Preoperative tranexamic acid does not reduce transfusion rates in major oncologic surgery: Results of a randomized, double-blind, and placebo-controlled trial

BACKGROUND AND OBJECTIVES

Allogeneic blood transfusions are associated with worse postoperative outcomes in oncologic surgery. The aim of this study was to introduce a preoperative intervention to reduce transfusion rates in this population.

METHODS

Adult patients undergoing major oncologic surgery in five categories with similar transfusion rates were recruited. Enrollees received a single preoperative intravenous dose of placebo or tranexamic acid (1000 mg). The primary outcome measure was perioperative transfusion rate. Secondary outcome measures included: estimated blood loss, thromboembolic events, morbidity, hospital length of stay, and readmission rate.

RESULTS

Seventy-six patients were enrolled, 39 in the tranexamic acid group and 37 in the placebo group, respectively. Demographics and surgery type were equivalent between groups. The transfusion rates were 8 out of 39 (20.5%) in the tranexamic acid group and 5 out of 37 (13.5%) in the placebo group, respectively (P = .418). Median estimated blood loss was 400 mL (interquartile range [IQR] = 150-600) in the tranexamic acid group compared with 300 mL (IQR = 150-800) in the placebo group (P = .983). There was one pulmonary embolism in each arm and no deep venous thrombosis (P > .999).

CONCLUSION

Preoperative administration of tranexamic acid at a 1000 mg intravenous dose does not decrease transfusion rates or estimated blood loss in patients undergoing major oncologic surgery.

Identification of pY654-β-catenin as a critical co-factor in hypoxia-inducible factor-1α signaling and tumor responses to hypoxia

Hypoxia is linked to epithelial-mesenchymal transition (EMT) and tumor progression in numerous carcinomas. Responses to hypoxia are thought to operate via hypoxia-inducible factors (HIFs), but the importance of co-factors that regulate HIF signaling within tumors is not well understood. Here, we elucidate a signaling pathway that physically and functionally couples tyrosine phosphorylation of β-catenin to HIF1α signaling and HIF1α-mediated tumor EMT. Primary human lung adenocarcinomas accumulate pY654-β-catenin and HIF1α. All pY654-β-catenin, and only the tyrosine phosphorylated form, was found complexed with HIF1α and active Src, both within the human tumors and in lung tumor cell lines exposed to hypoxia. Phosphorylation of Y654, generated by hypoxia mediated, reactive oxygen species (ROS)-dependent Src kinase activation, was required for β-catenin to interact with HIF1α and Src, to promote HIF1α transcriptional activity, and for hypoxia-induced EMT. Mice bearing hypoxic pancreatic islet adenomas, generated by treatment with anti-vascular endothelial growth factor antibodies, accumulate HIF1α/pY654-β-catenin complexes and develop an invasive phenotype. Concurrent administration of the ROS inhibitor N-acetylcysteine abrogated β-catenin/HIF pathway activity and restored adenoma architecture. Collectively, the findings implicate accumulation of pY654-β-catenin specifically complexed to HIF1α and Src kinase as critically involved in HIF1α signaling and tumor invasion. The findings also suggest that targeting ROS-dependent aspects of the pY654-β-catenin/ HIF1α pathway may attenuate untoward biological effects of anti-angiogenic agents and tumor hypoxia.

Comorbidity on disorders with loss of impulse-control: pathological gambling, addictions and personality disorders

OBJECTIVES

To analyze the comorbidity of pathological gamblers, mainly in disorders with loss of impulse-control as addictions and personality disorders (PD). Also, to discuss addictive and impulsive characteristics of pathological gambling (PG), and their implications in prognosis and treatment.

MATERIAL AND METHOD

Cross-sectional study on 162 patients with PG admitted for treatment in a specific residential unit. The SCID-I and II were used for the addiction and the PD diagnosis. For the diagnosis and evaluation of PG the SOGS, AGQ III and the Gambling Severity Index were also used.

RESULTS

The 61.1 % of the patients presented some PD, where the cluster B ones (impulsive group) were more frequent, followed by C and A ones. 63.3% of patients had had in their lives substance dependence criteria, where alcohol dependence was the most prevalent. The presence of PD is related to the gravity of the addiction by the dependence to more than one substance (chi2=7.15; p<0.008).

DISCUSSION

TP and substance-related disorders (SRD) are frequent comorbidities of the PG. Their co-presentation could mean worse prognosis of this patients. The PG as impulsive disorder could help to the understanding of the etiopathogenia of this disorder, but also of the prognosis. This hypothesis will add to the addictive one other treatment approaches that should be included in future studies of PG.

Familial aggregation of FEF(25-75) and FEF(25-75)/FVC in families with severe, early onset COPD

BACKGROUND

The Boston Early-Onset COPD study showed that current or ex-smoking first degree relatives of severe early onset COPD probands have significantly lower forced expiratory volume in 1 second (FEV(1)) and FEV(1)/forced vital capacity (FVC) values than current or ex-smoking control subjects, which suggests the existence of genetic risk factors for the development of COPD in response to cigarette smoking. We hypothesised that first degree relatives of early onset COPD probands may also have lower values of spirometric parameters such as forced expiratory flow at the mid-portion of forced vital capacity (FEF(25-75)) and FEF(25-75)/FVC.

METHODS

Using generalised estimating equations, FEF(25-75) and FEF(25-75)/FVC were analysed in 333 first degree relatives of probands with severe early onset COPD and 83 population based controls; analyses were also performed on data stratified by smoking status. Narrow sense heritability estimates were calculated using a variance component approach.

RESULTS

Significantly lower FEF(25-75) and FEF(25-75)/FVC were observed in smoking (FEF(25-75): beta -0.788 l/s (95% CI -1.118 to -0.457), FEF(25-75)/FVC: beta -20.4% (95% CI -29.3 to -11.6, p<0.0001 for both phenotypes) and non-smoking (FEF(25-75): beta -0.357 l/s (95% CI -0.673 to -0.041, p = 0.0271), FEF(25-75)/FVC: beta -9.5% (95% CI -17.1 to -1.9, p = 0.0145)) first degree relatives of early onset COPD probands. Narrow sense heritability estimates for FEF(25-75) (h(2) = 0.38) and FEF(25-75)/FVC (h(2) = 0.45) were similar to those for FEV(1) and FEV(1)/FVC.

CONCLUSION

Lower values of FEF(25-75) and FEF(25-75)/FVC in non-smoking first degree relatives of early onset COPD probands than in controls suggest a genetic susceptibility to develop obstructive lung disease, independent of smoking, which is magnified by exposure to deleterious environments as suggested by the further decrements in FEF(25-75) and FEF(25-75)/FVC seen in smoking first degree relatives. FEF(25-75) and FEF(25-75)/FVC have high heritability and are important intermediate phenotypes for inclusion in genetic epidemiological studies of COPD.

Deficiency of the cysteine protease cathepsin S impairs microvessel growth

During angiogenesis, microvascular endothelial cells (ECs) secrete proteinases that permit penetration of the vascular basement membrane as well as the interstitial extracellular matrix. This study tested the hypothesis that cathepsin S (Cat S) contributes to angiogenesis. Treatment of cultured ECs with inflammatory cytokines or angiogenic factors stimulated the expression of Cat S, whereas inhibition of Cat S activity reduced microtubule formation by impairing cell invasion. ECs from Cat S-deficient mice showed reduced collagenolytic activity and impaired invasion of collagens type I and IV. Cat S-deficient mice displayed defective microvessel development during wound repair. This abnormal angiogenesis occurred despite normal vascular endothelial growth factor and basic fibroblast growth factor levels, implying an essential role for extracellular matrix degradation by Cat S during microvessel formation. These results demonstrate a novel function of endothelium-derived Cat S in angiogenesis.

Regulation of CD1 function and NK1.1(+) T cell selection and maturation by cathepsin S

NK1.1(+) T cells develop and function through interactions with cell surface CD1 complexes. In I-A(b) mice lacking the invariant chain (Ii) processing enzyme, cathepsin S, NK1.1(+) T cell selection and function are impaired. In vitro, thymic dendritic cells (DCs) from cathepsin S(-/-) mice exhibit defective presentation of the CD1-restricted antigen, alpha-galactosylceramide (alpha-GalCer). CD1 dysfunction is secondary to defective trafficking of CD1, which colocalizes with Ii fragments and accumulates within endocytic compartments of cathepsin S(-/-) DCs. I-A(k), cathepsin S(-/-) mice do not accumulate class II-associated Ii fragments and accordingly do not display CD1 abnormalities. Thus, function of CD1 is critically linked to processing of Ii, revealing MHC class II haplotype and cathepsin S activity as regulators of NK T cells.

Urokinase receptors promote beta1 integrin function through interactions with integrin alpha3beta1

The urokinase receptor (uPAR) is linked to cellular migration through its capacity to promote pericellular proteolysis, regulate integrin function, and mediate cell signaling in response to urokinase (uPA) binding. The mechanisms for these activities remain incompletely defined, although uPAR was recently identified as a cis-acting ligand for the beta2 integrin CD11b/CD18 (Mac-1). Here we show that a major beta1 integrin partner for uPAR/uPA signaling is alpha3. In uPAR-transfected 293 cells uPAR complexed (>90%) with alpha3beta1 and antibodies to alpha3 blocked uPAR-dependent vitronectin (Vn) adhesion. Soluble uPAR bound to recombinant alpha3beta1 in a uPA-dependent manner (K(d) < 20 nM) and binding was blocked by a 17-mer alpha3beta1 integrin peptide (alpha325) homologous to the CD11b uPAR-binding site. uPAR colocalized with alpha3beta1 in MDA-MB-231 cells and uPA (1 nM) enhanced spreading and focal adhesion kinase phosphorylation on fibronectin (Fn) or collagen type I (Col) in a pertussis toxin- and alpha325-sensitive manner. A critical role of alpha3beta1 in uPA signaling was verified by studies of epithelial cells from alpha3-deficient mice. Thus, uPAR preferentially complexes with alpha3beta1, promoting direct (Vn) and indirect (Fn, Col) pathways of cell adhesion, the latter a heterotrimeric G protein-dependent mechanism of signaling between alpha3beta1 and other beta1 integrins.

Protease crosstalk with integrins: the urokinase receptor paradigm

Migratory cells use both adhesion receptors and proteolytic enzymes to regulate their interaction with and response to extracellular matrices. Cooperation between integrins and proteases operates at several levels: integrin signaling induces proteases, proteases co-localize with integrins, and proteases regulate the interface between integrins and the intracellular cytoskeleton. One protease system intimately connected to integrins is the urokinase/urokinase receptor(uPAR)/plasmin system. Recent studies indicate urokinase promotes the ligand-like binding of its receptor to a set of beta1 and beta2 integrins, this binding in turn affecting integrin signaling and cell migration. The glycolipid anchor of uPAR associates with cholesterol-rich membrane rafts. Binding of uPAR to integrins may enrich integrin clusters with signaling molecules such as src-family kinases that localize to rafts and are important to integrin function. Signals derived from integrin/uPAR complexes promote the function of other integrins. Thus the urokinase/plasmin system coordinates with integrins to regulate cell: matrix interactions.

Expression of cathepsins B and S in the progression of prostate carcinoma

Cathepsins B and S (CatB, CatS) are lysosomal cysteine proteases which, among other functions, appear to play a role in cancer progression in different tumor models due to their matrix-degrading properties. To investigate their possible involvement in the development of prostate carcinoma, we immunohistochemically analyzed CatB and CatS in 38 primary human prostatic adenocarcinomas, as well as concomitant high-grade prostatic intra-epithelial neoplasia, nodular hyperplasia and normal tissue. CatB expression was observed in 28 (74%) and CatS in 32 (84%) carcinomas, being concomitant in 24 cases (63%). High-grade intra-epithelial neoplasia expressed CatB in 20/23 cases (87%), and a similar result was obtained for CatS, with expression of both coinciding in 18 cases (78%). In non-neoplastic tissue, strong expression of both proteases was observed in macrophages, inflamed glands and transitional metaplasia, whereas atrophic glands and basal cells of normal glands displayed intense CatB positivity. We conclude that CatB and CatS are often expressed together in neoplastic prostatic cells from pre-invasive to invasive and clinically detectable stages, suggesting a putative role in local invasion, though other functions cannot be ruled out.

Expression of cathepsins B and S in the progression of prostate carcinoma

Cathepsins B and S (CatB, CatS) are lysosomal cysteine proteases which, among other functions, appear to play a role in cancer progression in different tumor models due to their matrix-degrading properties. To investigate their possible involvement in the development of prostate carcinoma, we immunohistochemically analyzed CatB and CatS in 38 primary human prostatic adenocarcinomas, as well as concomitant high-grade prostatic intra-epithelial neoplasia, nodular hyperplasia and normal tissue. CatB expression was observed in 28 (74%) and CatS in 32 (84%) carcinomas, being concomitant in 24 cases (63%). High-grade intra-epithelial neoplasia expressed CatB in 20/23 cases (87%), and a similar result was obtained for CatS, with expression of both coinciding in 18 cases (78%). In non-neoplastic tissue, strong expression of both proteases was observed in macrophages, inflamed glands and transitional metaplasia, whereas atrophic glands and basal cells of normal glands displayed intense CatB positivity. We conclude that CatB and CatS are often expressed together in neoplastic prostatic cells from pre-invasive to invasive and clinically detectable stages, suggesting a putative role in local invasion, though other functions cannot be ruled out.

Gender-related differences in severe, early-onset chronic obstructive pulmonary disease

Men have higher prevalence rates of chronic obstructive pulmonary disease (COPD) than women, which has been attributed to the historically higher rates of cigarette smoking in males. However, the increased rates of cigarette smoking in females within the last several decades have been associated with steadily increasing rates of COPD in women. As part of a study of the genetics of severe, early-onset COPD, we assembled a group of 84 probands with severe, early-onset COPD (without severe alpha(1)-antitrypsin deficiency) and 348 of their first-degree relatives. We found a markedly elevated prevalence (71.4%) of females among the early-onset COPD probands. Among the entire group of first-degree relatives of early-onset COPD probands, univariate analysis demonstrated similar spirometric values and bronchodilator responsiveness in males and females; however, among current or ex-smokers, female first-degree relatives had significantly lower FEV(1)/ FVC (81.4 +/- 17.2% in females versus 87.0 +/- 12.9% in males, p = 0.009) and significantly greater bronchodilator responsiveness (expressed as percentage of baseline FEV(1)) (7.7 +/- 9.4% pred in females versus 4.1 +/- 6.4% pred in males, p = 0.002). Female smoking first-degree relatives were significantly more likely to demonstrate profound reductions in FEV(1) (< 40% pred) than male smoking first-degree relatives (p = 0. 03). Multivariate analysis, performed with generalized estimating equations, demonstrated that current or ex-smoking female first-degree relatives had significantly greater risk of FEV(1) < 80% pred (OR 1.91, 95% CI 1.03- 3.54), FEV(1) < 40% pred (OR 3.56, 95% CI 1.08-11.71), and bronchodilator response greater than 10% of baseline FEV(1) (OR 4.74, 95% CI 1.91-11.75). These results suggest that women may be more susceptible to the development of severe COPD.

Inducible targeting of IL-13 to the adult lung causes matrix metalloproteinase- and cathepsin-dependent emphysema

Cigarette smoke exposure is the major cause of chronic obstructive pulmonary disease (COPD). However, only a minority of smokers develop significant COPD, and patients with asthma or asthma-like airway hyperresponsiveness or eosinophilia experience accelerated loss of lung function after cigarette smoke exposure. Pulmonary inflammation is a characteristic feature of lungs from patients with COPD. Surprisingly, the mediators of this inflammation and their contributions to the pathogenesis and varied natural history of COPD are not well defined. Here we show that IL-13, a critical cytokine in asthma, causes emphysema with enhanced lung volumes and compliance, mucus metaplasia, and inflammation, when inducibly overexpressed in the adult murine lung. MMP-2, -9, -12, -13, and -14 and cathepsins B, S, L, H, and K were induced by IL-13 in this setting. In addition, treatment with MMP or cysteine proteinase antagonists significantly decreased the emphysema and inflammation, but not the mucus in these animals. These studies demonstrate that IL-13 is a potent stimulator of MMP and cathepsin-based proteolytic pathways in the lung. They also demonstrate that IL-13 causes emphysema via a MMP- and cathepsin-dependent mechanism(s) and highlight common mechanisms that may underlie COPD and asthma.

Simple modifications of the serpin reactive site loop convert SCCA2 into a cysteine proteinase inhibitor: a critical role for the P3' proline in facilitating RSL cleavage

The human squamous cell carcinoma antigens (SCCA) 1 and 2 are members of the serpin family that are 92% identical in their amino acid sequence. Despite this similarity, they inhibit distinct classes of proteinases. SCCA1 neutralizes the papain-like cysteine proteinases, cathepsins (cat) S, L, and K; and SCCA2 inhibits the chymotrypsin-like serine proteinases, catG and human mast cell chymase. SCCA2 also can inhibit catS, as well as other papain-like cysteine proteinases, albeit at a rate 50-fold less than that of SCCA1. Analysis of the mechanism of inhibition by SCCA1 revealed that the reactive site loop (RSL) is important for cysteine proteinase inhibition. The inhibition of catS by a mutant SCCA2 containing the RSL of SCCA1 is comparable to that of wild-type SCCA1. This finding suggested that there were no motifs outside and only eight residues within the RSL that were directing catS-specific inhibition. The purpose of this study was to determine which of these residues might account for the marked difference in the ability of SCCA1 and SCCA2 to inhibit papain-like cysteine proteinases. SCCA2 molecules containing different RSL mutations showed that no single amino acid substitution could convert SCCA2 into a more potent cysteine proteinase inhibitor. Rather, different combinations of mutations led to incremental increases in catS inhibitory activity with residues in four positions (P1, P3', P4', and P11') accounting for 80% of the difference in activity between SCCA1 and SCCA2. Interestingly, the RSL cleavage site differed between wild-type SCCA2 and this mutant. Moreover, these data established the importance of a Pro residue in the P3' position for efficient inhibition of catS by both wild-type SCCA1 and mutated SCCA2. Molecular modeling studies suggested that this residue might facilitate positioning of the RSL within the active site of the cysteine proteinase.

Identification of a urokinase receptor-integrin interaction site. Promiscuous regulator of integrin function

Adhesion and signaling by integrins require their dynamic association with nonintegrin membrane proteins. One such protein, the glycolipid-anchored urokinase receptor (uPAR), associates with and modifies the function of the beta(2)-integrin Mac-1 (CD11b/CD18). In this study, a critical non-I-domain binding site for uPAR on CD11b (M25; residues 424-440) is identified by homology with a phage display peptide known to bind uPAR. Recombinant soluble uPAR and cells expressing uPAR bound to immobilized M25, binding being promoted by urokinase and blocked by soluble M25, but not a scrambled control or homologous peptides from other beta(2)-associated alpha-chains. Mac-1, but not a mutated Mac-1 in which M25 was replaced with the homologous sequence of CD11c, co-precipitated with uPAR. In the beta-propeller model of alpha-chain folding, M25 spans an exposed loop on the ligand-binding, upper surface of alphaM, identifying uPAR as an atypical alphaM ligand. Although not blocking ligand binding to Mac-1, M25 (25-100 microM) inhibited leukocyte adhesion to fibrinogen, vitronectin, and cytokine-stimulated endothelial cells. M25 also blocked the association of uPAR with beta(1)-integrins and impaired beta(1)-integrin-dependent spreading and migration of human vascular smooth muscle cells on fibronectin and collagen. These observations indicate that uPAR associates with integrins directly and that disruption of this association broadly impairs integrin function, suggesting a novel strategy for regulation of integrins in the settings of inflammation and tumor progression.

Nonproteolytic role for the urokinase receptor in cellular migration in vivo

The urokinase receptor (uPAR) binds and localizes urokinase activity at cellular surfaces, facilitating fibrinolysis and cellular migration at sites of tissue injury. uPAR also participates in cellular signaling and regulates integrin-dependent adhesion and migration in vitro. We now report evidence that uPAR occupancy regulates cellular migration in vivo in the absence of functional urokinase. Recombinant murine KC (1.5 microg), a potent neutrophil chemoattractant, was delivered to the lungs of wild-type, urokinase-deficient or uPAR-deficient mice 18 h after intraperitoneal injection of 200 microg human immunoglobulin G (IgG) or a fusion protein composed of an amino-terminal receptor-binding fragment of urokinase and a human IgG Fc fragment (GFD-Fc). Whole lung lavage for recovery of leukocytes was performed 4 h later. KC treatment resulted in a 100-fold increase in lavage neutrophils. GFD-Fc injection resulted in >50% reduction in neutrophil influx in both wild-type and urokinase-deficient animals but had no effect on uPAR -/- mice. A concomitant reduction in alveolar protein leakage but no change in numbers of circulating neutrophils accompanied this attenuated inflammatory response. The reduction in neutrophil influx induced by GFD-Fc is thus related to uPAR occupancy and yet not due to disruption of uPAR-mediated proteolysis. These observations verify that protease-independent functions of uPAR operate in vivo and identify uPAR as a potential target for regulation of inflammatory processes characterized by neutrophil-mediated injury.

Early endosomal maturation of MHC class II molecules independently of cysteine proteases and H-2DM

Major histocompatibility complex (MHC) class II molecules bind and present to CD4(+) T cells peptides derived from endocytosed antigens. Class II molecules associate in the endoplasmic reticulum with invariant chain (Ii), which (i) mediates the delivery of the class II-Ii complexes into the endocytic compartments where the antigenic peptides are generated; and (ii) blocks the peptide-binding site of the class II molecules until they reach their destination. Once there, Ii must be removed to allow peptide binding. The bulk of Ii-class II complexes reach late endocytic compartments where Ii is eliminated in a reaction in which the cysteine protease cathepsin S and the accessory molecule H-2DM play an essential role. Here, we here show that Ii is also eliminated in early endosomal compartments without the intervention of cysteine proteases or H-2DM. The Ii-free class II molecules generated by this alternative mechanism first bind high molecular weight polypeptides and then mature into peptide-loaded complexes.

Cathepsins and compartmentalization in antigen presentation

Intracellular trafficking and cell surface expression of MHC class II molecules is a tightly regulated process and is to a large extent, determined by the fate of the class II chaperone, the invariant chain. Inhibition of endosomal proteases critical to invariant chain proteolysis reveals marked shunting of class II complexes to lysosomal compartments. Regulation of endosomal protease activity by expression of cystatin C directs class II cell surface expression during maturation of dendritic cells. These studies highlight the taut interactions between class-II-invariant-chain complexes and endosomal proteases during MHC class II maturation.

Proteases involved in MHC class II antigen presentation

Major histocompatibility complex class II antigen presentation requires the participation of lysosomal proteases in two convergent processes. First, the antigens endocytosed by the antigen-presenting cells must be broken down into antigenic peptides. Second, class II molecules are synthesized with their peptide-binding site blocked by invariant chain (Ii), and they acquire the capacity to bind antigens only after Ii has been degraded in the compartments where peptides reside. The study of genetically modified mice deficient in single lysosomal proteases has allowed us to determine their role in these processes. Cathepsins (Cat) B and D, previously considered major players in MHC class II antigen presentation, are dispensable for degradation of Ii and for generation of several antigenic determinants. By contrast, Cat S plays an essential role in removal of Ii in B cells and dendritic cells, whereas Cat L apparently does so in thymic epithelial cells. Accordingly, the absence of Cat S and L have major consequences for the onset of humoral immune responses and for T-cell selection, respectively. It is likely that other as yet uncharacterized lysosomal enzymes also play a role in Ii degradation and in generation of antigenic determinants. Experiments involving drugs that interfere with protein traffic suggest that more than one mechanism for Ii removal, probably involving different proteases, can co-exist in the same antigen-presenting cell. These findings may allow the development of protease inhibitors with possible therapeutic applications.

Cystatin C deficiency in human atherosclerosis and aortic aneurysms

The pathogenesis of atherosclerosis and abdominal aortic aneurysm involves breakdown of the elastic laminae. Elastolytic cysteine proteases, including cathepsins S and K, are overexpressed at sites of arterial elastin damage, but whether endogenous local inhibitors counterbalance these proteases is unknown. We show here that, whereas cystatin C is normally expressed in vascular wall smooth muscle cells (SMCs), this cysteine protease inhibitor is severely reduced in both atherosclerotic and aneurysmal aortic lesions. Furthermore, increased abdominal aortic diameter among 122 patients screened by ultrasonography correlated inversely with serum cystatin C levels. In vitro, cytokine-stimulated vascular SMCs secrete cathepsins, whose elastolytic activity could be blocked when cystatin C secretion was induced by treatment with TGF-beta(1). The findings highlight a potentially important role for imbalance between cysteine proteases and cystatin C in arterial wall remodeling and establish that cystatin C deficiency occurs in vascular disease.

Role of urokinase receptor and caveolin in regulation of integrin signaling

Emerging evidence indicates a prominent role for non-integrin membrane adaptors in the dynamic regulation of integrin signaling. Two such integrin-associated proteins are the glycosylphosphatidyl-inositol (GPI)-linked urokinase receptor (u-PAR) and the cholesterol-binding protein, caveolin-1. Recent studies indicate that caveolin is required for the association of Src-family kinases with beta 1 integrins. Loss of caveolin/beta 1 integrin association results in loss of ligand-induced focal adhesion kinase (FAK) phosphorylation and impaired development of focal adhesion sites. Similarly, fibronectin-dependent fyn signaling through alpha 5/beta 1 leading to mitogen-activated protein (MAP) kinase activation requires the presence of caveolin-1. Caveolin binds Src-family kinases and such binding maintains these kinases in an inactive state. Current evidence favors a model in which ligand-induced integrin clustering, a central event in integrin activation, promotes caveolin oligomerization leading to release and/or activation of Src-family kinases and initiation of integrin signaling. The presence of u-PAR promotes these events because the extracellular domain(s) of u-PAR binds to beta 1 and beta 2 integrins and the GPI anchor of u-PAR, like that of other GPI-anchored proteins, interacts with cholesterol-rich membrane domains enriched in caveolin and tyrosine kinases. Integrins, caveolin, and u-PAR form interdependent functional complexes, promoting the association of integrins with caveolin-rich signaling domains. During states of accelerated cellular migration, such as during inflammation and tumorigenesis, expression of u-PAR may be a key facilitator of integrin signaling. Interruption of u-PAR/integrin interactions may be a strategy to regulate cellular migration in these settings.

A role for caveolin and the urokinase receptor in integrin-mediated adhesion and signaling

The assembly of signaling molecules surrounding the integrin family of adhesion receptors remains poorly understood. Recently, the membrane protein caveolin was found in complexes with beta1 integrins. Caveolin binds cholesterol and several signaling molecules potentially linked to integrin function, e.g., Src family kinases, although caveolin has not been directly implicated in integrin-dependent adhesion. Here we report that depletion of caveolin by antisense methodology in kidney 293 cells disrupts the association of Src kinases with beta1 integrins resulting in loss of focal adhesion sites, ligand-induced focal adhesion kinase (FAK) phosphorylation, and adhesion. The nonintegrin urokinase receptor (uPAR) associates with and stabilizes beta1 integrin/caveolin complexes. Depletion of caveolin in uPAR-expressing 293 cells also disrupts uPAR/integrin complexes and uPAR-dependent adhesion. Further, beta1 integrin/caveolin complexes could be disassociated by uPAR-binding peptides in both uPAR-transfected 293 cells and human vascular smooth muscle cells. Disruption of complexes by peptides in intact smooth muscle cells blocks the association of Src family kinases with beta1 integrins and markedly impairs their migration on fibronectin. We conclude that ligand-induced signaling necessary for normal beta1 integrin function requires caveolin and is regulated by uPAR. Caveolin and uPAR may operate within adhesion sites to organize kinase-rich lipid domains in proximity to integrins, promoting efficient signal transduction.

Cathepsin S required for normal MHC class II peptide loading and germinal center development

Major histocompatibility complex (MHC) class II molecules acquire antigenic peptides after degradation of the invariant chain (Ii), an MHC class II-associated protein that otherwise blocks peptide binding. Antigen-presenting cells of mice that lack the protease cathepsin S fail to process Ii beyond a 10 kDa fragment, resulting in delayed peptide loading and accumulation of cell surface MHC class II/10 kDa Ii complexes. Although cathepsin S-deficient mice have normal numbers of B and T cells and normal IgE responses, they show markedly impaired antibody class switching to IgG2a and IgG3. These results indicate cathepsin S is a major Ii-processing enzyme in splenocytes and dendritic cells. Its role in humoral immunity critically depends on how antigens access the immune system.

Human cathepsin F. Molecular cloning, functional expression, tissue localization, and enzymatic characterization

A cDNA for a novel human papain-like cysteine protease, designated cathepsin F, has been cloned from a lambdagt10-skeletal muscle cDNA library. The nucleotide sequence encoded a polypeptide of 302 amino acids composed of an 88-residue propeptide and a 214-residue mature protein. Protein sequence comparisons revealed 58% homology with cathepsin W; about 42-43% with cathepsins L, K, S, H, and O; and 38% with cathepsin B. Sequence comparisons of the propeptides indicated that cathepsin F and cathepsin W may form a new cathepsin subgroup. Northern blot analysis showed high expression levels in heart, skeletal muscle, brain, testis, and ovary; moderate levels in prostate, placenta, liver, and colon; and no detectable expression in peripheral leukocytes and thymus. The precursor polypeptide of human recombinant cathepsin F, produced in Pichia pastoris, was processed to its active mature form autocatalytically or by incubation with pepsin. Mature cathepsin F was highly active with comparable specific activities toward synthetic substrates as reported for cathepsin L. The protease had a broad pH optimum between 5.2 and 6.8. Similar to cathepsin L, its pH stability at cytosolic pH (7.2) was short, with a half-life of approximately 2 min. This may suggest a function in an acidic cellular compartment. Transient expression of T7-tagged cathepsin F in COS-7 cells revealed a vesicular distribution of the gene product in the juxtanuclear region of the cells. However, contrary to all known cathepsins, the open reading frame of the cathepsin F cDNA did not encode a signal sequence, thus suggesting that the protease is targeted to the lysosomal compartment via an N-terminal signal peptide-independent lysosomal targeting pathway.

Fc epsilon receptor I on dendritic cells delivers IgE-bound multivalent antigens into a cathepsin S-dependent pathway of MHC class II presentation

In this study, we elucidate the Fc epsilon RI-mediated Ag uptake and presentation mechanisms of dendritic cells (DC). We found that Fc epsilon RI-bound IgE, after polyvalent but not after monovalent ligation, is efficiently internalized into acidic, proteolytic compartments, degraded, and delivered into organelles containing MHC class II, HLA-DM, and lysosomal proteins. To follow the fate of the fragmented ligand, we sought to interfere with invariant chain (Ii) degradation, a process critical for peptide loading of nascent MHC class II molecules. We found DC to express cathepsin (Cat) S, a cysteine protease involved in Ii processing by B cells. Exposure of DC to a specific, active-site inhibitor of Cat S resulted in the loss of anti-Cat S immunoreactivity, led to the appearance of an N-terminal Ii remnant, and decreased the export of newly synthesized MHC class II to the DC surface. Furthermore, inactivation of Cat S as well as blockade of protein neosynthesis by cycloheximide strongly reduced IgE/Fc epsilon RI-mediated Ag presentation by DC. Thus, multimeric ligands of Fc epsilon RI, instead of being delivered into a recycling MHC class H pathway, are channeled efficiently into MIIC (MHC class II compartment)-like organelles of DC, in which Cat S-dependent Ii processing and peptide loading of newly synthesized MHC class II molecules occur. This IgE/Fc epsilon RI-dependent signaling pathway in DC may be a particularly effective route for immunization and a promising target for interfering with the early steps of allergen presentation.

Expression of the elastolytic cathepsins S and K in human atheroma and regulation of their production in smooth muscle cells

Formation of the atherosclerotic intima must involve altered metabolism of the elastin-rich arterial extracellular matrix. Proteases potentially involved in these processes remain unclear. This study examined the expression of the potent elastases cathepsins S and K in human atheroma. Normal arteries contained little or no cathepsin K or S. In contrast, macrophages in atheroma contained abundant immunoreactive cathepsins K and S. Intimal smooth muscle cells (SMC), especially cells appearing to traverse the internal elastic laminae, also contained these enzymes. Extracts of atheromatous tissues had approximately twofold greater elastase-specific activity than extracts of uninvolved arteries, mostly due to cysteine proteases. Cultured human SMC displayed no immunoreactive cathepsins K and S and exhibited little or no elastolytic activity when incubated with insoluble elastin. SMC stimulated with the atheroma-associated cytokines IL-1beta or IFN-gamma secreted active cathepsin S and degraded substantial insoluble elastin (15-20 microg/10(6) cells/24 h). A selective inhibitor of cathepsin S blocked > 80% of this elastolytic activity. The presence of cathepsins K and S at sites of vascular matrix remodeling and the ability of SMC and macrophages to use these enzymes to degrade elastin supports a role for elastolytic cathepsins in vessel wall remodeling and identifies novel therapeutic targets in regulating plaque stability.

Expression of the elastolytic cathepsins S and K in human atheroma and regulation of their production in smooth muscle cells

Formation of the atherosclerotic intima must involve altered metabolism of the elastin-rich arterial extracellular matrix. Proteases potentially involved in these processes remain unclear. This study examined the expression of the potent elastases cathepsins S and K in human atheroma. Normal arteries contained little or no cathepsin K or S. In contrast, macrophages in atheroma contained abundant immunoreactive cathepsins K and S. Intimal smooth muscle cells (SMC), especially cells appearing to traverse the internal elastic laminae, also contained these enzymes. Extracts of atheromatous tissues had approximately twofold greater elastase-specific activity than extracts of uninvolved arteries, mostly due to cysteine proteases. Cultured human SMC displayed no immunoreactive cathepsins K and S and exhibited little or no elastolytic activity when incubated with insoluble elastin. SMC stimulated with the atheroma-associated cytokines IL-1beta or IFN-gamma secreted active cathepsin S and degraded substantial insoluble elastin (15-20 microg/10(6) cells/24 h). A selective inhibitor of cathepsin S blocked > 80% of this elastolytic activity. The presence of cathepsins K and S at sites of vascular matrix remodeling and the ability of SMC and macrophages to use these enzymes to degrade elastin supports a role for elastolytic cathepsins in vessel wall remodeling and identifies novel therapeutic targets in regulating plaque stability.

Cathepsin S activity regulates antigen presentation and immunity

MHC class II molecules display antigenic peptides on cell surfaces for recognition by CD4(+) T cells. Proteolysis is required in this process both for degradation of invariant chain (Ii) from class II-Ii complexes to allow subsequent binding of peptides, and for generation of the antigenic peptides. The cysteine endoprotease, cathepsin S, mediates Ii degradation in human and mouse antigen-presenting cells. Studies described here examine the functional significance of cathepsin S inhibition on antigen presentation and immunity. Specific inhibition of cathepsin S in A20 cells markedly impaired presentation of an ovalbumin epitope by interfering with class II-peptide binding, not by obstructing generation of the antigen. Administration of a cathepsin S inhibitor to mice in vivo selectively inhibited activity of cathepsin S in splenocytes, resulting in accumulation of a class II-associated Ii breakdown product, attenuation of class II-peptide complex formation, and inhibition of antigen presentation. Mice treated with inhibitor had an attenuated antibody response when immunized with ovalbumin but not the T cell-independent antigen TNP-Ficoll. In a mouse model of pulmonary hypersensitivity, treatment with the inhibitor also abrogated a rise in IgE titers and profoundly blocked eosinophilic infiltration in the lung. Thus, inhibition of cathepsin S in vivo alters Ii processing, antigen presentation, and immunity. These data identify selective inhibition of cysteine proteases as a potential therapeutic strategy for asthma and autoimmune disease processes.

Genetic epidemiology of severe, early-onset chronic obstructive pulmonary disease. Risk to relatives for airflow obstruction and chronic bronchitis

Severe alpha-1-antitrypsin deficiency is the only proven genetic risk factor for chronic obstructive pulmonary disease (COPD). We have assembled a cohort of 44 probands with severe, early-onset COPD, who do not have severe alpha-1-antitrypsin deficiency. A surprisingly high prevalence of females (79.6%) was found. Assessment of the risk to relatives of these early-onset COPD probands for airflow obstruction and chronic bronchitis was performed to determine whether significant familial aggregation for COPD, independent of alpha-1-antitrypsin deficiency, could be demonstrated. First- degree relatives of early-onset COPD probands had significantly lower FEV1 and FEV1/FVC values than control subjects (p < 0.01), despite similar pack-years of smoking. Reduced spirometric values in first-degree relatives of early-onset COPD probands were found only in current or ex-cigarette smokers. The mean FEV1 in current or ex-smoking first-degree relatives was 76.1 +/- 20.9% predicted compared to 89.2 +/- 14.4% predicted in current or ex-smoking control subjects (p < 0.01); in lifelong nonsmokers, the mean FEV1 was 93.4% predicted for both control subjects and first-degree relatives of early-onset COPD probands. Generalized estimating equations, adjusting for age and pack-years of smoking, demonstrated increased odds of reduced FEV1 and chronic bronchitis in current or ex-smoking first-degree relatives of early-onset COPD probands. Using a new method to estimate relative risk from relative odds, we estimate that the relative risks for FEV1 below 60%, FEV1 below 80%, and chronic bronchitis are each approximately three in current or ex-smoking first-degree relatives of early-onset COPD probands. The increased risk to relatives of early-onset COPD probands for reduced FEV1 and chronic bronchitis, limited to current or ex-smokers, suggests genetic risk factor(s) for COPD that are expressed in response to cigarette smoking.

Cross-class inhibition of the cysteine proteinases cathepsins K, L, and S by the serpin squamous cell carcinoma antigen 1: a kinetic analysis

The human squamous cell carcinoma antigens (SCCA) 1 and 2 are tandemly arrayed genes that encode two high-molecular-weight serine proteinase inhibitors (serpins). Although these proteins are 92% identical, differences in their reactive site loops suggest that they inhibit different types of proteinases. Our previous studies show that SCCA2 inhibits chymotrypsin-like serine proteinases [Schick et al. (1997) J. Biol. Chem. 272, 1849-1855]. We now show that, unlike SCCA2, SCCA1 lacks inhibitory activity against any of the more common types of serine proteinases but is a potent cross-class inhibitor of the archetypal lysosomal cysteine proteinases cathepsins K, L, and S. Kinetic analysis revealed that SCCA1 interacted with cathepsins K, L, and S at 1:1 stoichiometry and with second-order rate constants >/= 1 x 10(5) M-1 s-1. These rate constants were comparable to those obtained with the prototypical physiological cysteine proteinase inhibitor, cystatin C. Also relative to cystatin C, SCCA1 was a more potent inhibitor of cathepsin K-mediated elastolytic activity by forming longer lived inhibitor-proteinase complexes. The t1/2 of SCCA1-cathepsin S complexes was >1155 min, whereas that of cystatin C-cathepsin complexes was 55 min. Cleavage between the Gly and Ser residues of the reactive site loop and detection of a stable SCCA1-cathepsin S complex by sodium dodecyl sulfate-polyacrylamide gel electrophoresis suggested that the serpin interacted with the cysteine proteinase in a manner similar to that observed for typical serpin-serine proteinase interactions. These data suggest that, contingent upon their reactive site loop sequences, mammalian serpins, in general, utilize their dynamic tertiary structure to trap proteinases from more than one mechanistic class and that SCCA1, in particular, may be involved in a novel inhibitory pathway aimed at regulating a powerful array of lysosomal cysteine proteinases.

Endosomal proteolysis and MHC class II function

Newly synthesized MHC class II alpha and beta chains associate with a protein chaperone, the invariant chain, which promotes the proper assembly of MHC class II complexes and their trafficking through cells and prevents their untimely loading with peptides. Efficient loading of MHC class II heterodimers with antigenic peptides requires concurrent proteolytic processing of both the invariant chain and endocytosed proteins. Recent studies have elucidated the critical roles of specific cysteine proteases, especially cathepsins S and L, in degrading the invariant chain and regulating the convergence of processed antigen and MHC class II dimers competent for peptide loading.

Plasminogen activators, integrins, and the coordinated regulation of cell adhesion and migration

Cellular migration is critically dependent on an interplay between forces of attachment and detachment. Recent studies show that the serine protease urokinase and its major inhibitor and receptor regulate the adhesive properties of integrins, at least in part through initiation of cellular signals. These new functions for an old protease system imply intricate connections between proteolysis and adhesion that operate at the cell surface to regulate migration.

Partners' stress underestimations lead to women's distress: a study of pregnant inner-city women

The authors examined how men's underestimation of the stress that their pregnant female partners reported influenced women's psychological distress and their sense that they were not supported. Participants included 68 pregnant inner-city women and their partners, among whom African Americans and European Americans were represented. Women who reported a greater number of stressful life events had increased depression if their partners did not report them as encountering these events. However, if their partners reported them as encountering a high number of stressful events, the otherwise negative impact of stress was buffered. Partners' stress report had no appreciable effect when women reported a low number of stressful events. This partner underestimation effect was independent of the influence of women's report of social support.

Degradation of mouse invariant chain: roles of cathepsins S and D and the influence of major histocompatibility complex polymorphism

Antigen-presenting cells (APC) degrade endocytosed antigens into peptides that are bound and presented to T cells by major histocompatibility complex (MHC) class II molecules. Class II molecules are delivered to endocytic compartments by the class II accessory molecule invariant chain (Ii), which itself must be eliminated to allow peptide binding. The cellular location of Ii degradation, as well as the enzymology of this event, are important in determining the sets of antigenic peptides that will bind to class II molecules. Here, we show that the cysteine protease cathepsin S acts in a concerted fashion with other cysteine and noncysteine proteases to degrade mouse Ii in a stepwise fashion. Inactivation of cysteine proteases results in incomplete degradation of Ii, but the extent to which peptide loading is blocked by such treatment varies widely among MHC class II allelic products. These observations suggest that, first, class II molecules associated with larger Ii remnants can be converted efficiently to class II-peptide complexes and, second, that most class II-associated peptides can still be generated in cells treated with inhibitors of cysteine proteases. Surprisingly, maturation of MHC class II in mice deficient in cathepsin D is unaffected, showing that this major aspartyl protease is not involved in degradation of Ii or in generation of the bulk of antigenic peptides.

Partners' stress underestimations lead to women's distress: a study of pregnant inner-city women

The authors examined how men's underestimation of the stress that their pregnant female partners reported influenced women's psychological distress and their sense that they were not supported. Participants included 68 pregnant inner-city women and their partners, among whom African Americans and European Americans were represented. Women who reported a greater number of stressful life events had increased depression if their partners did not report them as encountering these events. However, if their partners reported them as encountering a high number of stressful events, the otherwise negative impact of stress was buffered. Partners' stress report had no appreciable effect when women reported a low number of stressful events. This partner underestimation effect was independent of the influence of women's report of social support.

Plasmin and plasminogen activator inhibitor type 1 promote cellular motility by regulating the interaction between the urokinase receptor and vitronectin

The urokinase receptor (uPAR) coordinates plasmin-mediated cell-surface proteolysis and promotes cellular adhesion via a binding site for vitronectin on uPAR. Because vitronectin also binds plasminogen activator inhibitor type 1 (PAI-1), and plasmin cleavage of vitronectin reduces PAI-1 binding, we explored the effects of plasmin and PAI-1 on the interaction between uPAR and vitronectin. PAI-1 blocked cellular binding of and adhesion to vitronectin by over 80% (IC50 approximately 5 nM), promoted detachment of uPAR-bearing cells from vitronectin, and increased cellular migration on vitronectin. Limited cleavage of vitronectin by plasmin also abolished cellular binding and adhesion and induced cellular detachment. A series of peptides surrounding a plasmin cleavage site (arginine 361) near the carboxy-terminal end of vitronectin were synthesized. Two peptides spanning res 364-380 blocked binding of uPAR to vitronectin (IC50 approximately 8-25 microM) identifying this region as an important site of uPAR-vitronectin interaction. These data illuminate a complex regulatory scheme for uPAR-dependent cellular adhesion to vitronectin: Active urokinase promotes adhesion and also subsequent detachment through activation of plasmin or complex formation with PAI-1. Excess PAI-1 may also promote migration by blocking cellular adhesion and/or promoting detachment, possibly accounting in part for the strong correlation between PAI-1 expression and tumor cell metastasis.

Structure and chromosomal assignment of the human cathepsin K gene

Cathepsin K is a recently identified lysosomal cysteine proteinase that is the major protease responsible for bone resorption and remodeling. Mutations in this gene cause the sclerosing osteochondrodysplasia pycnodysostosis. To assess its evolutionary relatedness to other cysteine proteases and to facilitate mutation identification in patients with pycnodysostosis, a genomic clone, 74e16, containing the cathepsin K gene was isolated from a human PAC library, and the cathepsin K genomic structure was determined. The cathepsin K gene contained eight exons and spanned approximately 9 kb. The transcription initiation site, determined by primer extension analysis, was 169 nucleotides upstream from the translation initiation site. The 5'-flanking region lacked a TATA box but contained two AP1 sites. Comparison of genomic and cDNA sequences suggested that this flanking sequence may be the major promoter in osteoclasts and macrophages. Cathepsin K was mapped to chromosome 1q21 by fluorescence in situ hybridization and found to reside within 150 kb of an evolutionarily related cysteine protease, cathepsin S. These findings expand our understanding of the papain family lysosomal cysteine proteases and should facilitate mutation analysis in pycnodysostosis.

Emerging roles for cysteine proteases in human biology

Cysteine proteases have traditionally been viewed as lysosomal mediators of terminal protein degradation. However, recent findings refute this limited view and suggest a more expanded role for cysteine proteases in human biology. Several newly discovered members of this enzyme class are regulated proteases with limited tissue expression, which implies specific roles in cellular physiology. These roles appear to include apoptosis, MHC class II immune responses, prohormone processing, and extracellular matrix remodeling important to bone development. The ability of macrophages and other cells to mobilize elastolytic cysteine proteases to their surfaces under specialized conditions may also lead to accelerated collagen and elastin degradation at sites of inflammation in diseases such as atherosclerosis and emphysema. The development of inhibitors of specific cysteine proteases promises to provide new drugs for modifying immunity, osteoporosis, and chronic inflammation.

Mac-1 (CD11b/CD18) and the urokinase receptor (CD87) form a functional unit on monocytic cells

The leukocyte integrin Mac-1 (CD11b/CD18) and the urokinase receptor (uPAR, CD87) mediate complementary functions in myelomonocytic cells. Both receptors promote degradation of fibrin(ogen) and also confer adhesive properties on cells because Mac-1 and uPAR bind fibrin and vitronectin, respectively. Staining of lung biopsy specimens from patients with acute lung injury indicated that fibrin and vitronectin colocalize at exudative sites in which macrophages bearing these receptors accumulate. Because of the parallel roles and physical proximity of Mac-1 and uPAR, the capacity of these receptors to functionally interact was explored. Induction of Mac-1 and uPAR expression on monocytic cell lines by transforming growth factor- beta 1 and 1.25-(OH)2 vitamin D3 conferred urokinase and uPAR-dependent adhesion to vitronectin, which was further promoted by engagement of Mac-1. Vitronectin attachment promoted subsequent Mac-1-mediated fibrinogen degradation threefold to fourfold. In contrast, enhancement of uPAR occupancy by exogenous urokinase or receptor binding fragments thereof inhibited Mac-1 function. Addition of urokinase progressively inhibited Mac-1-mediated fibrinogen binding and degradation (maximal inhibition, 91% +/- 14% and 72% +/- 15%, respectively). Saturation of uPAR with urokinase also inhibited binding of the procoagulant Mac-1 ligand, Factor X. These inhibitory effects of uPAR were reproduced in fresh monocytes, cultured monocytic cells, and in Chinese hamster ovary (CHO) cells transfected with both human Mac-1 and human uPAR. These data show that the procoagulant and fibrinolytic potential of monocytic cells is co-ordinately regulated by ligand binding to both Mac-1 and uPAR and identify uPAR as a regulator of integrin function. Vitronectin-enhanced fibrin(ogen) turnover by Mac-1 may operate as a salvage pathway in the setting of urokinase and plasmin inhibitors to promote clearance of the provisional matrix and subsequent healing.

Regulation of integrin function by the urokinase receptor

Integrin function is central to inflammation, immunity, and tumor progression. The urokinase-type plasminogen activator receptor (uPAR) and integrins formed stable complexes that both inhibited native integrin adhesive function and promoted adhesion to vitronectin via a ligand binding site on uPAR. Interaction of soluble uPAR with the active conformer of integrins mimicked the inhibitory effects of membrane uPAR. Both uPAR-mediated adhesion and altered integrin function were blocked by a peptide that bound to uPAR and disrupted complexes. These data provide a paradigm for regulation of integrins in which a nonintegrin membrane receptor interacts with and modifies the function of activated integrins.

Pycnodysostosis, a lysosomal disease caused by cathepsin K deficiency

Pycnodysostosis, an autosomal recessive osteochondrodysplasia characterized by osteosclerosis and short stature, maps to chromosome 1q21. Cathepsin K, a cysteine protease gene that is highly expressed in osteoclasts, localized to the pycnodysostosis region. Nonsense, missense, and stop codon mutations in the gene encoding cathepsin K were identified in patients. Transient expression of complementary DNA containing the stop codon mutation resulted in messenger RNA but no immunologically detectable protein. Thus, pycnodysostosis results from gene defects in a lysosomal protease with highest expression in osteoclasts. These findings suggest that cathepsin K is a major protease in bone resorption, providing a possible rationale for the treatment of disorders such as osteoporosis and certain forms of arthritis.

Mechanisms of pertussis toxin-induced myelomonocytic cell adhesion: role of Mac-1(CD11b/CD18) and urokinase receptor (CD87)

Stimulation of monoblastic U937 cells with transforming growth factor beta 1 and 1,25-(OH)2 vitamin D3 (TGF-beta 1/D3) upregulates urokinase receptor (uPAR) and confers urokinase-dependent adhesiveness to the cells for serum- or vitronectin-coated surfaces. Recent studies show that uPAR itself is a high-affinity adhesion receptor for vitronectin and that urokinase (uPA) is an activator of this adhesive function. In the course of exploring possible G-protein involvement in this adhesion it was observed that TGF-beta 1/D3-primed U937 cells became adhesive to vitronectin in an uPAR-dependent manner when exposed to pertussis toxin (PTX). The adherent response is concentration- and time-dependent, and was not due to the ADP-ribosyltransferase activity of the toxin because the purified B-subunit of PTX was equally effective. Although promoting adhesion to serum- or vitronectin-coated surfaces, PTX blocked spontaneous cell adhesion to fibrinogen, an endogenous ligand for the Mac-1 receptor (CD11b/CD18). Flow cytometry study showed that expression of the alpha-subunit of Mac-1 (CD11b) on primed cells was increased by nearly threefold. Monoclonal antibody to CD11b abolished the PTX-induced cell adhesion and the binding of the primed cells to PTX-coated plates. Activation of Mac-1 receptor by its endogenous ligand fibrinogen induced cell adherent response similar to PTX. PTX, but not uPA, triggered a rapid rise in [Ca2+]i in primed U937 cells, and PTX-induced adhesion was significantly attenuated by 1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid/acetoxy-methyl ester (BAPTA/AM), a selective membrane-permeant [Ca2+]i chelator. PTX-induced cell adhesion was also prevented by antibodies to uPAR and by conditioned medium containing soluble uPAR. Together these data indicate that PTX B-subunit may bind to Mac-1 integrin, which leads to a rapid rise in [Ca2+]i and subsequent activation of uPAR for adherence to vitronectin, suggesting a functional link between Mac-1 and activation of uPAR important to cellular trafficking and host defence in response to Bordetella pertussis infection.

Essential role for cathepsin S in MHC class II-associated invariant chain processing and peptide loading

Destruction of li by proteolysis is required for MHC class II molecules to bind antigenic peptides, and for transport of the resulting complexes to the cell surface. The cysteine protease cathepsin S is highly expressed in spleen, lymphocytes, monocytes, and other class II-positive cells, and is inducible with interferon-gamma. Specific inhibition of cathepsin S in B lymphoblastoid cells prevented complete proteolysis of li, resulting in accumulation of a class II-associated 13 kDa li fragment in vivo. Consequently, the formation of SDS-stable complexes was markedly reduced. Purified cathepsin S, but not cathepsin B, H, or D, specifically digested li from alpha beta li trimers, generating alpha beta-CLIP complexes capable of binding exogenously added peptide in vitro. Thus, cathepsin S is essential in B cells for effective li proteolysis necessary to render class II molecules competent for binding peptides.

Lysosomal processing of amyloid precursor protein to A beta peptides: a distinct role for cathepsin S

To investigate the potential contribution of the lysosomal compartment in the processing of amyloid precursor protein (APP) to amyloid beta-peptides (A beta s), we stably overexpressed a series of lysosomal proteases (the cysteine proteases, cathepsins B, L and S, and the aspartic protease, cathepsin D) in a human kidney epithelial cell line (293) transfected to express high levels of beta APP. Preliminary experiments indicated that 293 cells endogenously synthesize cathepsins B, L and D, but not cathepsin S. A beta secretion was assessed by immunoprecipitation and ELISA and found to be increased approximately 2-fold following cathepsin S expression, but to be unchanged (cathepsins B, L) or decreased (cathepsin D) in the other double transfectants. E-64d, an inhibitor of lysosomal cysteine proteases, significantly reduced A beta secretion by the cathepsin S transfectants, but had no effect on cells expressing the other proteases. Radiosequencing of A beta secreted by cathepsin S-expressing cells revealed that a previously unreported variant beginning at Met -1 (relative to the most common A beta N-terminus, Asp -1) accounted for most of the increase in A beta secretion. Immunostaining of human brain sections revealed cathepsin S in cortical neurons and glia in samples of brain from patients with Alzheimer's disease. These results provide evidence in living cells for a pathway in which cathepsin S generates A beta from amyloidogenic fragments of beta APP in the endosomal/lysosomal compartment. This pathway appears to be inducible, distinct from a constitutive pathway used by 293 and other cells to generate A beta, and may be relevant to the pathogenesis of Alzheimer's disease.

Urokinase receptor is a multifunctional protein: influence of receptor occupancy on macrophage gene expression

Binding of urokinase to the glycolipid-anchored urokinase receptor (uPAR) has been implicated in macrophage differentiation. However, no biochemical markers of differentiation have yet been directly linked to uPAR occupancy. As extensive changes in proteolytic profile characterize monocytic differentiation, we have examined the role of uPAR occupancy on protease expression by differentiating phagocytes. Antibodies to either urokinase or to uPAR that prevent receptor binding inhibited induction of cathepsin B in cultured monocytes and both cathepsin B and 92-kD gelatinase mRNA and protein in phorbol diester-stimulated myeloid cells. Mannosamine, an inhibitor of glycolipid anchor assembly, also blocked protease expression. Anti-catalytic urokinase antibodies, excess inactive urokinase, or aprotinin had no effect, indicating that receptor occupancy per se regulated protease expression. Antibodies to the integrins CD11a and CD29 or to the glycolipid-anchored proteins CD14 and CD55 also had no effect. Protease induction was independent of matrix attachment. Antibodies to urokinase or uPAR affected neither the decrease in cathepsin G nor the increase in tumor necrosis factor-alpha in phorbol ester-stimulated cells. These data establish that uPAR is a multifunctional receptor, not only promoting pericellular proteolysis and matrix attachment, but also effecting cysteine- and metallo-protease expression during macrophage differentiation.

The lysosomal cysteine protease, cathepsin S, is increased in Alzheimer's disease and Down syndrome brain. An immunocytochemical study

Expression of cathepsin (cat) S, a lysosomal cysteine protease, has recently been shown to cause an increase in production of amyloid beta-peptides in transfected human cells. In this study, we examined the presence and localization of cat S by immunocytochemistry in 21 control, 24 Alzheimer's disease (AD), and 10 Down syndrome (DS) postmortem brains. An antiserum to a human cat S fusion protein was affinity purified and its specificity confirmed by abolition of immunoreactivity after adsorption with cat S but not cat L fusion protein. A small minority of control cases showed light, focal staining of scattered cortical neurons. Many control cases, as well as most AD and DS cases, showed prominent staining of vascular smooth muscle cells, particularly in leptomeningeal vessels. Both AD and DS brain tissue showed increased immunoreactivity in a subset of neocortical and hippocampal neurons and glia. Cat S immunoreactivity occurred in a granular, cytoplasmic pattern in some neurons or in a more dense staining pattern in certain neurofibrillary tangle-bearing neurons. Cat S-positive neurons were also present in amygdala and basal forebrain in AD brains. A subset of astrocytes were immunoreactive with the cat S antibody in AD and DS but not in control brains. In rare AD cases, cat S immunostaining was observed in astrocytes in the periphery of amyloid-beta-containing plaques. These results suggest that cat S is up-regulated in AD and DS brain. The association of cat S immunoreactivity with tangle-bearing neurons, astrocytes, and rare senile plaques implies a role for altered cat S activity in the pathogenesis of AD.

Molecular cloning of human cathepsin O, a novel endoproteinase and homologue of rabbit OC2

A 1670-bp cDNA coding for a novel human cysteine protease has been isolated from a monocyte-derived macrophage cDNA library. This cDNA predicts a 329-amino acid preprocathepsin with more than 50% identity to both human cathepsin S and cathepsin L and 94% identity to a rabbit cDNA, termed OC2, recently isolated from osteoclasts. Based on its high homology to OC2, we have named the human enzyme cathepsin O. Cathepsin O mRNA was identified as a single approximately 1.7 kb transcript in cultures of 15-day-old monocyte-derived macrophages, but was not expressed in human monocytes or alveolar macrophages. When transfected into COS-7 cells, cathepsin O displayed potent endoprotease activity against fibrinogen at acid pH. This novel endoprotease may play an important role in extracellular matrix degradation.