Inhibition of CGRP signaling impairs fracture healing in mice

Calcitonin gene-related peptide (CGRP) is a neuropeptide produced by sensory nerves and functions as a pain sensor. It acts by binding to the calcitonin-like receptor (CLR, protein; Calcrl, gene). CGRP inhibition has been recently introduced as therapeutic treatment of migraine-associated pain. Previous studies have shown that CGRP stimulates bone formation. The aim of our study is to determine whether the inhibition of CGRP signaling negatively impacted fracture healing. Using α-smooth muscle actin (αSMA) Cre animals crossed with Ai9 reporter mice, we showed that CGRP-expressing nerves are near αSMA + cells in the periosteum. In vitro experiments revealed that periosteal cells express Calcrl and receptor activity modifying protein 1; and CGRP stimulation increased periosteal cell proliferation. Using a tamoxifen-inducible model αSMACre/CLRfl/fl , we targeted the deletion of CLR to periosteal progenitor cells and examined fracture healing. Microcomputed tomography of fractured femurs showed a reduction in bone mass in αSMACre+/CLRfl/fl female mice relative to controls and callus volume in males. Pharmacological CGRP-CLR inhibition was achieved by subcutaneous delivery of customized pellets with small molecule inhibitor olcegepant (BIBN-4096) at a dose of 10 μg/day. BIBN-4096-treated C57BL/6J mice had a higher latency toward thermal nociception than placebo-treated mice, indicating impaired sensory function through CGRP inhibition. CGRP inhibition also resulted in reduced callus volume, bone mass, and bone strength compared to placebo controls. These results indicate that inhibiting CGRP by deleting CLR or by using BIBN-4096, contributes to delayed bone healing.

Calcitonin gene‐related peptide: An intra‐articular therapeutic target for TMJ disorders

Objectives

The goal of this project was to evaluate the role of calcitonin gene‐related peptide (CGRP) in the development of arthritis.

Methods

Herein, we employed somatic mosaic analysis in two different joints by FIV(CGRP) intra‐articular inoculation in the knees or temporomandibular joints (TMJ) of young adult male C57/BL6 mice. FIV(CGRP) is a feline immunodeficiency virus over‐expressing full‐length CGRP. Joint pathology and function were evaluated at the histopathological and behavioral levels. In addition, CGRP signaling was inhibited by intra‐articular inoculation using FIV(CGRP_8‐37), such that the inhibitory peptide CGRP(8‐37) was overexpressed 4 weeks after induction of joint inflammation in the TMJ of IL‐1β^XAT transgenic mouse model. The mice were evaluated for behavior and killed for evaluation of knee and TMJ pathology.

Results

Overexpression of CGRP in the joints of wild‐type mice induced the development of joint anomalies, including meniscal hypertrophy and articular pathology, associated with nocifensive behavior. Intriguingly, overexpression of the CGRP(8‐37) inhibitory peptide in the knee and TMJ of IL‐1β^XAT transgenic mice with joint inflammation resulted in partial amelioration of the attendant joint pathology.

Conclusions

The results of this study suggest that CGRP is sufficient and necessary for the development of joint pathology and may serve as an intra‐articular therapeutic target using gene therapy or monoclonal antibody‐based therapies.

Receptor component protein, an endogenous allosteric modulator of family B G protein coupled receptors

Receptor component protein (RCP) is a 148 amino acid intracellular peripheral membrane protein, previously identified as promoting the coupling of CGRP to cAMP production at the CGRP receptor, a heterodimer of calcitonin receptor like-receptor (CLR), a family B G protein-coupled receptor (GPCR) and receptor activity modifying protein 1 (RAMP1). We extend these observations to show that it selectively enhances CGRP receptor coupling to Gs but not Gq or pERK activation. At other family B GPCRs, it enhances cAMP production at the calcitonin, corticotrophin releasing factor type 1a and glucagon-like peptide type 2 receptors with their cognate ligands but not at the adrenomedullin type 1 (AM₁), gastric inhibitory peptide and glucagon-like peptide type 1 receptors, all expressed in transfected HEK293S cells. However, there is also cell-line variability as RCP did not enhance cAMP production at the endogenous calcitonin receptor in HEK293T cells and it has previously been reported that it is active on the AM₁ receptor expressed on NIH3T3 cells. RCP appears to behave as a positive allosteric modulator at coupling a number of family B GPCRs to Gs, albeit in a manner that is regulated by cell-specific factors. It may exert its effects at the interface between the 2nd intracellular loop of the GPCR and Gs, although there is likely to be some overlap between this location and that occupied by the C-terminus of RAMPs if they bind to the GPCRs.

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RCP promotes coupling of the CGRP receptor to Gs but not Gi or ERK activation.

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RCP enhances Gs coupling for the calcitonin, CRF 1a and GLP-2 receptors.

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RCP does not act on adrenomedullin 1, GIP or GLP-1 receptors in HEK293S cells.

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The actions of RCP depend on the cell line background.

Maturation of suprathreshold auditory nerve activity involves cochlear CGRP-receptor complex formation

In adult animals, the neuropeptide calcitonin gene‐related peptide (CGRP) is contained in cochlear efferent fibers projecting out to the cochlea, and contributes to increased suprathreshold sound‐evoked activity in the adult auditory nerve. Similarly, CGRP applied to the lateral‐line organ (hair cell organ) increases afferent nerve activity in adult frogs (post‐metamorphic day 30), yet this increase is developmentally delayed from post‐metamorphic day 4–30. In this study, we discovered that there was also a developmental delay in increased suprathreshold sound‐evoked activity auditory nerve between juvenile and adult mice similar to what had been observed previously in frog. Moreover, juvenile mice with a targeted deletion of the αCGRP gene [CGRP null (−/−)] did not show a similar developmental increase in nerve activity, suggesting CGRP signaling is involved. This developmental delay is not due to a delay in CGRP expression, but instead is due to a delay in receptor formation. We observed that the increase in sound‐evoked nerve activity is correlated with increased formation of cochlear CGRP receptors, which require three complexed proteins (CLR, RAMP1, RCP) to be functional. CGRP receptor formation in the cochlea was incomplete at 1 month of age (juvenile), but complete by 3 months (adult), which corresponded to the onset of suprathreshold enhancement of sound‐evoked activity in wild‐type animals. Taken together, these data support a model for cochlear function that is enhanced by maturation of CGRP receptor complexes.

High-Efficiency Gene Transfection of Cells through Carbon Nanotube Arrays

Introducing nucleic acids into mammalian cells is a crucial step to elucidate biochemical pathways, and to modify gene expression and cellular development in immortalized cells, primary cells, and stem cells. Current transfection technologies are time consuming and limited by the size of genetic cargo, the inefficient introduction of test molecules into large populations of target cells, and the cytotoxicity of the techniques. A novel method of introducing genes and biomolecules into tens of thousands of mammalian cells has been developed through an array of aligned hollow carbon nanotubes, manufactured by template-based nanofabrication processes, to achieve rapid high-efficiency transfer with low cytotoxicity. The utilization of carbon nanotube arrays for gene transfection overcomes molecular weight limits of current technologies and can be adapted to deliver drugs or proteins in addition to nucleic acids.

Fluoxetine modulates breast cancer metastasis to the brain in a murine model

Background

Despite advances in the treatment of primary breast tumors, the outcome of metastatic breast cancer remains dismal. Brain metastases present a particularly difficult therapeutic target due to the “sanctuary” status of the brain, with resulting inability of most chemotherapeutic agents to effectively eliminate cancer cells in the brain parenchyma. A large number of breast cancer patients receive various neuroactive drugs to combat complications of systemic anti-tumor therapies and to treat concomitant diseases. One of the most prescribed groups of neuroactive medications is anti-depressants, in particular selective serotonin reuptake inhibitors (SSRIs). Since SSRIs have profound effects on the brain, it is possible that their use in breast cancer patients could affect the development of brain metastases. This would provide important insight into the mechanisms underlying brain metastasis. Surprisingly, this possibility has been poorly explored.

Methods

We studied the effect of fluoxetine, an SSRI, on the development of brain metastatic breast cancer using MDA-MB-231BR cells in a mouse model.

Results

The data demonstrate that fluoxetine treatment increases the number of brain metastases, an effect accompanied by elevated permeability of the blood–brain barrier, pro-inflammatory changes in the brain, and glial activation. This suggests a possible role of brain-resident immune cells and glia in promoting increased development of brain metastases.

Conclusion

Our results offer experimental evidence that neuroactive substances may influence the pathogenesis of brain metastatic disease. This provides a starting point for further investigations into possible mechanisms of interaction between various neuroactive drugs, tumor cells, and the brain microenvironment, which may lead to the discovery of compounds that inhibit metastasis to the brain.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-598) contains supplementary material, which is available to authorized users.

Involvement of calcitonin gene-related peptide and receptor component protein in experimental autoimmune encephalomyelitis

Calcitonin Gene-Related Peptide (CGRP) inhibits microglia inflammatory activation in vitro. We here analyzed the involvement of CGRP and Receptor Component Protein (RCP) in experimental autoimmune encephalomyelitis (EAE). Alpha-CGRP deficiency increased EAE scores which followed the scale alpha-CGRP null>heterozygote>wild type. In wild type mice, CGRP delivery into the cerebrospinal fluid (CSF) 1) reduced chronic EAE (C-EAE) signs, 2) inhibited microglia activation (revealed by quantitative shape analysis), and 3) did not alter GFAP expression, cell density, lymphocyte infiltration, and peripheral lymphocyte production of IFN-gamma, TNF-alpha, IL-17, IL-2, and IL-4. RCP (probe for receptor involvement) was expressed in white matter microglia, astrocytes, oligodendrocytes, and vascular-endothelial cells: in EAE, also in infiltrating lymphocytes. In relapsing-remitting EAE (R-EAE) RCP increased during relapse, without correlation with lymphocyte density. RCP nuclear localization (stimulated by CGRP in vitro) was I) increased in microglia and decreased in astrocytes (R-EAE), and II) increased in microglia by CGRP CSF delivery (C-EAE). Calcitonin like receptor was rarely localized in nuclei of control and relapse mice. CGRP increased in motoneurons. In conclusion, CGRP can inhibit microglia activation in vivo in EAE. CGRP and its receptor may represent novel protective factors in EAE, apparently acting through the differential cell-specific intracellular translocation of RCP.

Direct interactions between calcitonin-like receptor (CLR) and CGRP-receptor component protein (RCP) regulate CGRP receptor signaling

Calcitonin gene-related peptide (CGRP) is a neuropeptide with multiple neuroendocrine roles, including vasodilation, migraine, and pain. The receptor for CGRP is a G protein-coupled receptor (GPCR) that requires three proteins for function. CGRP binds to a heterodimer composed of the GPCR calcitonin-like receptor (CLR) and receptor activity-modifying protein (RAMP1), a single transmembrane protein required for pharmacological specificity and trafficking of the CLR/RAMP1 complex to the cell surface. In addition, the CLR/RAMP1 complex requires a third protein named CGRP-receptor component protein (RCP) for signaling. Previous studies have demonstrated that depletion of RCP from cells inhibits CLR signaling, and in vivo studies have demonstrated that expression of RCP correlates with CLR signaling and CGRP efficacy. It is not known whether RCP interacts directly with CLR to exert its effect. The current studies identified a direct interaction between RCP and an intracellular domain of CLR using yeast two-hybrid analysis and coimmunoprecipitation. When this interacting domain of CLR was expressed as a soluble fusion protein, it coimmunoprecipitated with RCP and inhibited signaling from endogenous CLR. Expression of this dominant-negative domain of CLR did not significantly inhibit trafficking of CLR to the cell surface, and thus RCP may not have a chaperone function for CLR. Instead, RCP may regulate CLR signaling in the cell membrane, and direct interaction between RCP and CLR is required for CLR activation. To date, RCP has been found to interact only with CLR and represents a novel neuroendocrine regulatory step in GPCR signaling.

Vascular reactivity to calcitonin gene-related peptide is enhanced in subtotal nephrectomy-salt induced hypertension

In subtotal nephrectomy (SN)- and salt-induced hypertension, calcitonin gene-related peptide (CGRP) plays a compensatory role to attenuate the blood pressure increase in the absence of an increase in the neuronal synthesis and release of this peptide. Therefore, the purpose of this study was to determine whether the mechanism of this antihypertensive activity is through enhanced sensitivity of the vasculature to the dilator actions of this neuropeptide. Hypertension was induced in Sprague-Dawley rats by SN and 1% saline drinking water. Control rats were sham-operated and given tap water to drink. After 11 days, rats had intravenous (drug administration) and arterial (continuous mean arterial pressure recording) catheters surgically placed and were studied in a conscious unrestrained state. Baseline mean arterial pressure was higher in the SN-salt rats (157 ± 5 mmHg) compared with controls (128 ± 3 mmHg). Administration of CGRP (and adrenomedullin) produced a significantly greater dose-dependent decrease in mean arterial pressure in SN-salt rats compared with controls (∼2.0-fold for both the low and high doses). Interestingly, isolated superior mesenteric arterioles from SN-salt rats were significantly more responsive to the dilator effects of CGRP (but not adenomedullin) than the controls (pEC(50), SN-salt, 14.0 ± 0.1 vs. control, 12.0 ± 0.1). Analysis of the CGRP receptor proteins showed that only the receptor component protein was increased significantly in arterioles from SN-salt rats. These data indicate that the compensatory antihypertensive effects of CGRP result from an increased sensitivity of the vasculature to dilator activity of this peptide. The mechanism may be via the upregulation of receptor component protein, thereby providing a more efficient coupling of the receptor to the signal transduction pathways.

Calcitonin gene-related peptide (CGRP) triggers Ca2+ responses in cultured astrocytes and in Bergmann glial cells from cerebellar slices

The neuropeptide calcitonin gene-related peptide (CGRP) is transiently expressed in cerebellar climbing fibers during development while its receptor is mainly expressed in astrocytes, in particular Bergmann glial cells. Here, we analyzed the effects of CGRP on astrocytic calcium signaling. Mouse cultured astrocytes from cerebellar or cerebral cortex as well as Bergmann glial cells from acutely isolated cerebellar slices were loaded with the Ca(2+) sensor Fura-2. CGRP triggered transient increases in intracellular Ca(2+) in astrocytes in culture as well as in acute slices. Responses were observed in the concentration range of 1 nm to 1 mm, in both the cell body and its processes. The calcium transients were dependent on release from intracellular stores as they were blocked by thapsigargin but not by the absence of extracellular calcium. In addition, after CGRP application a further delayed transient increase in calcium activity could be observed. Finally, cerebellar astrocytes from neonatal mice expressed receptor component protein, a component of the CGRP receptor, as revealed by immunofluorescence and confocal microscopy. It is thus proposed that the CGRP-containing afferent fibers in the cerebellum (the climbing fibers) modulate calcium in astrocytes by releasing the neuropeptide during development and hence possibly influence the differentiation of Purkinje cells.

Knockout of alpha-calcitonin gene-related peptide reduces cholangiocyte proliferation in bile duct ligated mice

The role of sensory innervation in the regulation of liver physiology and the pathogenesis of cholestatic liver disease are undefined. Biliary proliferation has been shown to be coordinately controlled by parasympathetic and sympathetic innervation of the liver. The aim of our study was to address the role of the sensory neuropeptide calcitonin gene-related peptide (alpha-CGRP) in the regulation of cholangiocyte proliferation during cholestasis induced by extrahepatic bile duct obstruction (BDL). Our study utilized a knockout (KO) mouse model, which lacks the sensory neuropeptide alpha-CGRP. Wild-type (WT) and alpha-CGRP KO mice were subjected to sham surgery or BDL for 3 and 7 days. In addition, immediately after BDL, WT and KO mice were administered the CGRP receptor antagonist (CGRP(8-37)) for 3 and 7 days by osmotic minipumps. Liver sections and isolated cholangiocytes were evaluated for proliferation markers. Isolated WT BDL (3 days) cholangiocytes were stimulated with alpha- and beta-CGRP and evaluated for proliferation and cAMP-mediated signaling. Lack of alpha-CGRP inhibits cholangiocyte proliferation induced by BDL at both 3 and 7 days. BDL-induced cholangiocyte proliferation in WT mice was associated with increases of circulating alpha-CGRP levels. In vitro, alpha- and beta-CGRP stimulated proliferation in purified BDL cholangiocytes, induced elevation of cAMP levels, and stimulated the activation of cAMP-dependent protein kinase A and cAMP response element binding protein DNA binding. In conclusion, sensory innervation of the liver and biliary expression of alpha-CGRP play an important role in the regulation of cholangiocyte proliferation during cholestasis.

Overexpression and purification of human calcitonin gene-related peptide-receptor component protein in Escherichia coli

Calcitonin gene-related peptide (CGRP) is a neuropeptide secreted by the central and peripheral nervous system nerves that has important physiological functions such as vasodilation, cardiotonic actions, metabolic and pro-inflammatory effects. The CGRP receptor is unique among G-protein coupled receptors in that a functional CGRP receptor consists of at least three proteins: calcitonin like receptor (CLR), receptor activity modifying protein (RAMP1) and receptor component protein (RCP). RCP is a required factor in CGRP-mediated signal transduction and it couples the CGRP receptor to the signal transduction pathway. Here, we describe methods to overexpress and purify RCP for structure-function studies. Human RCP was cloned and overexpressed with a poly-histidine tag and as a maltose binding protein (MBP) fusion in Escherichia coli using commercially available expression vectors. While His tagged RCP is prone to aggregation, solubility is improved when RCP is expressed as a MBP fusion. Expression and purification procedures for these constructs are described. Results from these studies will facilitate structural analysis of human RCP, and allow further understanding of RCP function.

Intraarticular induction of interleukin-1beta expression in the adult mouse, with resultant temporomandibular joint pathologic changes, dysfunction, and pain

OBJECTIVE

To examine the effects of intraarticular induction of interleukin-1beta (IL-1beta) expression in adult mice.

METHODS

We used somatic mosaic analysis in a novel transgenic mouse with an inducible IL-1beta transcription unit. Transgene activation was induced by Cre recombinase in the temporomandibular joints (TMJs) of adult transgenic mice (conditional knockin model). The effects of intraarticular IL-1beta induction were subsequently evaluated at the cellular, histopathologic, and behavioral levels.

RESULTS

We developed transgenic mice capable of germline transmission of a dormant transcription unit consisting of the mature form of human IL-1beta as well as the reporter gene beta-galactosidase driven by the rat procollagen 1A1 promoter. Transgene activation by a feline immunodeficiency virus Cre vector resulted in histopathologic changes, including articular surface fibrillations, cartilage remodeling, and chondrocyte cloning. We also demonstrated up-regulation of genes implicated in arthritis (cyclooxygenase 2, IL-6, matrix metalloproteinase 9). There was a lack of inflammatory cells in these joints. Behavioral changes, including increased orofacial grooming and decreased resistance to mouth opening, were used as measures of nociception and joint dysfunction, respectively. The significant increase in expression of the pain-related neurotransmitter calcitonin gene-related peptide (CGRP) in the sensory ganglia as well as the auxiliary protein CGRP receptor component protein of the calcitonin-like receptor in the brainstem further substantiated the induction of pain.

CONCLUSION

Induction of IL-1beta expression in the TMJs of adult mice led to pathologic development, dysfunction, and related pain in the joints. The somatic mosaic model presented herein may prove useful in the preclinical evaluation of existing and new treatments for the management of joint pathologic changes and pain, such as in osteoarthritis.

Calcitonin gene-related peptide receptor activation by receptor activity-modifying protein-1 gene transfer to vascular smooth muscle cells

The neuropeptide calcitonin gene-related peptide (CGRP) is a potent vasodilator that plays a protective role in the cardiovascular system. The receptor for CGRP is an unusual complex of the G protein-coupled calcitonin-like receptor and an obligate receptor activity modifying protein-1 (RAMP1). In this report we provide the first evidence that RAMP1 is rate limiting in vascular smooth muscle cells. Although cultured rat aorta smooth muscle cells express calcitonin like-receptor and RAMP1, we found that CGRP is not a potent activator of the receptor. After overexpression of RAMP1 by adenoviral gene transfer, there was a striking increase in CGRP-induced production of cAMP, with a 75-fold decrease in the EC(50) and a 1.5-fold increase in the maximal response. The biological consequence of this increased receptor activity was observed in three different paradigms. First, RAMP1 gene transfer caused a CGRP-dependent decrease in cell proliferation. Second, RAMP1 and CGRP treatment led to a 3-fold greater free radical-induced reduction in cell number. Finally, RAMP1 gene transfer resulted in a 5-fold CGRP-dependent increase in terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick end labeling-positive apoptotic cells upon serum withdrawal. The mechanisms underlying these effects involved cAMP-dependent pathways. We propose that RAMP1 gene transfer may be an effective strategy for increasing the effectiveness of CGRP-induced decrease in restenosis after aortic angioplasty.

Localization and modulation of calcitonin gene-related peptide-receptor component protein-immunoreactive cells in the rat central and peripheral nervous systems

Calcitonin gene-related peptide (CGRP) is widely distributed in the central and peripheral nervous system. Its highly diverse biological activities are mediated via the G protein-coupled receptor that uniquely requires two accessory proteins for optimal function. CGRP receptor component protein (RCP) is a coupling protein necessary for CGRP-receptor signaling. In this study, we established the anatomical distribution of RCP in the rat central and peripheral nervous system and its relationship to CGRP immunoreactivity. RCP-immunoreactive (IR) perikarya are widely and selectively distributed in the cerebral cortex, septal nuclei, hippocampus, various hypothalamic nuclei, amygdala, nucleus colliculus, periaqueductal gray, parabrachial nuclei, locus coeruleus, cochlear nuclei, dorsal raphe nuclei, the solitary tractus nucleus and gracile nucleus, cerebellar cortex, various brainstem motor nuclei, the spinal dorsal and ventral horns. A sub-population of neurons in the dorsal root ganglia (DRG) and trigeminal ganglia were strongly RCP-IR. Overall, the localization of RCP-IR closely matched with that of CGRP-IR. We also determined whether RCP in DRG and dorsal horn neurons can be modulated by CGRP receptor blockade and pain-related pathological stimuli. The intrathecal injection of the antagonist CGRP(8-37) markedly increased RCP expression in the lumbar DRG and spinal dorsal horn. Carrageenan-induced plantar inflammation produced a dramatic bilateral increase in RCP expression in the dorsal horn while a partial sciatic nerve ligation reduced RCP expression in the ipsilateral superficial dorsal horn. Our data suggest that the distribution of RCP immunoreactivity is closely matched with CGRP immunoreactivity in most of central and peripheral nervous systems. The co-localization of RCP and CGRP in motoneurons and primary sensory neurons suggests that CGRP has an autocrine or paracrine effect on these neurons. Moreover, our data also suggest that RCP expression in DRG and spinal cord can be modulated during CGRP receptor blockade, inflammation or neuropathic pain and this CGRP receptor-associated protein is dynamically regulated.

Localization of the calcitonin gene-related peptide receptor complex at the vertebrate neuromuscular junction and its role in regulating acetylcholinesterase expression

The calcitonin gene-related peptide (CGRP) is released by motor neurons where it exerts both short and long term effects on skeletal muscle fibers. In addition, sensory neurons release CGRP on the surrounding vasculature where it is in part responsible for local vasodilation following muscle contraction. Although CGRP-binding sites have been demonstrated in whole muscle tissue, the type of CGRP receptor and its associated proteins or its cellular localization within the tissue have not been described. Here we show that the CGRP-binding protein referred to as the calcitonin receptor-like receptor is highly concentrated at the avian neuromuscular junction together with its two accessory proteins, receptor activity modifying protein 1 and CGRP-receptor component protein, required for ligand specificity and signal transduction. Using tissue-cultured skeletal muscle we show that CGRP stimulates an increase in intracellular cAMP that in turn initiates down-regulation of acetylcholinesterase expression at the transcriptional level, and, more specifically, inhibits expression of the synaptically localized collagen-tailed form of the enzyme. Together, these studies suggest a specific role for CGRP released by spinal cord motoneurons in modulating synaptic transmission at the neuromuscular junction by locally inhibiting the expression of acetylcholinesterase, the enzyme responsible for terminating acetylcholine neurotransmission.

Receptor component protein (RCP): a member of a multi-protein complex required for G-protein-coupled signal transduction

The calcitonin-gene-related peptide (CGRP) receptor component protein (RCP) is a 148-amino-acid intracellular protein that is required for G-protein-coupled signal transduction at receptors for the neuropeptide CGRP. RCP works in conjunction with two other proteins to constitute a functional CGRP receptor: calcitonin-receptor-like receptor (CRLR) and receptor-activity-modifying protein 1 (RAMP1). CRLR has the stereotypical seven-transmembrane topology of a G-protein-coupled receptor; it requires RAMP1 for trafficking to the cell surface and for ligand specificity, and requires RCP for coupling to the cellular signal transduction pathway. We have made cell lines that expressed an antisense construct of RCP and determined that CGRP-mediated signal transduction was reduced, while CGRP binding was unaffected. Furthermore, signalling at two other endogenous G-protein-coupled receptors was unaffected, suggesting that RCP was specific for a limited subset of receptors.

Calcitonin gene-related peptide-receptor component protein expression in the uterine cervix, lumbosacral spinal cord, and dorsal root ganglia

The neuropeptide calcitonin gene-related peptide (CGRP) may play a role in neurogenic inflammation, tissue remodeling of the uterine cervix, promoting vasodilation, parturition, and processing of sensory information in the spinal cord. CGRP-immunoreactive nerves of the cervix and spinal cord have been studied but cellular identification of the CGRP receptor has received little attention. CGRP-receptor component protein (CGRP-RCP) is a small protein associated with the CGRP receptor; thus, immunostaining for the CGRP-RCP can be used to identify sites of the CGRP receptor. We determined sites of CGRP-RCP immunoreactivity relative to the presence of CGRP-ir nerve fibers in the female rat uterine cervix, spinal cord, and dorsal root ganglia. CGRP-RCP immunoreactivity was expressed in the dorsal horn of the spinal cord, venules of the uterine cervix, and perikarya of sensory neurons in dorsal root ganglia. CGRP-immunoreactive fibers were adjacent to CGRP-RCP-immunoreactive vessels in the cervix and among CGRP-RCP-immunoreactive structures in the dorsal horn of the spinal cord. This suggests CGRP-RCP is associated with structures innervated by CGRP nerves and these interactions may be changed in tissues in response to an appropriate stimulus.

The role of the CGRP-receptor component protein (RCP) in adrenomedullin receptor signal transduction

G protein-coupled receptors are usually thought to act as monomer receptors that bind ligand and then interact with G proteins to initiate signal transduction. In this study we report an intracellular peripheral membrane protein named the calcitonin gene-related peptide (CGRP)-receptor component protein (RCP) required for signal transduction at the G protein-coupled receptor for adrenomedullin. Cell lines were made that expressed an antisense construct of the RCP cDNA, and in these cells diminished RCP expression correlated with loss of adrenomedullin signal transduction. In contrast, loss of RCP did not diminish receptor density or affinity, therefore RCP does not appear to act as a chaperone protein. Instead, RCP represents a novel class of protein required to couple the adrenomedullin receptor to the cellular signal transduction pathway. A candidate adrenomedullin receptor named the calcitonin receptor-like receptor (CRLR) has been described, which forms high affinity adrenomedullin receptors when co-expressed with the accessory protein receptor-activity modifying protein 2 (RAMP2). RCP co-immunoprecipitated with CRLR and RAMP2, indicating that a functional adrenomedullin receptor is composed of at least three proteins: the ligand binding protein (CRLR), an accessory protein (RAMP2), and a coupling protein for signal transduction (RCP).

Site-directed mutagenesis of m1-toxin1: two amino acids responsible for stable toxin binding to M(1) muscarinic receptors

m1-Toxin1 binds specifically and irreversibly to M(1) muscarinic receptors and can slow the dissociation of [(3)H]N-methylscopolamine ([(3)H]NMS) from these receptors. Yet only 7 of its 65 amino acids are not conserved in six other mamba toxins that bind reversibly to M(2)-M(5) muscarinic receptors. Two of these seven residues (Phe(38), Lys(65)) were mutated to corresponding residues of the other toxins (Ile(38), Glu(65)), to evaluate amino acids in m1-toxin1 that confer its remarkable affinity and specificity. The cDNA for m1-toxin1 was cloned from venom gland mRNA using polymerase chain reaction (PCR)-based techniques. Its nucleotide sequence is remarkably similar to those of other short-chain neurotoxins. The cDNAs for mutant toxins Phe(38) to Ile(38) (F38I) and Lys(65) to Glu(65) (K65E) were constructed by PCR-based techniques. Each cDNA was expressed in yeast, and the toxins were purified from yeast media by cation-exchange and reversed phase chromatography. Recoveries were 40 to 152 microg/l. Recombinant m1-toxin1 was identical to the native toxin (observed mass: 7471 Da; irreversible blockade of [(3)H]NMS binding to cloned M(1) receptors at 25 degrees C; no blockade of M(2)-M(5) receptors; 6-fold slowing of [(3)H]NMS dissociation at 37 degrees C). F38I also bound specifically to M(1) receptors, but reversibly and without effect on NMS dissociation. Thus, Phe(38) contributes to the stability of toxin-receptor complexes, but not to M(1)-selectivity. K65E bound selectively and irreversibly to unliganded M(1) receptors but did not slow NMS dissociation. It is suggested that the C-terminal Lys(65) of m1-toxin1 may contact an outer loop of the M(1) receptor.

Cloning, characterization and central nervous system distribution of receptor activity modifying proteins in the rat

Calcitonin gene-related peptide (CGRP), adrenomedullin (ADM), amylin and calcitonin (CT) are structurally and functionally related neuropeptides. It has recently been shown that the molecular pharmacology of CGRP and ADM is determined by coexpression of one of three receptor activity-modifying proteins (RAMPs) with calcitonin receptor-like receptor (CRLR). Furthermore, RAMP proteins have also been shown to govern the pharmacology of the calcitonin receptor, which in association with RAMP1 or RAMP3, binds amylin with high affinity. In this study, we have cloned the rat RAMP family and characterized the pharmacology of rat CGRP and ADM receptors. Rat RAMP1, RAMP2 and RAMP3 shared 72%, 69% and 85% homology with their respective human homologues. As expected CRLR-RAMP1 coexpression conferred sensitivity to CGRP, whilst association of RAMP2 or RAMP3 with CRLR conferred high affinity ADM binding. Using specific oligonucleotides we have determined the expression of RAMP1, RAMP2 and RAMP3 mRNAs in the rat central nervous system by in situ hybridization. The localization of RAMP mRNAs was heterogeneous. RAMP1 mRNA was predominantly expressed in cortex, caudate putamen and olfactory tubercles; RAMP2 mRNA was most abundant in hypothalamus; and RAMP3 was restrictively expressed in thalamic nuclei. Interestingly, in specific brain areas only a single RAMP mRNA was often detected, suggesting mutual exclusivity in expression. These data allow predictions to be made of where each RAMP protein may heterodimerize with its partner G-protein-coupled receptor(s) at the cellular level and consequently advance current understanding of cellular sites of action of CGRP, ADM, amylin and CT. Furthermore, these localization data suggest that the RAMP family may associate and modify the behaviour of other, as yet unidentified neurotransmitter receptors.

CGRP-RCP, a novel protein required for signal transduction at calcitonin gene-related peptide and adrenomedullin receptors

It is becoming clear that receptors that initiate signal transduction by interacting with G-proteins do not function as monomers, but often require accessory proteins for function. Some of these accessory proteins are chaperones, required for correct transport of the receptor to the cell surface, but the function of many accessory proteins remains unknown. We determined the role of an accessory protein for the receptor for calcitonin gene-related peptide (CGRP), a potent vasodilator neuropeptide. We have previously shown that this accessory protein, the CGRP-receptor component protein (RCP), is expressed in CGRP responsive tissues and that RCP protein expression correlates with the biological efficacy of CGRP in vivo. However, the function of RCP has remained elusive. In this study stable cell lines were made that express antisense RCP RNA, and CGRP- and adrenomedullin-mediated signal transduction were greatly reduced. However, the loss of RCP did not effect CGRP binding or receptor density, indicating that RCP did not behave as a chaperone but was instead coupling the CGRP receptor to downstream effectors. A candidate CGRP receptor named calcitonin receptor-like receptor (CRLR) has been identified, and in this study RCP co-immunoprecipitated with CRLR indicating that these two proteins interact directly. Since CGRP and adrenomedullin can both signal through CRLR, which has been previously shown to require a chaperone protein for function, we now propose that a functional CGRP or adrenomedullin receptor consists of at least three proteins: the receptor (CRLR), the chaperone protein (RAMP), and RCP that couples the receptor to the cellular signal transduction pathway.

Characterization and localization of the rabbit ocular calcitonin gene-related peptide (CGRP)-receptor component protein (RCP)

PURPOSE

To determine whether the calcitonin gene-related peptide (CGRP) receptor component protein (RCP), a novel signal transduction molecule, is required for CGRP signaling in the eye and to determine potential ocular sites of CGRP action.

METHODS

The cDNA for the rabbit ocular RCP homologue was cloned using a combination of reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). Function of the rabbit ocular RCP was assessed using a sensitive oocyte-based assay, which utilizes the protein kinase A (PKA)-sensitive cystic fibrosis transmembrane conductance regulator (CFTR) as a sensor of cAMP formation. RCP expression in the rabbit eye was localized using immunohistochemistry.

RESULTS

A 2063-bp cDNA for the rabbit ocular RCP was cloned and sequenced. Expression of the rabbit RCP cDNA confers CGRP responsiveness in a sensitive oocyte-based assay. Antisense oligonucleotides made to the ocular RCP abolishes CGRP responsiveness of ciliary body and iris mRNA in the oocyte-CFTR assay. Localization of RCP protein in the rabbit eye using immunohistochemistry demonstrated RCP immunoreactivity in the ciliary body and iris blood vessels, as well as in layers of the ciliary epithelium.

CONCLUSIONS

The rabbit ocular RCP appears to be required for signal transduction at ocular CGRP receptors and is localized to sites previously reported to bind CGRP, which affect intraocular pressure and neurogenic inflammation.

Cloning and functional analysis of C. elegans 7B2

The neuroendocrine protein 7B2 is a binding protein for the prohormone convertase 2 (PC2) and is required for the intracellular conversion of proPC2 to active PC2. Both full-length 7B2 and its carboxy-terminal 31-residue peptide (CT peptide) are capable of potent inhibition of PC2; the 7B2 protein thus regulates both the biosynthesis and the activity of PC2. Vertebrate 7B2s are highly conserved (92%-97% homology), and thus, species comparison has not been informative in assessing the crucial protein domains responsible for bioactivity. We here report the cloning of the Caenorhabditis elegans 7B2 protein. Although weakly conserved with the vertebrate sequences (23% similarity with mouse 7B2), C. elegans 7B2 contains the signature PPNPCP motif as well as a highly conserved heptapeptide within the CT peptide. In in vitro assays, C. elegans 7B2 possessed significant inhibitory activity against recombinant vertebrate PC2 (IC50 130 nM), and in two functional tests, the amino-terminal domain of C. elegans 7B2 facilitated the activation of proPC2. We conclude that despite low amino acid conservation overall, both functional domains within 7B2 have been conserved between the C. elegans and the vertebrate proteins.

Inhibitory effect of calcitonin gene-related peptide on myometrial contractility is diminished at parturition

The uterus is innervated by calcitonin gene-related peptide (CGRP) immunoreactive neurons, and CGRP inhibits spontaneous and evoked contractions in the uterus and fallopian tubes. In the present study using isometric force measurements on myometrial strips, we determined that CGRP inhibition of acetylcholine-induced contractions was drastically reduced at parturition compared with earlier stages of pregnancy in mice. The levels of inhibition exerted by CGRP paralleled the expression of a novel protein recently implicated in CGRP receptor activation, the CGRP-receptor component protein (CGRP-RCP). The mouse CGRP-RCP complementary DNA was isolated from uterus, and expression of the CGRP-RCP was monitored during gestation by Northern and Western blot analysis. Although CGRP-RCP messenger RNA levels did not vary significantly during gestation and postpartum, CGRP-RCP protein was greatly diminished at parturition. This diminution correlated with the loss of CGRP inhibition of acetylcholine-induced contractions observed in the force experiments. A role for CGRP and CGRP-RCP in modulation of myometrial smooth muscle contractility during pregnancy and in labor is suggested.

Cloning, characterization, and expression of a calcitonin receptor from guinea pig brain

A calcitonin receptor was cloned from guinea pig brain by using a degenerate reverse transcription-polymerase chain reaction (RT-PCR) strategy. When the cloned guinea pig calcitonin receptor was transfected into COS 1 cells, salmon calcitonin stimulated intracellular cyclic AMP accumulation with an EC50 of 0.1 nM, whereas human calcitonin was >250-fold less potent (EC50 27.6 nM). Related neuropeptides rat alphaCGRP and rat amylin did not activate the guinea pig calcitonin receptor at physiologic concentrations. Stimulation of the transfected guinea pig calcitonin receptor by salmon calcitonin also resulted in phosphatidylinositol hydrolysis with an EC50 of 2.5 nM. Expression of the calcitonin receptor was mapped by a combination of RT-PCR, northern analysis, and expression in Xenopus oocytes. The guinea pig calcitonin receptor was most highly expressed in diencephalon and a single subtype was detected.

Isolation of a cDNA encoding a Kex2-like endoprotease with homology to furin from the nematode Caenorhabditis elegans

A cDNA was isolated from the nematode Caenorhabditis elegans that encodes an endoprotease which is a member of the Kex2 family of serine endoproteases. Degenerate oligonucleotide primers were designed based on conserved regions within the active sites of known Kex2-like endoproteases, and were used for reverse transcription-polymerase chain reaction (RT-PCR) of poly(A)+RNA isolated from C. elegans. A PCR product was isolated that had homology to the active sites of known furin endoproteases, and was used as a probe to screen a C. elegans cDNA library. A Kex2-like endoprotease (CelfurPC) which encoded a 692-amino-acid pre-proendoprotease, was identified. The deduced amino acid sequence for the catalytic domain of CelfurPC is homologous to the known Kex2-like endoproteases, with strongest structural homology to the furin/PACE4 family. However, all furins and PACE4 proteins contain a characteristic cysteine-rich domain, and all furins contain a transmembrane domain, neither of which is present in the CelfurPC protein. CelfurPC may thus represent a new class of Kex2-like endoprotease.

Endoproteolysis at tetrabasic amino acid sites in procalcitonin gene-related peptide by pituitary cell lines

The specificity of neuroendocrine prohormone convertases for tetrabasic amino acid sites was investigated. Mutations were introduced into the tetrabasic cleavage site of the procalcitonin gene-related peptide (proCGRP) cDNA and these mutated cDNA's were expressed in AtT-20 cells which predominantly express the endoprotease prohormone convertase-1 (PC1/3), and in GH3 cells which predominantly express prohormone convertase-2 (PC2). Mutations were introduced into the proCGRP cDNA which converted the wild-type ArgArgArgArg site to LysLysArgArg and ArgArgLysLys, and the proCGRP variants were stably transfected into AtT-20 and GH3 cells. ProCGRP containing each of the LysLysArgArg permutations were efficiently cleaved in both AtT-20 and GH3 cells. Cleavage of LysLysArgArg in exogenous proCGRP, but not in endogenous POMC, suggests that the specificity of cleavage at tetrabasic sites is not defined solely by the endoproteases expressed by the cell or by the amino acid sequence at the cleavage site, but is also dependent on the structure of the propeptide.

Identification of a protein that confers calcitonin gene-related peptide responsiveness to oocytes by using a cystic fibrosis transmembrane conductance regulator assay

An expression-cloning strategy was used to isolate a cDNA that encodes a protein that confers calcitonin gene-related peptide (CGRP) responsiveness to Xenopus laevis oocytes. A guinea pig organ of Corti (the mammalian hearing organ) cDNA library was screened by using an assay based on the cystic fibrosis transmembrane conductance regulator (CFTR). The CFTR is a chloride channel that is activated upon phosphorylation; this channel activity was used as a sensor for CGRP-induced activation of intracellular kinases. A cDNA library from guinea pig organ of Corti was screened by using this oocyte-CFTR assay. A cDNA was identified that contained an open reading frame coding for a small hydrophilic protein that is presumed to be either a CGRP receptor or a component of a CGRP receptor complex. This CGRP receptor component protein confers CGRP-specific activation to the CFTR assay, as no activation was detected upon application of calcitonin, amylin, neuropeptide Y, vasoactive intestinal peptide, or beta-endorphin. In situ hybridization demonstrated that the CGRP receptor component protein is expressed in outer hair cells of the organ of Corti and is colocalized with CGRP-containing efferent nerve terminals.

In situ hybridization reveals transient laminin B-chain expression by individual glial and muscle cells in embryonic leech central nervous system

Laminin, which strongly stimulates axon outgrowth in vitro, appears transiently within the central nervous system (CNS) in embryos. After CNS injury, laminin reportedly reappears along axonal pathways only in animal species in which central axon regeneration is successful, including the leech Hirudo medicinalis. Although glia have been suspected of making CNS laminin, in adult leeches glia are not required for laminin synthesis and evidently microglia, not present in the early embryo, produce laminin. To determine which embryonic cells make laminin, a 1.2 kb DNA fragment of leech laminin B1 chain, with homology to Drosophila, human, and mouse B1 laminins and rat S laminin, was isolated using reverse-transcription and degenerate polymerase chain reaction (PCR) cloning. In situ hybridization revealed that laminin expression began before embryonic day 8, and by days 8 and 9 it was seen in paired CNS muscle cells. By late day 9, the two neuropil glial cells began to express laminin. Lucifer Yellow dye was injected intracellularly and muscle cells stimulated to contract, confirming the identities of muscle and glial cells. Packet glial cells began to express B1 laminin by embryonic day 12. By day 15, the cells of the perineurial sheath expressed B1 laminin, whereas it was no longer detectable in CNS muscle and glia. The results agree with published immunohistochemistry showing laminin within the CNS among growing axons by day 8, and only later in the perineurial sheath, by which time laminin disappears from within the CNS. Therefore, different cells synthesize laminin in the embryo and during repair in adults.

The agonist binding site of the gamma-aminobutyric acid type A channel is not formed by the extracellular cysteine loop

The amino-terminal extracellular domain of the subunits comprising the gamma-aminobutyric acid (GABA) receptor contains two cysteine residues (designated at relative positions 1 and 15) separated by 13 amino acids. These two cysteines (presumably disulfide bonded) are located approximately 150 amino acids from the amino terminus. There is significant homology in the amino acid sequence of this cysteine loop both between the different subunits of the GABA receptor and with subunits of other members of this ligand-gated ion channel superfamily (nicotinic acetylcholine- and glycine-activated ion channels). A number of highly conserved amino acids within the cysteine loop have been postulated to play a role in agonist binding. Here, using site-directed mutagenesis and oocyte expression, we have examined the effects of mutating amino acids comprising the cysteine loop on the activation of recombinant GABA channels composed of rat alpha 1, beta 2 and gamma 2 subunits. Preventing the formation of the putative cysteine-cysteine disulfide bond in any of the subunits, by mutating the cysteine at position 15 to serine, prevented the functional expression of that subunit. For example, coexpression of gamma C15S with wild-type alpha and beta subunits resulted in GABA-activated currents with properties identical to those of GABA-activated currents from coexpression of alpha and beta subunits alone. These properties included sensitivity to activation by GABA (similar EC50 values), blockade by Zn2+, and lack of modulation by the benzodiazepine diazepam. We also mutated conserved amino acids in the beta subunit that had been specifically proposed to form the GABA binding site (beta R6, beta Y8, and beta D11). These mutations (as well as several others within or adjacent to the cysteine loop) produced either a very moderate effect or no effect on GABA sensitivity, suggesting that these particular amino acids do not play a key role in activation of the GABA channel. The data presented in this study support a role for the cysteine loop in subunit assembly, rather than channel activation.

Isolation and in situ localization of a cDNA encoding a Kex2-like prohormone convertase in the nematode Caenorhabditis elegans

1. A cDNA that encodes a Kex2-like prohormone convertase (PC) containing an active site similar to that of mammalian PC2 has been isolated from C. elegans. Total RNA was isolated from a mixed population of strain BA713 worms. After poly-(A)-selection and reverse transcription, degenerate/nested polymerase chain reactions (PCR) were performed using primers based on conserved regions within the active sites of the known vertebrate and invertebrate endoproteases. 2. Two distinct 300-bp PCR products that shared homologies with the active sites of known Kex2-like endoproteases were isolated. These two PCR products were used to screen a C. elegans cDNA library. 3. The complete cDNA for a Kex2-like endoprotease, designated CELPC2, was isolated and determined to be 2527 bp in length. This size was confirmed by northern analysis. The deduced amino acid sequence for the CELPC2 cDNA is very similar to the known Kex2-like endoproteases, especially at conserved regions within the active sites, but not identical to any one of them. The strongest structural homology was to vertebrate and invertebrate PC2 sequences. 4. In situ hybridization suggests that CELPC2 is synthesized primarily in cells associated with the circumpharyngeal nerve ring and the dorsorectal ganglion.

Cell-type specific posttranslational processing of peptides by different pituitary cell lines

In order to compare prohormone processing in two distinct pituitary cell types, somatomammotrope cells (GH3) and corticotrope cells (AtT-20) were stably transfected with vectors encoding preproneuropeptide Y (preproNPY) containing four different pairs of basic amino acids at the single endoproteolytic cleavage site: wildtype or KR (lysine-arginine), RR, RK, and KK. The GH-NPY cell lines cleaved proNPY to a similar extent, regardless of the sequence of the basic amino acids at the cleavage site (KR = RR = RK = KK). AtT-20-NPY cells are known to exhibit a strong hierarchy of cleavage site preference when processing wildtype and mutated proNPY forms (KR = RR greater than RK much greater than KK). All four types of GH-NPY and AtT-NPY cells faithfully produced NPY (1-36) NH2 from proNPY (1-69), regardless of the amino acid sequence at the cleavage site. All four types of GH-NPY cells produced some of the expected proNPY-COOH-terminal peptide with Ser40 at its NH2-terminal [proNPY (40-69)]. GH3 cells expressing the RR, RK, and KK forms of proNPY yielded in addition some proNPY-COOH-terminal peptide retaining the amino terminals Lys39 or Arg39 residue. In contrast, AtT-NPY-RK cells produced only the Lys39 form of proNPY-COOH-terminal peptide while the other three AtT-NPY lines (KR, RR, and KK) produced only the Ser40 form of proNPY-COOH-terminal peptide. The residence time of proNPY and NPY in GH3 cells was dramatically increased by treatment with insulin, estradiol, and epidermal growth factor, in concert with the expected increase in PRL synthesis and decrease in GH synthesis; increased residence time in the cells did not result in an increase in the extent of cleavage of proNPY to NPY. AtT-20 cells did not respond to the somatomammotrope-specific set of hormones. Thus, there are several important differences in the posttranslational processing and storage of peptide hormones in corticotropes and somatomammotropes.

Variants of the carboxyl-terminal KDEL sequence direct intracellular retention

Soluble proteins which reside in the lumen of the endoplasmic reticulum share a common carboxyl-terminal tetrapeptide Lys-Asp-Glu-Leu (KDEL). Addition of the tetrapeptide to a normally secreted protein is both necessary and sufficient to cause retention in the endoplasmic reticulum. In order to characterize the critical residues in the KDEL signal, cDNAs encoding proneuropeptide Y (pro-NPY) with the 4-amino acid carboxyl-terminal extension KDEL or a series of KDEL variants were expressed in the AtT-20 cell line. AtT-20 cells, a mouse anterior pituitary corticotrope cell line, synthesize, process, and secrete the pro-ACTH/endorphin precursor. Since post-translational processing in AtT-20 cells has been extensively characterized, it provides a model system in which the processing of a foreign peptide precursor (pro-NPY) and the endogenous precursor (pro-ACTH/endorphin) can be compared. Altered cDNAs encoding pro-NPY with KDEL, DKEL, RDEL, KNEL, KDQL, or KDEA at the COOH terminus were used to generate stable AtT-20 cell lines. The processing of pro-NPY to neuropeptide Y and the carboxyl-terminal peptide was studied using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, tryptic peptide mapping, and radiosequencing. Addition of the tetrapeptides KDEL, DKEL, RDEL, or KNEL to the COOH terminus of the neuropeptide Y precursor, a peptide hormone normally processed and secreted from neuronal cells, caused complete intracellular retention of the unprocessed prohormone in AtT-20 cells. However, KDQL and KDEA-extended pro-NPY molecules were processed and secreted like wild-type pro-NPY when expressed in AtT-20 cells. The secretion of proNPY-derived peptides in these cell lines paralleled secretion of endogenous pro-ACTH/endorphin-derived products under both basal and stimulated conditions. These mutagenesis studies demonstrate that variants of the KDEL retention signal can direct intracellular retention.

Biosynthesis and posttranslational processing of site-directed endoproteolytic cleavage mutants of pro-neuropeptide Y in mouse pituitary cells

Although pairs of basic amino acids are common endoproteolytic sites in prohormones, the enzymes responsible for these cleavages have not yet been characterized. To investigate the specificity of these endoproteases, cDNAs encoding pro-neuropeptide Y (pro-NPY) containing all four pairs of basic amino acids were expressed in AtT-20 cells. Pro-NPY was selected as a model substrate because it undergoes a single cleavage at the sequence -Lys-Arg- during posttranslational processing. AtT-20 cells, a mouse anterior pituitary corticotrope line, were selected because they synthesize pro-adrenocorticotropic hormone (pro-ACTH)/endorphin and cleave a well characterized subset of the eight pairs of basic amino acids in the precursor. Altered cDNAs encoding pro-NPY with -Arg-Arg-, -Arg-Lys-, or Lys-Lys- at the cleavage site were used to generate stable cell lines. The production of NPY and the carboxyl-terminal peptide was studied using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, gel filtration, reversed-phase high performance liquid chromatography, ion-exchange high performance liquid chromatography, tryptic peptide mapping, and microsequencing. Direct amino acid labeling confirmed the identity of the pair of basic amino acids at the cleavage site. Even when the four pairs of basic amino acids were presented in the same structural context, the rate, extent, and type of cleavage was substrate-specific. Pro-NPY(-Arg-Arg-) was cleaved at a rate similar to that observed for the wild-type pro-NPY(-Lys-Arg-). In contrast, pro-NPY(-Arg-Lys-) was cleaved at a much lower rate, and pro-NPY (-Lys-Lys-) was cleaved very poorly. Following endoproteolytic cleavage, the pair of basic amino acids present did not alter the production of mature NPY with a COOH-terminal Tyr-NH2. While two of the three mutant pro-NPY molecules were processed to wild-type carboxyl-terminal peptide, the carboxyl-terminal peptide derived from pro-NPY(-Arg-Lys-) contained an amino-terminal lysine residue, indicating that biosynthetic endoproteolysis occurred in the middle or at the amino terminus of the pair of basic amino acid residues at the cleavage site. Expression of wild-type or mutant pro-NPY inhibited cleavages within the endogenous pro-ACTH/endorphin; poorly cleaved pro-NPY mutants (Lys in the second position of the cleavage site) were the most potent inhibitors of pro-ACTH/endorphin cleavage.

Metallothionein-I promoter-directed expression of foreign proteins in a mouse pituitary corticotrope tumor cell line

Expressing foreign proteins in heterologous eukaryotic cells has been a powerful tool for analyzing protein structure and function. The inducible mouse metallothionein-I promoter has been particularly useful for expression studies. However, the levels of expression achieved with this promoter in heterologous eukaryotic expression systems have not equaled those observed in vivo for the metallothionein-I gene. We have constructed expression plasmids placing either the gene for chloramphenicol acetyltransferase (CAT) or the cDNA for human neuropeptide Y (NPY) under control of the mouse metallothionein-I promoter. These two expression vectors were used to transfect mouse anterior pituitary tumor cells, from which stable transformants were isolated. The resulting cell lines, Mt.NPY1a and Mt.CAT, were used to maximize functional product expression from the metallothionein-I promoter. In both cell lines, a 35-fold induction of mRNA accumulation, peptide synthesis, or CAT activity was observed.

Structure of the precursor to an enzyme mediating COOH-terminal amidation in peptide biosynthesis

Many bioactive peptides terminate with an amino acid alpha-amide at their COOH terminus. The enzyme responsible for this essential posttranslational modification is known as peptidyl-glycine alpha-amidating monooxygenase or PAM. We identified cDNAs encoding the enzyme by using antibodies to screen a bovine intermediate pituitary lambda gt11 expression library. Antibodies to a beta-galactosidase/PAM fusion protein removed PAM activity from bovine pituitary homogenates. The 108,207 dalton protein predicted by the complete cDNA is approximately twice the size of purified PAM. An NH2-terminal signal sequence and short propeptide precede the NH2 terminus of purified PAM. The sequences of several PAM cyanogen bromide peptides were localized in the NH2-terminal half of the predicted protein. The cDNA encodes an additional 430 amino acid intragranular domain followed by a putative membrane spanning domain and a hydrophilic cytoplasmic domain. The forms of PAM purified from bovine neurointermediate pituitary may be generated by endoproteolytic cleavage at a subset of the 10 pairs of basic amino acids in the precursor. High levels of PAM mRNA were found in bovine pituitary and cerebral cortex. In corticotropic tumor cells, levels of PAM mRNA and pro-ACTH/endorphin mRNA were regulated in parallel by glucocorticoids and CRF.

Transfected human neuropeptide Y cDNA expression in mouse pituitary cells. Inducible high expression, peptide characterization, and secretion

An expression vector was constructed that placed the cDNA for human neuropeptide Y (NPY) under the control of the mouse metallothionein promoter and was used to transfect the AtT-20 mouse anterior pituitary corticotrope cell line. AtT-20 cells normally process the pro-ACTH/endorphin precursor but do not produce detectable levels of NPY. The resulting AtT-20/NPY cell line (Mt.NPY1a) was used to study the ability of the corticotrope cells to synthesize, process, and secrete the foreign proNPY-related peptide products. The stable cell line created contains approximately 40 copies of proNPY cDNA per cell. NPY mRNA levels and proNPY synthesis were increased at least 35-fold when maximally induced with cadmium; proNPY synthesis was also induced by glucocorticoids. Upon induction the NPY secretion rate was equimolar to that of the endogenous peptides. ProNPY, NPY, and the COOH-terminal peptide produced by this cell line had molecular weight and amino acid-labeling pattern predicted from cDNA sequence data and from previous isolation of NPY-related molecules from NPY-producing cells. The structures of secreted proNPY, NPY, and COOH-terminal peptide, as well as determination of the site of proteolytic cleavage between NPY and the COOH-terminal peptide, were determined by tryptic mapping and Edman degradation of secreted biosynthetically labeled peptide products. The proNPY molecule appears to be processed in the same pathway responsible for cleavage of the endogenous pro-ACTH/endorphin precursor. Secretion of proNPY-derived peptides paralleled secretion of endogenous pro-ACTH/endorphin-derived products, under both basal and stimulated conditions. With induction proNPY expression there is a dose-dependent inhibition of both proNPY and pro-ACTH/endorphin proteolytic processing.