Tissue-type plasminogen activator induces opening of the blood-brain barrier via the LDL receptor-related protein

The regulation of cerebrovascular permeability is critical for normal brain homeostasis, and the "breakdown" of the blood-brain barrier (BBB) is associated with the development of vasogenic edema and intracranial hypertension in a number of neurological disorders. In this study we demonstrate that an increase in endogenous tissue-type plasminogen activator (tPA) activity in the perivascular tissue following cerebral ischemia induces opening of the BBB via a mechanism that is independent of both plasminogen (Plg) and MMP-9. We also show that injection of tPA into the cerebrospinal fluid in the absence of ischemia results in a rapid dose-dependent increase in vascular permeability. This activity is not seen with urokinase-type Plg activator (uPA) but is induced in Plg-/- mice, confirming that the effect is Plg-independent. However, the activity is blocked by antibodies to the LDL receptor-related protein (LRP) and by the LRP antagonist, receptor-associated protein (RAP), suggesting a receptor-mediated process. Together these studies demonstrate that tPA is both necessary and sufficient to directly increase vascular permeability in the early stages of BBB opening, and suggest that this occurs through a receptor-mediated cell signaling event and not through generalized degradation of the vascular basement membrane.

Plasminogen activator inhibitor-1 in tumor growth, angiogenesis and vascular remodeling

Plasminogen activator inhibitor-1 (PAI-1) is the principal inhibitor of urokinase type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA), and as such is thought to play an important role in the regulation of extracellular matrix remodeling. In blood, PAI-1 is bound to the adhesion protein vitronectin and is associated with vitronectin in fibrin clots and the provisional matrix. Elevated levels of PAI-1 are associated with atherosclerosis and an increased thrombotic tendency, while PAI-1 deficiency leads to increased fibrinolysis and bleeding. PAI-1 is also elevated in many solid tumors and is associated with a poor prognosis in cancer. PAI-1 has been shown to be a potent regulator of both vascular cell migration in vitro and of angiogenesis and tumor growth in vivo. PAI-1 can both promote and inhibit tumor growth and angiogenesis. Low concentrations of PAI-1 can stimulate tumor angiogenesis while treatment of animals with high doses of PAI-1 inhibits angiogenesis and tumor growth. Hence, PAI-1 appears to have a multifunctional role in regulating the migratory and fibrinolytic activity of vascular cells, and this, in turn, may help to explain the many varied actions of PAI-1.

Sequences within domain II of the urokinase receptor critical for differential ligand recognition

The receptor for urokinase-type plasminogen activator (uPAR) plays important roles in a number of physiological and pathological processes by virtue of its interactions with urokinase-type plasminogen activator (uPA), vitronectin (Vn), and several other proteins. The uPA binding site spans all three domains (D1 to D3) of uPAR. However, the nature of the Vn binding site within uPAR is still not clear. In this study, we conducted homolog-scanning mutagenesis on uPAR by switching 14 individual segments of 4-8 residues to their counterpart sequences of a uPAR homolog CD59. All 14 mutants were well expressed, reacted with a panel of monoclonal antibodies, and exhibited correct molecular weights. Of these 14 mutants, six mutants were defective in both uPA and Vn binding. Most importantly, we found two unique mutants uPAR(Asn172-Lys175) and uPAR(Glu183-Asn186) within the D2 domain, which displayed differential ligand binding activity: both had high affinity uPA binding, but completely lost Vn binding, indicating that these two sequences constitute a novel Vn binding site. Indeed, two peptides, P1 (153CPGSNGFHNNDTFHFLKC) and P2 (171CNTTKCNEGPILELENLPQ), derived from the sequences of the identified uPA and Vn binding pockets within D2, respectively, behaved like bona fide ligand binding sites: peptide P1 bound uPA but not Vn, whereas peptide P2 bound Vn and inhibited uPAR-mediated cell adhesion, but did not interact with uPA. Altogether, our data demonstrated that uPAR D2 contains two distinct ligand binding sites for uPA and Vn. Such information will help us better understand the complex roles of uPAR in cell adhesion, migration, and tumor metastasis.

A mutant, noninhibitory plasminogen activator inhibitor type 1 decreases matrix accumulation in experimental glomerulonephritis

In fibrotic renal disease, elevated TGF-beta and angiotensin II lead to increased plasminogen activator inhibitor type 1 (PAI-1). PAI-1 appears to reduce glomerular mesangial matrix turnover by inhibiting plasminogen activators, thereby decreasing plasmin generation and plasmin-mediated matrix degradation. We hypothesized that therapy with a mutant human PAI-1 (PAI-1R) that binds to matrix vitronectin but does not inhibit plasminogen activators, would enhance plasmin generation, increase matrix turnover, and decrease matrix accumulation in experimental glomerulonephritis. Three experimental groups included normal, untreated disease control, and PAI-1R-treated nephritic rats. Plasmin generation by isolated day 3 glomeruli was dramatically decreased by 69%, a decrease that was reversed 43% (P < 0.02) by in vivo PAI-1R treatment. At day 6, animals treated with PAI-1R showed significant reductions in proteinuria (48%, P < 0.02), glomerular staining for periodic acid-Schiff positive material (33%, P < 0.02), collagen I (28%, P < 0.01), collagen III (34%, P < 0.01), fibronectin (48%, P < 0.01), and laminin (41%, P < 0.01), and in collagen I (P < 0.01) and fibronectin mRNA levels (P < 0.02). Treatment did not alter overexpression of TGF-beta1 and PAI-1 mRNAs, although TGF-beta1 protein was significantly reduced. These observations strongly support our hypothesis that PAI-1R reduces glomerulosclerosis by competing with endogenous PAI-1, restoring plasmin generation, inhibiting inflammatory cell infiltration, decreasing local TGF-beta1 concentration, and reducing matrix accumulation.

Old dogs and new tricks: proteases, inhibitors, and cell migration

A new model for the actions of plasminogen activator inhibitors (PAIs) on cell migration may resolve the conflicting research data on these proteins in metastasis and angiogenesis. Results from two groups reveal a role for PAI-1 in promoting cycles of attachment and detachment of the cell from the extracellular matrix that is independent of its role as an enzymatic inhibitor of urokinase-type plasminogen activator (uPA). Through the formation of a complex of integrins, uPA and its receptor, and the clearance receptors of the low-density lipoprotein family, PAI-1 may promote endocytosis and recycling of these adhesion-controlling proteins, allowing cycling of cellular attachment and detachment.

Impaired fibrinolysis in multiple sclerosis: a role for tissue plasminogen activator inhibitors

Tissue plasminogen activator (tPA), a neuronal as well as the key fibrinolytic enzyme, is found concentrated on demyelinated axons in multiple sclerosis lesions together with fibrin(ogen) deposits. The decreased tPA activity in normal-appearing white and grey matter and lesions of multiple sclerosis is reflected in diminished fibrinolysis as measured by a clot lysis assay. Nonetheless, peptide products of fibrin, including D-dimer, accumulate on demyelinated axons-the result of fibrinogen entry through a compromised blood-brain barrier (BBB). Analysis of tissue samples on reducing and non-reducing polyacrylamide gels demonstrates complexes of tPA with plasminogen activator inhibitor-1 (PAI-1) but not with neuroserpin, a tPA-specific inhibitor concentrated in grey matter. As total tPA protein remains unchanged in acute lesions and the concentration of PAI-1 rises several fold, complex formation is a probable cause of the impaired fibrinolysis. Although the tPA-plasmin cascade promotes neurodegeneration in excitotoxin-induced neuronal death, in inflammatory conditions with BBB disruption it has been demonstrated to have a protective role in removing fibrin, which exacerbates axonal injury. The impaired fibrinolytic capacity resulting from increased PAI-1 synthesis and complex formation with tPA, which is detectable prior to lesion formation, therefore has the potential to contribute to axonal damage in multiple sclerosis.

Progressive ankylosis (Ank) protein is expressed by neurons and Ank immunohistochemical reactivity is increased by limbic seizures

Ank is a 492-amino acid multipass transmembrane protein involved in the regulation of extracellular inorganic pyrophosphate levels and the control of tissue calcification. Previous Northern blot hybridization experiments revealed that Ank mRNA was expressed in the brain, but there have been no reports describing the anatomical sites or specific cell types in the brain that express Ank protein. In this study, we demonstrate that Ank is expressed primarily in human brain neurons, with the highest levels of expression observed in the thalamus, the III and V cortical layers, the Purkinje cells of the cerebellum, clusters of cells in the dorsal portion of the pons and midbrain, and neurons of the anterior horn of the spinal cord. In primary mouse neuronal cell cultures, Ank is detected on both the cell body and on cell extensions, mainly dendrites. In the rat brain, Ank mRNA is expressed at relatively high levels in the thalamus, midbrain, and spinal cord, and the Ank protein expression pattern is similar to that observed in the human brain. Finally, we observed a significant increase in Ank immunoreactivity in the rat amygdala, the CA-2 and CA-3 layers of the hippocampus, and the cerebral cortex after the induction of seizure activity. Ank regulation of ATP and/or inorganic pyrophosphate release from neurons may function to modulate the membrane excitability and cell death associated with seizure activity.

Mapping of a conformational epitope on plasminogen activator inhibitor-1 by random mutagenesis. Implications for serpin function

The mechanism for the conversion of plasminogen activator inhibitor-1 (PAI-1) from the active to the latent conformation is not well understood. Recently, a monoclonal antibody, 33B8, was described that rapidly converts PAI-1 to the latent conformation (Verhamme, I., Kvassman, J. O., Day, D., Debrock, S., Vleugels, N., Declerck, P. J., and Shore, J. D. (1999) J. Biol. Chem. 274, 17511-17517). In an attempt to understand this interaction, and more broadly to understand the mechanism of the natural transition of PAI-1 to the latent conformation, we have used random mutagenesis to identify the 33B8 epitope in PAI-1. This site involves at least 8 amino acids scattered over more than two-thirds of the linear sequence that form a compact epitope on the PAI-1 three-dimensional structure. Surface plasmon resonance studies indicate a high affinity interaction between latent PAI-1 and 33B8 that is approximately 100-fold higher than comparable binding to active PAI-1. Structural modeling results together with surface plasmon resonance analysis of parental and site-directed PAI-1 mutants with disrupted 33B8 binding suggest the existence of a specific PAI-1 intermediate structure that is stabilized by 33B8 binding. These analyses strongly suggest that this intermediate form of PAI-1 has a partial insertion of the reactive center loop into beta-sheet A, and together, these data have significant implications for the general serpin mechanism of proteinase inhibition.

Plasminogen promotes sarcoma growth and suppresses the accumulation of tumor-infiltrating macrophages

The specific functions of plasminogen, stromal plasminogen activator, stromal plasminogen activator receptor, and stromal plasminogen activator inhibitor in the progression of the murine soft tissue sarcoma, T241 were investigated. Negation of plasminogen to the tumor blunted the orthotopic growth of the sarcoma in syngeneic mice. The reduced tumor growth was associated with a dramatic increase in tumor-infiltrating F4/80-positive macrophages and a diminution of vessel density, but not with obvious differences in fibrin and collagen deposition, or invasiveness of the tumor. Ablation of plasminogen activation by the tumor stroma only modestly impaired the prolonged growth of the sarcoma, suggesting that tumor cell-produced plasminogen activator is sufficient to mediate productive plasminogen activation. Plasminogen facilitated sarcoma progression, angiogenesis, and suppression of macrophage infiltration in the absence of either stromal urokinase plasminogen activator receptor or stromal plasminogen activator inhibitor. These data demonstrate that tumor cell-produced plasminogen activator and host plasminogen cooperate to facilitate soft tissue sarcoma growth and suppress the accumulation of tumor-infiltrating macrophages.

Acyl-enzyme complexes between tissue-type plasminogen activator and neuroserpin are short-lived in vitro

The serine protease tissue-type plasminogen activator (t-PA) initiates the fibrinolytic protease cascade and plays a significant role in motor learning, memory, and neuronal cell death induced by excitotoxin and ischemia. In the fibrinolytic system, the serpin PAI-1 negatively regulates the enzymatic activity of both single-chain and two-chain t-PA (sct-PA and tct-PA). In the central nervous system, neuroserpin (NSP) is a serpin thought to regulate t-PA enzymatic activity. We report that although both sct-PA and tct-PA rapidly form acyl-enzyme complexes with NSP in vitro, the interactions are short-lived, rapidly progressing to complete cleavage of NSP and regeneration of fully active enzyme. All NSP molecules appear to transit through the detectable acyl-enzyme intermediate and progress to completion of cleavage; no subpopulation that functions as a pure substrate was detected. Likewise, all molecules were reactive, with no evidence of a latent subpopulation. The interactions between NSP and t-PA were distinct from those between plasmin and NSP, wherein the same peptide bond was cleaved but there was no evidence of a detectable plasmin-NSP acyl-enzyme complex. The interactions between t-PA and NSP contrast with the formation of long-lived, physiologically irreversible acyl-enzyme complexes between t-PA and PAI-1, suggesting that the physiologic effect of t-PA-NSP interactions may be more complex than previously thought.

Adjuvant treatment with neuroserpin increases the therapeutic window for tissue-type plasminogen activator administration in a rat model of embolic stroke

BACKGROUND

After stroke, the thrombolytic effect of tissue-type plasminogen activator (tPA) in the intravascular space is beneficial, whereas its extravascular effect on ischemic neurons is deleterious. We tested the hypothesis that neuroserpin, a natural inhibitor of tPA, reduces tPA-induced neuronal toxicity and increases its therapeutic window for treatment of embolic stroke.

METHODS AND RESULTS

Rats were subjected to embolic middle cerebral artery occlusion (MCAO). Ischemic brains were treated with neuroserpin in combination with recombinant human tPA (n=7), tPA alone (n=7), or saline (n=9). Neuroserpin (20 micro L of 16 micro mol/L active neuroserpin) was intracisternally injected 3 hours and tPA (10 mg/kg) was intravenously administered 4 hours after ischemia. MRI measurements were performed to study blood brain barrier (BBB) leakage and ischemic lesion volume. Administration of tPA alone 4 hours after ischemia significantly (P<0.05) increased BBB leakage in the ischemic core measured by Gd-DTPA-enhanced MRI compared with rats treated with saline. However, treatment with neuroserpin in combination with tPA significantly (P<0.05) reduced BBB leakage, brain edema, and ischemic lesion volume compared with rats treated with tPA alone, although ischemic lesion volumes were the same in both groups before the treatment. Immunostaining revealed that MCAO resulted in reduction of neuroserpin immunoreactivity in the ipsilateral hemisphere after 2 to 6 hours of ischemia. Zymographic assay showed increased plasminogen activity in areas with BBB leakage in rats treated with tPA.

CONCLUSIONS

Administration of neuroserpin after stroke is neuroprotective, seemingly because it blocks the extravascular effect of tPA, leading to subsequent decrease in stroke volume and widening of the therapeutic window for the thrombolytic effect of tPA.

Association between conformational mutations in neuroserpin and onset and severity of dementia

BACKGROUND

The aggregation of specific proteins is a common feature of the familial dementias, but whether the formation of neuronal inclusion bodies is a causative or incidental factor in the disease is not known. To clarify this issue, we investigated five families with typical neuroserpin inclusion bodies but with various neurological manifestations.

METHODS

Five families with neurodegenerative disease and typical neuronal inclusions had biopsy or autopsy material available for further examination. Immunostaining confirmed that the inclusions were formed of neuroserpin aggregates, and the responsible mutations in neuroserpin were identified by sequencing of the neuroserpin gene (SERPINI1) in DNA from blood samples or from extraction of histology specimens. Molecular modelling techniques were used to predict the effect of the gene mutations on three-dimensional protein structure. Brain sections were stained and the topographic distribution of the neuroserpin inclusions plotted.

FINDINGS

Each of the families was heterozygous for an amino acid substitution that affected the conformational stability of neuroserpin. The least disruptive of these mutations (S49P), as predicted by molecular modelling, resulted in dementia after age 45 years, and presence of neuroserpin inclusions in only a few neurons. By contrast, the most severely disruptive mutation (G392E) resulted, at age 13 years, in progressive myoclonus epilepsy, with many inclusions present in almost all neurons.

INTERPRETATION

The findings provide evidence that inclusion-body formation is in itself a sufficient cause of neurodegeneration, and that the onset and severity of the disease is associated with the rate and magnitude of neuronal protein aggregation.

Regulation of seizure spreading by neuroserpin and tissue-type plasminogen activator is plasminogen-independent

Tissue-type plasminogen activator (tPA) is a highly specific serine proteinase expressed in the CNS during events that require neuronal plasticity. In this study we demonstrate that endogenous tPA mediates the progression of kainic acid-induced (KA-induced) seizures by promoting the synchronization of neuronal activity required for seizure spreading, and that, unlike KA-induced cell death, this activity is plasminogen-independent. Specifically, seizure induction by KA injection into the amygdala induces tPA activity and cell death in both hippocampi, and unilateral treatment of rats with neuroserpin, a natural inhibitor of tPA in the brain, enhances neuronal survival in both hippocampi. Inhibition of tPA within the hippocampus by neuroserpin treatment does not prevent seizure onset but instead markedly delays the progression of seizure activity in both rats and wild-type mice. In tPA-deficient mice, seizure progression is significantly delayed, and neuroserpin treatment does not further delay seizure spreading. In contrast, plasminogen-deficient mice show a pattern of seizure spreading and a response to neuroserpin that is similar to that of wild-type animals. These findings indicate that tPA acts on a substrate other than plasminogen and that the effects of neuroserpin on seizure progression and neuronal cell survival are mediated through the inhibition of tPA.

Platelet-derived growth factor (PDGF)-induced tyrosine phosphorylation of the low density lipoprotein receptor-related protein (LRP). Evidence for integrated co-receptor function betwenn LRP and the PDGF

The low density lipoprotein receptor-related protein (LRP) functions in the catabolism of numerous ligands including proteinases, proteinase inhibitor complexes, and lipoproteins. In the current study we provide evidence indicating an expanded role for LRP in modulating cellular signaling events. Our results show that platelet-derived growth factor (PDGF) BB induces a transient tyrosine phosphorylation of the LRP cytoplasmic domain in a process dependent on PDGF receptor activation and c-Src family kinase activity. Other growth factors, including basic fibroblast growth factor, epidermal growth factor, insulin-like growth factor-1, were unable to mediate tyrosine phosphorylation of LRP. The basis for this selectivity may result from the ability of LRP to bind PDGFBB, because surface plasmon resonance experiments demonstrated that only PDGF, and not basic fibroblast growth factor, epidermal growth factor, or insulin-like growth factor-1, bound to purified LRP immobilized on a sensor chip. The use of LRP mini-receptor mutants as well as in vitro phosphorylation studies demonstrated that the tyrosine located within the second NPXY motif found in the LRP cytoplasmic domain is the primary site of tyrosine phosphorylation by Src and Src family kinases. Co-immunoprecipitation experiments revealed that PDGF-mediated tyrosine phosphorylation of LRPs cytoplasmic domain results in increased association of the adaptor protein Shc with LRP and that Shc recognizes the second NPXY motif within LRPs cytoplasmic domain. In the accompanying paper, Boucher et al. (Boucher, P., Liu, P. V., Gotthardt, M., Hiesberger, T., Anderson, R. G. W., and Herz, J. (2002) J. Biol. Chem. 275, 15507-15513) reveal that LRP is found in caveolae along with the PDGF receptor. Together, these studies suggest that LRP functions as a co-receptor that modulates signal transduction pathways initiated by the PDGF receptor.

Structural similarity of the covalent complexes formed between the serpin plasminogen activator inhibitor-1 and the arginine-specific proteinases trypsin, LMW u-PA, HMW u-PA, and t-PA: use of site-specific fluorescent probes of local environment

We have used two fluorescent probes, NBD and dansyl, attached site-specifically to the serpin plasminogen activator inhibitor-1 (PAI-1) to address the question of whether a common mechanism of proteinase translocation and full insertion of the reactive center loop is used by PAI-1 when it forms covalent SDS-stable complexes with four arginine-specific proteinases, which differ markedly in size and domain composition. Single-cysteine residues were incorporated at position 119 or 302 as sites for specific reporter labeling. These are positions approximately 30 A apart that allow discrimination between different types of complex structure. Fluorescent derivatives were prepared for each of these variants using both NBD and dansyl as reporters of local perturbations. Spectra of native and cleaved forms also allowed discrimination between direct proteinase-induced changes and effects solely due to conformational change within the serpin. Covalent complexes of these derivatized PAI-1 species were made with the proteinases trypsin, LMW u-PA, HMW u-PA, and t-PA. Whereas only minor perturbations of either NBD and dansyl were found for almost all complexes when label was at position 119, major perturbations in both wavelength maximum (blue shifts) and quantum yield (both increases and decreases) were found for all complexes for both NBD and dansyl at position 302. This is consistent with all four complexes having similar location of the proteinase catalytic domain and hence with all four using the same mechanism of full-loop insertion with consequent distortion of the proteinase wedged in at the bottom of the serpin.

Death receptor recruitment of endogenous caspase-10 and apoptosis initiation in the absence of caspase-8

Caspase-8 is believed to play an obligatory role in apoptosis initiation by death receptors, but the role of its structural relative, caspase-10, remains controversial. Although earlier evidence implicated caspase-10 in apoptosis signaling by CD95L and Apo2L/TRAIL, recent studies indicated that these death receptor ligands recruit caspase-8 but not caspase-10 to their death-inducing signaling complex (DISC) even in presence of abundant caspase-10. We characterized a series of caspase-10-specific antibodies and found that certain commercially available antibodies cross-react with HSP60, shedding new light on previous results. The majority of 55 lung and breast carcinoma cell lines expressed mRNA for both caspase-8 and -10; however, immunoblot analysis revealed that caspase-10 protein expression was more frequently absent than that of caspase-8, suggesting a possible selective pressure against caspase-10 production in cancer cells. In nontransfected cells expressing both caspases, CD95L and Apo2L/TRAIL recruited endogenous caspase-10 as well as caspase-8 to their DISC, where both enzymes were proteolytically processed with similar kinetics. Caspase-10 recruitment required the adaptor FADD/Mort1, and caspase-10 cleavage in vitro required DISC assembly, consistent with the processing of an apoptosis initiator. Cells expressing only one of the caspases underwent ligand-induced apoptosis, indicating that each caspase can initiate apoptosis independently of the other. Thus, apoptosis signaling by death receptors involves not only caspase-8 but also caspase-10, and both caspases may have equally important roles in apoptosis initiation.

Latent-TGF-beta: an overview

The latency associated with the transforming growth factor-betas (TGF-betas) was discovered in 1984. Since the two publications on this subject in that year, there has been on average over sixty reports in which latency was the dominant theme for each of the past 10 years, proof enough of the interest in this field of growth factor research. As the mature 25 kD forms of the TGF-betas are required for them to exert their many, diverse biological effects, it was inevitable that an explanation of the structure and of the activation of the latent complexes be sought. This overview provides a description of these essential points. Now that it has been clearly shown that dysregulation of particular components of the TGF-beta signalling pathway is implicated in many human diseases, the activation of the latent TGF-beta complexes has taken on added importance. Technical improvements enable the distinction of active and latent TGF-beta proteins in vivo and have started to reveal anomalies in the control of activation in relation to various pathological situations.

Plasminogen activator inhibitor-1 regulates tumor growth and angiogenesis

Elevated expression of plasminogen activator inhibitor-1 (PAI-1) in tumors is associated with a poor prognosis in many cancers. Reduced tumor growth and angiogenesis have also been reported in mice deficient in PAI-1. These results suggest that PAI-1 may be required for efficient angiogenesis and tumor growth. In the present study, we demonstrate that PAI-1 can both enhance and inhibit the growth of M21 human melanoma tumors in nude mice and that this appears to be due to PAI-1 regulation of angiogenesis. Quantitative analysis of angiogenesis in a Matrigel implant assay indicated that in PAI-1 null mice angiogenesis was reduced approximately 60% compared with wild-type mice, while in mice overexpressing PAI-1, angiogenesis was increased nearly 3-fold. Furthermore, addition of PAI-1 to implants in wild-type mice enhanced angiogenesis up to 3-fold at low concentrations but inhibited angiogenesis nearly completely at high concentrations. Together, these data demonstrate that PAI-1 is a potent regulator of angiogenesis and hence of tumor growth and suggest that understanding the mechanism of this activity may lead to the development of important new therapeutic agents for controlling pathologic angiogenesis.

Mechanisms for the cytotoxicity of cysteamine

The major aim of this study was to quantitatively assess the contribution of H2O2 generation to the cytotoxicity induced by cysteamine. Cysteamine produces H2O2 at levels that correlate with its toxicity between 23 and 160 microM. A maximum of 6.9 microM H2O2 is generated by 625 microM cysteamine. When compared to the toxicity of exogenous H2O2, cysteamine-derived peroxide accounted for 57% of its toxicity. This corresponded to the percent toxicity due to 23 to 91 microM cysteamine. The remaining 43% toxicity appears to involve the inhibition of glutathione peroxidase, because activity of both the cellular and purified enzyme were inhibited by 200 microM cysteamine concentrations. CCRF-CEM cells have no catalase activity, so the inhibition of glutathione peroxidase may sensitize these cells to the less than toxic levels of peroxide generated by this aminothiol. Cysteamine also stimulated the production of cellular glutathione in a manner that was not related to its H2O2 generation. The production of glutathione did not influence toxicity but may reflect the accumulation of cysteamine to levels that inhibit glutathione peroxidase.

Alteration of transforming growth factor-beta1 response involves down-regulation of Smad3 signaling in myofibroblasts from skin fibrosis

Fibrosis is an unregulated tissue repair process whose predominant characteristics are the proliferation of myofibroblasts and an excessive deposition of extracellular matrix. Transforming growth factor (TGF)-beta1 is considered as one of the most fibrogenic cytokines. However, the molecular mechanisms involved in its profibrotic role are not fully understood. Here, we addressed the role of TGF-beta1 on cell proliferation and intracellular signal transduction in a pig model of skin fibrosis induced by gamma-irradiation. Primary myofibroblasts were isolated from the fibrotic tissue and their response to TGF-beta1 was compared to that of normal skin fibroblasts. The present results show that the differentiation of myofibroblasts involves a lack of TGF-beta1 growth inhibition and an impaired TGF-beta1 signaling. Receptor activity and Smad2/4 or Smad3/4 complex formation were similar in both cell types after TGF-beta1 treatment. However, the translocation of Smad3 protein into the nucleus was reduced in myofibroblasts as compared to that in fibroblasts, as well as its binding to target DNA sequences and the activation of the Smad binding elements found in the PAI-1. Interestingly, Smad2 was translocated similarly to the nucleus in both cell types suggesting that this protein may function normally in myofibroblasts. We propose that uncoupling of antiproliferative and profibrotic actions of TGF-beta1 in fibrosis may occur through differential regulation of the activities of Smad2 and Smad3 transcription factors.

Inhibition of angiogenesis in vivo by plasminogen activator inhibitor-1

The process of angiogenesis is important in both normal and pathologic physiology. However, the mechanisms whereby factors such as basic fibroblast growth factor promote the formation of new blood vessels are not known. In the present study, we demonstrate that exogenously added plasminogen activator inhibitor-1 (PAI-1) at therapeutic concentrations is a potent inhibitor of basic fibroblast growth factor-induced angiogenesis in the chicken chorioallantoic membrane. By using specific PAI-1 mutants with either their vitronectin binding or proteinase inhibitor activities ablated, we show that the inhibition of angiogenesis appears to occur via two distinct but apparently overlapping pathways. The first is dependent on PAI-1 inhibition of proteinase activity, most likely chicken plasmin, while the second is independent of PAI-1's anti-proteinase activity and instead appears to act through PAI-1 binding to vitronectin. Together, these data suggest that PAI-1 may be an important factor regulating angiogenesis in vivo.

Endothelial cells inhibit flow-induced smooth muscle cell migration: role of plasminogen activator inhibitor-1

BACKGROUND

The endothelium may play a pivotal role in hemodynamic force-induced vascular remodeling. We investigated the role of endothelial cell (EC) plasminogen activator inhibitor-1 (PAI-1) in modulating flow-induced smooth muscle cell (SMC) migration.

METHODS AND RESULTS

Human SMCs cocultured with or without human ECs were exposed to static (0 mL/min) or flow (26 mL/min; shear stress 23 dyne/cm(2)) conditions for 24 hours in a perfused capillary culture system. SMC migration was then assessed with a Transwell migration assay. In the absence but not in the presence of ECs, pulsatile flow significantly increased the migration of SMCs (264+/-26%) compared with SMCs under static conditions, concomitant with a 3- and 4-fold increase in PAI-1 mRNA and protein, respectively, in cocultured ECs. In the presence of PAI-1-/- ECs, flow increased wild-type SMC migration (226+/-25%), an effect that was reversed by exogenous PAI-1. To determine whether the antimigratory activity of PAI-1 was dependent primarily on inhibition of PAs or its association with vitronectin, experiments were conducted with PAI-1R (a mutant PAI-1 that binds to vitronectin but does not inhibit PA) and PAI-1K (a mutant that inhibits PA but has reduced affinity for vitronectin). PAI-1R inhibited both basal and flow-induced migration, whereas PAI-1K inhibited flow-induced migration in the absence of any effect on baseline migration.

CONCLUSIONS

Flow-induced EC PAI-1 inhibits flow-induced SMC migration in vitro. EC PAI-1 expression may be one of the predominant mechanisms responsible for controlling the process of vascular remodeling.

Relationships between IFNgamma, IL-6, corticosterone, and Listeria monocytogenes pathogenesis in BALB/c mice

The relationships between Listeria monocytogenes (LM) pathogenesis, based on bacterial load, and serum levels of IL-6, IFNgamma, and corticosterone (CORT) were quantified. Serum IFNgamma levels increased along with the LM burden; however, with LM burdens > or =3 x 10(6) CFU per spleen, the serum IFNgamma level decreased along with a decrease in splenic weight. Serum IL-6 levels exponentially increased with increases of LM, and the CORT level positively correlated with the increase in IL-6 and LM. The serum level of IFNgamma appeared to be a good biomarker of the host's ability to combat the infection only when the LM burden did not exceed a critical level (>3 x 10(6) CFU per spleen). Interestingly, the LM load at which the IFNgamma level began to decline was near the dose at which the IL-6 concentration exponentially increased, suggesting a transition point shift from stress (assessed as CORT level) being immunoenhancing to becoming immunosuppressive. The IL-6:IFNgamma ratio may be a good indicator of disease severity and/or the ability to cope with an infection.

Protection of normal proliferating cells against chemotherapy by staurosporine-mediated, selective, and reversible G(1) arrest

BACKGROUND

A major limiting factor in human cancer chemotherapy is toxicity in normal tissues. Our goal was to determine whether normal proliferating cells could be protected from chemotherapeutic agents by taking advantage of the differential drug sensitivity of cell cycle G(1) checkpoint in normal and cancer cells.

METHODS

Normal mammary epithelial cells and mammary cancer cells were initially treated with staurosporine at a cytostatic (i.e., nonlethal) concentration, which preferentially arrests normal cells in the G(0)/G(1) phase of the cell cycle without affecting the proliferation of tumor cells. After the selective arrest of normal cells in G(0)/G(1), both normal and tumor cells were treated with doxorubicin or camptothecin, two cytotoxic (i.e., lethal) chemotherapeutic agents. Cells were then allowed to recover in drug-free medium for 12 days.

RESULTS

After pretreatment of both normal and tumor cells with staurosporine followed by treatment with doxorubicin or camptothecin, tumor cells were selectively killed by chemotherapeutic agents, whereas normal cells resumed proliferation after the drugs were removed. Pretreatment with staurosporine also protected normal circulating lymphocytes that had been induced to proliferate in vitro with phytohemagglutinin from chemotherapeutic agents. Staurosporine-induced arrest of normal cells in G(0)/G(1) phase was reversible, and arrested cells tolerated doses of camptothecin that were more than 100-fold higher than necessary to eradicate all tumor cells in culture. Staurosporine-mediated G(0)/G(1) arrest targets the retinoblastoma protein (pRb) pathway and was accompanied by a rapid decrease in cyclin-dependent kinase (CDK) 4 protein levels, increased binding of CDK inhibitors p21 and p27 to CDK2, and inhibition of CDK2 activity in normal cells.

CONCLUSIONS

Breast cancer cells with defective checkpoints regulated by the pRb pathway can be targeted specifically with chemotherapeutic agents, following staurosporine-mediated, selective and reversible G(0)/G(1) arrest in normal cells.

Neuroserpin mutation S52R causes neuroserpin accumulation in neurons and is associated with progressive myoclonus epilepsy

Mutations in the Neuroserpin gene have been reported to cause familial presenile dementia. We describe a new family in which the S52R Neuroserpin mutation is associated with progressive myoclonus epilepsy in 2 siblings. The proband presented myoclonus and epilepsy at age 24, his brother and mother presented a similar disorder when they were 25. A clinical diagnosis of progressive myoclonus epilepsy was made on the proband and his brother. Skin and liver biopsies did not reveal the presence of cytological alterations in the proband. His neurological status worsened over the subsequent 19 yr during which he became demented and had uncontrollable seizures. He died at 43 yr of age from aspiration pneumonia. Neuropathologically, eosinophilic bodies, which were positive for periodic acid-Schiff and immunoreactive with antibodies against human neuroserpin, were present in the perikarya and cell processes of the neurons. They were found in large numbers in the cerebral cortex and substantia nigra and to a lesser extent, in most subcortical gray areas, spinal cord, and dorsal root ganglia. By electron microscopy, the intracytoplasmic bodies were contained within the membranes of the rough endoplasmic reticulum. Occasionally neuroserpin immunopositivity was seen throughout the cytoplasm, even without the presence of well-defined bodies. Our study characterizes for the first time the neuropathologic phenotype associated with hereditary progressive myoclonus epilepsy caused by the S52R Neuroserpin mutation.

Immunotoxic effects of inorganic lead on host resistance of mice with different circling behavior preferences

We have observed differential immune responses in mice with different circling preferences, which are posited to reflect interindividual immune response differences influenced by brain laterality effects on neuroimmune circuits. In this study, we have investigated the influence of inorganic lead (Pb) and/or Listeria monocytogenes (LM) infection on the cytokine and corticosterone (CORT) levels of mice grouped by lateralized behavior. Pb increased the LM susceptibility of mice with both left (LC)- and right-circling (RC) preferences; however, Pb did not inhibit the host resistance of mice with no circling preference (NP mice). The basal serum IFNgamma levels were lowered in all groups after Pb exposure, which coincided with a decrease in host resistance in LC and RC mice, but not NP mice. Pb also altered the basal serum CORT levels, and these changes appear to correlate better with changes in the host resistance of all groups. The basal CORT levels were significantly lowered by Pb in mice with a circling preference, and Pb significantly suppressed the host resistance of mice with a circling preference. However, Pb slightly increased the serum CORT level of NP mice, and their host resistance was slightly improved by Pb. After infection, the increase in CORT levels was associated with an increase in the serum IL-6 levels, which may reflect cytokine influences on the hypothalamic-pituitary-adrenal axis. At 3 days after infection, the serum IL-6 level seems to be a good indicator of the severity of the infection. We suggest that environmental stressors can reorder the observed differential susceptibility to LM in mice with different circling preferences, in that relatively resistant mice (RC mice) become more susceptible than NP mice after exposure to Pb. The results suggest that environmental stressors may have differential effects among individuals with endogenous differences in their neuroimmune circuits, since brain laterality is known to influence immune functions.

The efficiency of maternal transfer of lead and its influence on plasma IgE and splenic cellularity of mice

Exposure to the well known environmental toxicant lead is typically assessed by blood and/or bone levels and has been implicated in the onset of a variety of diseases affecting multiple human systems. However, there are conflicting data regarding the efficiency of in utero versus lactational transfer of lead to offspring, and the immunomodulatory effects of lead in early life have not been well defined. Pregnant BALB/c mice were exposed to lead acetate in their drinking water beginning at approximately day 15 of gestation, and cross-fostering of exposed/nonexposed litters was performed at parturition. Significant increases of blood lead levels of all exposed offspring were found at 1 week of age with evidence for both transplacental and lactational transfer. Additionally, mice exposed to lead continuously beginning at approximately 6 days prior to birth showed significant decreases in their blood lead levels 2 weeks after weaning, despite continued exposure as adults. This result suggests maternal transfer of lead is more efficient than oral adult exposure and that substantial lead transfer occurs both transplacentally and lactationally. The incidence of childhood atopic responses including asthma has risen considerably in recent years, particularly within areas containing higher levels of environmental pollutants. Plasma IgE levels of 2-week-old neonates exposed to lead before and/or after birth were measured as an index of atopy. Neonates exposed to lead transplacentally and/or lactationally had significantly higher plasma IgE levels, a biomarker of atopy, and lower splenic white blood cell numbers than age-matched controls. These results resemble the lag in immunocompetency and increase in serum IgE noted in atopic children and suggest a role for environmental toxicants and non-allergen-specific immunology in the prevalence of atopy and asthma in children.

Neuronal cell death and reactive oxygen species

1. We have investigated the role of reactive oxygen species (ROS) in cell death induced by ischemia or application of the excitatory amino acid agonist, N-methyl-D-aspartate (NMDA) or kainate (KA), in acutely isolated rat cerebellar granule cell neurons, studied by flow cytometry. Various fluorescent dyes were used to monitor intracellular calcium concentration, ROS concentration, membrane potential, and viability in acutely dissociated neurons subjected to ischemia and reoxygenation alone, NMDA or kainate alone, and ischemia and reoxygenation plus NMDA or kainate. 2. With ischemia followed by reoxygenation, ROS concentrations rose slightly and there was only a modest increase in cell death after 60 min. 3. When NMDA or kainate alone was applied to the cells there was a large increase in ROS and in intracellular calcium concentration but only a small loss of cellular viability. However, when NMDA or kainate was applied during the reoxygenation period there was a large loss of viability, accompanied by membrane depolarization, but the elevations of ROS and intracellular calcium concentration were not greater than seen with the excitatory amino acids alone. 4. These observations indicate that other factors beyond ROS and intracellular calcium concentration contribute to cell death in cerebellar granule cell neurons.

Neuroserpin reduces cerebral infarct volume and protects neurons from ischemia-induced apoptosis

Neuroserpin, a recently identified inhibitor of tissue-type plasminogen activator (tPA), is primarily localized to neurons within the central nervous system, where it is thought to regulate tPA activity. In the present study neuroserpin expression and its potential therapeutic benefits were examined in a rat model of stroke. Neuroserpin expression increased in neurons surrounding the ischemic core (ischemic penumbra) within 6 hours of occlusion of the middle cerebral artery and remained elevated during the first week after the ischemic insult. Injection of neuroserpin directly into the brain immediately after infarct reduced stroke volume by 64% at 72 hours compared with control animals. In untreated animals both tPA and urokinase-type plasminogen activator (uPA) activity was significantly increased within the region of infarct by 6 hours after reperfusion. Activity of tPA then decreased to control levels by 72 hours, whereas uPA activity continued to rise and was dramatically increased by 72 hours. Both tPA and uPA activity were significantly reduced in neuroserpin-treated animals. Immunohistochemical staining of basement membrane laminin with a monoclonal antibody directed toward a cryptic epitope suggested that proteolysis of the basement membrane occurred as early as 10 minutes after reperfusion and that intracerebral administration of neuroserpin significantly reduced this proteolysis. Neuroserpin also decreased apoptotic cell counts in the ischemic penumbra by more than 50%. Thus, neuroserpin may be a naturally occurring neuroprotective proteinase inhibitor, whose therapeutic administration decreases stroke volume most likely by inhibiting proteinase activity and subsequent apoptosis associated with focal cerebral ischemia/reperfusion. (Blood. 2000;96:569-576)

Type 1 plasminogen activator inhibitor binds to fibrin via vitronectin

Type 1 plasminogen activator inhibitor (PAI-1), the primary inhibitor of tissue-type plasminogen activator (t-PA), circulates as a complex with the abundant plasma glycoprotein, vitronectin. This interaction stabilizes the inhibitor in its active conformation In this report, the effects of vitronectin on the interactions of PAI-1 with fibrin clots were studied. Confocal microscopic imaging of platelet-poor plasma clots reveals that essentially all fibrin-associated PAI-1 colocalizes with fibrin-bound vitronectin. Moreover, formation of platelet-poor plasma clots in the presence of polyclonal antibodies specific for vitronectin attenuated the inhibitory effects of PAI-1 on t-PA-mediated fibrinolysis. Addition of vitronectin during clot formation markedly potentiates PAI-1-mediated inhibition of lysis of (125)I-labeled fibrin clots by t-PA. This effect is dependent on direct binding interactions of vitronectin with fibrin. There is no significant effect of fibrin-associated vitronectin on fibrinolysis in the absence of PAI-1. The binding of PAI-1 to fibrin clots formed in the absence of vitronectin was characterized by a low affinity (K(d) approximately 3.5 micrometer) and rapid loss of PAI-1 inhibitory activity over time. In contrast, a high affinity and stabilization of PAI-1 activity characterized the cooperative binding of PAI-1 to fibrin formed in the presence of vitronectin. These findings indicate that plasma PAI-1.vitronectin complexes can be localized to the surface of fibrin clots; by this localization, they may modulate fibrinolysis and clot reorganization.

Apo2L/TRAIL-dependent recruitment of endogenous FADD and caspase-8 to death receptors 4 and 5

Fas (APO-1/CD95) and tumor necrosis factor receptor 1 (TNFR1) trigger apoptosis by recruiting the apoptosis initiator caspase-8 through the adaptor FADD. Fas binds FADD directly, whereas TNFR1 binds FADD indirectly, through TRADD. TRADD alternatively recruits the NF-kappaB-inducing adaptor RIP. The TNF homolog Apo2L/TRAIL triggers apoptosis through two distinct death receptors, DR4 and DR5; however, receptor over-expression studies have yielded conflicting results on the ligand's signaling mechanism. Apo2L/TRAIL induced homomeric and heteromeric complexes of DR4 and DR5 and stimulated recruitment of FADD and caspase-8 and caspase-8 activation in nontransfected cells. TRADD and RIP, which bound TNFR1, did not bind DR4 and DR5. Thus, Apo2L/TRAIL and FasL initiate apoptosis through similar mechanisms, and FADD may be a universal adaptor for death receptors.

Partitioning of serpin-proteinase reactions between stable inhibition and substrate cleavage is regulated by the rate of serpin reactive center loop insertion into beta-sheet A

The serpin family of serine proteinase inhibitors is a mechanistically unique class of naturally occurring proteinase inhibitors that trap target enzymes as stable covalent acyl-enzyme complexes. This mechanism appears to require both cleavage of the serpin reactive center loop (RCL) by the proteinase and a significant conformational change in the serpin structure involving rapid insertion of the RCL into the center of an existing beta-sheet, serpin beta-sheet A. The present study demonstrates that partitioning between inhibitor and substrate modes of reaction can be altered by varying either the rates of RCL insertion or deacylation using a library of serpin RCL mutants substituted in the critical P(14) hinge residue and three different proteinases. We further correlate the changes in partitioning with the actual rates of RCL insertion for several of the variants upon reaction with the different proteinases as determined by fluorescence spectroscopy of specific RCL-labeled inhibitor mutants. These data demonstrate that the serpin mechanism follows a branched pathway, and that the formation of a stable inhibited complex is dependent upon both the rate of the RCL conformational change and the rate of enzyme deacylation.

Central/peripheral nervous system and immune responses

Maintenance of health is dependent on numerous regulatory interactions between organ systems. This review discusses interorgan communication between the nervous, endocrine, and immune systems and environmental and genetic influences on this neuroendocrine immune circuitry. Stresses of multiple types, including psychological and exposure to chemicals and infectious agents, may combine to enhance neuroimmunotoxicology. Altered nervous system functions can alter immunity which could result in exacerbation of infections, cancers or other immune-associated problems. Inversely, aberrant immune system activities could lead to pathologies associated with altered nervous activities, such as Alzheimer's disease, chronic fatigue, or multiple sclerosis. The nervous, endocrine and immune circuitry is multi-directional, and a chemical, physical or emotional stress could upset the homeostasis.

Familial encephalopathy with neuroserpin inclusion bodies

We report on a new familial neurodegenerative disease with associated dementia that has presented clinically in the fifth decade, in both genders, and in each of several generations of a large family from New York State-a pattern of inheritance consistent with an autosomal dominant mode of transmission. A key pathological finding is the presence of neuronal inclusion bodies distributed throughout the gray matter of the cerebral cortex and in certain subcortical nuclei. These inclusions are distinct from any described previously and henceforth are identified as Collins bodies. The Collins bodies can be isolated by simple biochemical procedures and have a surprisingly simple composition; neuroserpin (a serine protease inhibitor) is their predominant component. An affinity-purified antibody against neuroserpin specifically labels the Collins bodies, confirming their chemical composition. Therefore, we propose a new disease entity-familial encephalopathy with neuroserpin inclusion bodies (FENIB). The conclusion that FENIB is a previously unrecognized neurodegenerative disease is supported by finding Collins bodies in a small kindred from Oregon with familial dementia who are unrelated to the New York family. The autosomal dominant inheritance strongly suggests that FENIB is caused by mutations in the neuroserpin gene, resulting in intracellular accumulation of the mutant protein.

Altered serum cytokine and immunoglobulin levels in the workers exposed to antimony

1 Antimony (Sb), an industrial and environmental toxicant, is known to cause dermatitis and pulmonary inflammations, but the immunomodulatory effects of environmental or occupational exposure to Sb have not been reported. To initiate investigation of Sb-induced alterations of the immune system, the concentrations of the IgG subclasses, IgE, interleukin-2, interferon-gamma, and interleukin-4 in sera obtained from workers exposed to Sb through antimony trioxide manufacture were determined and compared with those of control subjects. 2 The serum levels of IgG1, an immunoglobulin involved in host defense against many microbial infections, were significantly lower in the sera of Sb-exposed individuals than the controls. The serum concentrations of IgE, an immunoglobulin mediating allergic hypersensitivity, also were lower in the Sb-exposed workers than the controls. In addition, the levels of interleukin-2 and interferon-gamma, multifunctional cytokines for T-cell mediated immunity, were lowered in the factory workers. 3 A significant positive correlation between IgG4 and urine Sb levels was found among the Sb-exposed workers, indicating a possible role of IgG4 in Sb-mediated pulmonary or skin pathogenesis. 4 The present study provides the first report on immune alterations induced by occupational exposure to Sb and suggests that Sb exposure disturbs immunohomeostasis in humans observed as a function of aberrant serum cytokine and immunoglobulin levels, which could influence health.

New Zealand mixed mice: a genetic systemic lupus erythematosus model for assessing environmental effects

Systemic lupus erythematosus (SLE) is a multiphenotypic autoimmune disease. The hallmark of SLE is the production of anti-double-stranded DNA autoantibodies and the deposition of immune complexes in target tissues such as the kidney, skin, and brain. Additional phenotypic traits are the presence of arthritis, anemia, central nervous system involvement, and a variety of autoantibodies. Females of childbearing age are particularly at risk. Recent genetic analysis of murine SLE shows that susceptibility is under complex polygenic control. It is also apparent that environmental factors contribute to the induction and exacerbation of SLE. We describe here the genotypic and phenotypic characterization of a group of recombinant inbred strains of SLE-prone mice that were derived from NZB and NZW progenitors, the parental strains of the classic female F1 hybrid lupus model. Recombination and reassortment of these ancestral genomes resulted in the NZM (New Zealand mixed) strains with strain-specific patterns of renal disease penetrance and other autoimmune traits such as Coombs positive anemia and neurologic deficits. Multiple susceptibility loci of the ancestral strains demonstrate that SLE is inherited as a threshold trait. Because some of these loci co-localize with the susceptibility loci of the insulin-dependent diabetes of nonobese diabetic strain, it is apparent that there are disease-specific as well as autoimmunity-promoting genes. It is proposed that the NZM strains, particularly those with reduced disease penetrance or partial genotypes, provide an improved genetic model for assessment of the effects of environmental agents on SLE and autoimmunity.

Familial dementia caused by polymerization of mutant neuroserpin

Aberrant protein processing with tissue deposition is associated with many common neurodegenerative disorders; however, the complex interplay of genetic and environmental factors has made it difficult to decipher the sequence of events linking protein aggregation with clinical disease. Substantial progress has been made toward understanding the pathophysiology of prototypical conformational diseases and protein polymerization in the superfamily of serine proteinase inhibitors (serpins). Here we describe a new disease, familial encephalopathy with neuroserpin inclusion bodies, characterized clinically as an autosomal dominantly inherited dementia, histologically by unique neuronal inclusion bodies and biochemically by polymers of the neuron-specific serpin, neuroserpin. We report the cosegregation of point mutations in the neuroserpin gene (PI12) with the disease in two families. The significance of one mutation, S49P, is evident from its homology to a previously described serpin mutations, whereas that of the other, S52R, is predicted by modelling of the serpin template. Our findings provide a molecular mechanism for a familial dementia and imply that inhibitors of protein polymerization may be effective therapies for this disorder and perhaps for other more common neurodegenerative diseases.

Safety and antitumor activity of recombinant soluble Apo2 ligand

TNF and Fas ligand induce apoptosis in tumor cells; however, their severe toxicity toward normal tissues hampers their application to cancer therapy. Apo2 ligand (Apo2L, or TRAIL) is a related molecule that triggers tumor cell apoptosis. Apo2L mRNA is expressed in many tissues, suggesting that the ligand may be nontoxic to normal cells. To investigate Apo2L's therapeutic potential, we generated in bacteria a potently active soluble version of the native human protein. Several normal cell types were resistant in vitro to apoptosis induction by Apo2L. Repeated intravenous injections of Apo2L in nonhuman primates did not cause detectable toxicity to tissues and organs examined. Apo2L exerted cytostatic or cytotoxic effects in vitro on 32 of 39 cell lines from colon, lung, breast, kidney, brain, and skin cancer. Treatment of athymic mice with Apo2L shortly after tumor xenograft injection markedly reduced tumor incidence. Apo2L treatment of mice bearing solid tumors induced tumor cell apoptosis, suppressed tumor progression, and improved survival. Apo2L cooperated synergistically with the chemotherapeutic drugs 5-fluorouracil or CPT-11, causing substantial tumor regression or complete tumor ablation. Thus, Apo2L may have potent anticancer activity without significant toxicity toward normal tissues.

Altered complex formation between p21waf, p27kip and their partner G1 cyclins determines the stimulatory or inhibitory transforming growth factor-beta1 growth response of human fibroblasts

TGF-beta1 stimulates proliferation of WI38 human embryo fibroblasts but inhibits that of their SV40-transformed counterparts, VA13 cells. Protein expression levels of cyclins A, D1, E and that of cdk2 and cdk4 were not affected by TGF-beta1 in either of these cells. However, TGF-beta1-treatment increases cdk2 kinase activity in WI38 cells and reduces it in VA13 cells. The same treatment reduces the amount of p21waf present in complexes with cyclins D1 and E in growth-stimulated WI38 cells, but the reverse applies in growth-inhibited VA13 cells. Mitogenic stimulation of WI38 fibroblasts correlated with decreased expression of p27kip protein and reduced amounts of it in complex with cyclin E. In contrast, proliferative inhibition of VA13 fibroblasts by TGF-beta1 caused a reduction of p27kip in complexes with cyclin D1, but increased it in complexes with cyclin E, without affecting the overall level of p27kip protein expression. Thus, in this human fibroblast model, TGF-beta1-mediated stimulation or inhibition of proliferation depends on modulation in the amounts of p21waf and p27kip in complexes with cyclins D1 and E.

The active conformation of plasminogen activator inhibitor 1, a target for drugs to control fibrinolysis and cell adhesion

BACKGROUND

Plasminogen activator inhibitor 1 (PAI-1) is a serpin that has a key role in the control of fibrinolysis through proteinase inhibition. PAI-1 also has a role in regulating cell adhesion processes relevant to tissue remodeling and metastasis; this role is mediated by its binding to the adhesive glycoprotein vitronectin rather than by proteinase inhibition. Active PAI-1 is metastable and spontaneously transforms to an inactive latent conformation. Previous attempts to crystallize the active conformation of PAI-1 have failed.

RESULTS

The crystal structure of a stable quadruple mutant of PAI-1(Asn150-->His, Lys154-->Thr, Gln319-->Leu, Met354-->Ile) in its active conformation has been solved at a nominal 3 A resolution. In two of four independent molecules within the crystal, the flexible reactive center loop is unconstrained by crystal-packing contacts and is disordered. In the other two molecules, the reactive center loop forms intimate loop-sheet interactions with neighboring molecules, generating an infinite chain within the crystal. The overall conformation resembles that seen for other active inhibitory serpins.

CONCLUSIONS

The structure clarifies the molecular basis of the stabilizing mutations and the reduced affinity of PAI-1, on cleavage or in the latent form, for vitronectin. The infinite chain of linked molecules also suggests a new mechanism for the serpin polymerization associated with certain diseases. The results support the concept that the reactive center loop of an active serpin is flexible and has no defined conformation in the absence of intermolecular contacts. The determination of the structure of the active form constitutes an essential step for the rational design of PAI-1 inhibitors.

Growth stimulation of murine fibroblasts by TGF-beta1 depends on the expression of a functional p53 protein

Transforming Growth Factor-beta1 (TGF-beta1) inhibits the proliferation of most cells, but stimulates some mesenchymal cell types, including murine NIH3T3 fibroblasts. We show here that TGF-beta1 growth stimulation of NIH3T3 fibroblasts is reversed when these cells are transformed by SV40 or are transfected with a plasmid encoding the SV40 Large T antigen. Inversion of the TGF-beta1 growth stimulation of NIH3T3 cells is not observed when these cells are transfected with plasmids expressing either a mutant Large T, unable to bind P53, or the E1A adenovirus oncoprotein which binds the retinoblastoma protein pRB but not P53. But when the TGF-beta1-growth stimulated cells are transfected with a plasmid expressing a mutant form of Large T capable of binding to P53, but not to pRB, or with one expressing the E1B-55 kD adenovirus oncoprotein, which also binds to P53 but not to pRB, the cells are growth-inhibited by TGF-beta1. The cdk inhibitor p21Waf is decreased in TGF-beta1-stimulated NIH3T3 fibroblasts and increased in TGF-beta1-inhibited SV40-transformed cells. Finally, we show that T12 fibroblasts, from a P53 knockout mouse, are growth inhibited by TGF-beta1 and that they remain so upon transfection with a P53 which is mutant at restrictive temperature, but become growth-stimulated by this factor at permissive temperature when P53 is functional. These data strongly suggest that growth-stimulation of fibroblasts by TGF-beta1 depends on the presence of a functional P53 protein and that inversion of this response occurs if P53 is absent or inactivated.

Differential immune responses in mice with left- and right-turning preference

Humoral and cell-mediated immune responses of inbred BALB/c male mice were assayed for differential reactivities associated with behavioral sidedness, which was evaluated by spontaneous rotational behavior in a circular cage model system. Mice with left-turning preference had lower in vivo primary IgM and IgG anti-Keyhole Limpet Hemocyanin (KLH) antibody responses, delayed-type hypersensitivity (DTH) responses, and host-resistance against the intracellular bacteria, Listeria monocytogenes, than mice with right-turning preference. The only immune parameter not shown to be associated with turning preference was the secondary humoral immune response to KLH. The weak innate immune response of left-turners for clearance of Listeria showed close intercorrelation with elevated serum IL-6 levels. Serum corticosterone and splenic norepinephrine levels were differentially increased and decreased by infection, respectively. We suggest that the observed differential immune reactivities of individual animals with same age, gender, and genetic background are associated with functional asymmetries within the brain, that the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic innervation are involved in the regulatory brain: immune interconnection after infection, and that the HPA axis and sympathetic nervous system are involved in the brain laterality effects on immune responses.

Genomic amplification of a decoy receptor for Fas ligand in lung and colon cancer

Fas ligand (FasL) is produced by activated T cells and natural killer cells and it induces apoptosis (programmed cell death) in target cells through the death receptor Fas/Apol/CD95. One important role of FasL and Fas is to mediate immune-cytotoxic killing of cells that are potentially harmful to the organism, such as virus-infected or tumour cells. Here we report the discovery of a soluble decoy receptor, termed decoy receptor 3 (DcR3), that binds to FasL and inhibits FasL-induced apoptosis. The DcR3 gene was amplified in about half of 35 primary lung and colon tumours studied, and DcR3 messenger RNA was expressed in malignant tissue. Thus, certain tumours may escape FasL-dependent immune-cytotoxic attack by expressing a decoy receptor that blocks FasL.

WISP genes are members of the connective tissue growth factor family that are up-regulated in wnt-1-transformed cells and aberrantly expressed in human colon tumors

Wnt family members are critical to many developmental processes, and components of the Wnt signaling pathway have been linked to tumorigenesis in familial and sporadic colon carcinomas. Here we report the identification of two genes, WISP-1 and WISP-2, that are up-regulated in the mouse mammary epithelial cell line C57MG transformed by Wnt-1, but not by Wnt-4. Together with a third related gene, WISP-3, these proteins define a subfamily of the connective tissue growth factor family. Two distinct systems demonstrated WISP induction to be associated with the expression of Wnt-1. These included (i) C57MG cells infected with a Wnt-1 retroviral vector or expressing Wnt-1 under the control of a tetracyline repressible promoter, and (ii) Wnt-1 transgenic mice. The WISP-1 gene was localized to human chromosome 8q24.1-8q24.3. WISP-1 genomic DNA was amplified in colon cancer cell lines and in human colon tumors and its RNA overexpressed (2- to >30-fold) in 84% of the tumors examined compared with patient-matched normal mucosa. WISP-3 mapped to chromosome 6q22-6q23 and also was overexpressed (4- to >40-fold) in 63% of the colon tumors analyzed. In contrast, WISP-2 mapped to human chromosome 20q12-20q13 and its DNA was amplified, but RNA expression was reduced (2- to >30-fold) in 79% of the tumors. These results suggest that the WISP genes may be downstream of Wnt-1 signaling and that aberrant levels of WISP expression in colon cancer may play a role in colon tumorigenesis.