Transcriptional regulation of the human alpha2(I) collagen gene. Combined action of upstream stimulatory and inhibitory cis-acting elements

Targeting Type I Collagen for Cancer Treatment

Collagen is the most abundant protein in animals. Interactions between tumor cells and collagen influence every step of tumor development. Type I collagen is the main fibrillar collagen in the extracellular matrix and is frequently up-regulated during tumorigenesis. The binding of type I collagen to its receptors on tumor cells promotes tumor cell proliferation, epithelial-mesenchymal transition, and metastasis. Type I collagen also regulates the efficacy of tumor therapies, such as chemotherapy, radiotherapy, and immunotherapy. Furthermore, type I collagen fragments are diagnostic markers of metastatic tumors and have prognostic value. Inhibition of type I collagen synthesis has been reported to have anti-tumor effects in animal models. However, collagen has also been shown to possess anti-tumor activity. Therefore, the roles that type I collagen plays in tumor biology are complex and tumor type-dependent. In this review, we discuss the expression and regulation of synthesis of type I collagen, as well as the role up-regulated type I collagen plays in various stages of cancer progression. We also discuss the role of collagen in tumor therapy. Finally, we highlight several recent approaches targeting type I collagen for cancer treatment. This article is protected by copyright. All rights reserved.

Thyroid-Stimulating Hormone Favors Runx2-Mediated Matrix Mineralization in HOS and SaOS2 Cells: An In Vitro and In Silico Approach

Osteoporosis is a skeletal disease that is both systemic and silent characterized by an unbalanced activity of bone remodeling leading to bone loss. Rising evidences demonstrate that thyroid stimulating hormone (TSH) has an important role in the regulation on the metabolism of bone. However, TSH regulation on human osteoblast essential transcriptional factors has not been identified. Current study examined the role of TSH on human osteoblastic Runx2 expression and their functional genes by in vitro and in slico analysis. Human osteoblast like (HOS and SaoS-2) cells were cultured with DMEM and treated with hTSH at the concentration of 0.01 ng/mL and 10 ng/mL. After treatment, osteoblastic Runx2 and IGF-1R beta expression were studied using RT-PCR and western blot analysis. TSH treatment induced osteoblastic essential transcriptional factor, Runx2 in HOS and SaOS2 cells on 48 h duration and elevated the expression of IGF-IR β gene and Protein in SaoS-2 cells. TSH also promotes Runx2 responsive genes such as ALP, Collagen and osteocalcin in SaOS2 cells on day 2 to day 14 of 10 ng/mL of treatment and favors' matrix mineralization matrix in these cells. In addition, TSH facilitated human osteoblastic cells to mineralize their matrix confirmed by day 21 of alizarin red calcium staining. In silico study was performed to check CREB and ELK1 interaction with Runx2. Results of in silico analysis showed that TSH mediated signalling molecules such as CREB and ELK1 showed interaction with Runx2 which involve in osteobalstic gene expression and differentiation. Present findings confirm that TSH promotes Runx2 expression, osteoblastic responsive genes and bone matrix formation.

Tamibarotene Ameliorates Bleomycin-Induced Dermal Fibrosis by Modulating Phenotypes of Fibroblasts, Endothelial Cells, and Immune Cells

Tamibarotene (Am80) is a synthetic retinoid that modulates the pathologic processes of various autoimmune and inflammatory diseases and their animal models. We here investigated the therapeutic potential of Am80 against systemic sclerosis using its animal models. Am80 significantly attenuated dermal and hypodermal fibrosis in bleomycin (BLM)-treated mice and tight skin 1 mice, respectively. Consistently, Am80 significantly suppressed the expression of various molecules related to tissue fibrosis, including transforming growth factor-β1, connective tissue growth factor, IL-4, IL-10, IL-13, IL-17A, tumor necrosis factor-α, IFN-γ, and monocyte chemotactic protein 1 in the lesional skin of BLM-treated mice. Furthermore, Am80 decreased the proportion of effector T cells, while increasing that of naïve T cells among CD4+ T cells in the draining lymph nodes of BLM-treated mice. Moreover, a series of BLM-induced pathologic events, including endothelial-to-mesenchymal transition; ICAM-1 expression in endothelial cells; the infiltration of macrophages, mast cells, and lymphocytes; and M2 macrophage differentiation, were attenuated by Am80. Importantly, Am80 directly reversed the profibrotic phenotype of transforming growth factor-β1-treated dermal fibroblasts, suppressed ICAM-1 expression in endothelial cells, and promoted M1 macrophage differentiation in vitro. Collectively, Am80 inhibits the development of experimental dermal fibrosis by reversing the profibrotic phenotype of various cell types and would be a candidate for therapeutic drugs against dermal fibrosis of systemic sclerosis.

Sp1 Mediates a Therapeutic Role of MiR-7a/b in Angiotensin II-Induced Cardiac Fibrosis via Mechanism Involving the TGF-β and MAPKs Pathways in Cardiac Fibroblasts

MicroRNA-7a/b (miR-7a/b) protects cardiac myocytes from apoptosis during ischemia/reperfusion injury; however, its role in angiotensin II (ANG II)-stimulated cardiac fibroblasts (CFs) remains unknown. Therefore, the present study investigated the anti-fibrotic mechanism of miR-7a/b in ANG II-treated CFs. ANG II stimulated the expression of specific protein 1 (Sp1) and collagen I in a dose- and time-dependent manner, and the overexpression of miR-7a/b significantly down-regulated the expression of Sp1 and collagen I stimulated by ANG II (100 nM) for 24 h. miR-7a/b overexpression effectively inhibited MMP-2 expression/activity and MMP-9 expression, as well as CF proliferation and migration. In addition, miR-7a/b also repressed the activation of TGF-β, ERK, JNK and p38 by ANG II. The inhibition of Sp1 binding activity by mithramycin prevented collagen I overproduction; however, miR-7a/b down-regulation reversed this effect. Further studies revealed that Sp1 also mediated miR-7a/b-regulated MMP expression and CF migration, as well as TGF-β and ERK activation. In conclusion, miR-7a/b has an anti-fibrotic role in ANG II-treated CFs that is mediated by Sp1 mechanism involving the TGF-β and MAPKs pathways.

Decreased interleukin-20 expression in scleroderma skin contributes to cutaneous fibrosis

OBJECTIVE

To clarify the role of interleukin-20 (IL-20) in the regulatory mechanism of extracellular matrix expression and to determine the contribution of IL-20 to the phenotype of systemic sclerosis (SSc).

METHODS

Protein and messenger RNA (mRNA) levels of collagen, Fli-1, IL-20, and IL-20 receptor (IL-20R) were analyzed using polymerase chain reaction (PCR) array, immunoblotting, immunohistochemical staining, enzyme-linked immunosorbent assay, and real-time PCR.

RESULTS

PCR array revealed that IL-20 decreased gene expression of α2(I) collagen (0.03-fold), Smad3 (0.02-fold), and endoglin (0.05-fold) in cultured normal dermal fibroblasts. Fli-1 protein expression was induced by IL-20 (~2-fold). The inhibition of collagen by IL-20, the induction of Fli-1 by IL-20, and the reduction of Smad3 and endoglin by IL-20 were also observed in SSc fibroblasts. Serum IL-20 levels were reduced only slightly in SSc patients but were significantly decreased in patients with scleroderma spectrum disorders (the prodromal stage of SSc) compared with those in normal subjects (111.3 pg/ml versus 180.4 pg/ml; P < 0.05). On the other hand, IL-20 mRNA expression in SSc skin was decreased compared with that in normal skin (P < 0.05), which may result in the induction of collagen synthesis in SSc dermal fibroblasts. IL-20R was expressed in normal and SSc fibroblasts. Moreover, IL-20 supplementation by injection into the skin reversed skin fibrosis induced by bleomycin in mice (~0.5-fold).

CONCLUSION

IL-20 reduces basal collagen transcription via Fli-1 induction, while down-regulation of Smad3 and endoglin may cancel the effect of transforming growth factor β in SSc fibroblasts. To confirm the therapeutic value of IL-20 and IL-20R, their function and expression in vivo should be further studied.

Sp1 mediates microRNA-29c-regulated type I collagen production in renal tubular epithelial cells

Specificity protein 1 (Sp1), a ubiquitously expressed transcription factor, plays a potential pathogenic role for fibrotic disease in many organs by regulating the expression of several fibrosis-related genes, however, its role in kidney fibrosis and the mechanisms regulating its expression remain incompletely clarified. Here, we found that Sp1 was markedly induced and closely correlated with interstitial type I collagen accumulation in kidney tubular epithelia from obstructive nephropathy. In vitro, both Sp1 and type I collagen expression were up-regulated in TGF-β1-treated kidney tubular epithelial cells (NRK-52E), whereas knockdown of Sp1 largely abolished TGF-β1-induced type I collagen production, suggesting that Sp1 induction is partially responsible for type I collagen expression. In addition, we found that miR-29c expression was remarkably reduced in either the tubular epithelial cells from kidney with UUO nephropathy or TGF-β1-treated NRK-52E cells. Knockdown of miR-29c could sufficiently induce Sp1 and type I collagen expression, whereas ectopic expression of miR-29c largely abolished their expression stimulated by TGF-β1 in NRK-52E cells. Furthermore, knockdown of Sp1 effectively hindered type I collagen induction stimulated by miR-29c down-regulation. Collectively, this study demonstrates that Sp1 acts as an essential mediator for miR-29c in regulating type I collagen production in tubular epithelial cells, which may provide a novel mechanistic insight about miR-29c in renal fibrosis.

SHPS-1 and a synthetic peptide representing its ITIM inhibit the MyD88, but not TRIF, pathway of TLR signaling through activation of SHP and PI3K in THP-1 cells

BACKGROUND

Src homology 2 domain-containing protein tyrosine phosphatase substrate (SHPS)-1 is known to have regulatory effects on myeloid cells. However, its role in macrophage activation is not clearly understood.

METHODS AND RESULTS

In order to investigate the role of SHPS-1 in Toll-like receptor (TLR)-mediated activation, human monocytic cell lines were treated with anti-SHPS-1 monoclonal antibody. The triggering of SHPS-1 blocked the expression of IL-8 and TNF-α in cells treated with a TLR4 ligand that induces a signaling pathway involving myeloid differentiation factor 88 (MyD88) and Toll-interleukin-1 receptor (TIR)-domain-containing adapter-inducing interferon-β (TRIF). Interestingly, SHPS-1 inhibited TLR9/MyD88-mediated, but not TLR3/TRIF-mediated, expression of IL-8. Accordingly, a synthetic peptide representing the immunoreceptor tyrosine-based inhibition motif (ITIM) of SHPS-1 suppressed only the MyD88 pathway. Utilization of specific inhibitors and Western blot analysis indicated that the inhibitory effects were mediated by Src homology 2 domain-containing phosphatases (SHPs) and phosphoinositide 3-kinase (PI3K).

CONCLUSION

SHPS-1 negatively regulates the MyD88-dependent TLR signaling pathway through the inhibition of NF-κB activation.

The early growth response gene Egr2 (Alias Krox20) is a novel transcriptional target of transforming growth factor-β that is up-regulated in systemic sclerosis and mediates profibrotic responses

Although the early growth response-2 (Egr-2, alias Krox20) protein shows structural and functional similarities to Egr-1, these two related early-immediate transcription factors are nonredundant. Egr-2 plays essential roles in peripheral nerve myelination, adipogenesis, and immune tolerance; however, its regulation and role in tissue repair and fibrosis remain poorly understood. We show herein that transforming growth factor (TGF)-β induced a Smad3-dependent sustained stimulation of Egr2 gene expression in normal fibroblasts. Overexpression of Egr-2 was sufficient to stimulate collagen gene expression and myofibroblast differentiation, whereas these profibrotic TGF-β responses were attenuated in Egr-2-depleted fibroblasts. Genomewide transcriptional profiling revealed that multiple genes associated with tissue remodeling and wound healing were up-regulated by Egr-2, but the Egr-2-regulated gene expression profile overlapped only partially with the Egr-1-regulated gene profile. Levels of Egr-2 were elevated in lesional tissue from mice with bleomycin-induced scleroderma. Moreover, elevated Egr-2 was noted in biopsy specimens of skin and lung from patients with systemic sclerosis. These results provide the first evidence that Egr-2 is a functionally distinct transcription factor that is both necessary and sufficient for TGF-β-induced profibrotic responses and is aberrantly expressed in lesional tissue in systemic sclerosis and in a murine model of scleroderma. Together, these findings suggest that Egr-2 plays an important nonredundant role in the pathogenesis of fibrosis. Targeting Egr-2 might represent a novel therapeutic strategy to control fibrosis.

Expression of matrix metalloproteinase-13 is controlled by IL-13 via PI3K/Akt3 and PKC-δ in normal human dermal fibroblasts

IL-13, a T helper type 2 cytokine, is reported to be increased in the tissue of patients with atopic dermatitis (AD). In addition, chronic lichenified plaques in AD show thickened epidermis and dermis. We hypothesized that IL-13 is involved in tissue remodeling by altering the expression of matrix metalloproteinases (MMPs). In this study, we examined the MMP-related genes targeted by IL-13 in human dermal fibroblasts using a complementary DNA microarray. We focused on the MMP-13 gene, which was identified as one of the MMPs suppressed by IL-13. IL-13 downregulated both MMP-13 protein and mRNA expression. IL-13 suppressed MMP-13 expression more effectively in the presence of protein kinase C (PKC)-δ inhibitor, whereas IL-13 upregulated MMP-13 in the presence of inhibitors of phosphoinositide 3-kinase (PI3K)/Akt pathway or Akt3-specific small interfering RNA. Our results suggest that MMP-13 expression is negatively controlled by PI3K/Akt3 and positively regulated by PKC-δ in the presence of IL-13. Taken together, these findings indicate that IL-13 may induce the formation of thickened dermis in AD by decreasing collagen degradation. Blockade of IL-13 signaling cascades in AD patients may be a new therapeutic approach.

Prostaglandin F(2alpha) receptor signaling facilitates bleomycin-induced pulmonary fibrosis independently of transforming growth factor-beta

Idiopathic pulmonary fibrosis (IPF) is a progressive disease characterized by fibroblast proliferation and excess deposition of collagen and other extracellular matrix (ECM) proteins, which lead to distorted lung architecture and function. Given that anti-inflammatory or immunosuppressive therapy currently used for IPF does not improve disease progression therapies targeted to blocking the mechanisms of fibrogenesis are needed. Although transforming growth factor-beta (TGF-beta) functions are crucial in fibrosis, antagonizing this pathway in bleomycin-induced pulmonary fibrosis, an animal model of IPF, does not prevent fibrosis completely, indicating an additional pathway also has a key role in fibrogenesis. Given that the loss of cytosolic phospholipase A(2) (cPLA(2)) suppresses bleomycin-induced pulmonary fibrosis, we examined the roles of prostaglandins using mice lacking each prostoaglandin receptor. Here we show that loss of prostaglandin F (PGF) receptor (FP) selectively attenuates pulmonary fibrosis while maintaining similar levels of alveolar inflammation and TGF-beta stimulation as compared to wild-type (WT) mice, and that FP deficiency and inhibition of TGF-beta signaling additively decrease fibrosis. Furthermore, PGF(2alpha) is abundant in bronchoalveolar lavage fluid (BALF) of subjects with IPF and stimulates proliferation and collagen production of lung fibroblasts via FP, independently of TGF-beta. These findings show that PGF(2alpha)-FP signaling facilitates pulmonary fibrosis independently of TGF-beta and suggests this signaling pathway as a therapeutic target for IPF.

Peroxisome proliferator-activated receptor-gamma abrogates Smad-dependent collagen stimulation by targeting the p300 transcriptional coactivator

Ligands of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) abrogate the stimulation of collagen gene transcription induced by transforming growth factor-beta (TGF-beta). Here, we delineate the mechanisms underlying this important novel physiological function for PPAR-gamma in connective tissue homeostasis. First, we demonstrated that antagonistic regulation of TGF-beta activity by PPAR-gamma ligands involves cellular PPAR-gamma, since 15-deoxy-Delta12,14-prostaglandin J(2) (15d-PGJ(2)) failed to block TGF-beta-induced responses in either primary cultures of PPAR-gamma-null murine embryonic fibroblasts, or in normal human skin fibroblasts with RNAi-mediated knockdown of PPAR-gamma. Next, we examined the molecular basis underlying the abrogation of TGF-beta signaling by PPAR-gamma in normal human fibroblasts in culture. The results demonstrated that Smad-dependent transcriptional responses were blocked by PPAR-gamma without preventing Smad2/3 activation. In contrast, the interaction between activated Smad2/3 and the transcriptional coactivator and histone acetyltransferase p300 induced by TGF-beta, and the accumulation of p300 on consensus Smad-binding DNA sequences and histone H4 hyperacetylation at the COL1A2 locus, were all prevented by PPAR-gamma. Wild-type p300, but not a mutant form of p300 lacking functional histone acetyltransferase, was able to restore TGF-beta-induced stimulation of COL1A2 in the presence of PPAR-gamma ligands. Collectively, these results indicate that PPAR-gamma blocked Smad-mediated transcriptional responses by preventing p300 recruitment and histone H4 hyperacetylation, resulting in the inhibition of TGF-beta-induced collagen gene expression. Pharmacological activation of PPAR-gamma thus may represent a novel therapeutic approach to target p300-dependent TGF-beta profibrotic responses such as stimulation of collagen gene expression.

Oxidative and nitrosative stress and fibrogenic response

Uncontrolled production of collagen I is the main feature of liver fibrosis. Following a fibrogenic stimulus such as alcohol, hepatic stellate cells (HSC) transform into an activated collagen-producing cell. In alcoholic liver disease, numerous changes in gene expression are associated with HSC activation, including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses for understanding the molecular basis of the collagen I gene regulation have revealed a complex process involving reactive oxygen species (ROS) as key mediators. Less is known, however, about the contribution of reactive nitrogen species (RNS). In addition, a series of cytokines, growth factors, and chemokines, which activate extracellular matrix (ECM)-producing cells through paracrine and autocrine loops, contribute to the fibrogenic response.

Constitutive Smad signaling and Smad-dependent collagen gene expression in mouse embryonic fibroblasts lacking peroxisome proliferator-activated receptor-gamma

Transforming growth factor-beta (TGF-beta), a potent inducer of collagen synthesis, is implicated in pathological fibrosis. Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a nuclear hormone receptor that regulates adipogenesis and numerous other biological processes. Here, we demonstrate that collagen gene expression was markedly elevated in mouse embryonic fibroblasts (MEFs) lacking PPAR-gamma compared to heterozygous control MEFs. Treatment with the PPAR-gamma ligand 15d-PGJ(2) failed to down-regulate collagen gene expression in PPAR-gamma null MEFs, whereas reconstitution of these cells with ectopic PPAR-gamma resulted in their normalization. Compared to control MEFs, PPAR-gamma null MEFs displayed elevated levels of the Type I TGF-beta receptor (TbetaRI), and secreted more TGF-beta1 into the media. Furthermore, PPAR-gamma null MEFs showed constitutive phosphorylation of cellular Smad2 and Smad3, even in the absence of exogenous TGF-beta, which was abrogated by the ALK5 inhibitor SB431542. Constitutive Smad2/3 phosphorylation in PPAR-gamma null MEFs was associated with Smad3 binding to its cognate DNA recognition sequences, and interaction with coactivator p300 previously implicated in TGF-beta responses. Taken together, these results indicate that loss of PPAR-gamma in MEFs is associated with upregulation of collagen synthesis, and activation of intracellular Smad signal transduction, due, at least in part, to autocrine TGF-beta stimulation.

Akt blockade downregulates collagen and upregulates MMP1 in human dermal fibroblasts

Acutely transforming retrovirus AKT8 in rodent T-cell lymphoma (Akt) is a serine/threonine kinase that plays important roles in survival, cell-cycle progression, and cell proliferation, and has recently been implicated in collagen regulation. The aim of this study was to determine the role of Akt in collagen deposition by normal dermal fibroblasts, and to determine the sensitivity of cultured systemic sclerosis (SSc) fibroblasts to Akt inhibition. We show that blockade of Akt using pharmacological inhibitors, small interfering RNA (siRNA), and a dominant-negative Akt mutant led to inhibition of the basal type I collagen production. Furthermore, inhibition of Akt upregulated basal matrix metalloproteinase 1 (MMP1) production and reversed the inhibitory effect of transforming growth factor-beta (TGF-beta) on MMP1 gene expression. In addition, SSc fibroblasts were more sensitive to Akt inhibition, with respect to collagen and MMP1 production. These findings suggest that in human dermal fibroblasts, Akt has dual profibrotic effects, increasing collagen synthesis and decreasing its degradation via downregulation of MMP1. Akt could directly contribute to elevated collagen in SSc fibroblasts and it may represent an attractive target for therapy of SSc fibrosis.

Targeting of Sp1 transcription factor: a novel therapeutic approach for keloids, an in vitro analysis

Keloid scars are fibroproliferative disorders characterized by the accumulation of extracellular matrix (ECM) components resulting in a fibrotic condition. Several ECM promoters are regulated by Sp1. Thus, our aim was to investigate the role of Sp1 in keloid pathogenesis and investigate the antiproliferative and antifibrotic effects of Wp631 and mitoxantrone, potent inhibitors of Sp1-activated transcription. An elevated level of Sp1 was observed in tissue extracts obtained from keloid tissue. Serum stimulation elevated Sp1 levels in keloid fibroblasts (KF). Under coculture conditions Sp1 seemed to be downregulated. Wp631 and mitoxanthrone in serum growth factors resulted in a reduced expression of ECM components in KF. Both Wp631 and mitoxanthrone were also able to inhibit the proliferation of normal and keloid keratinocytes and fibroblasts significantly. As Wp631 seems to be potent in downregulating the ECM components in KF and also inhibiting the proliferation of these cells it could be explored as a possible therapeutic agent in the treatment of keloids.

Csk-homologous kinase interacts with SHPS-1 and enhances neurite outgrowth of PC12 cells

SHPS-1 is an immunoglobulin superfamily protein with four immunoreceptor tyrosine-based inhibitory motifs (ITIMs) in its cytoplasmic region. Various neurotrophic factors induce the tyrosine phosphorylation of SHPS-1 and the association of SHPS-1 with the protein tyrosine phosphatase SHP-2. Using a yeast two-hybrid screen, we identified a protein tyrosine kinase, Csk-homologous kinase (CHK), as an SHPS-1-interacting protein. Immunoprecipitation and pull-down assays using glutathione S-transferase (GST) fusion proteins containing the Src homology 2 (SH2) domain of CHK revealed that CHK associates with tyrosine-phosphorylated SHPS-1 via its SH2 domain. HIS3 assay in a yeast two-hybrid system using the tyrosine-to-phenylalanine mutants of SHPS-1 indicated that the first and second ITIMs of SHPS-1 are required to bind CHK. Over-expression of wild-type CHK, but not a kinase-inactive CHK mutant, enhanced the phosphorylation of SHPS-1 and its subsequent association with SHP-2. CHK phosphorylated each of four tyrosines in the cytoplasmic region of SHPS-1 in vitro. Co-expression of SHPS-1 and CHK enhanced neurite outgrowth in PC12 cells. Thus, CHK phosphorylates and associates with SHPS-1 and is involved in neural differentiation via SHP-2 activation.

Autocrine TGF-beta signaling in the pathogenesis of systemic sclerosis

Excessive extracellular matrix deposition in the skin, lung, and other organs is a hallmark of systemic sclerosis (SSc). Fibroblasts isolated from sclerotic lesions in patients with SSc and cultured in vitro are characterized by increased synthesis of collagen and other extracellular matrix components, consistent with the disease phenotype. Thus, cultured scleroderma fibroblasts serve as a principal experimental model for studying the mechanisms involved in extracellular matrix overproduction in SSc. The pathogenesis of SSc is still poorly understood, but increasing evidence suggests that transforming growth factor-beta (TGF-beta) is a key mediator of tissue fibrosis as a consequence of extracellular matrix accumulation in the pathology of SSc. TGF-beta regulates diverse biological activities including cell growth, cell death or apoptosis, cell differentiation, and extracellular matrix synthesis. TGF-beta is known to induce the expression of extracellular matrix proteins in mesenchymal cells and to stimulate the production of protease inhibitors that prevent enzymatic breakdown of the extracellular matrix. This review focuses on the possible role of autocrine TGF-beta signaling in the pathogenesis of SSc.

Involvement of the constitutive complex formation of c-Ski/SnoN with Smads in the impaired negative feedback regulation of transforming growth factor beta signaling in scleroderma fibroblasts

OBJECTIVE

The principal effect of transforming growth factor beta1 (TGFbeta1) on mesenchymal cells is its stimulation of extracellular matrix synthesis. Previous reports indicated the significance of the autocrine TGFbeta loop in the pathogenesis of scleroderma. The aim of this study was to examine c-Ski and SnoN, principal molecules in the negative regulation of TGFbeta signaling, to further understand the autocrine TGFbeta loop in scleroderma.

METHODS

Levels of expression of c-Ski/SnoN on cultured normal and scleroderma fibroblasts were determined by Western blotting, Northern blotting, and immunohistochemical staining. To determine the protein-protein interaction between c-Ski/SnoN, Smads, and p300, immunoprecipitation was performed. A transient transfection assay was performed to measure promoter activity of the alpha2(I) collagen gene and the 3TP-Lux plasmid construct.

RESULTS

Scleroderma fibroblasts exhibited increased c-Ski/SnoN levels compared with normal fibroblasts, both in vivo and in vitro. Although c-Ski/SnoN constitutively formed a complex with Smads by immunoprecipitation, the inhibitory effect of c-Ski/SnoN on the promoter activity of human alpha2(I) collagen and 3TP-Lux was impaired in scleroderma fibroblasts. Immunoprecipitation analyses also revealed that overexpressed c-Ski/SnoN could not compete with p300 in these cells.

CONCLUSION

These results indicate that impaired competition with p300 is the possible cause of dysfunction of c-Ski/SnoN in scleroderma fibroblasts and that this might contribute to maintenance of the autocrine TGFbeta loop in this disease.

Collagen loss and impaired wound healing is associated with c-Myb deficiency

Collagen type I serves as an abundant structural and signalling component of skin. It is also an established target gene of the transcription factor, c-Myb. When c-myb-/- embryos were examined it was observed that their skin was markedly thinner than normal. Importantly, immunohistochemical investigation showed complete absence of collagen type I. Although these homozygous knock-out embryos fail to develop beyond day 15, fibroblasts established from these embryos (mouse embryonic fibroblasts [MEFs]) show defective proliferative responses. Furthermore, in vitro scratch wound assays demonstrated that these c-myb-/- MEFs also exhibit slower closure than their wild-type counterparts. Embryonic lethality has meant that examination of the role of c-Myb in adult mouse skin has not been reported to date. However, in view of the abundance of collagen type I in normal skin, its role in skin integrity and the in vitro data showing proliferative and migration defects in c-myb-/- MEFs, we investigated the consequences of heterozygous c-myb loss in adult mice on the complex process of skin repair in response to injury. Our studies clearly demonstrate that heterozygous c-myb deficiency has a functional effect on wound repair, collagen type I levels and, in response to wounding, transforming growth factor-beta1 (an important collagen stimulating factor) induction expression is aberrantly high. Manipulation of c-Myb may therefore provide new therapeutic opportunities for improving wound repair while uncontrolled expression may underpin some fibrotic disorders.

Trichostatin A blocks TGF-beta-induced collagen gene expression in skin fibroblasts: involvement of Sp1

Transforming growth factor- beta (TGF-beta) stimulates Type I collagen synthesis by fibroblasts and is implicated in tissue fibrosis. Here, we demonstrate that histone deacetylase inhibitor Trichostatin A (TSA) suppresses the TGF-beta-induced Type I collagen synthesis but not induced PAI-1 synthesis suggesting the influence of TSA is gene specific. Results further reveal that there is no significant alteration in Smad activation and function in presence of TSA suggesting suppression of TGF-beta-induced collagen synthesis is not due to impaired Smad signaling. TGF-beta induces the levels of Sp1, an essential transcription factor of Smad-dependent stimulation of collagen synthesis. However, in presence of TSA, TGF-beta fails to induce Sp1 levels, its interaction with Smad complex and Sp1 binding site in COL1A2 promoter. Furthermore, overexpressed Sp1 reverses the TSA-mediated inhibition of TGF-beta-induced collagen gene expression. Collectively, these results suggest that TSA-mediated suppression of Smad-dependent TGF-beta-induced collagen synthesis is due to suppression of Sp1 activity in skin fibroblasts.

Epidermal growth factor up-regulates transforming growth factor-beta receptor type II in human dermal fibroblasts via p38 mitogen-activated protein kinase pathway

TGF-beta receptors (TbetaRs) are serine/threonine kinase receptors that bind to TGF-beta and propagate intracellular signaling through Smad proteins. TbetaRs are repressed in some human cancers and expressed at high levels in several fibrotic diseases. We demonstrated that epidermal growth factor (EGF) up-regulates type II TGF-beta receptor (TbetaRII) expression in human dermal fibroblasts. EGF-mediated induction of TbetaRII expression was inhibited by the treatment of fibroblasts with a specific p38 mitogen-activated protein kinase (MAPK) inhibitor, SB203580, whereas MEK inhibitor PD98059 did not block the up-regulation of TbetaRII by EGF. EGF induced the TbetaRII promoter activity, and this induction was significantly blocked by SB203580, but not by PD98059. The overexpression of the dominant negative form of p38alpha or p38beta significantly reduced the induction of TbetaRII promoter activity by EGF. These results indicate that the EGF-mediated induction of TbetaRII expression involves the p38 MAPK signaling pathway. The EGF-mediated induction of TbetaRII expression may participate in a synergistic interplay between EGF and TGF-beta signaling pathway.

Redox-sensitive myocardial remodeling and dysfunction in swine diet-induced experimental hypercholesterolemia

OBJECTIVES

The effects of hypercholesterolemia (HC) on the myocardium and the underlying mechanisms are unclear. We tested the hypothesis that diet-induced HC-induced myocardial fibrosis by regulating the transforming growth factor (TGF)-beta pathway and apoptosis through increased oxidative stress, and that these would be functionally consequential.

METHODS

Three groups of pigs (n=6 each) were studied after 12 weeks of normal or 2% HC diet, or HC+antioxidant supplementation. Cardiac function was evaluated by electron beam computed tomography, while fibrogenic mechanisms and apoptosis were evaluated in myocardial tissue.

RESULTS

HC-induced myocardial fibrosis was accompanied by increased ratio of interstitial collagen I/III (1.4+/-0.3 versus 0.5+/-0.1 in normal, p<0.05), expression of TGF-beta1 and its downstream smad mediators, as well as myocyte apoptosis. These alterations were also associated with a decrease in diastolic filling rate compared to normal (134.0+/-10.6 ml/s versus 70.3+/-14.3 ml/s, p<0.05), but were attenuated in HC animals chronically supplemented with antioxidants.

CONCLUSIONS

Myocardial injury elicited by experimental HC includes redox-sensitive increases in TGF-beta1 expression and apoptosis, which are associated with diastolic dysfunction. These observations underscore a role of increased oxidative stress in modulating myocardial tissue remodeling and dysfunction in vivo in HC.

Inhibition of collagen gene expression by interferon-gamma: novel role of the CCAAT/enhancer binding protein beta (C/EBPbeta)

By inhibiting collagen synthesis, interferon-gamma (IFN-gamma) plays a key role in maintaining connective tissue homeostasis, but the mechanisms are not well-understood. In addition to intracellular signaling through the canonical JAK-STAT transduction pathway, IFN-gamma was recently shown to regulate gene expression via the CCAAT/enhancer-binding protein beta (C/EBPbeta) as well. Because C/EBPbeta is a crucial mediator of immune and inflammatory responses, and has been implicated in regulation of collagen synthesis by tumor necrosis factor-alpha, we examined its role in the inhibitory effects of IFN-gamma. The results demonstrated that IFN-gamma caused increased C/EBPbeta expression in dermal fibroblasts and enhanced its binding to cognate DNA sequences in the alpha2(I) procollagen gene (COL1A2) promoter in vitro and in vivo. Disruption of C/EBP binding by deletion or site-directed mutagenesis abrogated the inhibition of collagen promoter activity in transient transfection assays, as did cotransfection with dominant negative C/EBPbeta, indicating a functional role of cellular C/EBPbeta in mediating the IFN-gamma response. Rapid phosphorylation of the ERK1/2 MAP kinases induced by IFN-gamma was accompanied by phosphorylation and nuclear translocation of cellular C/EBPbeta, and pretreatment of fibroblasts with ERK1/2 kinase inhibitor blocked C/EBPbeta phosphorylation, as well as inhibition of COL1A2 promoter activity, elicited by IFN-gamma. These results provide compelling evidence for a novel C/EBPbeta-dependent IFN-gamma signaling pathway responsible for inhibition of collagen gene transcription. Taken together with recent reports, the findings indicate that intracellular pathways mediating negative regulation of collagen synthesis in response to distinct inflammatory signals that converge on C/EBPbeta.

Transcriptional regulation of the human alpha2(I) collagen gene (COL1A2), an informative model system to study fibrotic diseases

During the past two decades, the human pro-alpha2(I) collagen gene (COL1A2) has emerged as an informative model in which to study the general principles that govern the transcriptional control of extracellular matrix deposition in normal and fibrotic conditions. Multiple studies have in fact delineated the genomic regions, cis-acting elements and trans-acting factors implicated in constitutive, cytokine-modulated and tissue-specific expression of COL1A2. These functional components are integrated into a regulatory network that consists of the proximal promoter, far-upstream enhancer and downstream repressor, and which operates according to two mechanisms. The first mechanism is one in which combinatorial interactions among promoter-bound proteins determine transcriptional outcome in different cellular and experimental contexts. The other mechanism is one whereby cooperative assembly of protein complexes at distantly located DNA elements directs spatiotemporal specificity. These transcriptional studies have also an additional value in translational research, in that they are providing the conceptual means to develop new animal models of and therapeutic strategies for fibrotic diseases.

The early-immediate gene EGR-1 is induced by transforming growth factor-beta and mediates stimulation of collagen gene expression

Transforming growth factor-beta (TGF-beta) stimulates collagen synthesis and accumulation, and aberrant TGF-beta signaling is implicated in pathological organ fibrosis. Regulation of type I procollagen gene (COL1A2) transcription by TGF-beta involves the canonical Smad signaling pathway as well as additional protein and lipid kinases, coactivators, and DNA-binding transcription factors that constitute alternate non-Smad pathways. By using Affymetrix microarrays to detect cellular genes whose expression is regulated by Smad3, we identified early growth response factor-1 (EGR-1) as a novel Smad3-inducible gene. Previous studies implicated Egr-1 in cell growth, differentiation, and survival. We found that TGF-beta induced rapid and transient accumulation of Egr-1 protein and mRNA in human skin fibroblasts. In transient transfection assays, TGF-beta stimulated the activity of the Egr-1 gene promoter, as well as that of a minimal Egr-1-responsive reporter construct. Furthermore, TGF-beta enhanced endogenous Egr-1 interaction with a consensus Egr-1-binding site element and with GC-rich DNA sequences of the human COL1A2 promoter in vitro and in vivo. Forced expression of Egr-1 by itself caused dose-dependent up-regulation of COL1A2 promoter activity and further enhanced the stimulation induced by TGF-beta. In contrast, the TGF-beta response was abrogated when the Egr-1-binding sites of the COL1A2 promoter were mutated or deleted. Furthermore, Egr-1-deficient embryonic mouse fibroblasts showed attenuated TGF-beta responses despite intact Smad activation, and forced expression of ectopic EGR-1 in these cells could restore COL1A2 stimulation in a dose-dependent manner. Taken together, these findings identify Egr-1 as a novel intracellular TGF-beta target that is necessary for maximal stimulation of collagen gene expression in fibroblasts. The results therefore implicate Egr-1 in the profibrotic responses elicited by TGF-beta and suggest that Egr-1 may play a new and important role in the pathogenesis of fibrosis.

Potential regulatory elements of the constitutive up-regulated α2(I) collagen gene in scleroderma dermal fibroblasts

The promoter activity of the full-length alpha2(I) collagen gene is higher in scleroderma fibroblasts, when compared to normal fibroblasts. In this study, to investigate the molecular mechanisms up-regulating the expression of the alpha2(I) collagen gene in scleroderma dermal fibroblasts more clearly, we compared promoter activities of serial 5'-deletion mutants and the substitution mutants of the alpha2(I) collagen promoter constructs between normal and scleroderma fibroblasts. The transient transfection assays using a series of 5'-deletions of the promoter revealed that the up-regulated fold-increase in scleroderma fibroblasts relative to that in normal fibroblasts was significantly decreased by the removal of bp -353 to -264 fragment or bp -264 to -186 fragment. The substitution mutations introduced into binding sites of Sp1 (bp -303 and -271), Ets1 (bp -285 and -282), as well as Smad (bp -263 and -258) also abrogated the fold-increase in promoter activity in scleroderma fibroblasts synergistically. A DNA affinity precipitation assay showed that the binding activity of Ets1 as well as Smad3 to their binding sites was increased in scleroderma fibroblasts compared with normal cells. Taken together, our promoter analysis emphasized that Ets1 form a transcriptionally active complex with Smad and Sp1 by autocrine transforming growth factor (TGF)-beta signaling, leading to the intrinsic up-regulation of alpha2(I) collagen promoter activity in scleroderma fibroblasts. The blockade of autocrine TGF-beta signaling is thought to be one of the most reliable approaches in the treatment of scleroderma, and further study targeting Ets1, Smad or Sp1 may contribute to this blockade.

Sp1 family of transcription factors regulates the human alpha2 (XI) collagen gene (COL11A2) in Saos-2 osteoblastic cells

Genes encoding type XI collagen, normally associated with chondrogenesis, are also expressed by osteoblasts. By studying Saos-2 cells, we showed that the transcription factors, Sp1, Sp3, and Sp7 (Osterix), regulate COL11A2 expression through its proximal promoter. The findings indicate both ubiquitous and osteoblast-specific mechanisms of collagen gene regulation.

INTRODUCTION

Type XI collagen is essential for skeletal morphogenesis. Collagen XI gene regulation has been studied in chondrocytes but not in osteoblasts.

MATERIALS AND METHODS

We cultured Saos-2 cells, a human osteosarcoma-derived line of osteoblasts, and analyzed them for alpha2(XI) protein and COL11A2 regulatory mechanisms.

RESULTS AND CONCLUSIONS

Although types I and V were the dominant collagens deposited by Saos-2 cells, they expressed COL11A2 mRNA, and alpha2(XI) chains were present in the extracellular matrix. The COL11A2 promoter region (from -149 to -40) containing three Sp1 binding sites was required for promoter activity in transient transfection assays. All three Sp1 sites were critical for binding by nuclear proteins in electrophoretic mobility shift assays. Further analysis using consensus oligonucleotides and specific antibodies as well as chromatin immunoprecipitation assay implicated Sp1 and Sp3 in binding to this promoter region. Overexpressing Sp1 or Sp3 significantly increased COL11A2 promoter activity and endogenous COL11A2 gene expression, an effect that was suppressed by the Sp1-binding inhibitor mithramycin A. Further experiments showed that Sp1, Sp3, CREB-binding protein (CBP), p300, and histone deacetylase (HDAC) were physically associated and HDAC inhibitors (trichostatin A or NaB) upregulated COL11A2 promoter activity and endogenous gene expression. Another Sp1 family member, Sp7 (Osterix), was expressed in Saos-2 cells, but not in chondrocytes, and was shown by chromatin immunoprecipitation to occupy the COL11A2 promoter. Overexpressing Sp7 increased COL11A2 promoter activity and endogenous gene expression, an effect also blocked by mithramycin A. Using siRNA to knockdown Sp1, Sp3, or Sp7, it was shown that depression of any of them decreased COL11A2 promoter activity and endogenous gene expression. Finally, primary cultures of osteoblasts expressed COL11A2 and Sp7, upregulated COL11A2 promoter activity and endogenous gene expression when Sp1, Sp3, or Sp7 were overexpressed, and downregulated them when Sp1, Sp3, or Sp7 were selectively depressed. The results establish that Sp1 proteins regulate COL11A2 transcription by binding to its proximal promoter and directly interacting with CBP, p300, and HDAC.

Platelet derived growth factor induced tenascin-C transcription is phosphoinositide 3-kinase/Akt-dependent and mediated by Ets family transcription factors

Previous studies have identified several cytokines as inducers of tenascin-C (TN-C) expression in various tissue culture systems. However, the signaling pathways of the regulation of TN-C expression are almost unknown. In this study, we clarified the molecular mechanism(s) underlying the regulation of the TN-C gene by platelet derived growth factor (PDGF) in cultured human dermal fibroblasts. PDGF induced the expression of TN-C protein as well as mRNA in a dose-dependent manner. Actinomycin D, an RNA synthesis inhibitor, significantly blocked the PDGF-mediated upregulation of TN-C mRNA expression, whereas cycloheximide, a protein synthesis inhibitor, did not. The PDGF-mediated induction of TN-C expression was inhibited by the treatment of fibroblasts with a selective phosphoinositide 3-kinase (PI3K) inhibitor, wortmannin, or LY294002. These results suggest that PDGF induced the expression of TN-C at a transcriptional level via phosphoinositide3-kinase/Akt signaling pathways. We performed serial 5' deletions and a transient transfection analysis to define the region in the TN-C promoter mediating the responsiveness to PDGF. Overexpression of Sp1, Ets1, or Ets2 activated the TN-C promoter and superinduced TN-C promoter activity stimulated by PDGF, whereas overexpression of Fli1 inhibited the effects of PDGF on TN-C expression. Mutation of the Sp1/3 binding sites or Ets binding sites in the TN-C promoter region responsible to PDGF abrogated the PDGF-inducible promoter activity. Immunoprecipitation analysis revealed that Sp1, Ets1, and Ets2 form a transcriptionally active complex. On the other hand, the interaction of Fli1 with Sp1 decreased after PDGF treatment. These results suggest that the upregulation of TN-C expression by PDGF involves Ets family transcription factors, co-operating with Sp1.

Upregulation of tenascin-C expression by IL-13 in human dermal fibroblasts via the phosphoinositide 3-kinase/Akt and the protein kinase C signaling pathways

In this study, we examined the genes targeted by IL-13 in human dermal fibroblasts using a cDNA microarray. We focused on the tenascin-C (TN-C) gene, which was identified as one of the genes induced by IL-13. IL-13 induced transcriptional activity of TN-C. IL-13-mediated TN-C expression was inhibited by treatment with wortmannin or LY294002, or Calphostin C. IL-13 induced the phosphorylation of the phosphoinositide 3-kinase (PI3K) regulatory subunit p85, induced tyrosine phosphorylation of Akt, upregulated Akt kinase activity, and activated protein kinase C (PKC)-delta and -epsilon. The IL-13-induced increase in TN-C protein expression was abrogated by the transfection of a dominant-negative mutant of Akt, PKC-delta, or PKC-epsilon. In conclusion, we showed that the PI3K/Akt and/or PKC signaling pathways are essential for the IL-13-mediated increase in TN-C. Both serum levels of IL-13 and the expression levels of TN-C in the dermis are increased in patients with systemic sclerosis. Our findings suggest that the expression of TN-C is upregulated in this disease due to IL-13 signaling, and that a blockade of the PI3K or PKC signaling pathway may also have therapeutic value by reducing the amount of TN-C produced during fibrosis.

Increased expression of integrin alphavbeta5 induces the myofibroblastic differentiation of dermal fibroblasts

The biological effect of cytokines is mainly determined by the cytokine-receptor interaction, which is modulated by the concentration and the activity of cytokines and/or their receptors. Because alphav-containing integrins can bind to and/or activate latent TGF-beta, these integrins have been thought to be involved in the pathogenesis of fibrotic disorders. Our recent observations that alphavbeta5 is up-regulated in scleroderma fibroblasts and that the transient overexpression of alphavbeta5 increases the human alpha2(I) collagen gene expression in normal fibroblasts suggest the involvement of alphavbeta5 in the self-activation system in scleroderma fibroblasts. In this study, we established stable transfectants with alphavbeta5 using normal dermal fibroblasts and demonstrated that such cells differentiated into myofibroblasts by the stimulation of autocrine TGF-beta. This observation is explained by 1) alphavbeta5 recruiting latent TGF-beta1 on the cell surface, 2) endogenous active TGF-beta localizing on the cell surface, and 3) alphavbeta5 interacting with TGF-beta receptors. Furthermore, blockade of alphavbeta5 reversed the myofibroblastic phenotype in scleroderma fibroblasts. These data identify a novel mechanism for the establishment of autocrine TGF-beta signaling in dermal fibroblasts by the up-regulation of alphavbeta5 and suggest the possibility of regulating fibrotic disorders, especially scleroderma, by targeting this integrin.

Characterization of SIS3, a novel specific inhibitor of Smad3, and its effect on transforming growth factor-beta1-induced extracellular matrix expression

This is the first report that characterizes specific inhibitor of Smad3 (SIS3) as a potent and selective inhibitor of Smad3 function. In the reporter assay, the increased luciferase activity of p3TP-lux by the overexpression of constitutively active form of ALK-5 was abrogated by the treatment with SIS3 in a dose-dependent manner. Immunoprecipitation revealed that SIS3 attenuated the transforming growth factor (TGF)-beta1-induced phosphorylation of Smad3 and interaction of Smad3 with Smad4. On the other hand, this reagent did not affect the phosphorylation of Smad2. Thereafter, we evaluated the ability of SIS3 in the suppression of the TGF-beta1-induced type I procollagen up-regulation in human dermal fibroblasts. We found that the addition of SIS3 attenuated the effects of TGF-beta1 by reducing the transcriptional activity. SIS3 also inhibited the myofibroblast differentiation of fibroblasts by TGF-beta1. Moreover, we demonstrated that SIS3 completely diminished the constitutive phosphorylation of Smad3 as well as the up-regulated type I collagen expression in scleroderma fibroblasts. Together, our study suggested that SIS3 is a useful tool to evaluate the TGF-beta-regulated cellular mechanisms via selective inhibition of Smad3.

Epidermal growth factor affects the synthesis and degradation of type I collagen in cultured human dermal fibroblasts

EGF and type I collagen are known to play important roles in wound healing. In the present study, we demonstrated that EGF down-regulates the expression of type I procollagen protein as well as alpha2(I) collagen mRNA in cultured human dermal fibroblasts. EGF induced the degradation of type I procollagen protein in conditioned medium through the up-regulation of MMP-1 expression. EGF down-regulated alpha2(I) mRNA expression partially at the post-transcriptional level by reducing the mRNA stability. In contrast, EGF up-regulated MMP-1 mRNA expression mostly at the transcriptional level, in that it had a stimulatory effect on MMP-1 promoter activity, but no effect on MMP-1 mRNA stability. The MEK/ERK signaling pathway was shown to be involved in EGF-mediated type I collagen and MMP-1 expression.

Increased expression of integrin alpha(v)beta3 contributes to the establishment of autocrine TGF-beta signaling in scleroderma fibroblasts

The constitutive secretion of latent TGF-beta by many cell types in culture suggests that extracellular mechanisms to control the activity of this potent cytokine are important in the pathogenesis of the diseases in which this cytokine may be involved, including fibrotic disorders. In this study, we focused on the alpha(v)beta3 integrin, which is recently demonstrated to function as an active receptor for latent TGF-beta1 through its interaction with latency-associated peptide-beta1, and investigated the involvement of this integrin in the pathogenesis of scleroderma. Scleroderma fibroblasts exhibited increased alpha(v)beta3 expression compared with normal fibroblasts in vivo and in vitro. In scleroderma fibroblasts, ERK pathway was constitutively activated and such abnormality induced the up-regulation of alpha(v)beta3. Transient overexpression of alpha(v)beta3 in normal fibroblasts induced the increase in the promoter activity of human alpha2(I) collagen gene and the decrease in that of human MMP-1 gene. These effects of alpha(v)beta3 were almost completely abolished by the treatment with anti-TGF-beta Ab or TGF-beta1 antisense oligonucleotide. Furthermore, the addition of anti-alpha(v)beta3) Ab reversed the expression of type I procollagen protein and MMP-1 protein, the promoter activity of human alpha2(I) collagen gene, and the myofibroblastic phenotype in scleroderma fibroblasts. These results suggest that the up-regulated expression of alpha(v)beta3 contributes to the establishment of autocrine TGF-beta loop in scleroderma fibroblasts, and this integrin is a potent target for the treatment of scleroderma.

IGF-I-induced VEGF expression in HUVEC involves phosphorylation and inhibition of poly(ADP-ribose)polymerase

Insulin-like growth factor-I (IGF-I) has been shown to promote angiogenesis by enhancing vascular endothelial growth factor (VEGF) expression. However, how IGF-I-induces VEGF expression is not yet fully understood. With this investigation, we propose a new possible mechanism involving downregulation of poly(ADP-ribosyl)ation (pADPR). We first demonstrated that IGF-I increased VEGF protein expression in endothelial cells. Inhibitors of mitogen activated kinase (PD 98059), phosphatidyl-3-inositol-kinase (LY 294002), and protein kinase C (staurosporine) diminished the IGF-I effect suggesting the involvement of signal transduction. Since there is an established link between pADPR and transcriptional activity, we focused on a possible role of poly(ADP-ribose)polymerase (PARP). The inhibition of PARP by 3-aminobenzamide or nicotinamide enhanced VEGF expression. Additionally, IGF-I markedly decreased PARP activity. Furthermore, the IGF-I-mediated inhibition of PARP could be demonstrated as a result of protein phosphorylation since phosphorylation of PARP decreased its activity in vitro and IGF-I treatment of endothelial cells induced PARP phosphorylation. The IGF-I-mediated phosphorylation and inhibition of PARP represent a novel mechanism of VEGF protein expression.

Constitutively phosphorylated Smad3 interacts with Sp1 and p300 in scleroderma fibroblasts

OBJECTIVE

To elucidate the role of transforming growth factor-beta (TGF-beta)/Smad signalling in the increased expression of the collagen gene in systemic sclerosis (SSc) fibroblasts.

METHODS

Dermal fibroblasts from seven patients with diffuse SSc of recent onset and from seven healthy individuals were studied. The expression levels of Smad2, Smad3 and Smad4 proteins were determined by immunoblotting. Smad3 phosphorylation and the interaction of Smad3 with Sp1 or p300 were analysed using immunoprecipitation. The effects of overexpression of Smad proteins or Sp1 on the human alpha2(I) collagen gene transcription were investigated with chloramphenicol acetyltransferase (CAT) assays using the -772 COL1A2/CAT construct.

RESULTS

Constitutive increased Smad3 phosphorylation was detected in SSc fibroblasts compared with normal fibroblasts. Increased interaction of Smad3 with Sp1 as well as p300 was also detected in SSc fibroblasts. The overexpression of Smad3 caused an increase of up to 5-fold in COL1A2 promoter activity in normal fibroblasts, while Smad3 caused a small increase in COL1A2 promoter activity in SSc fibroblasts. However, neither Smad2 nor Smad4 caused significant effects in COL1A2 promoter activity in normal fibroblasts or SSc fibroblasts. The overexpression of Sp1 caused further increase in COL1A2 promoter activity stimulated by TGF-beta in normal fibroblasts, but did not change COL1A2 promoter activity in the presence of TGF-beta in SSc fibroblasts. The combined overexpression of Smad3 and Sp1 significantly enhanced TGF-beta response in normal fibroblasts, but less markedly in SSc fibroblasts.

CONCLUSIONS

These results suggested that SSc fibroblasts are less sensitive to exogenous TGF-beta stimulation because they are already activated by the autocrine TGF-beta loop.

Involvement of alphavbeta5 integrin-mediated activation of latent transforming growth factor beta1 in autocrine transforming growth factor beta signaling in systemic sclerosis fibroblasts

OBJECTIVE

To confirm the involvement of alphavbeta5 in the self-activation system in systemic sclerosis (SSc) fibroblasts.

METHODS

Levels of alphavbeta5 expression were analyzed by immunoprecipitation. The promoter activity of the human alpha2(I) collagen gene was determined by transient transfection assay. Phosphorylation levels and DNA binding ability of Smad3 were investigated by immunoprecipitation and DNA affinity precipitation, respectively. The localization of active transforming growth factor beta (TGFbeta) was determined by coculture assay using TMLC cells (mink lung epithelial reporter cells that stably express a portion of the plasminogen activator inhibitor 1 promoter). The morphologic features of cells were determined by immunofluorescence analysis.

RESULTS

Levels of alphavbeta5 expression were significantly elevated in SSc fibroblasts compared with normal fibroblasts. Treatment with anti-alphavbeta5 antibody or beta5 antisense oligonucleotide significantly reduced human alpha2(I) collagen gene promoter activity in SSc fibroblasts. In SSc fibroblasts pretreated with TGFbeta1 antisense oligonucleotide, the exogenous latent TGFbeta1 stimulation significantly increased human alpha2(I) collagen gene promoter activity; this effect was significantly reduced in the presence of anti-alphavbeta5 antibody. Phosphorylation levels and DNA binding ability of Smad3 in SSc fibroblasts were significantly reduced by treatment with beta5 antisense oligonucleotide. The luciferase activity of TMLC cells cocultured with SSc fibroblasts was significantly elevated compared with that of TMLC cells cocultured with normal fibroblasts and was significantly reduced in the presence of anti-alphavbeta5 antibody. Anti-alphavbeta5 antibody reversed the myofibroblastic features of SSc fibroblasts.

CONCLUSION

Up-regulated expression of alphavbeta5 contributes to the establishment of autocrine TGFbeta signaling in SSc fibroblasts through activation of endogenous latent TGFbeta1.

Scleroderma, fibroblasts, signaling, and excessive extracellular matrix

Excessive extracellular matrix (ECM) deposition in the skin, lung, and other organs is a hallmark of systemic sclerosis (SSc). The pathogenesis of SSc is still poorly understood, but increasing evidence suggests that various cytokines such as transforming growth factor (TGF)-beta and their signaling pathways are key mediators of tissue fibrosis as a consequence of ECM accumulation in the pathogenesis of fibrosis such as SSc. TGF-beta regulates diverse biologic activities including cell growth, cell death or apoptosis, cell differentiation, and ECM synthesis. TGF-beta is known to induce the expression of ECM proteins in mesenchymal cells, and to stimulate the production of protease inhibitors that prevent enzymatic breakdown of the ECM. This paper focuses on the possible role of ECM, various cytokines, especially TGF-beta signal transduction pathways in the pathogenesis of fibrosis in SSc.

APBP-1, a DNA/RNA-binding protein, interacts with the chick aggrecan regulatory region

Expression of the extracellular proteoglycan aggrecan is both cell-specific and developmentally regulated. Previous studies identified six functionally defined cis elements in the aggrecan promoter region which were shown to repress aggrecan gene expression (1). Using competition electrophoretic mobility shift assays (EMSAs) we have now identified in nuclear extracts a functional repressor cis element, (T/C)TCCCCT(A/C)RRC, which occurs at multiple locations within the chick aggrecan regulatory region. We purified the factor that binds to this cis element and established that it, APBP-1 (aggrecan promoter-binding protein-1), is a 19-kDa protein that has significant homology to CIRP (cold inducible RNA-binding protein). Recombinantly expressed APBP-1 mimics the native cis element-trans factor interaction in EMSAs. In situ hybridization demonstrates that aggrecan and APBP-1 RNA expression are restricted to complementary tissues in the developing limb, and Northern blot analysis of chick limb bud mRNA shows that APBP-1 mRNA expression is inversely correlated with aggrecan mRNA expression. Functional analyses by transient transfections and Northern blot analyses suggest APBP-1 has the capacity to repress aggrecan expression, indicating that this factor may be important regulator of aggrecan gene expression.

Increased Phosphorylation and Activation of Mitogen-Activated Protein Kinase p38 in Scleroderma Fibroblasts

Transforming growth factor-beta (TGF-beta) stimulates the transcription of the alpha2(I) collagen gene. The dermal fibroblast activation in systemic sclerosis (SSc) may be a result of stimulation by autocrine TGF-beta. In this study, we investigated whether p38 mitogen-activated protein kinase (MAPK) is involved in TGF-beta-induced transcriptional activation of the human alpha2(I) collagen gene in normal dermal fibroblasts and in upregulated extracellular matrix (ECM) expression in SSc fibroblasts. Type I collagen expression induced by TGF-beta was suppressed by the specific p38 MAPK inhibitors SB203580 or SB202190 in normal fibroblasts. TGF-beta induced phosphorylation and activation of p38 MAPK in normal dermal fibroblasts. Transient transfection of dominant-negative mutant p38 MAPK into normal fibroblasts abolished TGF-beta-induced promoter activity of the human alpha2(I) collagen gene in normal fibroblasts. Moreover, constitutive phosphorylation and activation of p38 MAPK was demonstrated in SSc fibroblasts, and the inhibition of p38 MAPK using specific p38 MAPK inhibitors or dominant-negative mutant p38 MAPK abolished the upregulated expression of type I collagen or fibronectin in SSc fibroblasts. These results strongly suggest the contribution of p38 MAPK signaling to the TGF-beta-mediated regulation of the human alpha2(I) collagen gene in normal dermal fibroblasts and constitutive upregulated expression of type I collagen and fibronectin in SSc fibroblasts.

Species-specific regulation of the alpha-2(I) procollagen gene by proximal promoter elements

Transcriptional regulation of the human alpha 2(I) procollagen proximal promoter involves the interaction of trans-acting factors at the inverted CCAAT box (G/CBE) located at position -80 and an adjacent GGAGGCCC-box at -70. Both these elements have previously been shown to be essential for activity of the human promoter. This study investigated nucleotide differences at three sites (-74, -72 and -71) between the human and mouse promoters that were sufficient to abolish trans-acting factor binding with the mouse sequence (GGAGACGT). Two distinct DNA-protein interactions were detected on the human -107/+54 promoter fragment while a single interaction was observed at the equivalent mouse promoter. One of these factors is the CCAAT-binding factor (CBF) and it's binding was observed on both the human and mouse promoters. Although the GGAGGCCC DNA-binding element was not detected on the mouse promoter, GGAGGCC-binding proteins were present in mouse nuclear extracts as observed by their interaction with the human promoter. Functional analysis of the human and mouse -343/+54 and -107/+54 promoter regions revealed significant differences between species; the human constructs having higher activity than the mouse. The differences in promoter activity between species may in part be a result of the nucleotide differences in the GGAGGCCC-box. Mutations in this region of the human -107/+54 promoter prevented DNA-protein interaction and lowered promoter activity. These results support the hypothesis that the GGAGGCCC-box in the human alpha 2(1) procollagen promoter has a regulatory function and that there exists a species-specific difference in transcription factor binding and regulation of the gene.

CCL18-stimulated upregulation of collagen production in lung fibroblasts requires Sp1 signaling and basal Smad3 activity

A CC chemokine CCL18 stimulates collagen production in pulmonary fibroblasts through an unknown signaling mechanism. In this study, involvement of Sp1 and Smad3 in CCL18 signaling in primary human pulmonary fibroblast cultures was investigated. Phosphorylation of Sp1, DNA-binding by Sp1, and the activity of an Sp1-dependent reporter were all increased in response to CCL18 stimulation. CCL18 did not stimulate a detectable increase in Smad3 phosphorylation or Smad3/4 DNA-binding activity, although some basal phosphorylation and DNA binding by Smad3/4 were noted. Transient overexpression of dominant negative mutants of Sp1 and Smad3 abrogated CCL18-dependent upregulation as well as basal production of collagen. These observations suggested that CCL18 activates collagen production in pulmonary fibroblasts through an Sp1-dependent pathway that also requires basal Smad3 activity. Possible involvement of autocrine TGF-beta in CCL18 signaling was considered. CCL18 stimulated increases in collagen mRNA and protein production without detectable changes in TGF-beta1, -beta2, and -beta3 mRNA or protein levels. Neutralizing anti-TGF-beta antibodies, latency-associated peptide, ALK5-specific inhibitor SD431542, and an inhibitor of the protease-dependent TGF-beta activation aprotinin, each failed to block CCL18-stimulated collagen production. These observations suggest that both CCL18 signaling in pulmonary fibroblasts and basal Smad3 activity are independent of autocrine TGF-beta.

Matrix metalloproteinase-1 up-regulation by hepatocyte growth factor in human dermal fibroblasts via ERK signaling pathway involves Ets1 and Fli1

In this study, we clarified the molecular mechanism(s) underlying the regulation of matrix metalloproteinase (MMP)-1 gene by hepatocyte growth factor (HGF) in cultured human dermal fibroblasts. HGF induced MMP-1 protein as well as mRNA at a transcriptional level via extracellular signal-regulated kinase (ERK) signaling pathway. The region in the MMP-1 promoter mediating the inducible responsiveness to HGF, defined by the transient transfection analysis of the serial 5′ deletion constructs, contained an Ets binding site. Mutation of this Ets binding site abrogated the HGF-inducible promoter activity. Ets1 up-regulated the expression of MMP-1 promoter activity, whereas Fli1 had antagonistic effects on them. After HGF treatment, the protein level and the binding activity of Ets1 was increased and those of Fli1 was decreased, which were canceled by PD98059. These results suggest that HGF up-regulates MMP-1 expression via ERK signaling pathway through the balance of Ets1 and Fli1, which may be a novel mechanism of regulating MMP-1 gene expression.

Constitutive thrombospondin-1 overexpression contributes to autocrine transforming growth factor-beta signaling in cultured scleroderma fibroblasts

The extracellular matrix (ECM) glycoprotein thrombospondin-1 (TSP-1) has been reported to activate the latent complex of transforming growth factor-beta (TGF-beta), the major effects of which in mesenchymal cells is stimulation of the synthesis of ECM. Previous reports suggested the involvement of an autocrine TGF-beta loop in the pathogenesis of scleroderma. In this study, we examined whether TSP-1 plays a role in maintaining the autocrine TGF-beta loop in scleroderma. TSP-1 expression was increased in scleroderma patients compared with in healthy controls in vivo and in vitro. TGF-beta blocking antibody or TGF-beta1 antisense oligonucleotide markedly reduced the up-regulated TSP-1 expression in scleroderma fibroblasts but had little effect on normal fibroblasts. The expression of TSP-1 is up-regulated in scleroderma fibroblasts, possibly at the post-transcriptional level just like in normal fibroblasts stimulated with exogenous TGF-beta1. TSP-1 blocking peptide or antisense oligonucleotide had an inhibitory effect on the up-regulated alpha2I collagen and phosopho-Smad3 levels in scleroderma fibroblasts but had little effects on normal fibroblasts. The transient overexpression of TSP-1 up-regulated alpha2I collagen and phospho-Smad3 levels in normal fibroblasts but had no major effect on scleroderma fibroblasts. Furthermore, these effects of transiently overexpressed TSP-1, which possibly occurred via the activation of latent TGF-beta1, were abolished by the TGF-beta1 antisense oligonucleotide. These results indicate that the constitutive overexpression of TSP-1 may play an important role in autocrine TGF-beta signaling and accumulation of ECM in scleroderma fibroblasts.

Fibroblast expression of the coactivator p300 governs the intensity of profibrotic response to transforming growth factor beta

OBJECTIVE

Transforming growth factor beta (TGFbeta) induces profibrotic responses in normal fibroblasts, and plays a fundamental role in the pathogenesis of fibrosis in scleroderma (systemic sclerosis [SSc]). The intensity of cellular responses elicited by cytokines is modulated by transcriptional coactivators such as the histone acetylase p300. The objective of these studies was to delineate the physiologic role of p300 in Smad-dependent profibrotic responses elicited by TGFbeta.

METHODS

Ectopic p300 was transiently expressed in normal dermal fibroblasts. Cellular p300 levels were suppressed using p300-specific ribozymes. The regulation of gene expression was examined by transient transfection assays, Northern blotting, and immunoblot analysis. The expression of p300 in normal and scleroderma fibroblasts was evaluated by confocal microscopy and immunoblotting, and p300 levels in skin from mice with experimental scleroderma were assessed by immunohistochemistry.

RESULTS

In normal fibroblasts, TGFbeta induced an increase in the levels of p300. Forced expression of ectopic p300 in these cells dramatically enhanced the magnitude of TGFbeta responses, whereas selective depletion of p300 using ribozyme resulted in abrogation of TGFbeta-induced collagen synthesis and promoter activity. Furthermore, TGFbeta lost its ability to induce Smad-dependent transcription in p300-depleted fibroblasts. These responses could be fully rescued with ectopic p300. Abrogation of Smad-mediated TGFbeta signaling was not due to alterations in the levels or the ligand-dependent phosphorylation or intracellular trafficking of endogenous Smads. Immunohistochemical analysis demonstrated substantially increased p300 expression in lesional skin from mice with chronic graft-versus-host disease, an animal model of scleroderma. Furthermore, levels of p300 were 2-3-fold higher in cultured fibroblasts derived from SSc patients than in fibroblasts from matched normal controls.

CONCLUSION

These results establish, for the first time, that the coactivator histone acetylase p300, itself a target of TGFbeta regulation, is an essential component of the cellular TGFbeta signal transduction pathways mediating stimulation of collagen synthesis in fibroblasts. Since the cellular abundance of p300 appears to govern the intensity of profibrotic responses elicited by TGFbeta, elevated p300 expression in lesional tissue may contribute to the progression of skin fibrosis in scleroderma.

Cell type-specific regulation of the TGF-beta-responsive alpha2(I) collagen gene by CpG methylation

The alpha2(I) collagen gene shows cell type-specific expression, however, the mechanism behind this specificity remains to be determined. We demonstrate here that transforming growth factor-beta (TGF-beta)-mediated induction of alpha2(I) collagen gene is regulated by DNA methylation in a cell type-specific manner. Human alpha2(I) collagen mRNA and type I collagen protein were expressed in normal human fibroblasts (NHF), and also strongly enhanced by TGF-beta; they were not detected in HaCaT, HeLa, or HepG2 cells (termed "collagen-induction resistant (CIR) cells") even following stimulation with TGF-beta. On the other hand, the transcriptional activity of exogenously transfected alpha2(I) collagen promoter was clearly up-regulated by TGF-beta in the CIR cells as well as in NHF. In the CIR cells, CpG clusters around the transcription start site of the alpha2(I) collagen gene were heavily methylated, whereas no methylation was detected in NHF. Moreover, alpha2(I) collagen gene was reactivated in the CIR cells by 5-Aza-2-deoxycytidine (5-AdC) treatment to some extent. However, demethylation by 5-AdC was limited and it was unable to recover the TGF-beta responsiveness. In NHF, the alpha2(I) collagen gene has a Smad3-accessible chromatin structure and acetylated histones in the promoter regions. By contrast, in the CIR cells, Smad3 failed to bind to the chromatin and histones were not acetylated in this area. Furthermore, in vitro methylation of the reporter gene containing the alpha2(I) collagen promoter significantly reduced both basal and TGF-beta-induced enhancement of the transcriptional activity in NHF. Thus, we propose that alpha2(I) collagen gene provides the first example of the TGF-beta responsive gene whose cell type-specificity is regulated by CpG methylation.

Effects of hepatocyte growth factor on the expression of type I collagen and matrix metalloproteinase-1 in normal and scleroderma dermal fibroblasts

We investigated the direct effect of hepatocyte growth factor (HGF) on the expression of type I collagen in normal and scleroderma dermal fibroblasts, and analyzed the mechanisms underlying the effect in vitro. HGF did not change the protein expression of type I procollagen in the medium of normal human fibroblasts, whereas it reduced the expression in scleroderma fibroblasts. But mRNA levels and the promoter activity of alpha2(I) collagen gene were not significantly affected by HGF in either of the cells. On the other hand, matrix metalloproteinase-1 expression or activity was increased by HGF in both cells, but HGF had stronger effects in scleroderma fibroblasts than normal fibroblasts. Scleroderma fibroblasts overexpressed c-met protein, the receptor for HGF. The overexpression in scleroderma fibroblasts was abolished by the addition of antisense transforming growth factor (TGF)-beta1 oligonucleotide. Our study indicated that HGF may reduce type I collagen accumulation only in scleroderma fibroblasts by enhancing collagenolysis activity, probably because of the overexpression of c-met because of autocrine TGF-beta signaling. Thus, further investigation of the effects of HGF on collagen metabolism may contribute to the treatment of fibrosis in scleroderma.