1. Summary Fibrosis is defined as a fibroproliferative or abnormal fibroblast activation–related disease., Deregulation of wound healing leads to hyperactivation of fibroblasts and excessive accumulation of extracellular matrix (ECM) proteins in the wound area, the pathological manifestation of fibrosis. The accumulation of excessive levels of collagen in the extracellular matrix depends on two factors: an increased rate of collagen synthesis and or decreased rate of collagen degradation by cellular proteolytic activities. The urokinase-type/tissue-type plasminogen activator (uPA/tPA) and plasmin play significant roles in the cellular proteolytic degradation of ECM proteins and the maintenance of tissue homeostasis. The activities of uPA/tPA/plasmin and plasmin-dependent MMPs rely mostly on the activity of a potent inhibitor of uPA/tPA, plasminogen activator inhibitor-1 (PAI-1). Under normal physiologic conditions, PAI-1 controls the activities of uPA/tPA/plasmin/MMP proteolytic activities and thus maintains the tissue homeostasis. During wound healing, elevated levels of PAI-1 inhibit uPA/tPA/plasmin and plasmin-dependent MMP activities and thus help expedite wound healing. In contrast to this scenario, under pathologic conditions, excessive PAI-1 contributes to excessive accumulation of collagen and other ECM protein in the wound area and thus preserves scarring. While the level of PAI-1 is significantly elevated in fibrotic tissues, lack of PAI-1 protects different organs from fibrosis in response to injury-related profibrotic signals. Thus PAI-1 is implicated in the pathology of fibrosis in different organs including the heart, lung, kidney, liver and skin. Paradoxically, PAI-1 deficiency promotes spontaneous cardiac-selective fibrosis. In this review we discuss the significance of PAI-1 in the pathogenesis of fibrosis in multiple organs.

Type I collagen, the major component of extracellular matrix in skin and other tissues, is a heterotrimer of two α1 and one α2 collagen polypeptides. The synthesis of both chains is highly regulated by different cytokines at the transcriptional level. Excessive synthesis and deposition of collagen in the dermal region causes thick and hard skin, a clinical manifestation of scleroderma. To better understand the causes of scleroderma or other tissue fibrosis, it is very Important to investigate the molecular mechanisms that cause upregulation of the Type I collagen synthesis in these tissues. Several cis-acting regulatory elements and trans-acting protein factors, which are involved in basal as well as cytokine-modulated Type I collagen gene expression, have been identified and characterized. Hypertranscription of Type I collagen in scleroderma skin fibroblasts may be due to abnormal activities of different positive or negative transcription factors In response to different abnormally induced signaling pathways. In this review, I discuss the present day understanding about the involvement of different factors in the regulation of basal as well as cytokine-modulated Type I collagen gene expression and its implication in scleroderma research.

The nuclear hormone receptor , peroxisome proliferator-activated receptor (PPAR)-␥ , originally identified as a key mediator of adipogenesis , is expressed widely and implicated in diverse biological responses. Both natural and synthetic agonists of PPAR-␥ abrogated the stimulation of collagen synthesis and myofibroblast differentiation induced by transforming growth factor (TGF)-␤ in vitro. To characterize the role of PPAR-␥ in the fibrotic process in vivo, the synthetic agonist rosiglitazone was used in a mouse model of scleroderma. Rosiglitazone attenuated bleomycin-induced skin inflammation and dermal fibrosis as well as subcutaneous lipoatrophy and counteracted the up-regulation of collagen gene expression and myofibroblast accumulation in the lesioned skin. Rosiglitazone treatment reduced the induction of the early-immediate transcription factor Egr-1 in situ without also blocking the activation of Smad2/3. In both explanted fibroblasts and skin organ cultures, rosiglitazone prevented the stimulation of collagen gene transcription and cell migration elicited by TGF-␤. Rosiglitazone-driven adipogenic differentiation of both fibroblasts and preadipocytes was abrogated in the presence of TGF-␤; this effect was accompanied by the concomitant down-regulation of cellular PPAR-␥ mRNA expression. Collectively, these results indicate that rosiglitazone treatment attenuates inflammation, dermal fibrosis, and subcutaneous lipoatrophy via PPAR-␥ in a mouse model of scleroderma and suggest that pharmacological PPAR-␥ ligands, widely used as insulin sensitizers in the treatment of type-2 diabetes mellitus, may be potential therapies for scleroderma. (Am J Pathol

Among the extracellular signals that modulate the synthesis of collagen, transforming growth factor-beta (TGF-beta) and interferon-gamma (IFN-gamma) are preeminent. These two cytokines exert antagonistic effects on fibroblasts, and play important roles in the physiologic regulation of extracellular matrix turnover. We have shown previously that in normal skin fibroblasts, TGF-beta positively regulates alpha2(I) procollagen gene (COL1A2) promoter activity through the cellular Smad signal transduction pathway. In contrast, IFN-gamma activates Stat1alpha, down-regulates COL1A2 transcription, and abrogates its stimulation induced by TGF-beta. The level of integration of the two pathways mediating antagonistic collagen regulation is unknown. We now report that IFN-gamma abrogates TGF-beta-stimulated COL1A2 transcription in fibroblasts by inhibiting Smad activities. IFN-gamma appears to induce competition between activated Stat1alpha and Smad3 for interaction with limiting amounts of cellular p300/CBP. Overexpression of p300 restored COL1A2 stimulation by TGF-beta in the presence of IFN-gamma, and potentiated IFN-gamma-dependent positive transcriptional responses. In contrast to fibroblasts, in U4A cells lacking Jak1 and consequently unable to activate Stat1alpha-mediated responses, IFN-gamma failed to repress TGF-beta-induced transcription. These results indicate that as essential coactivators for both Smad3 and Stat1alpha, nuclear p300/CBP integrate signals that positively or negatively regulate COL1A2 transcription. The findings implicate a novel mechanism to account for antagonistic interaction of Smad and Jak-Stat pathways in regulation of target genes. In fibroblasts responding to cytokines with opposing effects on collagen transcription, the relative levels of cellular coactivators, and their interaction with regulated transcription factors, may govern the net effect.

Transforming growth factor-b (TGF-b) stimulation of Type I collagen gene (COL1A2) transcription involves the Smad signal transduction pathway, but the mechanisms of Smad-mediated transcriptional activation are not fully understood. We now demonstrate that the ubiquitous transcriptional coactivators p300 and CREB-binding protein (CBP) enhanced basal as well as TGF-b-or Smad3-induced COL1A2 promoter activity, and stimulated the expression of endogenous Type I collagen. The adenoviral E1A oncoprotein abrogated stimulation of COL1A2 activity in transfected ®broblasts, and reduced the basal level of collagen gene expression. This e ect was due to speci®c interaction of E1A with cellular p300/CBP because (a) a mutant form of E1A defective in p300 binding failed to abrogate stimulation, and (b) forced expression of p300/CBP restored the ability of TGF-b to stimulate COL1A2 promoter activity in the presence of E1A. The e ect of p300 on COL1A2 transcription appeared to be due, in part, to its intrinsic acetyltransferase activity, as stimulation induced by a histone acetyltransferasede®cient mutant p300 was substantially reduced. Transactivation of COL1A2 by p300 involved the Smad signaling pathway, as Smad4-de®cient cells failed to respond to p300, and stimulation was rescued by overexpression of Smad4. Furthermore, minimal constructs containing only the Smad-binding CAGACA element of COL1A2 were transactivated by p300 in the presence of TGF-b. These results indicate, for the ®rst time, that the multifunctional p300/CBP coactivators play a major role in Smad-dependent TGF-b stimulation of collagen gene expression in ®broblasts.

Microvesicles (MVs) released by malignant cancer cells constitute an important part of the tumor microenvironment. They can transfer various messages to target cells and may be critical to disease progression. Here, we demonstrate that MVs circulating in plasma of B-cell chronic lymphocytic leukemia (CLL) patients exhibit a phenotypic shift from predominantly platelet derived in early stage to leukemic B-cell derived at advanced stage. Furthermore, the total MV level in CLL was significantly greater compared with healthy subjects. To understand the functional implication, we examined whether MVs can interact and modulate CLL bone marrow stromal cells (BMSCs) known to provide a "homing and nurturing" environment for CLL B cells. We found that CLL-MV can activate the AKT/mammalian target of rapamycin/p70S6K/hypoxiainducible factor-1␣ axis in CLL-BMSCs with production of vascular endothelial growth factor, a survival factor for CLL B cells. Moreover, MV-mediated AKT activation led to modulation of the ␤-catenin pathway and increased expression of cyclin D1 and c-myc in BMSCs. We found MV delivered phospho-receptor tyrosine kinase Axl directly to the BMSCs in association with AKT activation. This study demonstrates the existence of separate MV phenotypes during leukemic disease progression and underscores the important role of MVs in activation of the tumor microenvironment. (Blood. 2010;115:1755-1764) Introduction B-cell chronic lymphocytic leukemia (B-CLL) has been predominantly characterized as a clonal B-cell disorder 1 in which the defective apoptosis of CLL B cells is ascribed not only to intrinsic defects of the neoplastic cells but also to extrinsic factors that influence their behavior in the tissue microenvironment. The issue of CLL heterogeneity and the exact reasons for the clinical variety of disease progression are unknown. One important factor associated with disease progression is unfavorable prognostic features that may influence apoptotic resistance in the CLL B-cell clone but could be related to the ability of the clone to manipulate the microenvironment to its advantage. A recent study 2 demonstrated the importance of communication between tumor cells and their microenvironment through the shedding of membrane microvesicles (MVs), which can fuse to nearby cells within their circulatory pathways.MVs are shed from the cell surface of normal healthy or malignant cells and can "hijack" membrane components and engulf cytoplasmic contents from either type of cell. The shedding of membrane-derived MVs is a physiologic phenomenon that accompanies cell activation and growth. 3 MVs contain numerous proteins and lipids similar to those present in the membranes of the origination cells, and this likely facilitates their integration into cells they come in contact with during circulation. 2 The content of MVs and their impact on biologic function are dependent upon the cell of origin. 4 Thus, it is known that ovarian cancer MVs stimulate angiogenesis and that platelet-derived MVs promote tumor progression and...

Objective. In fibroblasts, transforming growth factor ␤ (TGF␤) stimulates collagen synthesis and myofibroblast transdifferentiation through the Smad intracellular signal transduction pathway. TGF␤-mediated fibroblast activation is the hallmark of scleroderma and related fibrotic conditions, and disrupting the intracellular TGF␤/Smad signaling may provide a novel approach to controlling fibrosis. Because of its potential role in modulating inflammatory and fibrotic responses, we examined the expression of the nuclear hormone receptor peroxisome proliferator-activated receptor ␥ (PPAR␥) in normal skin fibroblasts and its effect on TGF␤-induced cellular responses.Methods. The expression and activity of PPAR␥ in normal dermal fibroblasts were examined by Northern and Western blot analyses, immunocytochemistry, flow cytometry, and transient transfections with reporter constructs. The same approaches were used to evaluate the effects of PPAR␥ activation by naturally occurring and synthetic ligands on collagen synthesis and ␣-smooth muscle actin (␣-SMA) expression. Modulation of Smad-mediated transcriptional responses was examined by transient transfection assays using wild-type and dominant-negative PPAR␥ expression constructs. Abnormal synthesis and tissue accumulation of collagen are hallmarks of scleroderma and are responsible for the damage and failure of affected organs. Lesional scleroderma fibroblasts display an activated phenotype characterized by accelerated transcription of genes coding for collagen and other extracellular matrix proteins, increased expression of cell surface receptors for transforming growth factor ␤ (TGF␤), and sustained production of TGF␤, connective tissue growth factor, Supported by grants from the NIH (AR-46390 and AR-42309) and the Scleroderma Foundation. Results

We have previously demonstrated that hepatitis C virus (HCV) NS5A protein promotes cell growth and transcriptionally regulates the p21/waf1 promoter, a downstream effector gene of p53. In this study, we investigated the molecular mechanism of NS5A-mediated transcriptional repression of p21/waf1. We observed that transcriptional repression of the p21/waf1 gene by NS5A is p53 dependent by using p53 wild-type (؉/؉) and null (؊/؊) cells. Interestingly, p53-mediated transcriptional activation from a synthetic promoter containing multiple p53 binding sites (PG13-LUC) was abrogated following expression of HCV NS5A. Additional studies using pull-down experiments, in vivo coimmunoprecipitation, and mammalian two-hybrid assays demonstrated that NS5A physically associates with p53. Confocal microscopy revealed sequestration of p53 in the perinuclear membrane and colocalization with NS5A in transfected HepG2 and Saos-2 cells. Together these results suggest that an association of NS5A and p53 allows transcriptional modulation of the p21/waf1 gene and may contribute to HCV-mediated pathogenesis.