pro-opiomelanocortinergic (POMC) neurons as important mediators in the regulation of feeding behavior, insulin levels and, ultimately, body weight. One of these mouse obesity models, the lethal yellow mouse, constitutively overexpresses the agouti protein, an endogenous antagonist of both the melanocortin 1 (MC1) and melanocortin 4 (MC4) receptors. A second mouse obesity model was created by knocking out the MC4 receptor. Investigations using both the autosomal dominant lethal yellow mouse and MC4 receptor knockout mouse have provided clear evidence for the role of hypothalamic POMC neurons and the MC4 receptor in the regulation of weight homeostasis in the rodent. Furthermore, the recent discovery of agouti-related protein (AGRP), an agouti-like peptide naturally found in the hypothalamus, provides further evidence for the importance of POMC neurons in the regulation of weight. Although the significance of central POMC and AGRP in the rodent is apparent, the role of POMC neurons in the regulation of weight and feeding behavior in humans is only now being appreciated.

Accumulated frameshift mutations at coding nucleotide repeats during the progression of gastric carcinoma with microsatellite instability

Microsatellite instability (MSI) and frameshift mutations in genes containing nucleotide repeats have been reported in a subset of gastric carcinomas, but the mutational profiles in precancerous lesions have not been characterized. To characterize the genetic events during gastric carcinogenesis, we analyzed DNA from 56 gastric adenomas and 167 gastric carcinomas for MSI using five microsatellite markers and for frameshift mutations at coding nucleotide repeats of the type II transforming growth factor beta receptor, BAX, hMSH3, hMSH6, IGF II receptor, and E2F-4 genes. On the basis of the number of markers displaying instability per tumor, the tumors were divided into three groups: those with two or more of the five markers showing instability (high MSI [MSI-H]), those with one of the five markers showing instability (low MSI [MSI-L]), and those with no instability. MSI-H was found in 8 adenomas (14%) and 19 carcinomas (11%), and MSI-L was found in 8 adenomas (14%) and 9 carcinomas (5%). These groups were tested for correlations with several clinicopathologic parameters. MSI-H gastric adenomas were related to the high histologic grade of composing dysplastic glands (p = 0.004), and MSI-H gastric carcinomas were associated with exophytic tumor growth (p = 0.005). We found 48 frameshift mutations at coding nucleotide repeats of the six genes, and all mutations except one were found in MSI-H gastric tumors. Only one of the 17 MSI-L tumors showed frameshift mutations at coding nucleotide repeats of the transforming growth factor beta receptor II gene. Compared with MSI-H gastric carcinomas, MSI-H adenomas had no mutations in the hMSH6 and the IGF II receptor genes, less frequent mutations in the transforming growth factor beta receptor II (38% versus 63%), BAX (13% versus 37%), and hMSH3 (13% versus 37%) genes, and more frequent mutations in the E2F-4 (50% versus 37%) gene. Our findings suggest that MSI and E2F-4 mutations are early genetic events and that mutations of the other five genes are accumulated during the progression of gastric carcinomas with MSI.

A newly characterized melanotropin in proopiomelanocortin in pituitaries of an elasmobranch, Squalus acanthias

Proopiomelanocortin (POMC) is a precursor for corticotropin (ACTH), three or fewer molecular types of melanotropin (MSH), and beta-endorphin. This protein is thought to have evolved by duplication of MSH genomic segments. Here we report that the POMC in the dogfish, an elasmobranch, contains a fourth type of MSH in addition to classical alpha-, beta-, and gamma-MSH. POMC cDNA was amplified by PCR from double-strand cDNA prepared from dogfish pituitary and ligated into lambdaZAP II. The POMC cDNA is composed of 1315 bp without a poly(A) tail. Northern blot analysis detected a 1.4-kb signal of dogfish POMC mRNA. An open reading frame of the POMC cDNA encodes 320 amino acids, including a signal peptide of 26 amino acids. The dogfish POMC includes gamma-MSH, ACTH, alpha-MSH, beta-MSH, and beta-endorphin at positions 50-61, 115-153, 115-127, 239-256, and 259-294, respectively. In addition to these classical peptides, a newly discovered MSH, which we have termed delta-MSH, is present in dogfish POMC at position (184-195). The four dogfish MSHs can be separated into two groups based on their sequence identities: one pair consists of alpha-MSH and gamma-MSH, and the other consists of beta-MSH and delta-MSH, suggesting that gamma-MSH and delta-MSH may have been duplicated evolutionarily from alpha-MSH and beta-MSH, respectively. gamma-MSH might first have appeared in early gnathostomes because it is absent in the most primitive vertebrate group, the agnathans. delta-MSH, which at this time is found only in chondrichthians, might have appeared after the divergence of chondrichthians from a lineage leading to osteichthyans and tetrapods.

Expression of proopiomelanocortin (POMC)-derived melanocyte-stimulating hormone (MSH) and adrenocorticotropic hormone (ACTH) peptides in skin of basal cell carcinoma patients

We proposed that local expression and production of proopiomelanocortin (POMC) peptides may play a role in human skin physiology and pathology, including the development and progression of skin cancers. Reverse transcription polymerase chain reaction (RT-PCR) and Northern blotting hybridization techniques were used to study gene expression. Reversed-phase (RP) high-pressure liquid chromatography (HPLC) separation with subsequent radioimmunoassays were used to identify alpha-melanocyte-stimulating hormone (alpha-MSH) and adrenocorticotropic hormone (ACTH) peptides. Immunocytochemistry (IHC) was used to localize ACTH, alpha-MSH, and beta-MSH antigens in skin. RT-PCR, RP-HPLC, and IHC analyses documented the expression of POMC mRNA and production of ACTH and alpha-MSH peptides in lesional and perilesional skin of basal cell carcinoma (BCC) patients and in cultured keratinocytes, which was accompanied by the expression of the MC1-R gene encoding the receptor activated by MSH and ACTH. Thirty specimens were analyzed by IHC. Immunoreactive alpha-MSH, beta-MSH, and ACTH were detected, in 21 of 21, in 11 of 20, and in 6 of 8 of lesional skin, and in 6 of 6, in 5 of 7, and in 6 of 8 perilesional skin specimens analyzed, respectively. Antigen distribution was heterogenous and present in BCC, epidermis, hair follicles, dermal mononuclear cells, and extracellular matrix. We conclude that messenger RNA for POMC, MC1-R, and the peptides MSH and ACTH are produced in skin of BCC patients. Because keratinocytes are a target for MSH and ACTH bioregulation, the production of these peptides is stimulated by UVB, and the peptides can act as immunosupressors, we suggest that MSH and ACTH may facilitate development of BCC.

Effect of morphine on proopiomelanocortin gene expression and peptide levels in the hypothalamus

Opiates have been reported to suppress POMC in the medial basal hypothalamus (MBH) but studies have been complicated by the fact that acutely, in the rat, opiates stimulate corticosterone and inhibit gonadal steroid release, which could both affect POMC in brain. We have therefore examined POMC gene expression and peptide levels in the MBH of castrated rats after 10 days of treatment with subcutaneous morphine or placebo pellets and after pellet removal. POMC mRNA was measured by solution hybridization assay and beta-endorphin (beta-EP) and alpha-MSH were measured by RIA. In castrated male rats, the mean POMC mRNA concentration in the MBH was 1.67 +/- 0.11 pg/microgram RNA in the control animals and decreased to 1.17 +/- 0.11 pg/microgram RNA in the morphine-treated animals (P < 0.01). Similarly in castrated, estradiol replaced female rats, the mean POMC mRNA level in the MBH was 1.36 +/- 0.19 pg/microgram RNA and decreased to 0.82 +/- 0.08 pg/microgram RNA after morphine treatment (P < 0.05). beta-EP levels were not significantly different in either study. When castrated male rats were similarly morphine pelleted and killed either on day 10 or 2 days later after pellet removal, the mean POMC mRNA level again fell from 1.83 +/- 0.21 in the controls to 1.28 +/- 0.20 pg/microgram RNA after 10 days of morphine; 2 days after pellet removal levels remained suppressed at 0.80 +/- 0.08 pg/microgram RNA (P < 0.01). In this study the concentrations of beta-EP and alpha-MSH were both noted to decline in the MBH after morphine treatment (P < 0.05). When the forms of beta-EP in the MBH were characterized by HPLC, a decrease in the concentration of beta-EP was again seen after morphine but no significant differences in the pattern of beta-EP processing or in the relative amounts of beta-EP1-31 compared to beta-EP1-27 and beta-EP1-26 were noted in morphine-treated animals. There was also no significant effect of 10(-6)-10(-4) M morphine on basal or KCl-stimulated release of beta-EP or gamma 3-MSH release from the perifused rat hypothalamus in vitro. We conclude that morphine suppresses POMC gene expression in the hypothalamus of chronically treated male and female rats. Persistent changes were also noted during morphine withdrawal. In some cases this was accompanied by a fall in beta-EP peptide content. These effects were seen in castrated animals with and without sex steroid replacement and are thus independent of the effects of morphine on the pituitary-gonadal axis. These results show that opiate drugs modify endogenous opioid systems in the brain and provide further support for the hypothesis that such changes may contribute to mechanisms of opiate dependence and withdrawal.

Microsatellite instability in keratoacanthoma

BACKGROUND

Tumors from patients with hereditary nonpolyposis colorectal cancer (HNPCC) and from a subset of patients with the related Muir-Torre syndrome (MTS) exhibit a novel type of genomic instability known as microsatellite instability (MIN). In general, this form of genomic instability results from mutations that inactivate DNA mismatch repair genes. The detection of MIN in a keratoacanthoma (KA) from a patient with MTS suggested that defective mismatch repair may play a role in the pathogenesis of these neoplasms.

METHODS

Randomly selected paraffin embedded KA from 53 patients and paraffin embedded tumors from an additional 12 patients diagnosed with KA and colorectal carcinoma were examined for MIN at six loci. In addition, several KA were examined for mutations within the hMSH2 gene.

RESULTS

Six of the 53 randomly selected KAs had MIN at two or more loci. One of these six patients had HNPCC, whereas another had MTS. Two patients with KAs lacking MIN had colon tumors that exhibited widespread MIN, and one of these patients had MTS. Three of the 12 additional patients diagnosed with a KA and a colorectal carcinoma had at least one tumor that had MIN at two or more loci, and one of these patients had HNPCC: A 2-base pair somatic deletion in exon 3 of the hMSH2 gene was identified in one of the MIN+ KAs.

CONCLUSIONS

Defective mismatch repair appears to play a role in the process of tumorigenesis in some KAs. Microsatellite instability in a KA or the cooccurrence of a colorectal carcinoma and a KA in a patient suggests that the patient may have either HNPCC or its phenotypic variant MTS.

Melanotropin and corticotropin are encoded on two distinct genes in the lamprey, the earliest evolved extant vertebrate

In the lamprey, which is a member of the oldest extant class of vertebrates, the agnathans, melanotropins (MSH) and corticotropin (ACTH) were found to be encoded on two distinct genes. In all other vertebrates, a single precursor gene, proopiomelanocortin (POMC), encodes MSH and ACTH, as well as beta-endorphin (END). Two different cDNAs were cloned from a lamprey pituitary lambda gt11 cDNA library using antisera against lamprey MSH-B and ACTH(1-16). One cDNA encoded MSH-B, MSH-A and beta-END, while the other cDNA encoded nasohypophysial factor (NHF), ACTH and a different beta-END, but not MSH-A and MSH-B. Northern blot analysis demonstrated that in the adult lamprey pituitary, genes for MSH and ACTH are expressed in the pars intermedia (PI) and pars distalis (PD), respectively.

The appearance of proopiomelanocortin early in vertebrate evolution: cloning and sequencing of POMC from a Lamprey pituitary cDNA library

A proopiomelanocortin (POMC)-like hormone has been cloned and sequenced from a pituitary cDNA library of upstream migrant (prespawning) sea lamprey, Petromyzon marinus. The clone, designated LPP-1, consisted of 986 nucleotides, with an open reading frame of 277 amino acids, including a signal peptide of 22 amino acids. Like POMCs from more recently evolved vertebrates, lamprey POMC contained domains which corresponded to alpha-MSH, ACTH, and beta-endorphin. However, sequences corresponding to gamma- and beta-MSH are absent or likely nonfunctional, respectively, in this cDNA. Northern blot analyses showed low but detectable expression levels of LPP-1 in larvae and strong expression in parasitic adults and prespawning animals. These observations indicate that a recognizable POMC, distinct from proenkephalin, has an ancient lineage within subphylum Vertebrata, likely dating back to the last common ancestor of the lamprey and gnathostome lines.

Noncompetitive enzyme immunoassay (hetero-two-site enzyme immunoassay) for gamma 2-melanocyte-stimulating hormone (gamma 2-MSH) and measurement of immunoreactive gamma 2-MSH in plasma of healthy subjects

A noncompetitive enzyme immunoassay (hetero-two-site enzyme immunoassay) for gamma 2-melanocyte-stimulating hormone (gamma 2-MSH) was developed. gamma 2-MSH (1-12) was biotinylated, trapped onto an anti-gamma 2-MSH (1-12) IgG-coated polystyrene bead, eluted at pH 1 after washing to eliminate other biotinylated substances, and measured using two streptavidin-coated polystyrene beads and affinity-purified anti-gamma 2-MSH (1-12) Fab'-peroxidase conjugate. The detection limit of gamma 2-MSH (1-12) was 10-30 amol (16-48 fg)/assay and 130-400 fmol (210-630 pg)/L of plasma. There was little or only slight cross reaction with alpha-MSH, beta-MSH, and gamma 1-MSH. By this immunoassay, the concentration and molecular size of immunoreactive gamma 2-MSH in plasma of healthy subjects were examined, and the results were compared with those by competitive enzyme immunoassay. Immunoreactive gamma 2-MSH measured by competitive enzyme immunoassay was a mixture of substances with high molecular weights (100-500 kDa), and its concentration was calculated to be 50-60 pmol/L using gamma 2-MSH (1-12) as standard. Immunoreactive gamma 2-MSH detected by the noncompetitive enzyme immunoassay after removal of high molecular weight substances was not homogeneous and smaller than gamma 2-MSH (1-12), and its concentration was approximately 1 pmol/L. The exact nature of these immunoreactive gamma 2-MSHs remains to be elucidated. gamma 2-MSH (1-12) added to plasma was degraded rapidly, and the concentration of gamma 2-MSH (1-12) was very low, if any, in plasma of healthy subjects.

Peptidylglycine alpha-amidating monooxygenase and other processing enzymes in the neurointermediate pituitary

Studies on the mRNAs encoding PAM and on the various PAM proteins have begun to reveal some of the intricate mechanisms used to optimize the ability of this enzyme to carry out the alpha-amidation of peptides. Comparison of the regulatory elements governing expression of the various enzymes involved in peptide processing should reveal common elements. Knowledge of the processing enzymes themselves should help us to understand how these enzymes function in the secretory granule environment. In addition to their catalytic domains, other processing enzymes, like PAM, may well have processing domains and routing domains designed to optimize their ability to function in secretory granules.

Molecular cloning of a novel melanocortin receptor

Using the technique of the polymerase chain reaction primed with oligonucleotides based on the homologous transmembrane regions of seven transmembrane G protein-linked receptors, we isolated three full-length human genes that encode a novel subgroup of this receptor family. Recently, two of these receptors were identified as specific for alpha-melanocyte-stimulating hormone (alpha-MSH) and adrenocorticotropic hormone. We report the molecular cloning and pharmacologic characterization of a third member of this subgroup. The gene for this receptor encodes a protein of 361 amino acids in length. Its pharmacology characterizes it as an MSH receptor specific to the heptapeptide core common to adrenocorticotropic hormone and alpha-, beta-, and gamma-MSH. By Northern blot hybridization and polymerase chain reaction, it is expressed in brain, placental, and gut tissues but not in melanoma cells or in the adrenal gland. These findings may yield insight into the physiology of peptides derived from pro-opiomelanocortin post-translational processing.

Combined non-radioactive detection of peptide hormones and their mRNA's in endocrine cells

Non-radioactive in situ hybridization employing detection of biotin-labeled probes by an alkaline phosphatase-based procedure has proven useful for demonstrating a wide variety of mRNA species. With certain developers, the alkaline phosphatase reaction product is both light microscopically visible and fluorescent. We have exploited this to perform simple double-stainings for mRNA's and their corresponding peptide products in human insulin and gastrin cells and in rat ACTH, MSH and gastrin cells. Such stainings show that nearly all of these cells simultaneously contain both the peptide hormone and its corresponding mRNA. Human gastrin cells show a differentiated localization of gastrin mRNA and gastrin. Thus, while gastrin immunofluorescence predominates in secretory granules present in the basolateral region of the cells, gastrin mRNA is virtually restricted to the supranuclear region of the cells. Here it may be preferentially associated with granular endoplasmic reticulum. The strict subcellular localization of gastrin mRNA differs from that of general polyadenylated RNA in the G cells and raises questions whether specific transport routes or sites of accumulation for defined mRNA species exist.

Diphtheria toxin-related alpha-melanocyte-stimulating hormone fusion toxin. Internal in-frame deletion from Thr387 to His485 results in the formation of a highly potent fusion toxin which is resistant to proteolytic degradation

We have previously reported the genetic construction and properties of a fusion protein which was composed of the enzymatically active and membrane translocation domains of the diphtheria toxin and the receptor-specific ligand alpha-melanocyte-stimulating hormone (alpha-MSH) (Murphy, J.R., Bishai, W., Borowski, M., Miyanohara, A., Boyd, J., and Nagle, S. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 8258-8262). While this fusion toxin was found to be selectively toxic for MSH receptor-bearing cells in vitro, it was subject to profound proteolytic degradation in recombinant Escherichia coli making purification difficult. We now report that the deletion of diphtheria toxin fragment B sequences between Thr387 and His485 results in a protease-resistant form of the fusion toxin, DAB389-alpha-MSH. We show that DAB389-alpha-MSH is expressed in high yield in recombinant Escherichia coli, that it is readily purified from crude bacterial lysates by immunoaffinity and high performance liquid chromatography, and its cytotoxic activity toward both human and murine malignant melanoma cell lines is mediated through the MSH receptor.

Antisense peptides: tools for receptor isolation? Lack of antisense MSH and ACTH to interact with their sense peptides and to induce receptor-specific antibodies

The use of antisense peptides for receptor isolation as proposed by Blalock and his colleagues (e.g. TIBTECH 8, 140-144, 1990) was tested for human ACTH as well as alpha- and beta-MSH. We synthesized the corresponding antisense peptides HTCAh, HSM-alpha and HSM-beta and analyzed them for specific interaction with the sense peptides using several types of binding assay and bioassay. Similarly HTCAh antibodies were tested for binding to ACTH receptors and ACTH antibodies. All these experiments were negative, i.e. there was no specific interaction between sense and antisense peptides nor between the corresponding antibodies. Receptor binding of the sense peptides was not affected by the antisense peptides or HTCAh antibodies. Unexpectedly, HTCAh but not HSM-alpha or HSM-beta was a weak MSH agonist acting through a site independent of the MSH receptor. A detailed analysis of the concept of antisense peptides revealed that the theoretical background of the hypothesis of the 'molecular recognition theory' is rather weak, explaining the failure of various attempts to obtain specific receptor antibodies.

Absence of a gamma-melanocyte-stimulating hormone sequence in proopiomelanocortin mRNA of chum salmon Oncorhynchus keta

1. Complete nucleotide sequence of one of the salmon proopiomelanocortin mRNAs (POMC mRNAs) was determined. 2. The region corresponding to gamma-melanocyte-stimulating hormone (gamma-MSH) was lacking in salmon POMC mRNA, although overall organization of the multi-hormone structure was exactly the same as that of mammalian POMC mRNAs. 3. The possible evolutional history of POMC mRNA in mammalian species may be revealed from the finding of this characteristic that salmon POMC mRNA lacks the region corresponding to gamma-MSH.

Genetic construction, expression, and melanoma-selective cytotoxicity of a diphtheria toxin-related alpha-melanocyte-stimulating hormone fusion protein

The structural gene for diphtheria toxin, tox, has been modified at its Sph I site by the introduction of an oligonucleotide linker encoding a unique Pst I restriction endonuclease site and a synthetic oligonucleotide encoding alpha-melanocyte-stimulating hormone (alpha-MSH). The resulting fusion gene directs the expression of a diphtheria toxin-related alpha-MSH hybrid protein in which the diphtheria toxin receptor-binding domain has been replaced with alpha-MSH sequences. The chimeric toxin has been partially purified from periplasmic extracts of recombinant Escherichia coli K-12 and has been found to be selectively toxic for alpha-MSH receptor-positive human malignant melanoma NEL-M1 cells in vitro.

Posttranslational processing of proadrenocorticotropin/endorphin-derived peptides during postnatal development in the rat pituitary

The anterior pituitary content of pro-ACTH/endorphin-related peptides increased 5-fold from birth to 4 weeks and increased another 3-fold by adulthood. In contrast, the neurointermediate lobe content of pro-ACTH/endorphin-related peptides increased 15-fold from birth to 4 weeks and another 10-fold by adulthood. Despite the dramatic increase in content, posttranslational processing of pro-ACTH/endorphin in the neurointermediate lobe of the neonate closely resembled intermediate lobe processing in the adult; alpha MSH- and beta-endorphin-sized molecules (rather than ACTH and beta-lipotropin) accounted for more than 90% of the immunoreactivity in both neonates and adults. In the neurointermediate pituitary of both the neonate and the adult, the alpha MSH-sized material was largely diacetylated, and the beta-endorphin was both alpha-N-acetylated and C-terminally shortened. However, the extent of C-terminal shortening of beta-endorphin in the neurointermediate lobe of the neonate was not as great as that observed by postnatal day 21 or that in the adult. In the anterior pituitary, distinct differences in processing occurred between birth and adulthood. Proteolytic processing of pro-ACTH/endorphin was not as extensive on day 1 as in the adult, and pro-ACTH/endorphin accounted for 40-50% of the total immunoreactive peptide. The extent of processing of precursor increased around day 21, and a higher percentage of ACTH-(1-39) and beta-endorphin-(1-31)-sized material was found. Neonatal anterior pituitary contained substantial amounts of alpha MSH-sized material, whereas in adult anterior pituitary, less than 1-2% of the ACTH-related material was alpha MSH-sized. Despite these differences in the extent of proteolytic processing, neonatal anterior pituitary corticotropes resembled those of adults, in that they did not alpha-N-acetylate beta-endorphin or alpha MSH. Immunocytochemical studies demonstrated that a subset of the neonatal anterior pituitary corticotropes produced alpha MSH-related molecules.

[Biologically active fragments of protein hormones]

As shown in a number of experiments, corticotropin-like and opiate hormones are synthesized in a body as high molecular protein precursors, involving their biologically-active fragments. Pharmacological properties and perspectives for practical use of somatotropin fragments, synthetic opiate peptides as well as the peptides active in stimulation of pancreatic hormones secretion are considered in details.

Glucocorticoid regulation of pro-opiomelanocortin gene transcription in the rat pituitary

The effect of glucocorticoids on pro-opiomelanocortin (POMC) gene transcription in the rat pituitary has been investigated by an in vitro nuclear runoff transcription assay. Both dexamethasone and corticosterone had rapid inhibitory effects on POMC transcription in the anterior lobe but not in the intermediate lobe of the pituitary. These effects were maximal during the first hour after injection of the steroid. Bilateral adrenalectomy had a time-dependent stimulatory effect on anterior lobe POMC transcription, presumably because of the removal of endogenous glucocorticoids. This study shows that the well documented inhibitory effects of glucocorticoids on POMC mRNA in the pituitary anterior lobe are due at least in part to an inhibition in POMC mRNA synthesis.

Identification of proopiomelanocortin neurones in rat hypothalamus by in situ cDNA-mRNA hybridization

Ardrenocorticotropic hormone (ACTH), beta-endorphin and the melanotropins (MSHs) are all derived from a single large precursor molecule, proopiomelanocortin (POMC) by individual processing through a series of co- and post-translational modifications. Although the primary site of synthesis is in the pituitary, POMC-derived peptides have been identified in various tissues, notably the brain (see refs 6, 7 for review). A major question concerning brain POMC is whether it is synthesized within the central nervous system (CNS) itself or whether it is taken up from plasma flowing in a retrograde fashion from the pituitary. POMC peptides have been detected immunohistochemically and biochemically in the medial basal hypothalamus, the amygdala and throughout the brain stem. POMC peptide-containing cell bodies have been identified only in two cell groups, however, principally in the periarcuate region of the hypothalamus and to a lesser extent in the nucleus of the tractus solitarius. These and other observations have suggested that POMC peptides are synthesized locally in the medial basal hypothalamus and reach other regions of the CNS by axonal transport. Civelli et al. identified POMC mRNAs in nucleic acid extracts of rat and bovine hypothalami by solution hybridization as well as Northern gel blot analysis, but because of the close proximity of the hypothalamus to the pituitary and the extremely low amounts of POMC mRNA being measured in the hypothalamus, the possibility of tissue contamination during dissection could not be ruled out. We report here the anatomical co-localization of POMC-related peptides and POMC-specific mRNAs to a single major cell group in the medial basal hypothalamus. The presence of POMC-specific mRNA in a POMC peptide-containing cell in the brain is strong support for POMC biosynthesis within brain tissue.

Ectopic pro-opiolipomelanocortin: sequence of cDNA coding for beta-melanocyte-stimulating hormone and beta-endorphin

A recombinant bacterial plasmid, pMS1, was constructed that contains 318 nucleotides complementary to a portion of pro-opiolipomelanocortin (proOLMC) messenger RNA from an ectopic adrenocorticotropin-producing tumor. The cloned complementary DNA insert, which contains the sequence that codes for all of the beta-melanocyte-stimulating hormone and beta-endorphin portions of proOLMC, as well as the 3' nontranslated section, is identical to the genomic sequence. Hybridization of tumor proOLMC complementary DNA to RNA subjected to electrophoresis and transferred to a nitrocellulose filter revealed two proOLMC messenger RNA species in the tumor polyadenylated RNA, but only one in pituitary polyadenylated RNA. At least one of the tumor proOLMC messenger RNA's is similar, if not identical, to human pituitary proOLMC messenger RNA.