Components of the nuclear signaling cascade that regulate collagenase gene expression in response to integrin-derived signals

Vascular Mechanobiology: Homeostasis, Adaptation, and Disease

Cells of the vascular wall are exquisitely sensitive to changes in their mechanical environment. In healthy vessels, mechanical forces regulate signaling and gene expression to direct the remodeling needed for the vessel wall to maintain optimal function. Major diseases of arteries involve maladaptive remodeling with compromised or lost homeostatic mechanisms. Whereas homeostasis invokes negative feedback loops at multiple scales to mediate mechanobiological stability, disease progression often occurs via positive feedback that generates mechanobiological instabilities. In this review, we focus on the cell biology, wall mechanics, and regulatory pathways associated with arterial health and how changes in these processes lead to disease. We discuss how positive feedback loops arise via biomechanical and biochemical means. We conclude that inflammation plays a central role in overriding homeostatic pathways and suggest future directions for addressing therapeutic needs.

Profile of Matrix-Remodeling Proteinases in Osteoarthritis: Impact of Fibronectin

The extracellular matrix (ECM) is a complex and specialized three-dimensional macromolecular network, present in nearly all tissues, that also interacts with cell surface receptors on joint resident cells. Changes in the composition and physical properties of the ECM lead to the development of many diseases, including osteoarthritis (OA). OA is a chronic degenerative rheumatic disease characterized by a progressive loss of synovial joint function as a consequence of the degradation of articular cartilage, also associated with alterations in the synovial membrane and subchondral bone. During OA, ECM-degrading enzymes, including urokinase-type plasminogen activator (uPA), matrix metalloproteinases (MMPs), and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs), cleave ECM components, such as fibronectin (Fn), generating fibronectin fragments (Fn-fs) with catabolic properties. In turn, Fn-fs promote activation of these proteinases, establishing a degradative and inflammatory feedback loop. Thus, the aim of this review is to update the contribution of ECM-degrading proteinases to the physiopathology of OA as well as their modulation by Fn-fs.

Protective Effects and Mechanisms of Pourthiaea villosa (Thunb.) Decne. Extract on Hydrogen Peroxide-Induced Skin Aging in Human Dermal Fibroblasts

Skin aging is associated with increased reactive oxygen species (ROS) produced by human cells. These radicals are the main causes of skin aging, and skin cells have developed antioxidant enzymes for protection against ROS-induced damage. Antioxidants play critical roles to prevent ROS-induced aging symptoms. In this study, the antioxidant properties of Pourthiaea villosa (Thunb.) Decne. extract (PVDE) were studied. Human dermal fibroblast (HDF) cells were treated with PVDE to evaluate its antioxidant and antiaging activities and to investigate the underlying mechanisms. The identified compounds were polyols, and phenolic and flavonoid compounds from PVDE by UHPLC-LTQ-IT-MS/MS. PVDE exhibited significant antioxidant effects, as evaluated with reducing power, and ABTS and DPPH radical scavenging activity. Furthermore, PVDE treatment significantly increased antioxidant enzyme expressions and effectively blocked H₂O₂-induced matrix metalloproteinase activity through MAPK signaling pathways in HDFs. Therefore, these results showed that PVDE affords an advantage of being a functional natural material with antioxidant and antiaging effects for the skin.

Tiron Inhibits UVB-Induced AP-1 Binding Sites Transcriptional Activation on MMP-1 and MMP-3 Promoters by MAPK Signaling Pathway in Human Dermal Fibroblasts

Recent research found that Tiron was an effective antioxidant that could act as the intracellular reactive oxygen species (ROS) scavenger or alleviate the acute toxic metal overload in vivo. In this study, we investigated the inhibitory effect of Tiron on matrix metalloproteinase (MMP)-1 and MMP-3 expression in human dermal fibroblast cells. Western blot and ELISA analysis revealed that Tiron inhibited ultraviolet B (UVB)-induced protein expression of MMP-1 and MMP-3. Real-time quantitative PCR confirmed that Tiron could inhibit UVB-induced mRNA expression of MMP-1 and MMP-3. Furthermore, Tiron significantly blocked UVB-induced activation of the MAPK signaling pathway and activator protein (AP)-1 in the downstream of this transduction pathway in fibroblasts. Through the AP-1 binding site mutation, it was found that Tiron could inhibit AP-1-induced upregulation of MMP-1 and MMP-3 expression through blocking AP-1 binding to the AP-1 binding sites in the MMP-1 and MMP-3 promoter region. In conclusion, Tiron may be a novel antioxidant for preventing and treating skin photoaging UV-induced.

Cardiac fibroblasts form and function

The formation and structure of the extracellular matrix (ECM) that makes up the cardiac interstitum is well known yet the underlying mechanisms that regulate the interstitum are poorly known. This review focuses on the role of the cardiac fibroblast in the formation and regulation of the ECM components during cardiac development and in response to physiological and pathological stimulation. The role of ECM receptors (integrins), cellular phenotype, and chemical and mechanical signaling by cardiac fibroblasts are discussed.

Granzyme B mediates both direct and indirect cleavage of extracellular matrix in skin after chronic low-dose ultraviolet light irradiation

Extracellular matrix (ECM) degradation is a hallmark of many chronic inflammatory diseases that can lead to a loss of function, aging, and disease progression. Ultraviolet light (UV) irradiation from the sun is widely considered as the major cause of visible human skin aging, causing increased inflammation and enhanced ECM degradation. Granzyme B (GzmB), a serine protease that is expressed by a variety of cells, accumulates in the extracellular milieu during chronic inflammation and cleaves a number of ECM proteins. We hypothesized that GzmB contributes to ECM degradation in the skin after UV irradiation through both direct cleavage of ECM proteins and indirectly through the induction of other proteinases. Wild-type and GzmB-knockout mice were repeatedly exposed to minimal erythemal doses of solar-simulated UV irradiation for 20 weeks. GzmB expression was significantly increased in wild-type treated skin compared to nonirradiated controls, colocalizing to keratinocytes and to an increased mast cell population. GzmB deficiency significantly protected against the formation of wrinkles and the loss of dermal collagen density, which was related to the cleavage of decorin, an abundant proteoglycan involved in collagen fibrillogenesis and integrity. GzmB also cleaved fibronectin, and GzmB-mediated fibronectin fragments increased the expression of collagen-degrading matrix metalloproteinase-1 (MMP-1) in fibroblasts. Collectively, these findings indicate a significant role for GzmB in ECM degradation that may have implications in many age-related chronic inflammatory diseases.

Platinum-sensitive recurrence in ovarian cancer: the role of tumor microenvironment

Despite several advances in the understanding of ovarian cancer pathobiology, in terms of driver genetic alterations in high-grade serous cancer, histologic heterogeneity of epithelial ovarian cancer, cell-of-origin for ovarian cancer, the survival rate from ovarian cancer is disappointingly low when compared to that of breast or prostate cancer. One of the factors contributing to the poor survival rate from ovarian cancer is the development of chemotherapy resistance following several rounds of chemotherapy. Although unicellular drug resistance mechanisms contribute to chemotherapy resistance, tumor microenvironment and the extracellular matrix (ECM), in particular, is emerging as a significant determinant of a tumor’s response to chemotherapy. In this review, we discuss the potential role of the tumor microenvironment in ovarian cancer recurrence and resistance to chemotherapy. Finally, we propose an alternative view of platinum-sensitive recurrence to describe a potential role of the ECM in the process.

Analytic study of three-dimensional single cell migration with and without proteolytic enzymes

Cell motility is a fundamental physiological process that regulates cellular fate in healthy and diseased systems. Cells cultured in 3D environments often exhibit biphasic dependence of migration speed with cell adhesion. Much is not understood about this very common behavior. A phenomenological model for 3D single-cell migration that exhibits biphasic behavior and highlights the important role of steric hindrance is developed and studied analytically. Changes in the biphasic behavior in the presence of proteolytic enzymes are investigated. Our methods produce a framework to determine analytic formulae for the mean cell speed, allowing general statements in terms of parameters to be explored, which will be useful when interpreting future experimental results. Our formula for mean cell speed as a function of ligand concentration generalizes and extends previous computational models that have shown good agreement with in vitro experiments.

Immunohistochemical analysis of TIMP-2 and collagen types I and IV in experimental spinal cord ischemia-reperfusion injury in rats

BACKGROUND

Thoracic and thoracoabdominal aortic intervention carries a significant risk of spinal cord ischemia. The pathophysiologic mechanisms that cause hypoxic/ischemic injury to the spinal cord have not been totally explained. In normal spinal cord, neurons and glial cells do not express type IV collagen. Type IV collagen produced by reactive astrocytes is reported to participate in glial scar formation. Tissue inhibitors of metalloproteinases (TIMPs) are endogenous inhibitors that regulate the activity of the matrix metalloproteinases (MMPs). TIMP-2 binds strongly with MMP-2, facilitating activation by membrane-type MMP. Imbalance between TIMPs and MMPs can lead to excessive degradation of matrix components. Type IV collagen involved in the blood-brain barrier disruption and glial scar formation, TIMP-2 influences MMP-2 that controls degradation of collagen I and IV.

OBJECTIVE

To examine the immunohistochemical analysis of TIMP-2 and collagen types I-IV in experimental spinal cord ischemia-reperfusion in rats.

METHODS

Thirty-two male Wistar rats weighing 250-300 g were divided into four groups: group S: sham group (n = 8); group 0P: 30-minute occlusion without perfusion (n = 8); group 3P: 30-minute occlusion and 3-hour perfusion (n = 8); and group 24P: 30-minute occlusion and 24-hour perfusion (n = 8). Infrarenal aorta was cross-clamped at two sites by using two aneurysm clips for 30 minutes. Reperfusion was provided after removal of the clips. Lumbar spinal cord segments were removed for immunohistochemical analysis.

RESULTS

TIMP-2 and collagen staining in 3-hour perfused (3P) group were nearly the same with sham group (S). TIMP-2 and collagen staining increased in the 24-hour perfused group.

CONCLUSION

Alterations in collagen levels may relate to the biphasic breakdown of the blood-brain barrier and collagen staining in new cell types with relation to glial scar formation. Our results demonstrate that 3-hour perfusion after occlusion in hypoxic/ischemic spinal cord injury seems to be the critical reversible period.

Induction of MMP-1 (collagenase-1) by relaxin in fibrocartilaginous cells requires both the AP-1 and PEA-3 promoter sites

OBJECTIVES - Relaxin induces the matrix metalloproteinase MMP-1 (collagenase-1) in TMJ fibrocartilaginous cells, and this response is potentiated by beta-estradiol. We identified the MMP-1 promoter sites and transcription factors that are induced by relaxin with or without beta-estradiol in fibrocartilaginous cells. MATERIAL AND METHODS - Early passage cells were transiently transfected with the pBLCAT2 plasmid containing specific segments of the human MMP-1 promoter regulating the chloramphenicol acyl transferase (CAT) gene and co-transfected with a plasmid containing the beta-galactosidase gene. The cells were cultured in serum-free medium alone or medium containing 0.1 ng/ml relaxin, or 20 ng/ml beta-estradiol or both hormones, and lysates assayed for CAT and beta-galactosidase activity. RESULTS - Cells transfected with the -1200/-42 or -139/-42 bp MMP-1 promoter-reporter constructs showed 1.5-fold and 3-fold induction of CAT by relaxin in the absence or presence of beta-estradiol, respectively. Relaxin failed to induce CAT in the absence of the -137/-69 region of the MMP-1 promoter, which contains the AP-1-and PEA3-binding sites. Using wild type or mutated minimal AP-1 and PEA-3 promoters we found that both these promoter sites are essential for the induction of MMP-1 by relaxin. The mRNAs for transcription factors c-fos and c-jun, which together form the AP-1 heterodimer, and Ets-1 that modulates the PEA-3 site, were upregulated by relaxin or beta-estradiol plus relaxin. CONCLUSION - These studies show that both the AP-1 and PEA-3 promoter sites are necessary for the induction of MMP-1 by relaxin in fibrocartilaginous cells.

Integrins as "functional hubs" in the regulation of pathological angiogenesis

It is well accepted that complex biological processes such as angiogenesis are not controlled by a single family of molecules or individually isolated signaling pathways. In this regard, new insight into the interconnected mechanisms that regulate angiogenesis might be gained by examining this process from a more global network perspective. The coordination of signaling cues from both outside and inside many different cell types is required for the successful completion of angiogenesis. Evidence is accumulating that the multifunctional integrin family of cell adhesion receptors represent an important group of molecules that play active roles in sensing, integrating, and distributing a diverse set of signals that regulate many cellular events required for angiogenesis. Given the ability of integrins to bind numerous extracellular ligands and transmit signals in a bi-directional fashion, we will discuss the multiple ways by which integrins may serve as a functional hub during pathological angiogenesis. In addition, we will highlight potential imaging and therapeutic strategies based on the expanding new insight into integrin function.

Convergence of integrins and EGF receptor signaling via PI3K/Akt/FoxO pathway in early gene Egr-1 expression

The early gene early growth response (Egr-1), a broadly expressed member of the zing-finger family of transcription factors, is induced in many cell types by a variety of growth and differentiation stimuli, including epidermal growth factor (EGF). Here we demonstrate that Egr-1 expression is mainly regulated by integrin-mediated adhesion. Integrin-dependent adhesion plays a dual role in Egr-1 regulation, either being sufficient "per se" to induce Egr-1, or required for EGF-dependent expression of Egr-1, which occurs only in adherent cells and not in cells in suspension. To dissect the molecular basis of integrin-dependent Egr-1 regulation, we show by FLIM-based FRET that in living cells beta1-integrin associates with the EGF receptor (EGFR) and that EGF further increases the extent complex formation. Interestingly, Egr-1 induction depends on integrin-dependent PI3K/Akt activation, as indicated by the decrease in Egr-1 levels in presence of the pharmacological inhibitor LY294002, the kinase-defective Akt mutant and Akt1/2 shRNAs. Indeed, upon adhesion activated Akt translocates into the nucleus and phosphorylates FoxO1, a Forkhead transcription factors. Consistently, FoxO1silencing results in Egr-1-increased levels, indicating that FoxO1 behaves as a negative regulator of Egr-1 expression. These data demonstrate that integrin/EGFR cross-talk is required for expression of Egr-1 through a novel regulatory cascade involving the activation of the PI3K/Akt/Forkhead pathway.

The influence of surface roughness of titanium on β1- and β3-integrin adhesion and the organization of fibronectin in human osteoblastic cells

Mechanisms of cell adhesion and extracellular matrix formation are primary processes in the interaction with the material surface of an implant which are controlled by integrin receptors. The aim of our study was to find out whether beta1- and beta3-integrins of osteoblastic cells sense the surface topography of titanium, and if structural alterations of integrin adhesions were involved in the organization of fibronectin. Pure titanium surfaces were modified by polishing (P), machining (NT), blasting with glass spheres (GB), and blasting with corundum particles (CB) resulting in increasing roughness. Confocal microscopic investigations revealed fibrillar adhesions of beta1- and alpha5-integrins on P, NT, and GB, but on CB with its sharp edges these integrin subunits did not form fibrillar adhesions. beta3 generally appeared in focal adhesions. We observed aligned fibrillar structures of fibronectin on NT not only on the basal site but interestingly, also on the apical cell surface. In contrast, on CB, fibronectin appeared apically clustered. We suggest that this alignment of fibronectin fibrils depends on the directed actin cytoskeleton and in particular, on the capability of the beta1-integrins to form fibrillar adhesions, which is affected by the surface roughness of titanium.

Production of matrix metalloproteinases by cultured bovine theca and granulosa cells

Matrix metalloproteinases (MMPs) degrade the proteinaceous components of the extracellular matrix and are presumably essential for follicular growth culminating in ovulation or atresia. The objectives of this study were to characterize the gelatinolytic and caseinolytic MMPs secreted by cultured bovine thecal and granulosal cells and to determine the effect of luteinizing hormone (LH) on MMP secretion. Thecal and granulosal cells were collected from small bovine follicles (<5 mm) on day 2 or 5 of the estrous cycle (day 0 = estrus). A serum-free culture system was utilized in which bovine thecal and granulosal cells do not spontaneously luteinize, but produce androstenedione and estradiol in response to physiological concentrations of LH and follicle-stimulating hormone (FSH) respectively. The effect of LH (0, 1 or 100 ng/ml) on MMP production was determined in conditioned media collected every 48 h for 144 h. MMPs were detected by gelatin and casein zymography and MMP activity was quantified by image analysis. Thecal and granulosal cell conditioned media contained MMPs that had a relative molecular size (Mr) ranging from 53 000 to 200 000 and addition of 1,10 phenanthroline (MMP inhibitor) blocked gelatinolytic and caseinolytic activity. Patterns of gelatinolytic activity in thecal and granulosal cell conditioned media differed over time with theMr62 000 and 83 000 MMPs being increased (P< 0.05) and theMr53 000 MMP being decreased (P< 0.05) at 96 h of culture. LH (1 or 100 ng/ml) increased (P< 0.05) gelatinolytic activity of theMr53 000 and 62 000 gelatinases within thecal cell conditioned media but not granulosal cell conditioned media. TheMr62 000 and 83 000 gelatinolytic activities corresponded to the active forms of gelatinase A (Mr62 000) and B (Mr, 83 000) and gelatinase A was detected in thecal cell conditioned media by Western blot analysis. Caseinolytic activity (Mr83 000) was detected in both thecal and granulosal cell conditioned media and increased from 48 to 96 h. In summary, thecal and granulosal cells secrete gelatinolytic and caseinolytic MMPs and thecal cell production of gelatinase A was stimulated by LH.

The clinical role of the PEA3 transcription factor in ovarian and breast carcinoma in effusions

Ets transcription factors play a central role in invasion and metastasis through regulation of synthesis of proteolytic enzymes and angiogenic molecules. The objective of this study was to investigate the role of PEA3 in tumor progression of ovarian and breast carcinoma metastatic to effusions, and to evaluate the expression of Ets-2 and Erg in ovarian carcinoma. Ovarian (83 malignant effusions, 102 corresponding solid lesions) and breast (33 malignant effusions, 40 corresponding solid lesions) carcinomas were evaluated for expression of PEA3 using mRNA in situ Hybridization (ISH). Expression of Ets-2 and Erg mRNA was analyzed in 50 ovarian carcinoma effusions using the same method. PEA3 mRNA expression was comparable at all sites in ovarian carcinoma (44 out of 83; 53% of effusions, 48 out of 102; 47% of solid tumors). PEA3 mRNA expression in effusions correlated with mRNA expression of the previously studied alphav (P = 0.022), alpha6 (P < 0.001) and beta1 (P < 0.001) integrin subunits, the matrix metalloproteinase (MMP) inducer EMMPRIN (P = 0.015) and interleukin-8 (IL-8) (P = 0.033). Erg and Ets-2 mRNA was expressed in 15 out of 50 (30%) and 18 out of 50 (36%) effusions, respectively, and co-localized with PEA3 (P = 0.017 for Erg, P = 0.004 for Ets-2). In breast carcinoma, PEA3 expression was seen in 19/40 (48%) of solid lesions, with a significant upregulation in corresponding effusions compared to primary tumors (24 out of 33; 73%, P = 0.038). PEA3 mRNA expression in effusions obtained prior to the institution of chemotherapy predicted significantly shorter overall survival in univariate analysis (24 vs 37 months, P = 0.03), with a similar trend for Erg (13 vs 30 months, P = 0.1). In conclusion, PEA3 is expressed at all anatomic sites in serous ovarian cancer and co-localizes with Erg, Ets-2 and several metastasis-associated molecules. PEA3 mRNA expression is a novel marker for tumor progression to malignant effusion in breast carcinoma, and predicts poor outcome in effusions sampled prior to therapeutic intervention in ovarian carcinoma. These findings support a biological role for Ets transcription factors in these malignancies and suggests that they may be targets for therapeutic intervention.

AlphaV integrins play an important role in myofibroblast differentiation

Transforming growth factor-beta1 is a potent mediator of the differentiation of fibroblasts into myofibroblasts, which is characterized by the appearance of the cytoskeletal protein alpha-smooth muscle actin. The aim of this study was to investigate the role of integrin extracellular matrix receptors in transforming growth factor-beta1-induced myofibroblast differentiation. We show that blockade of the alphav and/or beta1 integrins prevents the transforming growth factor-beta1-induced myofibroblast differentiation, seen by the increased expression of alpha-smooth muscle actin and enhanced collagen gel contraction in three human fibroblast cell lines (from the mouth, skin, and kidney). Further, blockade of alphav specific integrins alphavbeta5 and alphavbeta3 suppressed myofibroblast differentiation in fibroblasts from the mouth and skin; however, in the kidney cells, the prevention of differentiation was seen only with blockade of alphavbeta5 integrin but not alphavbeta3. A possible reason for this result may be different degrees of responsiveness to transforming growth factor-beta1 treatment seen from different anatomical origins of the cell lines. These data indicate a novel role for alphav integrins in the differentiation of human fibroblasts from the mouth, skin, and kidney into myofibroblasts and suggest that there is a common differentiation pathway.

Increased expression levels of integrin alphavbeta5 on scleroderma fibroblasts

Integrin alphavbeta5 is a receptor for vitronectin, a plasma glycoprotein that is also distributed in extracellular matrix of various tissues. Matrix-bound vitronectin has the potential to stabilize the active form of plasminogen activator inhibitor-1, resulting in the inhibition of the plasmin-mediated pericellular proteolytic cascade. In this study, we compared the levels of alphavbeta5 and matrix-bound vitronectin between normal and scleroderma fibroblasts and investigated the association with fibrosis. We demonstrated that alphavbeta5 was up-regulated on scleroderma fibroblasts. The up-regulated alphavbeta5 contributed to the increase in vitronectin-binding ability in scleroderma fibroblasts, which led to the vitronectin-dependent activation of plasminogen activator inhibitor-1. In immunohistochemistry, the alphav and beta5 subunits were stained strongly on scleroderma fibroblasts and the amount of vitronectin was increased in the pericellular matrix of those cells. The transient overexpression of alphavbeta5 on normal fibroblasts enhanced the human alpha2(I) collagen promoter activity through Sp-1 and Smad3 as well as the vitronectin-dependent plasminogen activator inhibitor-1 activity. This effect on the promoter activity was also observed in the absence of vitronectin and completely disappeared in the presence of anti-alphavbeta5 antibody. These results indicate that the up-regulated alphavbeta5 may contribute to the phenotypical alteration of scleroderma fibroblasts, while at the same time suppressing the plasmin-mediated pericellular proteolytic cascade.

Ex vivo static tensile loading inhibits MMP-1 expression in rat tail tendon cells through a cytoskeletally based mechanotransduction mechanism

To determine the effect of various degrees of ex vivo static tensile loading on the expression of collagenase (MMP-1) in tendon cells, rat tail tendons were statically loaded in tension at 0.16, 0.77, 1.38 or 2.6 MPa for 24 h. Northern blot analysis was used to assay for mRNA expression of MMP-1 in freshly harvested, 24 h load deprived, and 24 h statically loaded tendons. Western blot analysis was used to assay for pro-MMP-1 and MMP-1 protein expression in fresh and 24 h load deprived tendons. Freshly harvested rat tail tendons demonstrated no evidence of MMP-1 mRNA expression and no evidence of the pro-MMP-1 or MMP-1 protein. Ex vivo load deprivation for 24 h resulted in a marked increase in the mRNA expression of MMP-1 which coincided with a marked increase of both pro-MMP-1 and MMP-1 protein expression. When tendons were subjected to ex vivo static tensile loading during the 24 h culture period, a significant inhibition of this upregulation of MMP-1 mRNA expression was found with increasing load (p<0.05). A strong (r2=0.78) and significant (p<0.001) inverse correlation existed between the level of static tensile load and the expression of MMP-1. Disruption of the actin cytoskeleton with cytochalasin D abolished the inhibitory effect of ex vivo static tensile loading on MMP-1 expression. The results of this study suggest that up-regulation of MMP-1 expression in tendon cells ex vivo can be inhibited by static tensile loading, presumably through a cytoskeletally based mechanotransduction pathway.

Increased plasminogen activator inhibitor-1 in keloid fibroblasts may account for their elevated collagen accumulation in fibrin gel cultures

Proteolytic degradation of the provisional fibrin matrix and subsequent substitution by fibroblast-produced collagen are essential features of injury repair. Immunohistochemical studies revealed that although dermal fibroblasts of normal scars and keloids expressed both urokinase type plasminogen activator (uPA) and plasminogen activator inhibitor-1 (PAI-1), keloid fibroblasts had a much higher PAI-1 expression. In long-term three-dimensional fibrin gel cultures (the in vitro fibroplasia model), normal fibroblasts expressed moderate and modulated activity levels of uPA and PAI-1. In contrast, keloid fibroblasts expressed a persistently high level of PAI-1 and a low level of uPA. The high PAI-1 activity of keloid fibroblasts correlated with their elevated collagen accumulation in fibrin gel cultures. Substituting collagen for fibrin in the gel matrix resulted in increased uPA activity and reduced collagen accumulation of keloid fibroblasts. Furthermore, decreasing PAI-1 activity of keloid fibroblasts in fibrin gel cultures with anti-PAI-1-neutralizing antibodies also resulted in a reduction in collagen accumulation by keloid fibroblasts. Cumulatively, these results suggest that PAI-1 overexpression is a consistent feature of keloid fibroblasts both in vitro and in vivo, and PAI-1 may play a causative role in elevated collagen accumulation of keloid fibroblasts.

Glucose-induced changes in integrins and matrix-related functions in cultured human glomerular epithelial cells

In cultured human glomerular epithelial cells (HGEC), 25 mM glucose resulted in decreased expression of alpha(3)-, alpha(2)-, and beta(1)-integrins and increased expression of alpha(5)- and alpha(v)beta(3)-integrins. This change was accompanied by decreased binding of HGEC to type IV collagen. In the presence of normal (5 mM) glucose concentration, cell binding to type IV collagen was primarily mediated by alpha(2)beta(1)- and alpha(5)beta(1)-integrins, as indicated by experiments in which cell adhesion to type IV collagen was competed by specific anti-integrin monoclonal antibodies. In the presence of high (25 mM) glucose, the upregulated alpha(5)- and alpha(v)beta(3)-integrins were mainly involved in cell binding to type IV collagen. Furthermore, high glucose decreased expression of matrix metalloproteinase-2 (MMP-2), a collagenase regulated in part by alpha(3)beta(1)-integrin, as suggested by the use of ligand-mimicking antibodies against these integrins, which resulted in release of increased amounts of MMP-2 in the culture medium. Finally, tissue inhibitor of metalloproteinase-2, the specific inhibitor of MMP-2, was upregulated in high glucose and could contribute to matrix accumulation. These changes could help explain basement membrane thickening in diabetes.

Regulation of trophoblastic gelatinases by proto-oncogenes

During the first trimester of pregnancy, certain cytotrophoblastic cells (CTB) of anchoring villi invade the underlying decidua. Regulation of this invasive behaviour depends on cytokines and growth factors secreted by decidua and trophoblast, which modulate metalloproteinase (MMP) secretion of CTB. Since MMP-9 expression by CTB is a prerequisite for matrigel invasion and since the promoter region of the MMP-9 gene contains two AP-1 binding sites, we hypothesized, that transient activation of c-jun and c-fos oncogenes (which bind to form AP-1) by tumour necrosis factor (TNFalpha), or the phorbol ester TPA will promote the invasive phenotype of CTB and induce the production of MMP-9.TNFalpha or TPA when added to primary cultures of CTB increase MMP-9 activity and MMP-9 mRNA. This effect is inhibited by cycloheximide indicating the necessity of protein synthesis. TPA or TNFalpha induces also the binding of nuclear proteins (extracted from treated CTB) to a radiolabelled oligonucleotide corresponding to the consensus sequence of the TPA responsive element. Antibodies to Jun and Fos can displace this binding. Transient transfection of antisense mRNA to jun or fos into CTB inhibits the immunoreactivity and gelatinolytic activity of MMP-9. We conclude that AP-1 is necessary but may not be sufficient for transactivation of the MMP-9 gene in human CTB.

Matrix metalloproteinase-2 is involved in A549 cell migration on laminin-10/11

We have reported that laminin-10/11 strongly promotes migration of A549 human lung carcinoma cells by activating the alpha3beta1 integrin-dependent signaling pathway. To elucidate the mechanism involved, we investigated whether matrix metalloproteinases (MMPs) are involved in cell migration on laminin-10/11. Here, we demonstrate that laminin-10/11, but not fibronectin which does not greatly promote A549 cell movement, stimulated MMP-2 secretion approximately 3-fold. The cell migration-promoting activity of laminin-10/11 was down-regulated by an MMP inhibitor. In addition, cell motility was significantly increased when cells adhered to a mixture of fibronectin and laminin-10/11 with a concomitant decrease of focal contacts, compared with those adhering to fibronectin alone. The enhanced cell migration was partially suppressed by the MMP inhibitor. Furthermore, an anti-alpha3 integrin, but not an anti-alpha5 integrin, antibody induced the activated form of MMP-2. These data suggest that MMP-2 may play an important role in A549 cell migration on laminin-10/11 through an alpha3beta1 integrin-dependent pathway.

Proximal tubular epithelial cell integrins respond to high glucose by altered cell-matrix interactions and differentially regulate matrixin expression

Thickening of the tubular basement membrane (TBM) occurs in diabetic nephropathy, but the effects of high glucose on the functional aspects of proximal tubular epithelial cells are not clearly understood. In the present study, we examined the effects of elevated glucose concentrations on (a) integrin expression by human proximal tubular epithelial cells (HK-2) and integrin-mediated interactions with type IV collagen (colIV) and laminin, major components of TBM; (b) the expression of matrixins/matrix metalloproteinases (MMPs), which is regulated by integrins; and (c) the expression of tissue inhibitors of metalloproteinases (TIMPs). HK-2 cells cultured in 25 mM glucose underwent a reduction of the expression of alpha3, beta1, alpha(v)beta3, and alpha5 integrin subunits, with a concomitant increase of the alpha2 subunit, compared with cells grown in 5 mM glucose. Adhesion experiments demonstrated that high glucose led to increased cell adhesion on either colIV or laminin. Experiments of competition of adhesion using anti-integrin antibodies indicated that HK-2 cells in 5 mM glucose used mainly alpha(v)beta3 and alpha5beta1 integrins to adhere to colIV, whereas in 25 mM glucose they additionally used alpha2beta1. In the case of laminin, a beta1-mediated adhesion was observed when HK-2 cells were in 5 mM glucose, whereas in 25 mM glucose, alpha2beta1 and alpha(v)beta3 were also involved. Elevated glucose concentrations resulted in decreased expression of MMP-9 and MMP-2, whereas an increase in TIMP-1 and a decrease in TIMP-2 expression were observed. We also examined which integrins mediated the expression and secretion of matrixins MMP-2 and MMP-9. Ligation of alpha3beta1 with mAbs resulted in induction of MMP-2 expression and secretion, whereas antibody ligation of alpha(v)beta3 led to down-regulation of MMP-9. The above data implicate integrins of proximal tubular epithelial cells in the regulation of MMPs and in the development of TBM thickening in diabetic nephropathy.

Proteolytic events of wound-healing--coordinated interactions among matrix metalloproteinases (MMPs), integrins, and extracellular matrix molecules

During wound-healing, cells are required to migrate rapidly into the wound site via a proteolytically generated pathway in the provisional matrix, to produce new extracellular matrix, and, subsequently, to remodel the newly formed tissue matrix during the maturation phase. Two classes of molecules cooperate closely to achieve this goal, namely, the matrix adhesion and signaling receptors, the integrins, and matrix-degrading and -processing enzymes, the matrix metalloproteinases (MMPs). There is now substantial experimental evidence that blocking key molecules of either group will prevent or seriously delay wound-healing. It has been known for some time now that cell adhesion by means of the integrins regulates the expression of MMPs. In addition, certain MMPs can bind to integrins or other receptors on the cell surface involved in enzyme activation, thereby providing a mechanism for localized matrix degradation. By proteolytically modifying the existing matrix molecules, the MMPs can then induce changes in cell behavior and function from a state of rest to migration. During wound repair, the expression of integrins and MMPs is simultaneously up-regulated. This review will focus on those aspects of the extensive knowledge of fibroblast and keratinocyte MMPs and integrins in biological processes that relate to wound-healing.

Cyclooxygenase-2 is overexpressed in HER-2/neu-positive breast cancer: evidence for involvement of AP-1 and PEA3

Markedly increased levels of cyclooxygenase-2 (COX-2) mRNA, protein, and prostaglandin E(2) synthesis were detected in HER-2/neu-transformed human mammary epithelial cells (184B5/HER) compared with its nontransformed partner cell line (184B5). HER-2/neu stimulated COX-2 transcription via the Ras --> Raf --> MAPK pathway. The inductive effects of HER-2/neu were mediated, in part, by enhanced binding of AP-1 (c-Jun, c-Fos, and ATF-2) to the cyclic AMP-response element (-59/-53) of the COX-2 promoter. The potential contribution of the transcription factor PEA3 was also investigated. Elevated levels of PEA3 were detected in 184B5/HER cells. A PEA3 site (-75/-72) was identified juxtaposed to the cyclic AMP-response element. HER-2/neu-mediated activation of the COX-2 promoter was blocked by mutagenizing the PEA3 site or overexpressing antisense to PEA3. To determine whether HER-2/neu status was also a determinant of COX-2 expression in vivo, we compared levels of COX-2 protein in HER-2/neu-positive and -negative human breast cancers. Increased amounts of COX-2 were detected in HER-2/neu-positive tumors. Taken together, these results suggest that closely spaced PEA3 and cyclic AMP-response elements are required for HER-2/neu-mediated induction of COX-2 transcription. The clear relationship between HER-2/neu status and COX-2 expression in human breast tumors suggests that this mechanism is likely to be operative in vivo.

Matrix metalloproteinases in disease and repair processes in the anterior segment

The pathogenesis of many anterior segment disorders and ocular complications following surgery are secondary to the wound healing response. The extent of clinical damage observed is closely related to the amount of scarring and tissue contraction. Matrix metalloproteinases (MMPs) are a family of enzymes that play a vital role in all stages of the wound healing process. They degrade all extracellular matrix components and also have the ability to synthesize collagen and extracellular matrix members, and are therefore important in the remodeling of a wound. Overexpression of MMPs results in excessive extracellular matrix degradation, leading to tissue destruction and loss of organ function. In the case of the anterior segment, this may mean the loss of visual function. This review focuses on the role MMPs have in the development of various anterior segment disorders. The importance of MMPs in the wound healing response and its potential modulation to manipulate the scarring response is being recognized, and current developments will be described.

Control of MMP-9 expression at the maternal-fetal interface

Cytotrophoblastic cells (CTB) from first trimester placenta form columns of invasive CTB. This invasive behaviour is due to the ability of CTB to secrete matrix metalloproteinases (MMPs) since tissue inhibitor of MMP (TIMP) inhibits their invasiveness. Although CTB behave like metastatic cells, in vivo they are only transiently invasive (first trimester) and their invasion is normally limited only to the endometrium and to the proximal third of the myometrium. This temporal and spatial regulation of trophoblast invasion is believed to be mediated in an autocrine way by trophoblastic factors and in a paracrine way by uterine factors. Several types of regulators have been investigated: hormones, extra-cellular matrix glycoproteins and cytokines or growth factors. This review is not intended to be an exhaustive catalogue of potential regulators of trophoblastic MMP-9 secretion but is aimed at summarising the most important signalling pathways involved in MMP-9 regulation.

Analysis of immunohistochemical label of Fos protein in the suprachiasmatic nucleus: comparison of different methods of quantification

The induction of the proto-oncogene c-fos, and its phosphoprotein product Fos, has been extensively used to study the effects of light on the circadian pacemaker in the suprachiasmatic nucleus (SCN). Experimental approaches to the quantification of Fos induction have mainly been based on immunohistochemistry and subsequent measure of Fos immunoreactivity (IR) in sections of the SCN. In this study, the authors compare several methods of quantification using optical density image analysis or counts of Fos-IR labeled cells. To assess whether optical density measures using image analysis reflect the amount of Fos in brain tissue, the authors developed standards of known concentrations of Fos protein in an agar matrix. The agar standards were sectioned and treated simultaneously with sections of the SCN from animals exposed to different levels of irradiance. Optical density was found to be proportional to the quantity of Fos in the sections, indicating that this measure accurately reflects relative levels of Fos protein induction. Quantification by optical density analysis allows an objective measure in which the various parameters, conditions of illumination, and threshold can be maintained constant throughout the analysis. Counting cells by visual observation is more subjective because threshold values cannot be precisely defined and can vary according to the observer, illumination, degree of label, and other factors. In addition, cell counts involving direct visual observation, automated cell counts, or stereological methods do not take into account the difference in the density of label between cells, thus giving equal weight to lightly or densely stained cells. These measures are more or less weakly correlated with measures of optical density and thus do not accurately reflect the amount of bound Fos protein in the tissue sections. In contrast, labeled surface area as measured by image analysis shows a linear relationship with optical density. The main outcome of this study is that computer-assisted image analysis provides an accurate and rapid method to determine the relative amount of Fos protein in the SCN and the effects of light on intracellular signaling mechanisms involved in the circadian clock.

Signal transduction of beta2m-induced expression of VCAM-1 and COX-2 in synovial fibroblasts

BACKGROUND

beta2 microglobulin (beta2m) amyloidosis is a destructive articular disease affecting dialysis patients. We have demonstrated that beta2m increases the expression of vascular cell adhesion molecule (VCAM-1) and cyclooxygenase-2 (COX-2) in human osteoarthritic synovial fibroblasts (SFLs).

METHODS

To determine the cell signaling pathways, SFLs were incubated with beta2m in the presence or absence of various inhibitors for 24 hours. Intracellular calcium ([Ca2+]i) was measured by fluorometric techniques and vascular cell adhesion molecule-1 (VCAM-1) and cyclooxygenase-2 (COX-2) expression was determined by immunohistochemistry and Western blotting.

RESULTS

beta2m increased [Ca2+]i levels in a dose dependent manner (P < 0.05) in SFLs. BAPTA-AM, a [Ca2+]i chelator, completely inhibited beta2m-induced expression of VCAM-1 and COX-2. U73122 [phospholipase C (PLC) inhibitor] or 2-APB [specific inhibitor of inositol 1,4,5-trisphosphate (IP3)-induced [Ca2+]i release] completely blocked the beta2m-induced increase in [Ca2+]i and the up-regulation of VCAM-1 and COX-2. However, pretreatment with staurosporin, a protein kinase C inhibitor, had no effect. Disruption of the actin cytoskeleton by treatment with cytochalasin D or latrunculin A blocked beta2m up-regulation of VCAM-1 and COX-2. Finally, cells treated with phosphatidylinositol-3 kinase (PI-3 kinase) inhibitors wortmannin or LY294002 also failed to express VCAM-1 and COX-2.

CONCLUSIONS

These results demonstrate that IP3-mediated [Ca2+]i release, PI-3 kinase, and actin cytoskeleton reorganization are involved in beta2m-induced expression of VCAM-1 and COX-2 in human SFLs. Understanding the potential pathways by which beta2m exerts its inflammatory-like effects may lead to the development of future therapies.

Antisense CD11b integrin inhibits the development of a differentiated monocyte/macrophage phenotype in human leukemia cells

Macrophage-like development of myeloid leukemia cells which can be induced by agents such as phorbol esters (TPA) is accompanied by integrin expression and cell adhesion. Thus, in differentiating myeloid leukemia cells CD11b is predominantly expressed which can associate with CD18 to form the functional heterodimeric integrin Mac-1. To elucidate the role of cell adhesion during macrophage-like differentiation, we transfected human U937 myeloid leukemia cells with a vector containing the CD11b gene in antisense orientation. Expression of the CD11b antisense gene in stably transfected U937 cells (as-CD11b cells) resulted in an attenuated response to TPA. As-CD11b cells demonstrated poor adhesion to solid substrate upon TPA treatment in contrast to U937 control cells. Constitutive expression of c-myc in as-CD11b transfectants was higher than in control cells and failed to be repressed by TPA treatment. Moreover, unlike control cells, antisense transfectants failed to induce expression of early response genes such as c-jun and the redox factor ref-1 upon TPA stimulation. Consequently, the induction of monocytic differentiation markers such as the activity of alpha-naphthyl acetate esterase, the capacity to reduce nitroblue tetrazolium and the expression of the vimentin gene was much lower in antisense transfectants than in control U937 cells. According to the failure to undergo a monocytic differentiation program, TPA treatment of as-CD11b cells resulted in a progressively increasing amount of apoptotic cells whereas the differentiated population of U937 control cells remained alive. Taken together, these data suggest that the integrin-mediated (particularly CD11b-mediated) adhesion of myeloid leukemia cells in the course of induced monocytic differentiation is crucial for cell attachment, development of a monocytic phenotype and subsequent survival.

The role of proteases in fibronectin matrix remodeling in thyroid epithelial cell monolayer cultures

Fischer rat thyroid (FRT) cells organize a matrix of extracellular fibronectin (FN) fibrils, which undergoes extensive remodeling according to cell culture confluence. In non-confluent cells FN forms a fibrillar array associated with the ventral cell surface. However, basal FN is progressively removed in confluent cultures and substituted by non-fibrillar FN deposits at lateral cell domains in regions of cell-cell contacts. FRT cells secrete and expose on the plasma membrane the tissue-type plasminogen activator and, in serum-free cultures, plasminogen induces a rapid loss of FN fibrils. Incubation with plasmin inhibitors greatly reduces this effect. FRT cells also express annexin II, a plasminogen receptor, suggesting that plasmin activity is associated with the pericellular enviroment. This is in agreement with the observation that a great reduction in FN degradation is observed if the cells are pre-incubated with carboxypeptidase B, which prevents plasminogen binding to the cells. A gelatinolytic activity with a molecular weigth equivalent to MMP-2 has been demonstrated by zymography of culture media, and the presence of MMP-2 and MT1-MMP on the cell plasma membrane has been detected by immunofluorescence. These results indicate that in the FN remodeling process, occurring during FRT epithelium maturation, both plasmin-dependent (tPA activated) and plasmin-independent proteolytic activities are involved.

Phagocytosis mediated by Yersinia invasin induces collagenase-1 expression in rabbit synovial fibroblasts through a proinflammatory cascade

We show that the interaction of the Yersinia surface protein, invasin, with rabbit synovial fibroblasts mediates bead phagocytosis and induces expression of interleukin 1α (IL-1α), tumor necrosis factor-α (TNF-α) and MMP-1/collagenase-1 (CL-1). Presentation of invasin as a ligand on the surface of 4.5 μm beads induced phagocytosis and increased CL-1 expression 20-fold after 24 hours. By contrast, presentation of invasin as a spreading substrate did not induce CL-1 expression. CL-1 induction following phagocytosis of invasin-coated beads was mediated by a mechanism dependent on high-affinity binding to β1 integrins and the function of the small GTPase RhoA. Expression of a function-perturbing mutant, RhoAN19, abrogated bead-induced CL-1 expression. RhoA activation coupled bead phagocytosis with signal transduction because expression of constitutively active mutant RhoV14 was sufficient to trigger CL-1 expression. The signal-transduction cascade elicited by bead phagocytosis triggered NFκB activation, stimulating a proinflammatory cellular response with transient increases in TNF-α production that peaked at 2 hours and induction of IL-1α that was sustained for at least 10 hours. Inhibition of IL-1α function by blocking antibodies or IL-1 receptor antagonist showed that IL-1α is the autocrine intermediary for subsequent CL-1 induction.

Impaired migration, integrin function, and actin cytoskeletal organization in dermal fibroblasts from a subset of aged human donors

Deficits in the motility of fibroblasts contribute to age-related impairment of wound healing. We analyzed 'young' fibroblasts from four healthy donors 22-30 years old and 'aged' fibroblasts from six healthy donors 81-92 years old for migratory ability on type I collagen, secretion of matrix metalloproteases (MMPs), attachment to matrices and, expression and function of integrin alpha2beta1. Cells from each donor were analyzed separately in each experiment. Whereas migration of young fibroblasts was uniformly robust, three aged lines migrated well and three migrated poorly. Synthesis of MMP1 and TIMP1, but not MMP2 or MMP9, was increased in the aged fibroblasts relative to the young fibroblast lines irrespective of their motility. All lines of young and aged fibroblasts attached to plastic or collagen with similar efficiency. Although young and aged fibroblasts expressed comparable levels of the alpha2 integrin; the lines of aged fibroblasts that were poor migrators exhibited a significant reduction in alpha2beta1 function relative to fibroblasts with normal migratory capacities. Moreover, the lines of aged fibroblasts that exhibited poor migration demonstrated a disordered actin cytoskeleton and a reduced ability to contract collagen gels. In conclusion, aged fibroblasts, unlike young fibroblasts, displayed variable migratory capacities. Deficient migration by specific lines of aged fibroblasts was not related to the capacity to attach, express alpha2 integrin, or secrete MMPs and TIMP1, but was characterized by disorganized cytoskeletal actin and reduced alpha2beta1 function.

Integrin alpha(v)beta(3)/vitronectin interaction affects expression of the urokinase system in human ovarian cancer cells

The urokinase type plasminogen activator (uPA), together with its receptor uPAR and the plasminogen activator inhibitor type-1 (PAI-1) plays a pivotal role during tumor invasion and metastasis. Integrins, via interaction with the extracellular matrix (ECM), control cell adhesion and motility. The two systems are functionally linked because uPAR and PAI-1 bind to the ECM component vitronectin (VN). Because integrin signaling alters gene expression patterns, we investigated whether the expression levels of uPA, uPAR, and PAI-1 are affected by ECM/integrin interactions. Expression of uPA, uPAR, and PAI-1 was significantly enhanced when human ovarian cancer cells (OV-MZ-6) were cultivated on fibronectin or collagen type IV. In contrast, VN induced down-regulation of uPA and uPAR while increasing PAI-1 by up to 4-fold. VN-dependent decrease of uPA protein was paralleled by a significant reduction of uPA promoter activity that was even more pronounced upon alpha(v)beta(3) overexpression and depended on the presence of intact Rel protein-binding sites. The activity of Rel transcription factors was also significantly reduced upon alpha(v)beta(3)-mediated cell adhesion to VN. The activity of the Rel-unresponsive PAI-1 promoter was up to 5-fold induced as a function of alpha(v)beta(3)/VN interaction. Thus, the balance between available concentrations of uPA, uPAR, PAI-1, and integrins in human ovarian cancer cells might provide a switch within the regulation of their invasive phenotype.

Specific expression of matrix metalloproteinases 1, 3, 9 and 13 associated with invasiveness of breast cancer cells in vitro

Several matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) were studied in highly invasive (MDA-MB-231) and slightly invasive (MCF-7, T47D, BT-20) breast cancer cell lines. Investigations were carried out at the protein level and/or at the mRNA level, either in cells cultured as monolayers on plastic, or in cells seeded on a thin layer of Matrigel basement membrane matrix. Analysis of MMP expression by RT-PCR showed expression of MMP-1. MMP-3, and MMP-13 in highly invasive MDA-MB-231 cells, but not in slightly invasive cell lines. The extracellular secretion of MMP-1 and MMP-3 by MDA-MB 231 cells could be also shown by ELISA. TIMP-1 and TIMP-2 mRNAs were found in all cell lines, however, the extracellular secretion of both TIMPs was much higher in MDA-MB-231 cells than in the other cell lines. When the cells were cultured on Matrigel matrix, MMP-9 expression was induced in MDA-MB-231 cells only, as assessed by RT-PCR and zymography experiments. The invasive potential of MDA-MB-231 cells evaluated in vitro through Matrigel was significantly inhibited by the MMP inhibitor BB-2516, by 25% and 50% at the concentrations of 2 x 10(-6) M and 10(-5) M, respectively. In conclusion, our data show that highly invasive MDA-MB-231 cells but not slightly invasive T47D, MCF-7 and BT-20 cells express MMP-1, MMP-3, MMP-9 and MMP-13. MMP-9 which is specifically up-regulated by cell contact to Matrigel, may play a key role in the invasiveness of MDA-MB-231 cells through basement membranes.

Conformational dependence of collagenase (matrix metalloproteinase-1) up-regulation by elastin peptides in cultured fibroblasts

We have established that treatment of cultured human skin fibroblasts with tropoelastin or with heterogenic peptides, obtained after organo-alkaline or leukocyte elastase hydrolysis of insoluble elastin, induces a high expression of pro-collagenase-1 (pro-matrix metalloproteinase-1 (pro-MMP-1)). The identical effect was achieved after stimulation with a VGVAPG synthetic peptide, reflecting the elastin-derived domain known to bind to the 67-kDa elastin-binding protein. This clearly indicated involvement of this receptor in the described phenomenon. This notion was further reinforced by the fact that elastin peptides-dependent MMP-1 up-regulation has not been demonstrated in cultures preincubated with 1 mm lactose, which causes shedding of the elastin-binding protein and with pertussis toxin, which blocks the elastin-binding protein-dependent signaling pathway involving G protein, phospholipase C, and protein kinase C. Moreover, we demonstrated that diverse peptides maintaining GXXPG sequences can also induce similar cellular effects as a "principal" VGVAPG ligand of the elastin receptor. Results of our biophysical studies suggest that this peculiar consensus sequence stabilizes a type VIII beta-turn in several similar, but not identical, peptides that maintain a sufficient conformation to be recognized by the elastin receptor. We have also established that GXXPG elastin-derived peptides, in addition to pro-MMP-1, cause up-regulation of pro-matrix metalloproteinase-3 (pro-stromelysin 1). Furthermore, we found that the presence of plasmin in the culture medium activated these MMP proenzymes, leading to a consequent degradation of collagen substrate. Our results may be, therefore, relevant to pathobiology of inflammation, in which elastin-derived peptides bearing the GXXPG conformation (created after leukocyte-dependent proteolysis) bind to the elastin receptor of local fibroblasts and trigger signals leading to expression and activation of MMP-1 and MMP-3, which in turn exacerbate local connective tissue damage.

JAB1/CSN5 and the COP9 signalosome. A complex situation

The Jun activating binding protein (JAB1) specifically stabilizes complexes of c-Jun or JunD with AP-1 sites, increasing the specificity of target gene activation by AP-1 proteins. JAB1 is also known as COP9 signalosome subunit 5 (CSN5), which is a component of the COP9 signalosome regulatory complex (CSN). Over the past year, JAB1/CSN5 has been implicated in numerous signaling pathways including those that regulate light signaling in plants, larval development in Drosophila, and integrin signaling, cell cycle control, and steroid hormone signaling in a number of systems. However, the general role of the CSN complex, and the specific role of JAB1/CSN5, still remain obscure. This review attempts to integrate the available data to help explain the role of JAB1/CSN5 and the COP9 signalosome in regulating multiple pathways (in this review, both JAB1 and CSN5 terminologies are used interchangeably, depending on the source material).

Induction of metalloproteinases by glomerular mesangial cells stimulated by proteins of the extracellular matrix

Human glomerular mesangial cells (HMC) are embedded in the mesangial matrix (MM) and control its turnover through a dynamic equilibrium between synthesis and degradation. Degradation is controlled by matrix metalloproteinases (MMP), whose activity has been causally implicated in the progression of glomerular disease. In other systems, MMP secretion may be directly affected by exposure to specific matrix proteins. The present study, therefore, investigated the effect of different matrix components on the adherence of HMC and on their secretion and activation of the gelatinases MMP2 and MMP9. HMC adhered strongly (quantified using crystal violet staining) to collagen IV and collagen I (P < 0.01, relative to binding to control, bovine serum albumin (BSA)-coated wells) and to a lesser extent to gelatin IV and fibronectin (P < 0.05). Binding to vitronectin and laminin was not statistically different to control wells. After the addition of these matrix proteins (0.1 microg/ml to 100 microg/ml) to growth-arrested HMC for 72 h, zymography of the conditioned medium established that only fibronectin and collagens I and IV dose-dependently increased latent (72 kD) MMP2 secretion and activation. Fibronectin, however, also induced the secretion of MMP9. Membranes from HMC that had been co-cultured with fibronectin for 72 h were prepared to investigate whether the activation of MMP2 in this system was due to the action of membrane-type (MT)-MMP. When incubated with latent MMP2 for times up to 24 h, these membranes activated the enzyme in a time- and dose-dependent manner. The results demonstrate that specific matrix components increased the secretion of MMP2 and MMP9 from HMC. In addition, MT-MMP activity, selectively induced by fibronectin, was implicated in the activation of the secreted proteinases.

Coordinate induction of collagenase-1, stromelysin-1 and urokinase plasminogen activator (uPA) by the 120-kDa cell-binding fibronectin fragment in fibrocartilaginous cells: uPA contributes to activation of procollagenase-1

Specific fibronectin (Fn) fragments found in synovial fluid of arthritic joints potentially contribute to the loss of cartilage proteoglycans by inducing matrix metalloproteinase (MMP) expression. However, whether or not the Fn fragment-modulated changes in expression of MMPs result in a net increase in matrix-degradative activity through alterations in the balance between MMP activation and inhibition has not been established. To understand the mechanisms by which proteolytic Fn fragments may contribute to joint degeneration, conditioned medium from fibrocartilaginous cells exposed to Fn, its 30-kDa fragment containing the collagen/gelatin-binding domain, its 120-kDa fragment containing the central cell-binding domain, and the RGD peptide were assayed for MMPs, and MMP activators and inhibitors. We found that the 120-kDa fragment of Fn (but not intact Fn), the 30-kDa fragment, and the RGD peptide, dose-dependently induced procollagenase-1 and prostromelysin-1 and decreased levels of the tissue inhibitor of metalloproteinases (TIMPs) -1 and -2. The alpha5beta1 integrin was implicated in the induction of collagenase by the 120-kDa Fn fragment, since collagenase induction was abrogated in the presence of blocking antibody to this integrin. Conditioned medium from cells exposed to the 120-kDa Fn fragment also demonstrated increased levels of the activated collagenase-1, which resulted in significantly elevated collagen degradative activity. That the urokinase plasminogen activator (uPA) was involved in the activation of procollagenase-1 was suggested by findings that the 120-kDa Fn fragment induced uPA coordinately with procollagenase-1, and the activation of procollagenase-1 was dose-dependently inhibited in the presence of plasminogen activator inhibitor-1. These data demonstrate that the 120-kDa cell-binding fragment of Fn induces a net increase in matrix-degradative activity in fibrocartilaginous cells by concomitantly inducing MMPs and their activator, uPA, while decreasing TIMPs.

Regulation of a multigenic invasion programme by the transcription factor, AP-1: re-expression of a down-regulated gene, TSC-36, inhibits invasion

The transcription factor AP-1 (activator protein-1) is required for transformation by many oncogenes, which function upstream of it in the growth factor-ras signal transduction pathway. Previously, we proposed that one role of AP-1 in transformation is to regulate the expression of a multigenic invasion programme. As a test of this proposal we sought to identify AP-1 regulated genes based upon their differential expression in 208F rat fibroblasts transformed by FBR-v-fos (FBR), and to determine if they functioned in the invasion programme. Subtracted cDNA libraries specific for up- or down-regulated genes in FBRs compared to 208Fs were constructed and analysed. Northern analysis revealed that the cDNAs in both libraries represented differentially expressed genes. Nucleic acid sequence analysis of randomly selected cDNA clones from each library coupled with searches of nucleic acid and amino acid sequence databases determined that many of the cDNAs represented proteins that function in various aspects of the invasion process. Functional analysis of one the down-regulated genes, TSC-36/follistatin-related protein (TSC-36/Frp), which has not previously been associated with invasion, demonstrated that its expression in FBRs inhibited in vitro invasion. These results support the proposal that AP-1 in transformed cells regulates a multigenic invasion programme.

Molecular mediators of implantation

Because cytotrophoblastic cells (CTB) from first-trimester placenta form columns of invasive CTB they have been considered as a model for blastocyst implantation. This invasive behaviour is due to the ability of CTB to secret matrix metalloproteinases (MMPs) because tissue inhibitor of MMP (TIMP) inhibits their invasiveness. Although CTB behave like metastatic cells, in vivo they are only transiently invasive (first trimester) and their invasion is normally limited only to the endometrium and to the proximal third of the myometrium. This temporal and spatial regulation of trophoblast invasion is believed to be mediated in an autocrine way by trophoblastic factors and in a paracrine way by uterine factors. Several types of regulators have been investigated: hormones, extracellular matrix (ECM) glycoproteins and cytokines or growth factors. This review is not intended to be an exhaustive catalogue of all the potential regulators but is aimed at describing the mechanism of action of certain factors relevant in trophoblast-endometrial interactions.

Biomechanical regulation of human monocyte/macrophage molecular function

When the monocyte infiltrates a tissue, adhesion to the extracellular matrix provides structural anchors, and the cell may be deformed through these attachments. To test the hypothesis that human monocytes/macrophages are mechanically responsive, we studied the effects of small cyclic mechanical deformations on cultured human monocytes/macrophages. When monocytes/macrophages were subjected to 4% strain at 1 Hz for 24 hours, neither matrix metalloproteinase (MMP)-1 nor MMP-3 was induced; however, in the presence of phorbol myristate acetate, strain augmented MMP-1 expression by 5.1 +/- 0.7-fold (P < 0.05) and MMP-3 expression by 1. 6 +/- 0.1-fold (P < 0.05). In contrast, MMP-9 expression was not changed by mechanical strain in the presence or absence of phorbol myristate acetate. Deformation rapidly induced the immediate early response genes c-fos and c-jun. In addition, mechanical deformation induced the transcription factor PU.1, an ets family member that is essential in monocyte differentiation, as well as mRNA for the M-CSF receptor. These studies demonstrate that human monocytes/macrophages respond to mechanical deformation with selective augmentation of MMPs, induction of immediate early genes, and induction of the M-CSF receptor. In addition to enhancing the proteolytic activity of macrophages within repairing tissues, cellular deformation within tissues may play a role in monocyte differentiation.

Integrin LFA-1 interacts with the transcriptional co-activator JAB1 to modulate AP-1 activity

Integrin adhesion receptors transduce signals that control complex cell functions which require the regulation of gene expression, such as proliferation, differentiation and survival. Their intracellular domain has no catalytic function, indicating that interaction with other transducing molecules is crucial for integrin-mediated signalling. Here we have identified a protein that interacts with the cytoplasmic domain of the beta2 subunit of the alphaL/beta2 integrin LFA-1. This protein is JAB1 (Jun activation domain-binding protein 1), a coactivator of the c-Jun transcription factor. We found that JAB1 is present both in the nucleus and in the cytoplasm of cells and that a fraction of JAB1 colocalizes with LFA-1 at the cell membrane. LFA-1 engagement is followed by an increase of the nuclear pool of JAB1, paralleled by enhanced binding of c-Jun-containing AP-1 complexes to their DNA consensus site and increased transactivation of an AP-1-dependent promoter. We suggest that signalling through the LFA-1 integrin may affect c-Jun-driven transcription by regulating JAB1 nuclear localization. This represents a new pathway for integrin-dependent modulation of gene expression.

Bi-directional signal transduction by integrin receptors

The integrin family of cell surface glycoproteins functions primarily as receptors for extracellular matrix ligands. There are now many well characterized integrin-ligand interactions which are known to influence many aspects of cell behaviour including cell morphology, cell adhesion, cell migration as well as cellular proliferation and differentiation. However, in fulfilling these functions, integrins are not simple adhesion receptors that physically mediate connections across the plasma membrane. Rather, integrin function itself is highly regulated, largely through the formation of specific associations with both structural and regulatory components within cells. It is these intracellular interactions which allow integrin function to effect many biochemical signalling pathways and therefore to impinge upon complex cellular activities. Recently, much research has focused on elucidating the molecular mechanisms which control integrin function and the molecular processes which transduce integrin-mediated signalling events. In this review, we discuss progress in the field of integrin signal transduction including, where applicable, potential therapeutic applications arising from the research.

Type VIII collagen stimulates smooth muscle cell migration and matrix metalloproteinase synthesis after arterial injury

Type VIII collagen is a matrix protein expressed in a number of tissues undergoing active remodeling, including injured arteries during neointimal formation and in human atherosclerotic plaques; however, very little is known about its function. We have investigated whether the type VIII collagen stimulates smooth muscle cell (SMC) migration and invasion by binding to integrin receptors and up-regulating matrix metalloproteinase (MMP) production. SMCs attached to plates coated with type VIII collagen in a dose-dependent manner, with maximal attachment occurring with coating solutions containing 25 microgram/ml collagen. Type VIII collagen at 100 microgram/ml stimulated an 83-fold increase in the migration of SMCs in a chemotaxis chamber. Antibodies against beta1 integrin receptors prevented attachment and migration of SMCs. Antibodies against alpha1 or alpha2 integrins reduced attachment of SMCs to type VIII collagen by 29% and 77%, respectively. We found that SMCs grown from the rat neointima, but not medial SMCs, increased their production of MMP-2 and -9 on adherence to type VIII collagen. This suggests that there is an important difference in phenotype between intimal and medial SMCs and that intimal SMCs have distinct matrix-dependent signaling mechanisms. Our findings suggest that type VIII collagen deposited in vascular lesions functions to promote SMC attachment and chemotaxis, and signals through integrin receptors to stimulate MMP synthesis, all of which are important mechanisms used in cell migration and invasion.

Attenuation of plasminogen activator inhibitor type-1 promoter activity in serum-stimulated renal epithelial cells by a distal 5' flanking region

Urokinase plasminogen activator (u-PA) and its fast acting type-1 inhibitor (PAI-1) localize to cellular focal adhesive structures and the adjoining proximal undersurface region, respectively (Kutz et al., J. Cell. Physiol. 176:8-18, 1997). PAI-1 may function in this locale to modulate pericellular proteolytic activity, cell-to-substrate adhesion, or matrix-dependent motility. While PAI-1 synthesis is regulated in an immediate-early response manner in growth "activated" renal cells coincident with cytoskeletal restructuring, adhesive influences both repress the amplitude and prolong the time course of serum-induced PAI-1 transcription (Ryan et al., Biochem. J. 314:1041-1046, 1996). To identify potential adhesion-responsive elements within the PAI-1 gene that function in this complex mode of expression control, reporter constructs containing defined directionally deleted PAI-1 5' genomic fragments cloned upstream of a CAT gene were employed in transient transfection assays. A 483-bp distal PAI-1 flanking segment (corresponding to nucleotides -2395 to -1912) conferred significant adhesion-dependent attenuation on serum-induced PAI-1 transcription. This 483-bp distal PAI-1 segment functioned as a repressor of reporter (CAT) activity under both adhesive and suspension culture conditions, however, when ligated upstream of either an SV40 promoter/enhancer or a minimal PAI-1 promoter. These data suggest that repressor elements located between -2395 and -1912 bp interact with more proximal adhesion-dependent regulatory elements to affect PAI-1 expression attenuation during serum stimulation of adherent renal epithelial cells.

Steady-state mRNA levels of interleukin-1, integrins, cJun, and cFos in hairless mouse skin during short-term chronic UV exposure and the effect of topical tretinoin

We have proposed that UV activation of cytokine and integrin signaling pathways may initiate the photoaging process and that one of the effects of tretinoin treatment may be to alter the cytokine and integrin patterns. In previous results, steady-state mRNA levels of interleukin-1alpha, tumor necrosis factor alpha, transforming growth factor beta, collagenase, stromelysin, collagen, and integrins (alpha1 and alpha2) were increased in the skin of hairless mice that were either UV treated or concurrently treated with UV followed by topical tretinoin for 5 weeks. The aim of this study was to focus on the expression of alpha1, alpha2 and alpha5 integrins, IL-1alpha, IL-1beta, cJun, and cFos at an earlier time point (3 weeks). Animals were UV irradiated thrice weekly for 3 weeks and were treated topically with either 0.05% tretinoin or the vehicle immediately after each exposure. Total RNA was prepared and used in RT-PCR with radiolabeled dCTP and specific primers. UV slightly increased steady-state mRNA levels for alpha1, alpha2 and alpha5 integrins whereas UV + tretinoin increased their expression (3-, 2- and 7-fold respectively). Steady-state mRNA levels for IL-1alpha, IL-1beta and cJun were increased with UV (3-, 12- and 6-fold respectively) and with UV + tretinoin (6-, 7- and 9-fold respectively). In contrast, cFos expression was unchanged. In situ staining for IL-1alpha mRNA was slightly more abundant in mice treated for 3 weeks with UV and UV + tretinoin than in controls whereas 5 weeks of UV + tretinoin treatment gave strongly positive staining. Results are consistent with cytokines and integrins mediating the effects of UV on the skin, with modulation of these effects by tretinoin.