What’s in an intron? CCN1 mRNA splicing in cancer

The CCN family of matricellular signaling regulators shares a common domain structure. Variants of individual CCN proteins exist, which contain different combinations of these domains. Although mRNA splicing is likely to play a key role on CCN biology, this hypothesis has not been thoroughly tested. In a recent report, Hirschfeld and colleagues (Cancer Res 69:2082-90, 2009), show that CCN1 (cyr61) mRNA is normally present in a form in which intron 3 is retained. In cancers, or upon hypoxia, intron 3 is removed resulting in the appearance of CCN1 protein. The significance of this paper is discussed

Scar wars: is TGFβ the phantom menace in scleroderma?

The autoimmune disease scleroderma (systemic sclerosis (SSc)) is characterized by extensive tissue fibrosis, causing significant morbidity. There is no therapy for the fibrosis observed in SSc; indeed, the underlying cause of the scarring observed in this disease is unknown. Transforming growth factor-β (TGFβ) has long been hypothesized to be a major contributor to pathological fibrotic diseases, including SSc. Recently, the signaling pathways through which TGFβ activates a fibrotic program have been elucidated and, as a consequence, several possible points for anti-fibrotic drug intervention in SSc have emerged

Wnt 10b activates the CCN2 promoter in NIH 3T3 fibroblasts through the Smad response element

Wnt proteins elevate expression of the CCN family. For example, Wnt10b induces the fibrogenic pro-adhesive molecule connective tissue growth factor (CTGF, CCN2) in NIH 3T3 fibroblasts. Wnt10b activates the CCN2 minimal promoter. In this report, we map the Wnt10b response element in the CCN2 minimal promoter to the previously identified Smad response element. These results suggest that Wnts may cross-talk with the Smad signaling pathway to induce fibrotic responses in fibroblasts

Trial by CCN2: a standardized test for fibroproliferative disease?

A major issue concerning clinical trials is the availability of standardized assays to evaluate drug efficacy. Ideally, such assays should test the effect of a putative drug on the expression of a biomarker in biological fluids. In a recent study by Kuiper et al. (PLOS One, 3(7): e2675). The relative levels of vascular endothelial growth factor (VEGF) and CCN2 (connective tissue growth factor [CTGF]) were examined in proliferative diabetic retinopathy (PDR). This paper is the subject of this commentary

Egr-1 inhibits the expression of extracellular matrix genes in chondrocytes by TNFα-induced MEK/ERK signalling

Introduction TNFα is increased in the synovial fluid of patients with rheumatoid arthritis and osteoarthritis. TNFα activates mitogen-activated kinase kinase (MEK)/extracellular regulated kinase (ERK) in chondrocytes; however, the overall functional relevance of MEK/ERK to TNFα-regulated gene expression in chondrocytes is unknown. Methods Chondrocytes were treated with TNFα with or without the MEK1/2 inhibitor U0126 for 24 hours. Microarray analysis and real-time PCR analyses were used to identify genes regulated by TNFα in a MEK1/2-dependent fashion. Promoter/ reporter, immunoblot, and electrophoretic mobility shift assays were used to identify transcription factors whose activity in response to TNFα was MEK1/2 dependent. Decoy oligodeoxynucleotides bearing consensus transcription factor binding sites were introduced into chondrocytes to determine the functionality of our results. Results Approximately 20% of the genes regulated by TNFα in chondrocytes were sensitive to U0126. Transcript regulation of the cartilage-selective matrix genes Col2a1, Agc1 and Hapln1, and of the matrix metalloproteinase genes Mmp-12 and Mmp-9, were U0126 sensitive – whereas regulation of the inflammatory gene macrophage Csf-1 was U0126 insensitive. TNFα-induced regulation of Sox9 and NFKB activity was also U0126 insensitive. Conversely, TNFα-increased early growth response 1 (Egr-1) DNA binding was U0126 sensitive. Transfection of chondrocytes with cognate Egr-1 oligodeoxynucleotides attenuated the ability of TNFα to suppress Col2a1, Agc1 or Hapln1 mRNA expression. Conclusions Our results suggest that MEK/ERK and Egr1 are required for TNFα-regulated catabolic and anabolic genes of the cartilage extracellular matrix, and hence may represent potential targets for drug intervention in osteoarthritis or rheumatoid arthritis

The skinny on CCN2

The CCN family of matricellular proteins directly or indirectly affects development and differentiation. A recent report written by Tan and colleagues (Am J Physiol Cell Physiol 295: C740–C751 2008) shows that CCN2 inhibits adipocyte differentiation. This commentary summarizes these observations

TAK1 Is Required for Dermal Wound Healing and Homeostasis

Dermal connective tissue is a supportive structure required for skin’s barrier function; dysregulated dermal homeostasis results in chronic wounds and fibrotic diseases. The multifunctional cytokine transforming growth factor (TGF) β promotes connective tissue deposition, repair, and fibrosis. TGF-β acts through well-defined canonical pathways; however, the non-canonical pathways through which TGF-β selectively promotes connective tissue deposition are unclear. In dermal fibroblasts, we show that inhibition of the non-canonical TGF-β-activated kinase 1 (TAK1) selectively reduced the ability of TGF-β to induce expression of a cohort of wound healing genes, such as collagens, CCN2, TGF-β1, and IL-6. Fibroblast-specific TAK1-knockout mice showed impaired cutaneous tissue repair and decreased collagen deposition, α-smooth muscle actin and CCN2 expression, proliferating cell nuclear antigen staining, and c-Jun N-terminal kinase and p38, but not Smad3, phosphorylation. TAK1-deficient fibroblasts showed reduced cell proliferation, migration, cell attachment/spreading, and contraction of a floating collagen gel matrix. TAK1-deficient mice also showed progressively reduced skin thickness and collagen deposition. Thus, TAK1 is essential for connective tissue deposition in the dermis

ACTIVATION OF LATENT TGFβ BY ΑVΒ1 INTEGRIN: OF POTENTIAL IMPORTANCE IN MYOFIBROBLAST ACTIVATION IN FIBROSIS

ABSTRACT Cell--mediated activation of latent TGF--β1 is intimately involved with tissue repair and fibrosis in all organs. Previously, it was shown that the integrin β1 subunit was requred for activation of latent TGF--β1 and skin fibrosis. A recent study by Henderson and colleagues (Nature Medicine 19,1617-1624, 2013) used three different in vivo models of fibrosis to show that integrin αv subunit was required for fibrogenesis. Through a process of elimination, the authors conclude that in vivo, the little--studied αvβ1 could be the major integrin responsible for TGF--β activation by myofibroblasts. Thus targeting this integrin might be a useful therapy for fibrosis

Yin and Yang: CCN3 inhibits the pro-fibrotic effects of CCN2

Fibrotic disease is a significant cause of mortality. CCN2 (connective tissue growth factor [CTGF]), a member of the CCN family of matricellular proteins, plays a significant role in driving the fibrogenic effects of cytokines such as transforming growth factor β (TGFβ). It has been proposed that other members of the CCN family can either promote or antagonize the action of CCN2, depending on the context. A recent elegant study published by Bruce Riser and colleagues (Am J Pathol. 174:1725–34, 2009) illustrates that CCN3 (nov) antagonizes the fibrogenic effects of CCN2. This paper, the subject of this commentary, raises the intriguing possibility that CCN3 may be used as a novel anti-fibrotic therapy

Hijacking ZIP codes: posttanscriptional regulation of CCN2 by nucleophosmin

CCN2 (connective tissue growth factor [CTGF]/hypertrophic chondrocyte-specific gene product 24 [Hcs24]) is regulated at the transcriptional and posttranscriptional level. For example, an element in the its 3′ untranslated region (3′-UTR) of the CCN2 mRNA controls message stability in chondrocytes. In a recent study, Mukudai et al. (Mol Cell Biol 28:6134-6147, 2008) purified and identified a trans-factor protein binding to the minimal repressive cis element in the 3′-UTR of ccn2 mRNA and identify this protein as the multifunctional nucleolar phosphoprotein nucleophosmin (NPM) This commentary summarizes these observations