Nerve growth factor

Nerve growth factor in rheumatic diseases

OBJECTIVES

The nervous system modulates the immune response in many autoimmune syndromes by neurogenic inflammation. One of the pivotal mediators is nerve growth factor (NGF), which is known for its effects on neuronal survival and growth. There is considerable evidence that NGF acts as an important mediator of many immune responses. This article reviews the role of NGF in rheumatic diseases and strategies for potential therapeutic interventions.

METHODS

We conducted a database search using Medline and Medpilot. Eight hundred abstracts containing the keyword NGF and 1 of the following terms were reviewed: arthritis, neurogenic inflammation, rheumatoid arthritis, osteoarthritis, collagen arthritis, arteritis, psoriasis, psoriatic arthritis, Sjogren syndrome, systemic lupus erythematosus, gout, osteoporosis, lower back pain, lumbar disc herniation, nerve root compression, spondyloarthritis, spondylarthropathy, algoneurodystrophy, fibromyalgia, Kawasaki syndrome, polyarteritis nodosa, cytokine, vasculitis, pain, therapy, and antagonist. Articles were analyzed based on relevance and content. Most clinical trials and studies with human specimens were included. Studies with experimental animal models were selected if they contained relevant data.

RESULTS

NGF is overexpressed in many inflammatory and degenerative rheumatic diseases. Concentrations differ to some extent and sometimes even show contradictory results. NGF is found in serum, synovial fluid, and cerebrospinal fluid, and tissue specimens. NGF concentrations can be correlated with the extent of inflammation and/or clinical activity in many conditions. In rheumatoid arthritis, NGF levels are significantly higher as compared with osteoarthritis.

CONCLUSIONS

NGF is a significant mediator and modulator of inflammation. NGF sometimes shows detrimental and sometimes regenerative activity. These findings indicate potential therapeutic interventions using either NGF antagonists or recombinant NGF.

Construction of a mutated pro-nerve growth factor resistant to degradation and suitable for biophysical and cellular utilization

Precursor of nerve growth factor (proNGF) has been found to be proapoptotic in several cell types and mediates its effects by binding to p75 neurotrophin receptor (p75NTR) and sortilin. The proNGF molecule is processed by proteases at three dibasic sites found in the pro domain to form mature NGF (termed herein as sites 1, 2, and 3 from the proNGF N terminus). Of these processing sites, site 3, adjacent to the N terminus of mature NGF, was thought to be the major site responsible for processing of proNGF to mature NGF. We found that mutating this major processing site (site 3) resulted in a form of proNGF that was only partially stable. On introducing additional mutations in the pro domain at the other two dibasic sites, we found the stability of proNGF to increase significantly. Here we describe the construction, expression, and purification of this more stable proNGF molecule. The two consecutive basic residues at each of the three sites were mutated to neutral alanine residues. Expression was performed in stably transfected Sf21 insect cells. Purification involved strong cation-exchange chromatography and N60 immunoaffinity column chromatography. The construct with all three sites mutated (termed proNGF123) gave all proNGF with no mature NGF and was not cleaved by three proconvertases (furin, PACE-4, and PC-2) known to proteolyze proneurotrophins in vivo. This stable proNGF molecule demonstrated proapoptotic activity on rat pheocytochroma PC12 cells, PC12nnr cells, C6 glioblastoma cells, and RN22 schwannoma cells.

Proliferation and differentiation of human embryonic germ cell derivatives in bioactive polymeric fibrous scaffold

Human embryonic germ cell derivatives, a heterogeneous population of uncommitted embryoid body derived (EBD) cells, were studied in a bioactive three-dimensional (3D) fibrous culture. Their proliferation, morphology, gene expression and differentiation were investigated to gain insights on development of 3D bioactive scaffold for pluripotent stem cells. The expansion of the EBD cells in 3D environment was significantly higher than their two-dimensional controls after 21 days. No apparent differentiation of the EBD cells cultured in the 3D environment, as indicated by histology and gene expression profile analysis, was evident. Extracellular matrix production was weak in the long-term 3D culture, and the EBD cells maintained their multilineage gene expressions for the period studied. When nerve growth factor (NGF) was surface-immobilized on the fibrous scaffold via chemically-modified Pluronic, the EBD cells cultured in this scaffold showed evidence of entering the neural pathway. An upregulation of tyrosine hydroxylase mRNA expression was observed when EBD cells were cultured in the NGF-immobilized fibrous scaffold, as demonstrated by real-time PCR and immunofluorescence staining. The study suggests the value of such fibrous 3D culture in manipulating stem cell proliferation/differentiation and as a model for developing a bioactive scaffold.

Peripheral nerve regeneration with sustained release of poly(phosphoester) microencapsulated nerve growth factor within nerve guide conduits

Prolonged delivery of neurotrophic proteins to the target tissue is valuable in the treatment of various disorders of the nervous system. We have tested in this study whether sustained release of nerve growth factor (NGF) within nerve guide conduits (NGCs), a device used to repair injured nerves, would augment peripheral nerve regeneration. NGF-containing polymeric microspheres fabricated from a biodegradable poly(phosphoester) (PPE) polymer were loaded into silicone or PPE conduits to provide for prolonged, site-specific delivery of NGF. The conduits were used to bridge a 10 mm gap in a rat sciatic nerve model. Three months after implantation, morphological analysis revealed higher values of fiber diameter, fiber population and fiber density and lower G-ratio at the distal end of regenerated nerve cables collected from NGF microsphere-loaded silicone conduits, as compared with those from control conduits loaded with either saline alone, BSA microspheres, or NGF protein without microencapsulation. Beneficial effects on fiber diameter, G-ratio and fiber density were also observed in the permeable PPE NGCs. Thus, the results confirm a long-term promoting effect of exogenous NGF on morphological regeneration of peripheral nerves. The tissue-engineering approach reported in this study of incorporation of a microsphere protein release system into NGCs holds potential for improved functional recovery in patients whose injured nerves are reconstructed by entubulation.

Nerve growth factor expression and innervation of the painful intervertebral disc

Following a previous description of nociceptive nerve fibre growth into usually aneural inner parts of painful intervertebral disc (IVD), this study has investigated whether nociceptive nerve ingrowth into painful IVD is stimulated by local production of neurotrophins. Immunohistochemistry and in situ hybridization have been used to investigate expression of the candidate neurotrophin, nerve growth factor (NGF), and its high- and low-affinity receptors trk-A and p75, respectively, in painful IVD excised for the management of low back pain. IVD from patients with back pain were of two types: those that when examined by discography reproduced the patient symptoms (pain level IVD) and those that did not (non-pain level IVD). Microvascular blood vessels accompanied nerve fibres growing into pain level IVD and these expressed NGF. The adjacent nerves expressed the high-affinity NGF receptor trk-A. These vessels entered the normally avascular IVD through the discal end plates. NGF expression was not identified in non-pain level or control IVD. Some non-pain level IVD had vessels within them, which entered through the annulus fibrosus. These did not express NGF nor did nerves accompany them. These findings show that nociceptive nerve ingrowth into painful IVD is causally linked with NGF production by blood vessels growing into the IVD, from adjacent vertebral bodies.

Early days of the nerve growth factor proteins

Adult male mouse submaxillary glands served as the preferred starting material for the isolation of the nerve growth factor (NGF) proteins in most of the isolation studies done. Two types of NGF proteins were isolated from extracts of the gland, a high-molecular-weight 7S NGF complex and a low-molecular-weight protein variously called NGF, betaNGF, or 2.5S NGF. The latter, which mediated all known biological functions of NGF, were closely related forms of a basic NGF dimer in which the N and C termini of two monomers (chains) were modified by proteolytic enzymes to different extents with no effect on biological activity. The betaNGF dimer showed a novel protein structure in which the two chains interacted non-covalently over a wide surface. Correspondingly, the betaNGF dimer was found to be unusually stable and the form through which NGFs actions were mediated at physiological concentrations. The betaNGF dimer was one of three subunits in 7S NGF; the other two were the gamma subunit, an arginine esteropeptidase or kallikrein, and the alpha subunit, an inactive kallikrein. Two zinc ions were also present in the complex and contributed greatly to its stability. There was much debate about whether 7S NGF was a specific protein complex of interacting subunits and, if so, what functions it might play in the biology of NGF. Observations of the inhibition of the enzyme activity of the gamma subunit and of the biological activity of betaNGF in 7S NGF were important in determining that 7S NGF was a naturally occurring complex and the sole source of NGF in the gland extract or in saliva. Specific interactions between the active site of the gamma subunit and the C-terminal arginine residues of the NGF chains, confirmed in the three-dimensional structure of 7S NGF, suggested a role for the gamma subunit in pro-NGF processing during the assembly of 7S NGF. In spite of the detailed knowledge of 7S NGF structure, no information on the role of this complex in the neurobiology of NGF has emerged. With the exception of the submaxillary gland of an African rodent, no other source of NGF has been convincingly shown to synthesize the alpha and gamma subunits, and they may well be irrelevant to NGFs actions.

Nerve growth factor alpha subunit: effect of site-directed mutations on catalytic activity and 7S NGF complex formation

Mouse alpha- and gamma-nerve growth factor (NGF) are glandular kallikreins that form a non-covalent complex (7S NGF) with beta-NGF. gamma-NGF is an active arginine-specific esteropeptidase; the alpha-subunit is catalytically inactive and has a zymogen-like conformation. Site-directed mutagenesis of alpha-NGF to alter the N-terminus and three residues in loop 7, a region that contributes to the catalytic center, restored substantial catalytic activity against N-benzoyl arginine-p-nitroanilide as substrate in two derivatives although they were not as active as recombinant gamma-NGF. Seven of the 15 derivatives that remained more alpha-like were able to substitute for native alpha-NGF in reforming 7S complexes; the other eight derivatives that were more gamma-like showed greatly reduced ability to do so. However, the most gamma-like alpha-NGF derivative could not substitute for native gamma-NGF in 7S complex formation. These findings suggest that the alpha-NGF backbone can be corrected to a functional enzyme by the addition of a normal N-terminal structure and two catalytic site substitutions and that the 7S complex requires one kallikrein subunit in the zymogen form and one in an active conformation.

Structural determinants of neurotrophin action

Five decades of research on NGF have led to the discovery of a small family of evolutionarily conserved proteins, which have vital functions in the survival and neuronal development of specific neuronal populations. The generation of mice lacking neurotrophin expression has recapitulated classic experiments using anti-NGF antibodies to dissect the physiological effects of trophic factor deprivation (73). Very similar outcomes resulted from both the NGF immunodepletion experiments and the transgenic mouse experiments. The genetic results also verify the structural predictions made from binding results in heterologous cells. The findings in cell culture and animal experiments clearly indicate the efficacy of neurotrophic factors for promoting the survival of prominent neuronal populations such as sensory and motor neurons. The high degree of conservation of neurotrophin structure is accompanied by a surprising variation in the amino acid contacts used by each neurotrophin with p75 and the trk receptor family members. It is this variation that may provide specificity for each ligand-receptor complex. The future challenge will be to make use of this knowledge to design effective therapeutic strategies to treat neurodegeneration and nerve injury.

Small peptide mimics of nerve growth factor bind TrkA receptors and affect biological responses

Small monomeric cyclic analogs that mimic the beta-turn regions of nerve growth factor (NGF) were designed and synthesized. Potent competitive antagonists were derived from the NGF beta-turn C-D, which inhibited [125I] NGF binding to TrkA receptors and specifically inhibited optimal NGF-mediated neurite outgrowth in PC12 cells. The cyclic beta-turn A'-A" analog also inhibited NGF binding to TrkA receptors but with lower potency. These data indicate that beta-turns C-D and A'-A" are critical for TrkA binding and may confer neurotrophin receptor specificity. Furthermore, structural requirements for binding are absolute, because unconstrained analogs derived from the same regions had no effect. Compounds that mimic NGF will be useful in deciphering the interactions of NGF and its receptors and in rational drug design.

Nerve growth factor: structure/function relationships

Nerve growth factor (NGF), which has a tertiary structure based on a cluster of 3 cystine disulfides and 2 very extended, but distorted beta-hairpins, is the prototype of a larger family of neurotrophins. Prior to the availability of cloning techniques, the mouse submandibular gland was the richest source of NGF and provided sufficient material to enable its biochemical characterization. It binds as a dimer to at least 2 cell-surface receptor types expressed in a variety of neuronal and non-neuronal cells. Residues involved in these interactions and in the maintenance of tertiary and quaternary structure have been identified by chemical modification and site-directed mutagenesis, and this information can be related to their location in the 3-dimensional structure. For example, interactions between aromatic residues contribute to the stability of the NGF dimer, and specific surface lysine residues participate in receptor contacts. The conclusion from these studies is that receptor interactions involve broad surface regions, which may be composed of residues from both promoters in the dimer.

Immunological determinants of nerve growth factor involved in p140trk (Trk) receptor binding

Monoclonal anti-NGF antibodies that specifically inhibit the biological activity of mouse beta-NGF were used to study the structural determinants involved in the interaction of NGF with its receptors gp75LNGFR and Trk. None of the three antibodies--N60, M15, and 27/21--showed any reactivity toward denatured NGF. Three experimental methods--radioimmunoassay (RIA), enzyme-linked immunoassay (ELISA), and slot blots--detected no significant cross reactivity between the antibodies and BDNF or NT-3. RIA showed that M15 and N60 recognize the same or an overlapping antigenic site, but 27/21 recognizes a different epitope. Only 27/21, and not N60 or M15, immunoprecipitated beta-NGF crosslinked to LNGFR receptor. Thus, the epitope recognized by 27/21 does not overlap the LNGFR receptor binding site. N60, M15, and 27/21 all block binding of NGF to Trk in a manner consistent with competitive inhibition. Purified Fab fragments of N60 and M15 gave similar results to the intact antibodies. The other subunits present in the 7S complex of NGF, i.e. the alpha and gamma subunits, competitively inhibited binding of antibodies to beta-NGF. Only the gamma subunit inhibited phosphorylation of Trk and biological activity of beta-NGF. These findings suggest that the M15, N60, and 27/21 antibodies bind to a specific site on the surface of NGF where they competitively inhibit binding to the Trk NGF receptor. The region encompassing the N-terminus, the C-terminus, and the loop on the surface of beta-NGF containing residues 60-80 is proposed as important for binding to the Trk receptor.

Sustained release of nerve growth factor from biodegradable polymer microspheres

Although grafted adrenal medullary tissue to the striatum has been used both experimentally and clinically in parkinsonism, there is a definite need to augment long-term survival. Infusion of nerve growth factor (NGF) or implantation of NGF-rich tissue into the area of the graft prolongs survival and induces differentiation into neural-like cells. To provide for prolonged, site-specific delivery of this growth factor to the grafted tissue in a convenient manner, we fabricated biodegradable polymer microspheres of poly(L-lactide)co-glycolide (70:30) containing NGF. Biologically active NGF was released from the microspheres, as assayed by neurite outgrowth in a dorsal root ganglion tissue culture system. Anti-NGF could block this outgrowth. An enzyme-linked immunosorbent assay detected NGF still being released in vitro for longer than 5 weeks. In vivo immunohistochemical studies showed release over a 4.5-week period. This technique should prove useful for incorporating NGF and other growth factors into polymers and delivering proteins and other macromolecules intracerebrally over a prolonged time period. These growth factor-containing polymer microspheres can be used in work aimed at prolonging graft survival, treating experimental Alzheimer's disease, and augmenting peripheral nerve regeneration.

New protein fold revealed by a 2.3-A resolution crystal structure of nerve growth factor

Nerve growth factor (NGF) is a member of an expanding family of neurotrophic factors (including brain-derived neurotrophic factor and the neurotrophins) that control the development and survival of certain neuronal populations both in the peripheral and in the central nervous systems. Its biological effects are mediated by a high-affinity ligand-receptor interaction and a tyrosine kinase signalling pathway. A potential use for NGF and its relatives in the treatment of neurological disorders such as Alzheimer's disease and Parkinson's disease requires an understanding of the structure-function relationships of NGF. NGF is a dimeric molecule, with 118 amino acids per protomer. We report the crystal structure of the murine NGF dimer at 2.3-A resolution, which reveals a novel protomer structure consisting of three antiparallel pairs of beta strands, together forming a flat surface. Two subunits associate through this surface, thus burying a total of 2,332 A. Four loop regions, which contain many of the variable residues observed between different NGF-related molecules, may determine the different receptor specificities. A clustering of positively charged side chains may provide a complementary interaction with the acidic low-affinity NGF receptor. The structure provides a model for rational design of analogues of NGF and its relatives and for testing the NGF-receptor recognition determinants critical for signal transduction.

Crystallization and characterization of the high molecular weight form of nerve growth factor (7 S NGF)

A high molecular weight form of nerve growth factor (7 S NGF) has been crystallized in two crystal forms from polyethylene glycol 4000 by the vapour diffusion technique. The orthorhombic form A belongs to the space group P2(1)2(1)2(1) and has cell dimensions of a = 95.6, b = 96.5 and c = 147.0 A. With synchrotron X-ray radiation, these crystals diffract to 2.8 A resolution. They contain an intact 7 S NGF complex in the asymmetric unit. The tetragonal form B, which grows at similar conditions to the A form, belongs to the space group P4(1)2(1)2 (or P4(3)2(1)2) with unit cell dimensions of a = 97.4, b = 97.4 and c = 308.3 A. These crystals diffract to 3.6 A resolution and contain one 7 S complex per asymmetric unit. Native X-ray data have been collected to 3.3 A for the A form and to 5.0 A for the B form, both using synchrotron radiation.

Structure and biosynthesis of nerve growth factor

Most of our knowledge about NGF comes from extensive study of the mouse submaxillary gland protein. NGF from this source is isolated as a high molecular weight complex consisting of beta-NGF and two subunits, alpha and gamma, belonging to the kallikrein family of serine proteases. There are few other tissues where NGF is found in sufficient quantities for protein purification and study, although new molecular biological techniques have accelerated the study of NGFs from a variety of species and tissues. Mouse submaxillary gland NGF is synthesized as a large precursor that is cleaved at both N- and C-terminals to produce mature NGF. This biologically active molecule can be further cleaved by submaxillary gland proteases. The roles of the alpha and gamma subunits in the processing of the beta-NGF precursor, the modulation of the biological activity of beta-NGF, and the protection of mature beta-NGF from degradation have been well studied in the mouse. However, the apparent lack of alpha and gamma subunits in most other tissues and species and the existence of a large family of murine kallikreins, many of which are expressed in the submaxillary gland, challenge the relevance of murine high molecular weight NGF as a proper model for NGF biosynthesis and regulation. It is important therefore to identify and characterize other NGF complexes and to study their subunit interactions, biosynthesis, processing, and regulation. This review points out a number of other species and tissues in which the study of NGF has just begun. At this time, there exist many more questions than answers regarding the presence and the functions of NGF processing and regulatory proteins. By studying NGF in other species and tissues and comparing the processing and regulation of NGF from several sources, we will discover the unifying concepts governing the expression of NGF biological activity.

Characterization of sodium currents in mammalian sensory neurons cultured in serum-free defined medium with and without nerve growth factor

The influence of nerve growth factor (NGF) on Na currents of rat dorsal root ganglia (DRG) was studied in neurons obtained from newborns and cultured for 2-30 hr in serum-free defined medium (SFM). Cell survival for the period studied was 78-87% both with and without NGF. Na currents were detected in all cells cultured for 6-9 hr. They were also detected after 2 hr in culture in 21.5% of the cells cultured without NGF (-NGF cells), and in 91.5% of the cells cultured with NGF (+NGF cells). Current density of the -NGF cells was 2.3 and 2 pA/microns 2 after growth for 2 and 6-9 hr, respectively, compared to 3.0 and 3.9 pA/microns 2 for the +NGF cells. The +NGF cells were separated into fast (F), Intermediate (I) and slow (S) cells, based on the Na current they expressed, while -NGF cells were all of the I type. F, I and S currents differed in their voltage-dependent inactivation (Vh50 = -79, -28 and -20 mV), kinetics of inactivation (tau h = 0.55, 1.3 and 7.75 msec), and TTX sensitivity (Ki = 60, 550 and 1100 nM). All currents were depressed by [Ca]0 with a KdCa of 22, 17 and 8 mM for F, I and S currents, respectively. Current density of F and S currents was 5.5 and 5 pA/micron 2 for the I current. The concentration-dependent curve of I current vs. TTX indicated that I current has two sites: one with F-like and another with S-like Ki for TTX. Hybridization of F and S currents yielded I-like currents. Thus, the major effect of NGF on Na currents in SFM is the acceleration of Na current acquisition and diversity, reflected in an increase of either the S or F type in a cell.

Substrate specificities of growth factor associated kallikreins of the mouse submandibular gland

The kinetic constants for the hydrolysis of a series of tripeptide p-nitroanilide substrates by mouse epidermal growth factor binding protein (EGF-BP), the gamma-subunit of mouse nerve growth factor (gamma-NGF), bovine pancreatic trypsin (BPT), and porcine pancreatic kallikrein (PPK) have been evaluated. These substrates correspond to the carboxyl-terminal three amino acids of the mature forms of epidermal growth factor (EGF) and beta-nerve growth factor (beta-NGF), as well as various substitutions in the penultimate and antepenultimate positions, and, as such, represent potential recognition sites for precursor processing. The mouse kallikreins (EGF-BP and gamma-NGF) preferentially hydrolyze the substrates with the sequences of their specifically associated growth factors; however, the constants derived from these reactions do not account for the association constants observed with the mature growth factors, and additional significant binding interactions between EGF-BP and EGF and between gamma-NGF and beta-NGF are predicted to exist outside of the catalytic binding site, i.e., the P3 to P1 positions. A comparison of the kinetic constants of BPT, PPK, and the mouse kallikreins indicates that EGF-BP and gamma-NGF display a hybrid catalytic character. A favorable substrate P1 arginine guanidinium group interaction exists for the mouse kallikreins, similar to that of BPT, but a preference for a hydrophobic side chain in the substrate P2 position makes the mouse kallikreins, especially EGF-BP, more closely resemble PPK than BPT. These findings have significant implications with regard to molecular modeling of the mouse kallikreins.

Isolation and sequence of a cDNA clone of beta-nerve growth factor from the guinea pig prostate gland

The guinea pig prostate gland contains high levels of nerve growth factor similarly to the mouse submandibular gland. Nerve growth factor from the guinea pig prostate gland cross-reacts weakly with antisera directed against mouse nerve growth factor, is associated with different proteins, and may be processed by a different mechanism. We have isolated a full-length cDNA clone for nerve growth factor from a library prepared from RNA of the guinea pig prostate gland. The guinea pig cDNA contains 1,075 nucleotides and is very similar to the shorter of two predominant nerve growth factor transcripts present in the mouse submandibular gland. The cDNA sequence predicts a precursor protein of 241 amino acids that is 86% identical to the mouse amino acid sequence. Only 10 amino acid changes are present in the C-terminal region corresponding to the mature 118 amino acid beta-nerve growth factor of the mouse. Dibasic amino acid processing sites that are present at the N- and C-termini of the mature protein sequence and two other dibasic amino acid sites, representing potential processing sites within the propeptide, are all conserved, suggesting a similar mechanism of processing.

Molecular cloning of a cDNA encoding the nerve growth factor precursor from Mastomys natalensis

Mastomys natalensis is an African rat that has high levels of nerve growth factor (NGF) in its submaxillary glands. Like in the mouse, Mastomys NGF is found as a high-molecular-weight complex. However, the Mastomys complex differs from the mouse complex, in that the gamma-subunit is either missing or is less tightly bound in the Mastomys NGF complex. In the mouse, the gamma-subunit has been implicated in the processing of the beta-NGF precursor. The possible lack of gamma-subunits in the Mastomys NGF high-molecular-weight complex suggested that the Mastomys beta-NGF precursor might differ from the mouse beta-NGF precursor in some of its processing sites. In particular, Mastomys beta-NGF might lack the C-terminal dipeptide cleavage site implicated in beta-gamma subunit interactions in mouse NGF. In order to test this hypothesis, we isolated and sequenced a cDNA clone for Mastomys beta-NGF. We report here the cloning and sequencing of a cDNA coding for beta-NGF from Mastomys natalensis. The cDNA library was prepared from Mastomys submaxillary gland mRNA and the beta-NGF clone was isolated using a mouse cDNA as a probe. The nucleotide sequence of Mastomys beta-NGF is 95% homologous to that of mouse beta-NGF. In particular, the Mastomys beta-NGF precursor contains the same three C-terminal residues as the mouse, suggesting that the Mastomys beta-NGF precursor could interact with a gamma-like subunit.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of the alpha subunit of 7S nerve growth factor in the mouse submandibular gland

alpha-NGF is an inactive serine protease that is associated in the mouse submandibular gland with a closely related serine protease, gamma-NGF, and the neurotrophic factor, beta-NGF. The heterogeneity of purified alpha-NGF has been examined by DEAE-cellulose chromatography and SDS polyacrylamide gel electrophoresis. A possible explanation for the observed heterogeneity is presented. Antibodies have been prepared against alpha-NGF and purified by affinity chromatography so that they do not cross-react with gamma-NGF. This antibody preparation recognizes two very similar proteins in male mouse submandibular gland RNA-directed cell-free translation mixtures. The expression of only one of these forms is regulated by testosterone. Oligonucleotide probes specific for each of the three NGF subunits have been prepared and used for Northern blot analysis of RNA from the mouse submandibular gland. The three subunits were found to be coordinately expressed and each were 30-fold more abundant in male than in female glands.

Serum effects on substrate oxidation by dissociated brain cells: possible sites of action

This report is an extension of recent studies indicating the presence of a factor in serum that preferentially inhibits 14CO2 production from labeled glucose. Experiments with dissociated cells revealed that the inhibitory effects of serum were only slightly changed over more than a 50-fold range in initial glucose concentration. Serum had no effect on the rate of glucose transport (uptake of 1,3[3H]2-deoxyglucose). The inhibitory effect of serum was greater on 14CO2 production from [6-14C]glucose than [1-14C]glucose. Other studies revealed that 14CO2 production from [1-14C]pyruvate was more than 5 times the rate obtained using [3-14C]pyruvate; however, the inhibitory effect of serum was much greater on the latter (20% vs 60% inhibition respectively) at 2 mM pyruvate and in the presence of 1% fetal bovine serum. Attempts to characterize the factor using Amicon filtration showed the highest inhibitory activity in a 10,000 mol. wt. fraction, although some inhibitory activity was found in commercial preparations of bovine serum albumin. Delipidation of serum had no effect. Based on these results, we postulate that the observed decrease in labeled CO2 production reflects the regulation of substrate utilization at the pyruvate carboxylase step by one or more factors in serum (with a mol. wt. of approximately 10,000).

Role of glandular kallikreins as growth factor processing enzymes: structural and evolutionary considerations

Hormones and growth factors are generally released from larger precursors by limited proteolysis. The causative agents remain poorly defined with respect to location and properties. One subset of proteases, the glandular kallikreins, have been implicated in a few cases, in part because of their specific association with mature forms of some hormones. However, limited distribution and low copy number in some species cast doubt on this hypothesis, and they may well play other physiological functions that remain to be elucidated.

Nerve growth factor (NGF) in serum: evaluation of serum NGF levels with a sensitive bioassay employing embryonic sensory neurons

Considerable controversy surrounds the question of whether or not nerve growth factor (NGF) or a related nerve growth-promoting factor is present in serum. Recently, supporting its role as a local neuronotrophic factor, the presence of NGF in glial cells and its production in target tissues of NGF-responsive neurons were demonstrated [Rush: Nature 312:364-367, 1984; Heumann, Korsching, Scott, Thoenen: EMBOJ 3:3183-3189, 1984; Shelton and Reichardt: Proc Natl Acad Sci USA 81:7952-7955, 1984]. At the same time, the concept that NGF may play a role as a humoral factor has been questioned, since careful analyses of serum with specific and sensitive radioimmunoassays [Suda, Barde, Thoenen: Proc Natl Acad Sci USA 75:4042-4046, 1978; Korsching and Thoenen; Proc Natl Acad Sci USA 80:3513-3516, 1983; Furukawa, Kamo, Furukawa, Akazawa, Satoyoshi, Itoh, Hayashi: J Neurochem 40:734-744, 1983] as well as bioassays [Skaper and Varon: Exp Neurol 76:655-665, 1982] have not confirmed earlier reports [Levi-Montalcini and Booker; Proc Natl Acad Sci USA 46:373-391, 1960; Banks, Banthorpe, Charlwood, Pearce, Vernon: Nature 246:503-504, 1973; Hendry: Biochem J 128:1265-1272, 1972] on NGF's representation in serum. In this study serum from mouse, rat, and man was analyzed with an in vitro bioassay system which employs sensory neurons from chicken embyro dorsal root ganglia and which allows the measurement of NGF concentrations as low as 0.8 pM. It was found that sera from all these species contained neuronotrophic activity (S-NGF). The target cell spectrum as well as characteristic parameters of the neuronal growth response of S-NGF and of NGF were identical. S-NGF of mouse serum was completely inhibitable by polyclonal and monoclonal antibodies to mouse submandibular gland beta NGF. On polyacrylamide isoelectric focussing gels mouse and human S-NGF could be recovered from the same position as NGF as well as from the region where alpha 2-macroglobulin and serum albumin focused. In newborn and adult male and female mice basal S-NGF levels were equivalent to 10-50 pM NGF. A fraction of the serum samples of male mice showed elevated S-NGF levels. The incidence of high S-NGF levels was more frequent in NMRI and C57BL/6 males than in BALB/c males. Following sialectomy of male mice only basal S-NGF levels were observed up to 5 weeks after the operation. This indicates that although the submandibular gland may contribute to S-NGF levels in serum under certain conditions that appeared to be stress related, it cannot be the only source of S-NGF.

Purification and partial characterization of prostate-derived growth factor

A potent growth-promoting polypeptide, the prostate-derived growth factor (PrDGF), has been purified to apparent homogeneity from acid extracts of rat prostatic tissue using ion-exchange, reverse-phase, and gel-permeation chromatography. PrDGF migrates as a single protein-staining band in NaDodSO4/PAGE in precise correspondence to extractable PrDGF activity in nonstained NaDodSO4 gels. PrDGF is acid- and heat-stable but is sensitive to reduction or protease treatment. PrDGF is an acidic (pI 5.0) protein of approximately equal to 25 kDa in NaDodSO4/polyacrylamide gels and of approximately equal to 6-8 kDa in reduced NaDodSO4/polyacrylamide gels. PrDGF stimulates the linear incorporation of [methyl-3H]thymidine into normal rat kidney cells between 0 and 16 ng/ml. PrDGF appears to differ from other known growth factors in chemical composition and biological properties, suggesting that PrDGF is a previously undescribed growth factor.

Anterior pituitary glandular kallikrein: trypsin activation and estrogen regulation

Discrepant reports exist regarding the presence of glandular kallikrein or other trypsin-like serine proteases in the pituitary. The existence of pituitary kallikreins in latent forms could explain these discrepancies. I report that trypsin treatment of rat anterior pituitary homogenates activates two serine proteases which generate kinins from kininogen and selectively cleave chromogenic substrates for kallikreins. One protease (enzymatically and immunologically resembling glandular kallikrein) and activated 5-fold by trypsin and was 20 times more abundant in female than in male lobes due to hormonal regulation by ovarian estrogens. The second kallikrein (activated 20-fold by trypsin) was unaffected by estrogens. The results demonstrate that rat anterior pituitary kallikreins predominantly exist in latent forms requiring activation for detection. Additionally, glandular kallikrein is a major estrogen-induced protein in the rat anterior pituitary. No other member of this large protease family is known to be regulated by estrogens.

Absence of the alpha and gamma subunits of 7S nerve growth factor in denervated rodent iris: immunocytochemical studies

Immunocytochemical studies were performed to determine if denervated rodent iris produces nerve growth factor (NGF) in a form chemically similar to that of the 7S NGF complex in mouse submandibular glands. Antisera to the alpha, beta, and gamma subunits of 7S NGF were raised in rabbits and characterized on immunoblots of SDS-containing polyacrylamide gels. Antisera were applied to stretch preparations of rat and mouse irides that were cultured for periods of 2 to 6 days or sympathetically denervated by superior cervical ganglionectomy and left in situ 4 days. Antibody binding was visualized by indirect immunofluorescence. In control studies done on plastic sections of mouse submandibular glands, antisera co-localized the three subunits of 7S NGF within secretory granules of granular tubule cells. In denervated rat iris, beta NGF immunoreactivity was evident in a cellular plexus that resembled in distribution and morphology nerve fibers in the normal iris, in agreement with a previous study (R.A. Rush (1984). Nature (London) 312, 364-367). Identical staining patterns were observed in mouse iris. In neither rat or mouse, however, did the nerve-like processes stain with antibodies suggests that the NGF-like protein in denervated rodent iris is not synthesized as part of the 7S NGF complex. Iris also did not react with antibodies to epidermal growth factor, a protein co-localized with NGF in mouse submandibular glands and in guinea pig prostate.

NGF-dependent and -independent growth of neurites from sympathetic ganglion cells of the aged human in a serum-free culture

Small pieces of tissue isolated from abdominal sympathetic ganglia in aged male patients were cultured in a chemically defined, serum-free medium. The growth of neurites from pieces of ganglia in cultures with and without 50 ng/ml mouse 2.5S nerve growth factor (NGF) was compared. The NGF stimulated significantly greater regeneration of neurites, causing the growth of long fibers from the ganglion pieces. Many short neurites grew, even in the absence of the NGF, but these were generally short, except for long neurites generated in several nerve cells. A method was devised for the evaluation of NGF-dependent growth of neurites in the culture. The rate of the NGF-dependent growth of neurites, which was calculated by the difference in the total lengths of the NGF-dependent neurites between 2- and 4-day-old cultures, was approximately 160 micron/day. The results indicate that although the growth of neurites from some sympathetic nerve cells of the aged human become independent of the NGF, most of the nerve cells remain dependent on the NGF, even in the stage of senescence.

Activation of a latent kinin-generating proteinase in the porcine anterior pituitary

This study was conducted to determine whether a kinin-generating proteinase (kininogenase) previously described in the porcine anterior pituitary exists in a latent form. Porcine anterior pituitaries were homogenized in 0.25 M sucrose (pH 7.5) and sequentially centrifuged at 1000 X g for 5 min, 1500 X g for 20 min, 10 000 X g for 20 min, and 105 000 X g for 60 min. The various fractions were assayed for their ability to generate kinins from kininogen and cleave H-D-Pro-Phe-Arg-p-nitroanilide (S-2302) before or after various activation procedures. Untreated pituitary fractions had a small amount of proteolytic activity. However, large increases in kininogenase and S-2302 hydrolytic activity were observed in the 105 000 X g pellet after dialysis, or incubation with trypsin. Repeated freezing and thawing, detergents, phospholipase A2, melittin, plasmin, thrombin, urokinase and Factor Xa failed to activate kininogenase activity in the 105 000 X g pellet. However, plasmin produced massive increases in S-2302 hydrolytic activity. The kininogenase and S-2302 hydrolytic activity was sensitive to inhibition by soybean trypsin inhibitor and aprotinin, and had a broad pH optimum between 7 and 9. The data indicate that the porcine anterior pituitary kininogenase largely exists in a latent form. Also, the porcine anterior pituitary appears to contain an additional latent proteinase which can hydrolyze S-2302.

Synthesis and partial maturation of the alpha- and gamma-subunits of the mouse submaxillary gland nerve growth factor in Xenopus laevis oocytes

Sera raised against the alpha-, beta- and gamma-subunits of the mouse 7 S NGF were used to characterize translation products coded by submaxillary gland mRNAs microinjected into Xenopus oocytes. Anti-beta NGF sera did not cross-react with any material. In contrast, the precursors of the alpha- and gamma-subunits, as well as that of renin were identified. Use of tunicamycin, and a comparison of the translation products obtained in oocytes or in the reticulocyte lysate indicated that oocytes achieved the cleavage of signal sequences, the glycosylation of the alpha- and gamma-precursors, and the subsequent secretion of the 3 proteins. In the submaxillary gland, however, the mature forms of alpha NGF, gamma NGF and renin are composed of peptides of smaller size than those produced by the oocytes. These latter appear to lack specific proteases involved in the terminal processing of the submaxillary gland proteins.

Comparative biochemistry of the guinea-pig: a partial checklist

A great deal is known about guinea-pig biochemistry, but the information is scattered and difficult to assemble. The guinea-pig also possesses a number of unusual biochemical features which add to its interest. For these reasons we have compiled a list of biochemical characteristics of the guinea-pig, organized in a series of tables, with brief discussions of some of the entries.

Partial amino-acid sequence of the epidermal growth-factor-binding protein

The partial amino acid sequence of the epidermal growth-factor-binding protein was determined. Residues in 108 unique positions, corresponding to 45% of the molecule, were identified. The protein is a serine protease, closely related to the nerve growth factor gamma subunit. It is suggested that the epidermal growth-factor-binding protein, like other serine protease, is synthesized as a single polypeptide chain which undergoes limited endoproteolysis. The isolated material also contained minor amounts of a second serine protease. This protease is closely related to the epidermal growth-factor-binding protein, differing from it in 7 out of the 45 amino acid positions available for comparison. The latter protease may be identical to the previously described protease A.

Antigenic sites on mouse 2.5S nerve growth factor

Cyanogen bromide and tryptic peptides of mouse 2.5S Nerve Growth Factor (NGF) have been used to inhibit competitively binding of rabbit antiserum anti-NGF to native NGF in a solid-phase radioimmunoassay. The results showed that the larger of the two peptides obtained by cyanogen bromide cleavage (amino-acid residues 10-118) was indistinguishable from NGF in this respect, whereas the smaller N-terminal peptide (residues 1-9) was virtually non-inhibitory. Ten peptides were purified from a tryptic digest of the larger cyanogen bromide fragment. One of them, peptide G7 (residues 58-59, 60-69, 104-114, linked by disulfide bridges), was capable of almost full inhibition of binding, though only when used at a concentration about 100 times higher than that necessary to get the same effect with NGF. One other peptide, G10-H1 (residues 70-74), showed some inhibition at relatively high concentrations, but the majority of peptides, including peptide DE-5 which has been shown to be active in the NGF bioassay, were essentially non-inhibitory. A significant co-operative effect was seen when peptides G7 and G10-H1 were used in conjunction. No such effects were observed with any other combination tested.

Purification of a new neurotrophic factor from mammalian brain

We report the purification from pig brain of a factor supporting the survival of, and fibre outgrowth from, cultured embryonic chick sensory neurons. The purified factor migrates as one single band, mol. wt. 12 300, on gel electrophoresis in the presence of sodium dodecylsulphate (SDS) and is a basic molecule (pI greater than or equal to 10.1). Approximately 1 microgram factor was isolated from 1.5 kg brain. The final degree of purification was estimated to be 1.4 X 10(6)-fold, and the specific activity 0.4 ng/ml/unit, which is similar to that of nerve growth factor (NGF) using the same assay system. This factor is the first neurotrophic factor to be purified since NGF, from which it is clearly distinguished because it has different antigenic and functional properties.