The alpha-subunit of mouse 7 S nerve growth factor is an inactive serine protease

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.

Structure of the glucanase inhibitor protein (GIP) family from phytophthora species suggests coevolution with plant endo-beta-1,3-glucanases

During invasion of their plant hosts, species of the oomycete genus Phytophthora secrete glucanase inhibitor proteins (GIPs) into the plant apoplast, which bind and inhibit the activity of plant extracellular endo-beta-1,3-glucanases (EGases). GIPs show structural homology to the chymotrypsin class of serine proteases (SP) but lack proteolytic activity due to the absence of an intact catalytic triad and, thus, belong to a broader class of proteins called serine protease homologs (SPH). To study the evolutionary relationship between GIPs and functional SP, database searches were used to identify 48 GIP homologs in the P. sojae, P. ramorum, and P. infestans genomes, composing GIPs, SPH, and potentially functional SP. Analyses of P. infestans-inoculated tomato leaves showed that P. infestans GIPs and tomato EGases are present in the apoplast and form stable complexes in planta. Studies of the temporal expression of a four-membered GIP family from P. infestans (PiGIP1 to PiGIP4) further revealed that the genes show distinctly different patterns during an infection timecourse. Codon evolution analyses of GIP homologs identified several positively selected peptide sites and structural modeling revealed them to be in close proximity to rapidly evolving EGase residues, suggesting that the interaction between GIPs and EGases has the hallmarks of a coevolving molecular arms race.

Nerve growth factor

In contrast to all other molecules which are labelled 'growth factor', NGF is not a mitogen. It is a neurotrophic molecule essential for the development and maintenance of function of specific populations of peripheral and possibly also central neurons. The availability of NGF in large quantities from exocrine glands (e.g. male mouse submandibular gland), where NGF does not play a neurotrophic role, has allowed the purification of NGF, the production of specific antibodies, the determination of its amino acid sequence and finally the molecular cloning of NGF leading to the elucidation of its precursor structure and its genomic organization. Comparison of the biological activities and the immunological properties of NGF isolated from different sources demonstrated that the active centre of the molecule has been highly conserved during evolution, whereas other parts of the molecule determining immunological properties have undergone considerable changes. After a survey of the essential biological actions of NGF, this paper concentrates on two actual questions of NGF research, namely the regulation of NGF synthesis in the target tissues of NGF-responsive neurons, and the molecular mechanism(s) of action of NGF on these neurons.

Proteinaceous inhibitors of endo-beta-glucanases

Both plants and filamentous phytopathogens secrete proteins that inhibit endo-beta-glucanases. The first endo-beta-glucanase inhibitor proteins to be discovered are XEGIP, a tomato protein that inhibits fungal xyloglucan-specific endo-beta-1,4-glucanases, and GIP1, an oomycete protein that inhibits endo-beta-1,3-glucanases produced by the plant host. These inhibitor proteins act by forming high-affinity complexes with their endoglucanase ligands. A family of XEGIP-like proteins has been identified. At least one member of this family (extracellular dermal glycoprotein, EDGP) has been shown to have endoglucanase-inhibitor activity, while other members have sequence similarity to a xylanase inhibitor from wheat (TAXI-1). The oomycete inhibitor GIP1 is a catalytically inactive serine protease homolog (SPH) whose structure is unrelated to XEGIP. Both types of inhibitor proteins are likely to affect the interactions of plants with filamentous phytopathogens, and a basic model describing their roles in pathogenesis is proposed.

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.

Structure of mouse 7S NGF: a complex of nerve growth factor with four binding proteins

BACKGROUND

Nerve growth factor (NGF) is a neurotrophic factor that promotes the differentiation and survival of certain populations of neurons in the central and peripheral nervous systems. 7S NGF is an alpha 2 beta 2 gamma 2 complex in which the beta-NGF dimer (the active neurotrophin) is associated with two alpha-NGF and two gamma-NGF subunits, which belong to the glandular kallikrein family of serine proteinases. The gamma-NGF subunit is an active serine proteinase capable of processing the precursor form of beta-NGF, whereas alpha-NGF is an inactive serine proteinase. The structure of 7S NGF could be used as a starting point to design inhibitors that prevent NGF binding to its receptors, as a potential treatment of neurodegenerative diseases.

RESULTS

The crystal structure of 7S NGF shows that the two gamma-NGF subunits make extensive interactions with each other around the twofold axis of the complex and have the C-terminal residues of the beta-NGF subunits bound within their active sites. The 'activation domain' of each of the alpha-NGF subunits is in an inactive (zymogen-like) conformation and makes extensive interactions with the beta-NGF dimer. The two zinc ions that stabilize the complex are located at the relatively small interfaces between the alpha-NGF and gamma-NGF subunits.

CONCLUSIONS

The structure of 7S NGF shows how the twofold axis of the central beta-NGF dimer organizes the symmetry of this multisubunit growth factor complex. The extensive surface of beta-NGF buried within the 7S complex explains the lack of neurotrophic activity observed for 7S NGF. The regions of the beta-NGF dimer that contact the alpha-NGF subunits overlap with those known to engage NGF receptors. Two disulphide-linked loops on alpha-NGF make multiple interactions with beta-NGF and suggest that it might be possible to design peptides that inhibit the binding of beta-NGF to its receptors.

A conserved histidine residue of Escherichia coli outer-membrane phospholipase A is important for activity

Escherichia coli outer-membrane phospholipase A (OMPLA) is thought to be a member of the class of serine hydrolases, having a classical Asp-His-Ser catalytic triad [Horrevoets, A. J. G., Verheij, H. M. & de Haas, G. H. (1991) Eur. J. Biochem. 198, 247-253]. To identify the histidine residue that is important for catalytic activity, the four histidine residues in E. coli OMPLA that are conserved in other enterobacterial OMPLA enzymes were replaced by cysteine residues using PCR-directed, site-specific mutagenesis. The resulting mutant proteins were all well expressed and displayed heat modifiability, indicating that they were properly folded. Enzyme assays showed that only the His142Cys mutant protein was lacking enzymatic activity. In addition, a His142Gly mutant protein appeared to be inactive. These results show that His142 is important for the enzymatic activity of OMPLA.

The neurotrophins and their receptors: structure, function, and neuropathology

The neurotrophins are a family of polypeptides that promote differentiation and survival of select peripheral and central neurons. Nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, neurotrophin-4, and neurotrophin-5 are included in this group. In recent years, tremendous advances have been made in the study of these factors. This has stimulated our review of the field, characterizing the neurotrophins from initial isolation to molecular analysis. The review also discusses their synthesis, localization, and responsive tissues, in both the periphery and CNS. The complex receptor interactions of the neurotrophins are also analyzed, as are putative signal transduction mechanisms. Discussion of the observed and postulated involvement in neuropathological disorders leads to the conclusion that the neurotrophins are involved in the function and dysfunction of the nervous system.

Characterization of kallikrein cDNAs from the African rodent Mastomys

Kallikreins comprise a family of serine proteases that are required for the processing of hormone precursors, thereby controlling many physiological processes including blood flow, ion transport, and inflammation. In rodents such as mouse, rat, and Mastomys, many kallikreins are expressed in the submandibular gland (SMG), but only a limited number, notably true tissue (glandular) kallikrein, are expressed in the kidney. We report here the cloning and characterization of kallikrein cDNAs from the Mastomys SMG. Two of these are expressed in the kidney as well as in the SMG, and one may code for the true tissue kallikrein of Mastomys. A third kallikrein is expressed only in the SMG and bears some resemblance to a murine nerve growth factor-associated protein. The existence of a family of Mastomys SMG kallikreins suggests that these enzymes act as prohormone-processing enzymes in Mastomys. DNA sequence analysis and hybridization studies demonstrate that, although Mastomys kallikreins are very similar in structure to both mouse and rat kallikreins, their expression patterns differ. The expression of more than one Mastomys glandular kallikrein in the kidney is similar to that in the rat, but the sequence and nonsexually dimorphic expression of the putative tissue kallikrein most closely resembles mouse. Mastomys represents an interesting hybrid between mouse and rat, providing an important animal model for studies of kallikrein expression and regulation.

Prediction of the three-dimensional structures of the nerve growth factor and epidermal growth factor binding proteins (kallikreins) and an hypothetical structure of the high molecular weight complex of epidermal growth factor with its binding protein

We have predicted the three-dimensional structures of the serine protease subunits (gamma-NGF, alpha-NGF, and EGF-BP) of the high molecular weight complexes of nerve growth factor (7S NGF) and epidermal growth factor (HMW-EGF) from the mouse submandibular gland (from the X-ray crystal structures of two related glandular kallikreins). The conformations of three of the six loops surrounding the active site are relatively well defined in the models of gamma-NGF and EGF-BP, but three other loops are likely to have flexible conformations. Although the amino acid sequence of alpha-NGF is closely related to those of gamma-NGF and EGF-BP, it is catalytically inactive. Model-building studies on alpha-NGF suggested that mutations (in alpha-NGF) just prior to the active site serine (195) and an unusual N-terminal sequence are consistent with alpha-NGF having a zymogen-like conformation (similar to that in chymotrypsinogen). An hypothetical model of the quaternary structure of HMW-EGF has been constructed using this model of EGF-BP and the NMR structure of murine EGF. The C-terminal arm of EGF was modeled into the active site of EGF-BP based on data indicating that the C-terminal arginine of EGF occupies the S1 subsite of EGF-BP. Data suggesting one of the surface loops of EGF-BP is buried in the HMW-EGF complex and symmetry constraints were important in deriving a schematic model. A molecular docking program was used to fit EGF to EGF-BP.

beta-NGF-endopeptidase: structure and activity of a kallikrein encoded by the gene mGK-22

Mouse nerve growth factor (NGF) is cleaved at a histidine-methionine bond to release an NH2-terminal octapeptide (NGF1-8). The enzyme responsible, beta-NGF-endopeptidase, is structurally and functionally similar to gamma-NGF and epidermal growth factor-binding protein (EGF-BP) and cleaves mouse low molecular weight kininogen to produce bradykinin-like activity. These data have suggested that, like gamma-NGF and EGF-BP, beta-NGF-endopeptidase is a mouse glandular kallikrein. Evidence for a physiological role for NGF1-8 encouraged studies to further characterize the structure and function of this enzyme. Purified beta-NGF-endopeptidase migrated as a single band on isoelectric focusing and reducing SDS-polyacrylamide gels. As was expected, it removed NGF1-8 from NGF. Interestingly, enzymatic activity on an artificial substrate, and on NGF, was inhibited by NGF1-8 and by bradykinin. These studies further supported the view that beta-NGF-endopeptidase acts on both NGF and kininogen. The first 30 NH2-terminal amino acids of beta-NGF-endopeptidase were sequenced. This analysis demonstrated that the enzyme is encoded by the gene designated mGK-22 (Evans et al., 1987). The sequence of this gene corresponds to that of EGF-BP type A (Anundi et al., 1982; Drinkwater et al., 1987), and so studies were performed to determine whether or not beta-NGF-endopeptidase participates in EGF complex formation. Chromatographic and kinetic data gave no evidence that beta-NGF-endopeptidase is an EGF-binding protein. Our studies suggest that contamination of high molecular weight (HMW) EGF preparations with beta-NGF-endopeptidase erroneously led to earlier designation of the product of mGK-22 as an EGF-BP.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

The characterization of recombinant mouse glandular kallikreins from E. coli

A system has been developed for the expression in E. coli of 12 of the 14 expressed mouse submandibular gland kallikreins as cassettes subcloned directly from cDNA. Using the epidermal growth factor binding protein (mGK-9) and the gamma-subunit of nerve growth factor (mGK-3), as test cases, mature processed forms, obtained as functionally active proteins, as well as various precursor forms, were isolated. The expression system described allows rapid isolation of kallikrein protein from corresponding cDNA with yields of approximately 1.0 mg of purified protein from 10 g of initial cell paste. This expression system will facilitate structure/function studies of the mouse glandular kallikrein gene family and help elucidate the regions of the mature proteins responsible for the diverse catalytic behavior and growth factor interactions observed in this family of proteins.

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.

Focusing on IL-1-promotion of beta-amyloid precursor protein synthesis as an early event in Alzheimer's disease

A rationale for increased synthesis of beta-amyloid peptide percursor (APP) protein in Alzheimer's disease (AD) is developed in which Interleukin-1 (IL-1) plays a key role. This cytokine is elevated in AD, its receptors are on APP mRNA positive cells and it promotes APP gene expression. Potential involvement of the protease inhibitor (PI) activity of certain APP proteins in the activation process for IL-1 and Nerve Growth Factor (NGF) are proposed. The possibility of feedback loops among IL-1, APP and NGF and the implications for neuronal survival and function are discussed.

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)

The bovine pro-carboxypeptidase A-S6 ternary complex: a rare case of a secreted protein complex

Up to now, a non-covalent ternary complex in which the pro-carboxypeptidase A (subunit I) is associated to two functionally different proteins (subunits II and III) has only been found in the pancreas of ruminant species. In the other species studied so far, the pro-carboxypeptidase A is secreted either as a monomer or as a binary association with a functionally different protein. Subunit I is the immediate precursor of carboxypeptidase A. Subunit II is a chymotrypsinogen of the C-type, involved, like subunit I, in the degradation of proteins and peptides. Although closely related to the pancreatic serine endopeptidases, subunit III appears to be devoid of any specific enzymatic activity. Information about the spatial organization of the subunits in the ternary complex has been deduced from the sequential dissociation of the complex. In contrast to the mechanism of activation of subunits I and II, which is independent of their aggregation state, the catalytic properties of the resulting enzymes are sensitive to their aggregation state. Moreover, the structural basis of inactivity of subunit III as well as the physiological role of the ternary complex are also discussed in this review.

Detection of molecules with nerve growth factor binding activity in medium conditioned by L-929 fibroblasts

L-929 fibroblasts (L cells) secrete a high molecular weight form of nerve growth factor (NGF) that is non-covalently bound and contains as part of its structure a molecule similar, if not identical, to beta-NGF in mouse submandibular glands. The other components of the NGF complex have not been characterized. In this study we used radiolabeled beta-NGF as a probe to detect molecules with NGF binding activity in L cell conditioned medium. The L cell NGF complex was dissociated at low pH, or with denaturants or detergents, and allowed to reassociate in the presence of 125I-beta-NGF. Radioactivity became associated with a complex that eluted in a high molecular weight volume on columns of Sephadex G-200 and Sephacryl S-500. Incorporation was saturable and did not occur under non-dissociating conditions. The complex was affinity cross-linked and studied by SDS gel electrophoresis. Radiolabeled molecules were observed with molecular weights of 151,000, 56,000 and 53,000. Labeling did not occur in the presence of excess unlabeled NGF or when cross-linking was done with fetal bovine serum, indicating that binding is specific and that binding activity is not derived from serum added to tissue culture medium. Solutions containing 7S NGF from mouse salivary glands were cross-linked by similar procedures but different banding patterns were observed. The data show that NGF binding molecules dissimilar from those in salivary glands are present in L cell conditioned medium.

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.

Phenotypic differentiation of aphidicolin-selected human neuroblastoma cultures after long-term exposure to nerve growth factor

Human neuroblastoma SH-SY5Y (SY5Y) cultures, exposed to murine 7 S nerve growth factor (NGF) for 5 weeks and selected with aphidicolin (Aph) for 1 week, acquire several properties indicative of mature peripheral nerve cells. The mitotic activity of treated cultures decreases prior to Aph selection and ultimately reaches a level approximately 3% that of untreated cultures by Week 4 of treatment. The measured plasma membrane resting potential of the cells increases from -5 mV for untreated cells to -(45-56) mV for NGF/Aph-treated cells. Intracellular stores of monoamines are increased as determined by histochemical staining, and levels of neuron-specific enolase antigen increase as a result of NGF/Aph treatment. The resulting outgrowth of neurites is extensive and large bundles of processes commonly exceed 300 micron in length. NGF/Aph-treated cells acquire a dependence upon NGF for survival; however, with continued administration of NGF, the cultures appear to be capable of surviving indefinitely. Retinoic acid will also promote certain aspects of a differentiated phenotype under similar culture conditions. As judged by these criteria, cells of the SY5Y human neuroblastoma cell line have the potential for phenotypic and irreversible differentiation in vitro and can survive for prolonged periods under these culture conditions.

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.

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.