Distinct PKC isoforms mediate cell survival and DNA synthesis in thrombin-induced myofibroblasts
ABSTRACT Thrombin activates protease-activated receptor (PAR)-1 and induces a myofibroblast phenotype in normal lung fibroblasts that resembles the phenotype of scleroderma lung fibroblasts. We now demonstrate that PAR-1 expression is dramatically increased in lung tissue from scleroderma patients, where it is associated with inflammatory and fibroproliferative foci. We also observe that thrombin induces resistance to apoptosis in normal lung fibroblasts, and this process is regulated by protein kinase C (PKC)-epsilon but not by PKC-alpha. Overexpression of a constitutively active (c-a) form of PAR-1 or PKC-epsilon significantly inhibits Fas ligand-induced apoptosis in lung fibroblasts, whereas scleroderma lung fibroblasts are resistant to apoptosis de novo. Thrombin translocates p21Cip1/WAF1, a signaling molecule downstream of PKC, from the nucleus to cytoplasm in normal lung fibroblasts mimicking the localization of p21Cip1/WAF1 in scleroderma lung fibroblasts. Overexpression of c-a PKC-alpha or PKC-epsilon results in accumulation of p21Cip1/WAF1 in the cytoplasm. Depletion of PKC-alpha or inhibition of mitogen-activated protein kinase (MAPK) blocks thrombin-induced DNA synthesis in lung fibroblasts. Inhibition of PKC by calphostin or PKC-alpha, but not PKC-epsilon, by antisense oligonucleotides prevents thrombin-induced MAPK phosphorylation and accumulation of G(1) phase regulatory protein cyclin D1, suggesting that PKC-alpha, MAPK, and cyclin D1 mediate lung fibroblast proliferation. These data demonstrate that two distinct PKC isoforms mediate thrombin-induced resistance to apoptosis and proliferation and suggest that p21Cip1/WAF1 promotes both phenomena.
SourceAvailable from: Anil Karihaloo[Show abstract] [Hide abstract]
ABSTRACT: Previous work in our laboratory demonstrated that hyperoxia suppressed the expression of vascular endothelial growth factor (VEGF) by the embryonic lung, leading to increased epithelial cell apoptosis and failure of explant airway growth and branching that was rescued by the addition of Vegf165. The aims of this study were to determine protective pathways by which VEGF isoforms attenuate hyperoxic lung growth retardation and to identify the target cell for VEGF action. Timed pregnant CD-1 or fetal liver kinase (FLK1)-eGFP lung explants cultured in 3% or 50% oxygen were treated +/- Vegf121, VEGF164/Vegf165 or VEGF188 in the presence or absence of anti-rat neuropilin-1 (NRP1) antibody or GO6983 (protein kinase C (PKC) pan-inhibitor) and lung growth and branching quantified. Immunofluorescence studies were performed to determine apoptosis index and location of FLK1 phosphorylation and western blot studies of lung explants were performed to define the signaling pathways that mediate the protective effects of VEGF. Heparin-binding VEGF isoforms (VEGF164/Vegf165 and VEGF188) but not Vegf121 selectively reduced epithelial apoptosis and partially rescued lung bud branching and growth. These protective effects required NRP1-dependent FLK1 activation in endothelial cells. Analysis of downstream signaling pathways demonstrated that the VEGF-mediated anti-apoptotic effects were dependent on PKC activation. Vegf165 activates FLK1-NRP1 signaling in endothelial cells, leading to a PKC-dependent paracrine signal that in turn inhibits epithelial cell apoptosis.Respiratory research 03/2014; 15(1):32. DOI:10.1186/1465-9921-15-32 · 3.38 Impact Factor
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ABSTRACT: Apoptosis of alveolar epithelial cells (AEC) and survival of lung fibroblasts are critical events in the pathogenesis of pulmonary fibrosis; however, mechanisms underlying the apoptosis of AEC and the resistance of lung fibroblasts to apoptosis remain obscure. Herein, we demonstrate that the fate of these two cell types depends on the expression of CCAAT enhancer-binding homologous protein (CHOP). We observed that thrombin, which is over-expressed in scleroderma and other interstitial lung diseases (ILD), increases the expression of CHOP in primary AEC and in A549 cells via an Ets1-dependent pathway. Additionally, thrombin activates caspase-3 in AEC and induces apoptosis of these cells in a CHOP-dependent manner. In contrast, thrombin decreases ER stress-induced CHOP in lung fibroblasts through Myc-dependent mechanisms and protects such cells from apoptosis. Furthermore, when lung fibroblasts are transfected with recombinant CHOP, they then undergo apoptosis, even in the presence of thrombin, suggesting that CHOP signaling pathways are downstream of thrombin. In accordance with the differential effects of thrombin on AEC and lung fibroblasts, we observed strong expression of CHOP in AEC in fibrotic lung tissue isolated from patients with SSc-associated ILD (SSc-ILD), but not in lung myofibroblasts nor in normal lung tissue. Expression of CHOP in scleroderma lung is accompanied by positive staining for the thrombin receptor, PAR-1, and for TUNEL, suggesting roles for both thrombin and CHOP in AEC apoptosis in SSc-ILD. We conclude that regulation of CHOP by thrombin directs AEC towards apoptosis while promoting survival of lung fibroblasts, ultimately contributing to the persistent fibroproliferation seen in SSc-ILD and other fibrosing lung diseases.American Journal of Respiratory Cell and Molecular Biology 11/2013; 50(5). DOI:10.1165/rcmb.2013-0317OC · 4.11 Impact Factor
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ABSTRACT: Fibroblasts are the most common cell type of the connective tissues found throughout the body and the principal source of the extensive extracellular matrix (ECM) characteristic of these tissues. They are also the central mediators of the pathological fibrotic accumulation of ECM and the cellular proliferation and differentiation that occurs in response to prolonged tissue injury and chronic inflammation. The transformation of the fibroblast cell lineage involves classical developmental signaling programs and includes a surprisingly diverse range of precursor cell types-most notably, myofibroblasts that are the apex of the fibrotic phenotype. Myofibroblasts display exaggerated ECM production; constitutively secrete and are hypersensitive to chemical signals such as cytokines, chemokines, and growth factors; and are endowed with a contractile apparatus allowing them to manipulate the ECM fibers physically to close open wounds. In addition to ECM production, fibroblasts have multiple concomitant biological roles, such as in wound healing, inflammation, and angiogenesis, which are each interwoven with the process of fibrosis. We now recognize many common fibroblast-related features across various physiological and pathological protracted processes. Indeed, a new appreciation has emerged for the role of non-cancerous fibroblast interactions with tumors in cancer progression. Although the predominant current clinical treatments of fibrosis involve non-specific immunosuppressive and anti-proliferative drugs, a variety of potential therapies under investigation specifically target fibroblast biology.Frontiers in Pharmacology 05/2014; 5:123. DOI:10.3389/fphar.2014.00123