Xenopus Sox11 Partner Proteins and Functional Domains in Neurogenesis

Sox11, a member of the SoxC family of transcription factors, has distinct functions at different times in neural development. Studies in mouse, frog, chick, and zebrafish show that Sox11 promotes neural fate, neural differentiation, and neuron maturation in the central nervous system. These diverse roles are controlled in part by spatial and temporal-specific protein interactions. However, the partner proteins and Sox11-interaction domains underlying these diverse functions are not well defined. Here, we identify partner proteins and the domains of Xenopus laevis Sox11 required for protein interaction and function during neurogenesis. Our data show that Sox11 co-localizes and interacts with Pou3f2 and Neurog2 in the anterior neural plate and in early neurons, respectively. We also demonstrate that Sox11 does not interact with Neurog1, a high-affinity partner of Sox11 in the mouse cortex, suggesting that Sox11 has species-specific partner proteins. Additionally, we determined that the N-terminus including the HMG domain of Sox11 is necessary for interaction with Pou3f2 and Neurog2, and we established a novel role for the N-terminal 46 amino acids in the specification of placodal progenitors. This is the first identification of partner proteins for Sox11 and of domains required for partner-protein interactions and distinct roles in neurogenesis.

Cloning and developmental expression of the soxB2 genes, sox14 and sox21, during Xenopus laevis embryogenesis

The Sox family of transcription factors is thought to regulate gene expression in a wide variety of developmental processes. Here we describe the cloning of the X. laevis orthologs of the SoxB2 family of transcription factors, sox14 and sox21. In situ hybridization revealed that sox14 expression is restricted to the hypothalamus, dorsal thalamus, the optic tectum, a region of the somatic motornucleus in the midbrain and hindbrain, the vestibular nuclei in the hindbrain and a discrete ventral domain in the developing spinal cord. In contrast to the limited expression domain of sox14, sox21 is found throughout the developing central nervous system, including the olfactory placodes, with strongest expression at the boundary between the midbrain and hindbrain.

Xenopus Sox3 activates sox2 and geminin and indirectly represses Xvent2 expression to induce neural progenitor formation at the expense of non-neural ectodermal derivatives

The SRY-related, HMG box SoxB1 transcription factors are highly homologous, evolutionarily conserved proteins that are expressed in neuroepithelial cells throughout neural development. SoxB1 genes are down-regulated as cells exit the cell-cycle to differentiate and are considered functionally redundant in maintaining neural precursor populations. However, little is known about Sox3 function and its mode of action during primary neurogenesis. Using gain and loss-of-function studies, we analyzed Sox3 function in detail in Xenopus early neural development and compared it to that of Sox2. Through these studies we identified the first targets of a SoxB1 protein during primary neurogenesis. Sox3 functions as an activator to induce expression of the early neural genes, sox2 and geminin in the absence of protein synthesis and to indirectly inhibit the Bmp target Xvent2. As a result, Sox3 increases cell proliferation, delays neurogenesis and inhibits epidermal and neural crest formation to expand the neural plate. Our studies indicate that Sox3 and 2 have many similar functions in this process including the ability to activate expression of geminin in naïve ectodermal explants. However, there are some differences; Sox3 activates the expression of sox2, while Sox2 does not activate expression of sox3 and sox3 is uniquely expressed throughout the ectoderm prior to neural induction suggesting a role in neural competence. With morpholino-mediated knockdown of Sox3, we demonstrate that it is required for induction of neural tissue by BMP inhibition. Together these data indicate that Sox3 has multiple roles in early neural development including as a factor required for nogginmediated neural induction.

Sox3 expression is maintained by FGF signaling and restricted to the neural plate by Vent proteins in the Xenopus embryo

The formation of the nervous system is initiated when ectodermal cells adopt the neural fate. Studies in Xenopus demonstrate that inhibition of BMP results in the formation of neural tissue. However, the molecular mechanism driving the expression of early neural genes in response to this inhibition is unknown. Moreover, controversy remains regarding the sufficiency of BMP inhibition for neural induction. To address these questions, we performed a detailed analysis of the regulation of the soxB1 gene, sox3, one of the earliest genes expressed in the neuroectoderm. Using ectodermal explant assays, we analyzed the role of BMP, Wnt and FGF signaling in the regulation of sox3 and the closely related soxB1 gene, sox2. Our results demonstrate that both sox3 and sox2 are induced in response to BMP antagonism, but by distinct mechanisms and that the activation of both genes is independent of FGF signaling. However, both require FGF for the maintenance of their expression. Finally, sox3 genomic elements were identified and characterized and an element required for BMP-mediated repression via Vent proteins was identified through the use of transgenesis and computational analysis. Interestingly, none of the elements required for sox3 expression were identified in the sox2 locus. Together our data indicate that two closely related genes have unique mechanisms of gene regulation at the onset of neural development.

Biological and biochemical functions of RNA in the tetrahymena telomerase holoenzyme

Telomerase extends chromosome ends by the synthesis of tandem simple-sequence repeats. Studies of minimal recombinant telomerase ribonucleoprotein (RNP) reconstituted in vitro have revealed sequences within the telomerase RNA subunit (TER) that are required to establish its internal template and other unique features of enzyme activity. Here we test the significance of these motifs following TER assembly into telomerase holoenzyme in vivo. We established a method for stable expression of epitope-tagged TER and TER variants in place of wild-type Tetrahymena TER. We found that sequence substitutions in nontemplate regions of TER altered telomere length maintenance in vivo, with an increase or decrease in the set point for telomere length homeostasis. We also characterized the in vitro activity of the telomerase holoenzymes reconstituted with TER variants, following RNA-based RNP affinity purification from cell extracts. We found that nontemplate sequence substitutions imposed specific defects in the fidelity and processivity of template use. These findings demonstrate nontemplate functions of TER that are critical for the telomerase holoenzyme catalytic cycle and for proper telomere length maintenance in vivo.

Thrombin receptor signaling to cytoskeleton requires Hsp90

Thrombin is a serine protease that evokes various cellular responses involved in injury and repair of the nervous system through the activation of protease-activated receptor-1 (PAR-1). Signals that modulate cell morphology precede most PAR-1 effects, but the initial signal transduction molecules are not known. Using the yeast two-hybrid system, we identified Hsp90, a chaperone with known signaling properties, as a binding partner of PAR-1. The interaction was confirmed by glutathione S-transferase pull-down, overlay, and co-immunoprecipitation assays. Morphological assays in mouse astrocytes were carried out to evaluate the importance of Hsp90 during cytoskeletal signaling. Reducing Hsp90 levels by antisense treatment or disruption of the Hsp90.PAR-1 complex by the Hsp90-specific drug geldanamycin attenuated thrombin-mediated astrocyte shape changes. Furthermore, overexpression of the PAR-1 cytoplasmic tail abrogated thrombin-induced cytoskeletal changes in neuronal cells. Treatment with geldanamycin specifically inhibited activation of RhoA without affecting thrombin-mediated intracellular calcium release, revealing the regulation of a distinct signaling pathway by Hsp90. Taken together, these studies demonstrate that Hsp90 may be essential for PAR-1-mediated signaling to the cytoskeleton.

Creatine kinase, an ATP-generating enzyme, is required for thrombin receptor signaling to the cytoskeleton

Thrombin orchestrates cellular events after injury to the vascular system and extravasation of blood into surrounding tissues. The pathophysiological response to thrombin is mediated by protease-activated receptor-1 (PAR-1), a seven-transmembrane G protein-coupled receptor expressed in the nervous system that is identical to the thrombin receptor in platelets, fibroblasts, and endothelial cells. Once activated by thrombin, PAR-1 induces rapid and dramatic changes in cell morphology, notably the retraction of growth cones, axons, and dendrites in neurons and processes in astrocytes. The signal is conveyed by a series of localized ATP-dependent reactions directed to the actin cytoskeleton. How cells meet the dynamic and localized energy demands during signal transmission is unknown. Using the yeast two-hybrid system, we identified an interaction between PAR-1 cytoplasmic tail and the brain isoform of creatine kinase, a key ATP-generating enzyme that regulates ATP within subcellular compartments. The interaction was confirmed in vitro and in vivo. Reducing creatine kinase levels or its ATP-generating potential inhibited PAR-1-mediated cellular shape changes as well as a PAR-1 signaling pathway involving the activation of RhoA, a small G protein that relays signals to the cytoskeleton. Thrombin-stimulated intracellular calcium release was not affected. Our results suggest that creatine kinase is bound to PAR-1 where it may be poised to provide bursts of site-specific high-energy phosphate necessary for efficient receptor signal transduction during cytoskeletal reorganization.

Vacuum-assisted lancing of the forearm: an effective and less painful approach to blood glucose monitoring

A vacuum-lancet device was applied to the forearm for the purpose of obtaining capillary blood samples for glucose monitoring with minimal pain. In four clinical trials, a total of 215 individuals aged 12-77 years were tested four times using standard conditions and four times with either a different depth of lancing, different brand of lancet or a larger-sized device. The volume of blood collected using one-half atmosphere of vacuum in 40 sec was measured. The sensation and visual appearance of each lancet puncture on the forearm was recorded. Glucose was measured in forearm and in conventional fingerstick blood samples. The distribution of volumes was skewed to higher values with median values for each trial in the range of 3-10 microL. Ninety-five percent of the lancet sticks were judged as less painful than a fingerstick. Redness and bruising around the lanced sites were noted in some patients but disappeared within a few days. Overall correlation of the forearm versus fingerstick glucose values was 0.96. The vacuum-lancet device was very successful in obtaining capillary blood samples for glucose testing in a relatively painless manner. Incorporation of a glucose measuring system into the device might improve testing compliance among those who fear pain or the sight of blood.

Injury-related factors and conditions down-regulate the thrombin receptor (PAR-1) in a human neuronal cell line

Previous studies have demonstrated that thrombin can induce potent effects on neural cell morphology, biochemistry, and viability. Nearly all of these effects are mediated by proteolytic activation of the thrombin receptor (PAR-1). Mechanisms of PAR-1 regulation in several nonneural cell types have been shown to be novel and cell type specific; however, little is known about PAR-1 regulation in neural cells. In the present study, PAR-1 cell surface expression and regulation were examined in a transformed retinoblast (Ad12 HER 10) cell line using radioiodinated anti-PAR-1 monoclonal antibodies ATAP2, which recognizes intact and cleaved receptors, and SPAN12, which is specific for the intact form of the receptor. Scatchard analysis revealed high-affinity, specific binding to a single affinity class of receptors: K(D) = 3.13 and 5.25 nM, Bmax = 190.1 and 67.8 fmol/mg of protein for 125I-ATAP2 and 125I-SPAN12, respectively. Specificity for PAR-1 was confirmed by demonstrating rapid and near complete decreases for both antibodies following treatment with thrombin or PAR-1 activating peptide (SFLLRN). Differential antibody binding was used to demonstrate rapid and near complete thrombin-induced PAR-1 cleavage and internalization, with protein synthesis-dependent replacement of intact receptors occurring over longer time intervals, but only minimal recycling of cleaved receptors. A variety of factors and conditions were screened for their effects on PAR-1 expression. Significant decreases in PAR-1 expression were induced by the protein kinase C activator phorbol 12-myristate 13-acetate (87% at 3 h), the phospholipid inflammatory mediator lysophosphatidic acid (32% at 3 h), and the injury-related condition hypoglycemia (64 and 100% at 24 h in the absence and presence of dibutyryl cyclic AMP, respectively). The effect of hypoglycemia was shown by RNase protection to be at least partially pretranslational. Finally, thrombin's ability to enhance hypoglycemia-induced cell killing correlated temporally with PAR-1 cell surface expression.

Signaling pathways involved in thrombin-induced cell protection

This study examined the signal transduction pathways involved in thrombin-induced neuroprotection and compares these results with those of a similar study of thrombin-induced neuronal death. In thrombin-induced protection of astrocytes from hypoglycemia, pretreatment of astrocytes with tyrosine or serine/threonine kinase inhibitors, cytochalasin D, or exoenzyme C3, a potent inhibitor of the small GTPase RhoA, attenuated thrombin-induced protection. These same inhibitors were previously shown to block thrombin-induced cell death, implying a similarity in the cell death and cell-protective pathways. Biochemical assays determined that thrombin increased available RhoA activity, although more slowly and to a lesser extent than occurs in thrombin-induced cell death. A clear difference in these pathways was revealed when a time course study of thrombin-induced cell death indicated that unlike thrombin-induced protection, cells must be exposed to thrombin for >16 h to irreversibly enter the cell death pathway. Addition of lower doses of thrombin every 24 h also induced cell death. These studies indicate that exposure of cells to micromolar concentrations of thrombin alone does not induce cell death, but the continued exposure to thrombin is required. Thus the cell death and protective pathways may share initial signaling proteins, but differences in the amplitude as well as the duration of the signal may result in different final pathways.

Thrombin causes a marked delay in skeletal myogenesis that correlates with the delayed expression of myogenin and p21CIP1/WAF1

Thrombin is a multifunctional serine protease whose activity is regulated in the extravasculature by an extracellular inhibitor, protease nexin-1. Because protease nexin-1 expression has been shown to be regulated during skeletal muscle cell differentiation, we reasoned that thrombin inactivation may be an important requirement for this developmental process. To test this hypothesis, we examined the effects of thrombin on differentiating C2C12 myoblasts. We report here that myogenesis, as scored by myotube formation, is considerably delayed by thrombin. This regulation correlated with delayed expression of myogenin and p21(CIP1/WAF1), both considered critical components of the skeletal muscle cell differentiation program. Regulation occurred at the RNA level, indicating that the effect of thrombin is either transcriptional or post-transcriptional. Furthermore, we present evidence suggesting that this regulation is mediated by the thrombin receptor. Although thrombin is mitogenic for certain cell types, we found that delay of myogenesis in C2C12 cells did not involve a mitogenic signal. Taken together, these results imply that inhibition of the serine protease thrombin may be required for proper progression through the myogenic differentiation program. The data point to potentially important roles that thrombin and protease nexin-1 may play during skeletal muscle development.

Thrombin induces apoptosis in cultured neurons and astrocytes via a pathway requiring tyrosine kinase and RhoA activities

Thrombin activity is a factor in acute CNS trauma and may contribute to such chronic neurodegenerative diseases as Alzheimer's disease. Thrombin is a multifunctional serine protease that catalyses the final steps in blood coagulation. However, increasing evidence indicates that thrombin also elicits a variety of cellular and inflammatory responses, including responses from neural cells. Most recently, high concentrations of thrombin were shown to cause cell death in both astrocyte and hippocampal neuron cultures. The purpose of this study was to determine the mechanisms underlying thrombin-induced cell death. Our data show that thrombin appears to cause apoptosis as evidenced by cleavage of DNA into oligonucleosomal-sized fragments, fragmentation of nuclei, and prevention of death by inhibition of protein synthesis. Synthetic peptides that directly activate the thrombin receptor also induced apoptosis, indicating that thrombin-induced cell death occurred via activation of the thrombin receptor. The signal transduction cascade involves tyrosine and serine/threonine kinases and an intact actin cytoskeleton. Additional study revealed the involvement of the small GTP-binding protein RhoA. Thrombin induced RhoA activity in both astrocytes and hippocampal neurons, and inhibition of RhoA activity with exoenzyme C3 attenuated cell death, indicating that thrombin activation of RhoA was necessary for thrombin-induced cell death. Tyrosine kinase inhibitors blocked thrombin induction of RhoA, indicating that tyrosine kinase activity was required upstream of RhoA. These data suggest a sequential linkage of cellular events from which we propose a model for the second messenger cascade induced by thrombin in neural cells that can lead to apoptosis.

No .NO from NO synthase

The nitric-oxide synthase (NOS; EC 1.14.13.39) reaction is formulated as a partially tetrahydrobiopterin (H4Bip)-dependent 5-electron oxidation of a terminal guanidino nitrogen of L-arginine (Arg) associated with stoichiometric consumption of dioxygen (O2) and 1.5 mol of NADPH to form L-citrulline (Cit) and nitric oxide (.NO). Analysis of NOS activity has relied largely on indirect methods such as quantification of nitrite/nitrate or the coproduct Cit; we therefore sought to directly quantify .NO formation from purified NOS. However, by two independent methods, NOS did not yield detectable .NO unless superoxide dismutase (SOD; EC 1.15.1.1) was present. In the presence of H4Bip, internal .NO standards were only partially recovered and the dismutation of superoxide (O2-.), which otherwise scavenges. .NO to yield ONOO-, was a plausible mechanism of action of SOD. Under these conditions, a reaction between NADPH and ONOO- resulted in considerable overestimation of enzymatic NADPH consumption. SOD lowered the NADPH:Cit stoichiometry to 0.8-1.1, suggesting either that additional reducing equivalents besides NADPH are required to explain Arg oxidation to .NO or that .NO was not primarily formed. The latter was supported by an additional set of experiments in the absence of H4Bip. Here, recovery of internal .NO standards was unaffected. Thus, a second activity of SOD, the conversion of nitroxyl (NO-) to .NO, was a more likely mechanism of action of SOD. Detection of NOS-derived nitrous oxide (N2O) and hydroxylamine (NH2OH), which cannot arise from .NO decomposition, was consistent with formation of an .NO precursor molecule such as NO-. When, in the presence of SOD, glutathione was added, S-nitrosoglutathione was detected. Our results indicate that .NO is not the primary reaction product of NOS-catalyzed Arg turnover and an alternative reaction mechanism and stoichiometry have to be taken into account.

Sevoflurane degradation to compound A in anaesthesia breathing systems

Determination of an effective rate constant and activation energy allowed the application of steady-state theory to predict concentrations of compound A from sevoflurane concentrations, fresh gas flow rate, absorbent temperature and amount of absorbent. Studies by eight research groups were compared. Lower concentrations of compound A than predicted were observed at low flow rates, suggesting that its degradation by the absorbent is important in limiting the maximum observed concentrations in closed and low-flow breathing systems. Trial-to-trial and batch-to-batch variations in compound A concentrations were observed in model system tests of commercial and pilot-plant absorbents. Chemical modification of the absorbent with glycerol lowered concentrations of compound A, possibly by formation of a nucleophilic addition product. An ideal chemical scavenger would remain stable and non-volatile in the absorbent before irreversibly reacting with compound A to form a stable non-volatile product.

Characterization of the human protease nexin-1 promoter and its regulation by Sp1 through a G/C-rich activation domain

Protease nexin-1 (PN-1 ) is a potent inhibitor of serine proteases in the extracellular environment. It is abundantly expressed in the nervous system, where it is thought to participate in local injury and repair processes. Although some information has been obtained regarding PN-1 gene structure, relatively little is known about the cis- and trans-acting factors that regulate its expression. Elucidation of these factors should provide a better understanding of PN-1 function during development and wound repair. In this report we describe the characterization of the human PN-1 promoter and identify regulatory domains and a transactivator mediating its transcriptional activity. The promoter is highly G/C rich proximal to the transcriptional start site. It exhibits tissue specificity and is negatively regulated by a silencer element upstream of position -480. A positive regulatory element was mapped between -199 and -45, which contains multiple putative Sp1 consensus binding sites. Electrophoretic mobility shift analysis confirmed that Sp1 specifically binds this region of the PN-1 promoter. DNase I foot-printing revealed six potential Sp1 binding sites between -103 and -56 that were protected by recombinant Sp1. Cotransfection experiments into the Sp1-deficient Drosophila SL2 cell line also showed that Sp1 activates PN-1 promoter activity in a dose-dependent fashion. Thus, our analysis demonstrates that activation of PN-11 transcription is regulated by Sp1 through G/C-rich cis-acting elements in the 5'proximal promoter region.

Thrombin attenuates neuronal cell death and modulates astrocyte reactivity induced by beta-amyloid in vitro

beta-Amyloid protein has been implicated as a potential causative agent in the neuropathology associated with Alzheimer's disease. This possibility is supported by observations that beta-amyloid induces neuronal degeneration and astrocyte reactivity in vitro by as yet undefined mechanism(s). In this report, we present data demonstrating that the pathological effects of beta-amyloid on cultured cells are modulated by activation of the thrombin receptor. At concentrations between 50 and 500 nM, thrombin pretreatment significantly attenuates neurotoxicity mediated by fibrillar aggregates of beta 1-42 and beta 25-35 peptides. In cultured astrocytes, the stellate morphology induced by beta 1-42 and beta 25-35 aggregates can be prevented and reversed by thrombin exposures between 10 pM and 1 microM. In contrast, thrombin potentiates rather than attenuates the beta-amyloid-induced increased expression of basic fibroblast growth factor, suggesting that thrombin differentially modulates the effects of beta-amyloid on astrocytes. Thrombin's effects on both neurons and astrocytes are mimicked by thrombin receptor-activating peptide and inhibited by two potent thrombin inhibitors, hirudin and protease nexin-1. These data provide both new insight into the signaling pathways underlying the cellular effects of beta-amyloid and additional support for the role of thrombin as an important mediator of neuropathological events.

Decreases in protease nexins in Alzheimer's disease brain

A marked and significant reduction of protease nexin-1 (PN-1) and PN-2/amyloid beta protein precursor (A beta PP) was observed in selected regions of Alzheimer's disease (AD) brains as compared to those of aged-matched controls. Correlative analysis indicated a relationship between PN-1 reduction and the severity of pathologic alterations. A statistically significant inverse correlation was noted between the level of PN-1 activity and the density of tau-positive dystrophic neurites in the hippocampus. In view of the ability of thrombin and PN-1 activity to regulate neurite outgrowth, it is possible that abnormal thrombin and PN-1 interactions may play a role in dystrophic neurite formation. The presence of clusters of dystrophic neurites around the capillaries suggests that blood-brain barrier (BBB) dysfunction may enhance such abnormal interactions. The decrease in PN-2/A beta PP levels in AD brains could possibly contribute to neuronal degeneration in AD in view of the ability of PN-2/A beta PP to protect neurons against the toxic effects of the A beta.

Thrombin receptor activation protects neurons and astrocytes from cell death produced by environmental insults

Thrombin is a multifunctional serine protease that is rapidly produced from prothrombin at sites of tissue injury and catalyzes the final steps in blood coagulation. Thrombin also regulates gene expression and process outgrowth in neurons and astrocytes and stimulates proliferation of astrocytes. Since thrombin is produced immediately upon breakdown of the blood-brain barrier we examined its effects on astrocytes and neurons cultured under conditions which resemble those found in vivo following cerebrovascular injury. These studies showed that thrombin markedly protected rat primary astrocytes from cell death induced by hypoglycemia or oxidative stress. Thrombin also protected rat primary hippocampal neurons from cell death produced by hypoglycemia or growth supplement deprivation. Synthetic peptides which directly activate the thrombin receptor also protected astrocytes and neurons from these environmental insults, demonstrating that the thrombin effects were mediated through the thrombin receptor. In contrast to these results with stressed cells, high concentrations of thrombin killed both astrocytes and neurons cultured under normal conditions. All of the effects of thrombin on astrocytes and neurons were blocked by the brain thrombin inhibitor, protease nexin-1 (PN-1). This shows that the effects required the proteolytic activity of thrombin and is consistent with the known proteolytic mechanism by which thrombin activates its receptor. These results indicate that thrombin and PN-1 may regulate the viability of both astrocytes and neurons in early moments following trauma to the CNS or other conditions that alter the blood-brain barrier.

Analysis of sevoflurane degradation products in vapor phase samples

Sevoflurane degradation products were measured by GC-flame ionization detection in vapor phase samples using manual and automated injection methods. Sample handling techniques allowed the transfer and storage of samples for up to 72 h. Compound A, fluoromethyl 2,2-difluoro-1-(trifluoromethyl)vinyl ether, was the major vapor phase degradation product formed in simulated clinical conditions. Recoveries of 4-32 ppm (v/v) compound A concentrations using the manual method were in the range of 88-117% (n = 12, mean = 102%, R.S.D. = 9%).

Cellular localization of thrombin receptor mRNA in rat brain: expression by mesencephalic dopaminergic neurons and codistribution with prothrombin mRNA

Cell culture studies demonstrating that the serine protease thrombin can induce neuronal and glial process retraction, glial proliferation, and changes in gene expression suggest a role for thrombin in CNS development, plasticity, and response to injury. Most cellular responses to thrombin are mediated by proteolytic activation of the cloned thrombin receptor (TR), a member of the seven transmembrane domain, G-protein-coupled receptor superfamily. As a step toward understanding the role of thrombin and its receptor in the CNS, Northern blot, in situ hybridization, and immunohistochemical techniques were used to analyze the cellular localization of TR mRNA in weanling-age rat brain. TR mRNA was broadly distributed across the neuraxis, although expression was very focal and often anatomically limited within specific neural structures. The greatest hybridization was associated with individual neurons in neocortex, cingulate/retrosplenial cortex, and subiculum, subsets of nuclei in hypothalamus, thalamus, pretectum, and ventral mesencephalon, and discrete cell layers in the hippocampus, cerebellum, and olfactory bulb. Patterns of hybridization included neuronal, glial, and ependymal cells, although white matter was uniformly negative, as were most cerebrovascular endothelial cells. Expression of TR mRNA by astroglia and dopaminergic neurons was confirmed by colocalization with immunoreactivity for glial fibrillary acidic protein (GFAP) in hippocampus and tyrosine hydroxylase in the substantia nigra. Comparison between TR and prothrombin (thrombin's precursor) cRNA hybridization demonstrated distinct but overlapping brain distributions of these transcripts, most clearly evident in postnatally developing, laminated structures. These results suggest widespread utilization of, and multiple physiologic, and possibly pathophysiologic, functions for, the thrombin/TR cell signaling system in the CNS.

Thrombin receptor activation stimulates astrocyte proliferation and reversal of stellation by distinct pathways: involvement of tyrosine phosphorylation

Treatment of cultured type-1 astrocytes with thrombin leads to cell proliferation and reversal of stellation. The half-maximal concentrations of thrombin required for each response are 500 and 2 pM, respectively. To test whether they might be mediated by different receptors, we examined the contribution of the G protein-coupled thrombin receptor to these responses in purified rat astrocytes by using the agonist peptide SFLLRNP. In the absence of added growth factors, SFLLRNP fully mimicked the effects of thrombin at half-maximal concentrations of 30 microM for an increase in cell number and DNA synthesis and 100 nM for the reversal of stellation. The role of protein tyrosine phosphorylation in these events was investigated using antiphosphotyrosine antibodies. Thrombin and SFLLRNP at concentrations at least 10-fold greater than those required for half-maximal reversal of stellation but below those required for mitogenesis induced an identical pattern of tyrosine phosphorylation on several proteins of 55-65, 106, 110-115, and 120-130 kDa. The response was rapid (< 1 min) and transient with a peak response after approximately 2 min. The specific tyrosine kinase inhibitor herbimycin A did not affect thrombin- or SFLLRNP-mediated reversal of stellation at concentrations of up to 1 microM. In contrast, 1 microM herbimycin fully inhibited the ability of thrombin and SFLLRNP to increase cell number and stimulate DNA synthesis. Furthermore, this inhibition by 1 microM herbimycin A corresponded to inhibition of receptor-induced tyrosine phosphorylation. Thus, cell proliferation but not reversal of stellation is dependent on thrombin receptor-activated tyrosine kinase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Protease nexin-1, a potent thrombin inhibitor, is reduced around cerebral blood vessels in Alzheimer's disease

The clotting protease thrombin might contribute to the pathophysiology of central nervous system (CNS) injury and certain diseases by its ability to retract processes on neurons and astrocytes and to stimulate astrocyte proliferation. Protease nexin-1 (PN-1) is a 43 kDa thrombin inhibitor found predominantly in the brain where much of it resides around capillaries and large blood vessels. This location of PN-1 prompted the hypothesis that it may play a protective role against extravasated thrombin released following cerebrovascular injury or under certain pathological conditions. Recent studies indicated that the levels of PN-1 are markedly reduced in the postmortem brains of patients with Alzheimer's disease (AD). It was suggested that this reduction in PN-1 levels was due to the sequestration of PN-1 by extravasated thrombin. In the present study we examined the specific nature of this reduction by immunohistochemical staining of sections from control and AD brains using PN-1 specific antibodies. We show that the levels of PN-1 immunoreactivity around blood vessels and the number of blood vessels exhibiting PN-1 immunoreactivity were markedly reduced in the brains of patients with AD compared to age-matched controls; this reduction was reflected by a decrease in the levels of PN-1 activity and PN-1 protein. Thus an imbalance between PN-1 and thrombin may be a contributing factor in the pathology of AD.

Thrombin receptor activation induces secretion and nonamyloidogenic processing of amyloid beta-protein precursor

The amyloid beta-protein (A beta) and protease nexin-2/amyloid beta-protein precursor (PN-2/A beta PP) are major constituents of senile plaques and cerebrovascular deposits in individuals with Alzheimer's disease and related disorders. It has been suggested that the coagulation protease thrombin may process A beta PP in a manner leading to the formation of A beta. Here we investigated the effects of thrombin on the secretion and processing of PN-2/A beta PP and the production of A beta in a cellular system. Incubation of glioblastoma cells with thrombin (1-5 nM) resulted in the accumulation of abnormally processed, carboxyl-terminal-truncated forms of secreted PN-2/A beta PP (approximately 85 kDa) in the culture medium. Higher concentrations of thrombin (> 10 nM) also increased the levels of secreted PN-2/A beta PP in cultured untransfected glioblastoma cells and glioblastoma cells that were stably transfected to overproduce the 695 isoform of A beta PP. Increased secretion of PN-2/A beta PP required the proteolytic activity of thrombin, was induced by activation of the thrombin receptor by agonist peptides, and required activation of protein kinase C. Incubation of the untransfected and transfected glioblastoma cells with thrombin led to decreased levels of soluble A beta in the culture medium consistent with previously suggested mechanisms regarding the secretion of PN-2/A beta PP. Although the present studies suggest that thrombin does not directly contribute to A beta formation, its proteolysis of secreted PN-2/A beta PP may disrupt regions near the carboxyl terminus of the secreted proteins that account for their neuroprotective and cell adhesive properties.

Regulation of protease nexin-1 target protease specificity by collagen type IV

Recent studies have shown that serine protease inhibitors can be regulated in their activity, specificity, and location by glycoprotein or extracellular matrix (ECM) co-factors. Protease nexin-1 (PN-1) is a member of the serpin superfamily of serine protease inhibitors which can rapidly inhibit thrombin, urokinase, and plasmin. PN-1 binds tightly to and is regulated by the ECM. This interaction accelerates the inhibition of thrombin by PN-1 and blocks urokinase and plasmin inhibition by PN-1. Previous work showed that heparan sulfate proteoglycan is largely responsible for the acceleration of thrombin inhibition by PN-1. Our current studies were directed at identifying ECM component(s) that decreased the ability of PN-1 to inhibit urokinase and plasmin. These studies showed that collagen type IV decreased the formation of SDS-stable complexes between urokinase or plasmin and PN-1 without affecting formation of complexes between thrombin and PN-1. The second order rate constant for inhibition of urokinase by PN-1 was markedly decreased with increasing collagen type IV, whereas the second order rate constant for inhibition of thrombin by PN-1 was unaffected by addition of collagen type IV. Other ECM components (collagen type I, vitronectin, fibronectin, and heat-denatured collagen type IV) did not affect complex formation or the rate of inhibition of proteases by PN-1, indicating that these effects were specific to collagen type IV. Binding of PN-1 to immobilized collagen type IV was demonstrated using an enzyme-linked immunosorbent assay; the concentration of PN-1 necessary to obtain 50% saturation of the immobilized collagen type IV binding sites was approximately 15 nM. Collagen type IV was also copurified with PN-1 from fibroblast-conditioned medium. These results demonstrate a novel regulation of serpin specificity in which an ECM co-factor decreased the inhibition of certain proteases by the serpin without affecting the inhibition of its target protease.

Co-distribution of protease nexin-1 and protease nexin-2 in brains of non-human primates

The protease nexins are protease inhibitors which regulate key blood coagulation proteases and which appear to be involved in certain physiological and pathological processes in the brain. Protease nexin-1 (PN-1), a potent inhibitor of thrombin, can regulate processes on cultured neurons and astrocytes. Protease nexin-2 (PN-2), a potent inhibitor of coagulation factor XIa, is identical to the secreted form of the Alzheimer's amyloid beta-protein precursor. In the present studies, PN-1 and PN-2 were analyzed in different tissues of monkey using monoclonal antibodies for either quantitative immunoblotting or specific [125I]protease-binding assays. PN-1 was detected only in brain. PN-2 was most abundant in brain, followed by testis and to a lesser extent kidney. Other tissues examined including spinal cord, heart, pancreas, spleen, liver, lung and muscle were essentially devoid of both PN-1 and PN-2. Within the brain, the levels of PN-1 and PN-2 were highest in the parietal cortex and lowest in the cerebellum and brainstem. The thalamus and striatum contained intermediate amounts of both proteins. Aged Cebus monkey cerebral cortical tissue contained slightly lower levels of PN-1 than did the middle-aged or young monkey tissue. The co-distribution of PN-1 and PN-2 in brain, their relative abundance in brain cortex, and previous studies on their functions suggest that in the brain they may participate in the regulation of blood coagulation and cell growth and differentiation.

Protease nexin-1, a thrombin inhibitor, is regulated by interleukin-1 and dexamethasone in normal human fibroblasts

Thrombin participates in several regulatory events following injury as a result of its effects on blood coagulation and cell migration, proliferation, and differentiation. Protease nexin-1 (PN-1) is a potent thrombin inhibitor in the extracellular environment. Since injury-related factors are known to regulate the synthesis and secretion of PN-1, the inhibitor may serve to modulate the actions of thrombin during injury. Here we report the molecular mechanisms that underlie this regulation. In normal human fibroblasts, interleukin-1 (IL-1) beta stimulated the synthesis and secretion of PN-1. The stimulation correlated with an increase in steady-state levels of PN-1 mRNA. Treatment of cells with both cycloheximide and IL-1 reduced the levels of PN-1 mRNA. Nuclear run-on assays indicated that IL-1 modestly increased the rate of PN-1 transcription. However, experiments with actinomycin D demonstrated that IL-1 significantly increased the half-life of the PN-1 mRNA. In contrast, dexamethasone (DXM) repressed the synthesis and secretion of PN-1 from fibroblasts. This effect correlated with a decrease in PN-1 mRNA. A sustained decrease in PN-1 mRNA was also seen when cells were treated with cycloheximide and DXM. In nuclear run-on assays, DXM functioned as a transcriptional repressor of PN-1 synthesis. Treatment of cells with actinomycin D showed that DXM did not affect mRNA stability. Thus, our experiments demonstrate that IL-1 and DXM, which function biologically in different fashions, regulate the synthesis of PN-1 by separate molecular mechanisms. While DXM directly regulates PN-1 at the level of transcription, IL-1 in the presence of ongoing protein synthesis regulates PN-1 production predominantly in a post-transcriptional fashion by increasing the half-life of the PN-1 mRNA.

Regulation of protease nexin-1 synthesis and secretion in cultured brain cells by injury-related factors

The clotting protease thrombin might contribute to cell damage following brain injury by its ability to retract processes on neurons and astrocytes. Protease nexin-1 (PN-1), a potent inhibitor of thrombin, is localized around cerebral blood vessels where it may protect these cells from extravasated thrombin during injury or alteration of the blood-brain barrier. Here we examined the effects of several injury-related factors on the regulation of PN-1 in cultured brain cells. Interleukin-1, tumor necrosis factor-alpha, and transforming growth factor-beta stimulated the secretion of PN-1 by the neuroblastoma cell line SK-N-SH. This cell line comprises both neuronal and glial cells. Analyses using cloned derivatives of these two cell types showed that PN-1 was secreted by the glial cells; PN-1 secretion was stimulated 90-fold by interleukin-1, 15-fold by tumor necrosis factor-alpha, 10-fold by tumor growth factor-beta, and 4-fold by platelet-derived growth factor. Measurements of newly synthesised PN-1 demonstrated that these factors produced an equivalent stimulation of PN-1 synthesis. The neuronal cells secreted two thrombin-binding proteins distinct from PN-1. Interactions between these two cell types regulated the secretion of PN-1 and the two thrombin-binding proteins.

Aggregation of the amyloid precursor protein within degenerating neurons and dystrophic neurites in Alzheimer's disease

Using a monoclonal antibody raised against purified, native, human protease nexin-2/amyloid precursor protein, which recognizes an amino terminal epitope on the amyloid precursor protein and detects all major isoforms of amyloid precursor protein, we examined the localization of the amyloid precursor protein within Alzheimer's and aged control brains. Very light cytoplasmic neuronal amyloid precursor protein staining but no neuritic staining was visible in control brains. In the Alzheimer's brain, we detected numerous amyloid precursor protein-immunopositive neurons with moderate to strong staining in select regions. Many neurons also contained varying levels of discrete granular, intracellular accumulations of amyloid precursor protein, and a few pyramidal neurons in particular appeared completely filled with amyloid precursor protein granules. "Ghost"-like deposits of amyloid precursor protein granules arranged in pyramidal, plaque-like shapes were identified. We detected long, amyloid precursor protein-immunopositive neurites surrounding and entering plaques. Many contained swollen varicosities along their length or ended in bulbous tips. Amyloid precursor protein immunoreactivity in the Alzheimer's brain was primarily present as granular deposits (plaques). The amyloid precursor protein granules do not appear to co-localize within either astrocytes or microglia, as evidenced by double-labeling immunohistochemistry with anti-glial fibrillary acidic protein and anti-leukocyte common antigen antibodies or Rinucus cummunicus agglutin lectin. Amyloid precursor protein could occasionally be detected in blood vessels in Alzheimer's brains. The predominantly neuronal and neuritic localization of amyloid precursor protein immunoreactivity indicates a neuronal source for much of the amyloid precursor protein observed in Alzheimer's disease pathology, and suggests a time-course of plaque development beginning with neuronal amyloid precursor protein accumulation, then deposition into the extracellular space, subsequent processing by astrocytes or microglia, and resulting in beta-amyloid peptide accumulation in plaques.

Platelet protease nexin-2/amyloid beta-protein precursor. Possible pathologic and physiologic functions

The amyloid beta-protein and its parent protein, amyloid beta-protein precursor (APP), are major constituents of neuritic plaques and cerebrovascular deposits in Alzheimer's disease and Down's syndrome. We reported that the protease inhibitor protease nexin-2 (PN-2) is the secreted form of APP that contains the Kunitz protease inhibitor domain. Previous studies suggested that circulating forms of PN-2/APP exist. Recently, we reported that PN-2/APP is a platelet alpha granule protein and is secreted upon platelet activation. Subsequent studies revealed that platelets are the major circulating repository for PN-2/APP and may contribute to its deposition in Alzheimer's disease. Protease inhibition measurements demonstrated that PN-2/APP is a potent inhibitor of certain serine proteases, particularly intrinsic blood coagulation factor XIa. Together, these findings indicate that PN-2/APP regulates blood coagulation, and possibly other proteolytic events, at sites of vascular injury.

The predominant form of the amyloid beta-protein precursor in human brain is protease nexin 2

The amyloid beta protein and the amyloid beta-protein precursor (APP) are major constituents of senile plaques and cerebrovascular deposits in patients with Alzheimer disease and Down syndrome. Most human tissues contain mRNA that encodes forms of APP that contain the Kunitz protease inhibitor (KPI+) domain. A major 120-kDa protein corresponding to this KPI+ mRNA is also found in these tissues. This protein is identical to the protease inhibitor protease nexin 2. Brain contains an additional mRNA species that encodes a form of APP that lacks the KPI domain (KPI-). This latter mRNA has been suggested to encode a 105-kDa KPI- form of APP protein also found in brain. Using protease inhibitory functional assays, we show that both the 105-kDa and 120-kDa APP proteins in normal and Alzheimer disease brain contain the KPI domain. Moreover, KPI domain-specific precipitation assays reveal that KPI- forms of APP protein represent less than 14% of total brain APP. Lastly, an enriched fraction from total brain homogenate contains proteolytic activity that can process the purified 120-kDa KPI+ form of APP into a 105-kDa form, resulting in a high-molecular-mass doublet identical to that seen in brain. These findings indicate that although KPI- APP mRNA is abundant in brain, little corresponding protein is present. Thus, KPI+ APP protein (equivalent to protease nexin 2) is the predominant form of APP in human brain.

Protease nexin-2/amyloid beta-protein precursor in blood is a platelet-specific protein

The protease inhibitor, protease nexin-2 (PN-2), is the secreted form of the amyloid beta-protein precursor (APP) which contains the Kunitz protease inhibitor domain. PN-2/APP is an abundant platelet alpha-granule protein which is secreted upon platelet activation. PN-2/APP mRNA is present in cultured endothelial cells and the protein has been detected in plasma. In the present studies we quantitated PN-2/APP in platelets, plasma and several different cell types of the vasculature to identify the repository of the protein in the circulatory system. We report that PN-2/APP is predominantly a platelet protein in the vascular compartment. Lysates of unstimulated umbilical vein endothelial cells, granulocytes or monocytes contained little PN-2/APP based on sensitive functional protease binding and immunoblotting assays. Quantitative immunoblotting studies demonstrated that normal citrated-plasma contains less than or equal to 60 pM PN-2/APP. In contrast, platelets can contribute up to 30 nM PN-2/APP, indicating that they are the major source of the protein in blood.

Inhibitors of urokinase and thrombin in cultured neural cells

Recent studies have suggested important roles for certain proteases and protease inhibitors in the growth and development of the CNS. In the present studies, inhibitors of urokinase or thrombin in cultured neural cells and serum-free medium from the cells were identified by screening for components that formed sodium dodecyl sulfate-stable complexes with 125I-urokinase or 125I-thrombin. Rinsed glioblastoma possessed two components that complexed 125I-urokinase. One was type 1 plasminogen activator inhibitor (PAI-1), because the 125I-urokinase-containing complexes were immunoprecipitated with anti-PAI-1 antibodies. The other component formed complexes with 125I-urokinase that were not recognized by antibodies to PAI-1 or protease nexin-1 (PN-1). Its identity is unknown. In addition to these cell-bound components, the glioblastoma cells also secreted two inhibitors that formed complexes with 125I-urokinase; one was PAI-1, and the other was PN-1. The secreted PN-1 also formed complexes with 125I-thrombin. It was the only thrombin inhibitor detected in these studies. Human neuroblastoma cells did not contain components that formed detectable complexes with either 125I-urokinase or 125I-thrombin. However, human neuroblastoma cells did contain very low levels of PN-1 mRNA and PN-1 protein. Added PN-1 bound to the surface of both glioblastoma and neuroblastoma cells. This interaction accelerated the inhibition of thrombin by PN-1 and blocked the ability of PN-1 to form complexes with 125I-urokinase. Thus, cell-bound PN-1 was a specific thrombin inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)

Protease nexin-1. Localization in the human brain suggests a protective role against extravasated serine proteases

Protease nexin-1 (PN-1) is a potent thrombin inhibitor that is identical to the glia-derived neurite-promoting factor or glia-derived nexin. Here we report immunocytochemical studies of adult human cerebral cortex that revealed the presence of strong immunoreactivity for PN-1 in capillaries and in the smooth muscle cells of arteries and arterioles. Expression of PN-1 was also abundant in astroglial processes in the parenchyma and in perivascular astroglial endfeet of human cerebral cortex. In situ hybridization with an 35S-labeled RNA antisense probe for PN-1 resulted in significant labeling of astrocytes and blood vessels. Because thrombin is known to cause retraction of neurites and modification of astrocytic morphology at low concentrations, PN-1 around blood vessels may play a major protective role against extravasation of thrombin and possibly other serine protease into the human brain.

Immunopurification and protease inhibitory properties of protease nexin-2/amyloid beta-protein precursor

Protease nexin-2 (PN-2) is a protease inhibitor that is synthesized and secreted by a variety of extravascular cells including human fibroblasts. It forms sodium dodecyl sulfate-stable complexes with trypsin, the epidermal growth factor binding protein and the gamma-subunit of nerve growth factor. Recently we reported that PN-2 is the secreted form of the amyloid beta-protein precursor (APP) and is a potent inhibitor of chymotrypsin. Here we describe a two-step procedure to purify PN-2/APP using a monoclonal antibody immunoaffinity column. We also quantitated the protease inhibitory properties of purified PN-2/APP on a number of serine proteases. PN-2/APP was a potent inhibitor of coagulation factor XIa with a Ki = 2.9 x 10(-10). The inhibition of factor XIa by PN-2/APP was augmented by heparin and resulted in a Ki = 5.5 x 10(-11) M. Trypsin and chymotrypsin were also effectively inhibited with a Ki = 4.2 x 10(-10) and 1.6 x 10(-9), respectively. PN-2/APP also inhibited the epidermal growth factor binding protein, the gamma-subunit of nerve growth factor, and chymase and plasmin to a lesser extent. In view of recent findings that PN-2/APP is contained in alpha-granules of platelets and is secreted upon platelet activation, the potent inhibition of factor XIa suggests that PN-2/APP may play a regulatory role in the coagulation pathway at vascular wound sites. In addition, these studies define biochemical activities of PN-2/APP which may be involved in regulating proteases that lead to the generation and deposition of the beta-protein in neurodegenerative lesions associated with Alzheimer's disease and Down's syndrome.

Protease nexin-II (amyloid beta-protein precursor): a platelet alpha-granule protein

Protease nexin-II (PN-II) [amyloid beta-protein precursor (APP)] and the amyloid beta-protein are major constituents of neuritic plaques and cerebrovascular deposits in individuals with Alzheimer's disease and Down syndrome. Both the brain and the circulation have been implicated as sources of these molecules, although they have not been detected in blood. Human platelets have now been found to contain relatively large amounts of PN-II/APP. Platelet PN-II/APP was localized in platelet alpha-granules and was secreted upon platelet activation. Because PN-II/APP is a potent protease inhibitor and possesses growth factor activity, these results implicate PN-II/APP in wound repair. In certain disease states, alterations in platelet release and processing and clearance of PN-II/APP and its derived fragments could lead to pathological accumulation of these proteins.

Reciprocal modulation of astrocyte stellation by thrombin and protease nexin-1

When cultured astroglia are treated with agents that elevate intracellular cyclic AMP, they become process-bearing stellate cells and resemble differentiated astrocytes in vivo. Thrombin rapidly reversed the stellation induced by dibutyryl cyclic AMP, forskolin, or isoproterenol in cultured rat astrocytes; half-maximal and maximal effects occurred at 0.5 and 8 pM, respectively. The proteolytic activity of thrombin was required for stellation reversal, as thrombin derivatized at its catalytic site serine with a diisopropylphospho group was inactive. Two thrombin inhibitors, protease nexin-1 and hirudin, blocked and reversed the effect of thrombin. The stellation reversal effect of thrombin was specific, as 300-1,000-fold higher concentrations of other serine proteinases, including plasmin, urokinase, trypsin, and T cell serine proteinase-1, were ineffective. Thrombin is a mitogen for astrocytes at concentrations in excess of 30 pM. Thrombin increased both cell number and ornithine decarboxylase activity, an early marker for mitogenic stimulation, in astrocyte cultures. The lowest thrombin concentrations that completely reversed astrocyte stellation, however, did not increase ornithine decarboxylase activity. Moreover, several other mitogens for astrocytes did not reverse dibutyryl cyclic AMP-induced stellation. Thus, the stellation reversal effect of thrombin is distinct from the mitogenic response.

Neurite outgrowth activity of protease nexin-1 on neuroblastoma cells requires thrombin inhibition

Protease nexin-1 (PN-1) is a protein proteinase inhibitor recently shown to be identical with the glial-derived neurite-promoting factor or glial-derived nexin. It has been shown to promote neurite outgrowth in neuroblastoma cells and in sympathetic neurons. The present experiments were designed to further test the hypothesis that this activity on neuroblastoma cells is due to its ability to complex and inhibit thrombin. It has been suggested that PN-1:thrombin complexes might mediate the neurite outgrowth activity of PN-1. However, the present studies showed that such complexes, unlike free PN-1, did not promote neurite outgrowth. The neurite outgrowth activity of PN-1 was only detected in the presence of thrombin or serum (which contains thrombin). PN-1 did not affect the rate or extent of neurite outgrowth that occurred when neuroblastoma cells were placed in serum-free medium. Retraction of neurites by thrombin was indistinguishable in cells whose neurites had been extended in the presence or absence of PN-1. The neurite-promoting activity of PN-1 was inhibited by an anti-PN-1 monoclonal antibody, which blocks its capacity to complex serine proteinases. The plasma thrombin inhibitor, antithrombin III, stimulated neurite outgrowth but only when its thrombin inhibitory activity was accelerated by heparin. The neurite outgrowth activity of both antithrombin III and PN-1 corresponded to their inhibition of thrombin. Together, these observations show that PN-1 promotes neurite outgrowth from neuroblastoma cells by inhibiting thrombin and suggest that this depends on the ability of thrombin to retract neurites.

Protease nexin-1, an antithrombin with neurite outgrowth activity, is reduced in Alzheimer disease

Protease nexin-1 (PN-1) is a cell-secreted protein that inhibits certain proteases, particularly thrombin, by forming SDS-stable complexes with the catalytic site serine of the protease. PN-1 was recently shown to be identical to a glial-derived neurite-promoting factor/glial-derived nexin present in rat brain. Its neurite outgrowth activity depends on inhibition of thrombin, presumably because thrombin brings about neurite retraction. Here we show that human brain contains PN-1 and that PN-1 activity in brains of individuals with Alzheimer disease (AD) was only 14% of control values (total of 14 AD patients and 7 control individuals). PN-1 activity in the hippocampus, a region with marked neuropathology in AD, was 15% of control values (10 AD patients and 4 control individuals). Western blot analysis indicated a large decrease in free PN-1 protein and an increase in PN-1-containing complexes that comigrated with PN-1-thrombin complexes. Northern blot analysis indicated that PN-1 mRNA levels were about equal in brains from AD patients and control individuals. Thus these results suggest that the decreases in PN-1 activity and free PN-1 protein are due to formation of PN-1-protease complexes.

Protease nexin-II, a potent antichymotrypsin, shows identity to amyloid beta-protein precursor

Protease nexin-II (PN-II) is a protease inhibitor that forms SDS-resistant inhibitory complexes with the epidermal growth factor (EGF)-binding protein, the gamma-subunit of nerve growth factor, and trypsin. The properties of PN-II indicate that it has a role in the regulation of certain proteases in the extracellular environment. Here we describe more of the amino-acid sequence of PN-II and its identity to the deduced sequence of the amyloid beta-protein precursor (APP). Amyloid beta-protein is present in neuritic plaques and cerebrovascular deposits in individuals with Alzheimer's disease and Down's syndrome. A monoclonal antibody against PN-II (designated mAbP2-1) recognized PN-II in immunoblots of serum-free culture medium from human glioblastoma cells and neuroblastoma cells, as well as in homogenates of normal and Alzheimer's disease brains. In addition, mAbP2-1 stained neuritic plaques in Alzheimer's disease brain. PN-II was a potent inhibitor of chymotrypsin with an inhibition constant Ki of 6 x 10(-10)M. Together, these data demonstrate that PN-II and APP are probably the same protein. The regulation of extracellular proteolysis by PN-II and the deposition of at least parts of the molecule in senile plaques is consistent with previous reports that implicate altered proteolysis in the pathogenesis of Alzheimer's disease.