Encyclopedia of Signaling Molecules

2018 Edition
| Editors: Sangdun Choi


Reference work entry
DOI: https://doi.org/10.1007/978-3-319-67199-4_101754


Historical Background

CYR61/CCN1 belongs to the family of CCN matricellular proteins, first described 25 years ago. The other members consist of CTGF/CCN2 (connective tissue growth factor) and NOV/CCN3 (neuroblastoma overexpressed) and Wnt-induced signaling pathway proteins 1–3 (CCN4–CCN6). They constitute a family of proteins with conserved domain structures (Fig. 1). CCN1 was first described as an immediate early gene induced by mitogens in fibroblasts (O’Brien et al. 1990). It has now been implicated in numerous biological processes such as cell adhesion, migration, proliferation, and death with altered expression in cancer or vascular diseases (Emre and Imhof 2014).
CYR61/CCN1, Fig. 1

CCN protein family

The identification of its functions and receptors was delicate and is still undergoing intensive research. Indeed, CCN proteins are very special in the sense that once secreted, they stick both to the extracellular matrix (ECM) compounds and to the cell surface through integrins and heparan sulfate proteoglycans, thus playing a role in outside-in signaling (Yang and Lau 1991).

Phenotype of CCN1 Knockout Mice

The Ccn1/Cyr61 gene was disrupted by suppression of the translation initiation site, exon 1 and half of exon 2 (Mo et al. 2002). Heterozygote mice were fertile and viable, whereas all Ccn1 null died suffering embryonic death and none could survive more than a day after birth. Two thirds exhibited placental vascular insufficiency and impaired vessel integrity, while the others died from altered chorioallantoic fusion, thus establishing CCN1 as a key regulator of vascular development. Undervascularization of the placenta was correlated with impaired VEGF expression, indicating that CCN1 action is mediated through VEGF (Mo et al. 2002).

Integrin Signaling

Although CCN1 sequence does not contain the canonical RGD sequence, its functions are exerted mainly through its binding to specific integrins. Most of the work is involved in vitro biochemical assays with highly purified recombinant CCN1 protein that led to the discovery of integrins αIIbβ3, αMβ2, αDβ2, αLβ2, αVβ3, αVβ5, and α6β1 but also the heparan sulfate proteoglycan syndecan-4, as partners for CCN1 (Table 1) (Emre and Imhof 2014; Lau 2016). In the meantime, two knockin mice harboring mutant CCN1 were engineered to better assess the biological implications of CCN1 binding to integrins in vivo. Ccn1D125A/D125A and Ccn1DM/DM were unable to bind integrins αvβ3/αvβ5 and α6β1, respectively, validating specific integrin-mediated CCN1 functions observed in vitro (Choi et al. 2015; Jun et al. 2015; Jun and Lau 2010; Kim et al. 2015).
CYR61/CCN1, Table 1:

Receptors for CCN1







B cells, T cells, NK cells

Spleen CD11b+ cells

Integrin αIIbβ3



Integrin α6β1


Fibroblasts, hepatocytes, vascular smooth muscle cells, thymic epithelial cells, thymocytes, β-cells

Integrin αMβ2

Monocytes, CD34+ circulating progenitors

Monocytes, macrophages

Integrin αDβ2



Integrin αLβ2



Integrin αVβ3

CD34+ circulating progenitors, osteoclasts

Macrophages, cholangiocytes

Integrin αVβ5


Macrophages, osteoclasts, cholangiocytes


Fibroblasts, macrophages


Heparan sulfate proteoglycans

Vascular smooth muscle cells


Physiopathology of Tissue Repair

Fibrosis results from an aberrant wound-healing response following chronic injuries in various organs, including the liver, heart, or skin. Wound healing starts with an inflammatory process implying the recruitment of neutrophils and monocytes. After tissue formation (fibroblast proliferation and angiogenesis), a remodeling phase ensures tissue homeostasis by removing unneeded cells by programmed cell death.

CCN1 is dynamically expressed at sites of healing cutaneous wounds. It was required for the accumulation of senescent fibroblasts in healing wounds. Actually, CCN1 activated senescence and concomitant expression of anti-fibrotic genes in fibroblasts through the activation of p53 and RAC1-NOX1/reactive oxygen species pathways. Accumulation of senescent fibroblasts and expression of anti-fibrotic program were dependent on integrin α6β1 signaling, as demonstrated by aggravated fibrosis and was suppressed by senescence in Ccn1DM/DM knockin mice (Jun and Lau 2010). Similarly, CCN1 limited liver fibrosis through the induction of senescence of hepatic myofibroblasts (Kim et al. 2013). Neutrophils are quickly recruited to the wound site where they constitute the predominant cell type. Once their tasks completed, they are removed by macrophages in a process termed efferocytosis. In cutaneous wound healing, CCN1 was shown to bind phosphatidylserine on apoptotic neutrophils, promoting their engulfment by macrophages. Integrins αvβ3/αvβ5 in macrophages were primordial to trigger efferocytosis, as Ccn1D125A/D125A mice were unable to get rid of neutrophils that kept accumulating in the tissue. In addition, local treatment with recombinant CCN1 protein rescued Ccn1-deficient mice and the diabetic Leprdb/db mice, which exhibit wound-healing alteration (Jun et al. 2015). Therefore, CCN1 has two distinct roles in the resolution of wound healing, both promoting senescence of fibroblasts and efferocytosis of neutrophils.

Liver cholestasis leads to liver fibrosis that may develop into cirrhosis. Cholangiocyte proliferation and ductular reaction are common characteristics to cholestatic injury. CCN1 activated NF-κB-dependent JAG1/NOTCH signaling through integrin αvβ5vβ3 in cholangiocytes, promoting their proliferation, as notably demonstrated with the use of Ccn1D125A/D125A mice treated with soluble JAG1. In addition, CCN1 also activated JAG1 in hepatic stellate cells, promoting their differentiation into cholangiocytes. Treatment with recombinant CCN1 protein of mice blocked by inhibitors of NF-κB or NOTCH signaling restored cholangiocyte proliferation (Kim et al. 2015).

In the context of mucosal healing, CCN1 was of particular interest for mouse survival in dextran sodium sulfate (DSS)-induced colitis. Higher mortality and ineffective mucosal healing characterized Ccn1dm/dm knockin mice because of lower IL-6 production. Actually, integrins α6β1 and αMβ2 mediated CCN1 binding to fibroblasts and macrophages, respectively, and were required for IL-6 production to stimulate intestinal epithelial cell proliferation (Choi et al. 2015).

Cancer Development

Matricellular proteins have long been involved in cancer development and progression. Regarding CCN1, it is upregulated in glioma, breast, colorectal, ovarian, and prostate cancers, promoting cancer cell growth in murine models of these cancer types. In addition, a positive correlation between CCN1 and tumor aggressiveness and reduced survival in patients of these cancers were observed. On the contrary CCN1 is downregulated in chondrosarcoma and lung and gastric cancers. Interfering with Wnt, TGF-β, and Notch signaling pathways, CCN1 promotes cell proliferation or migration depending on the local microenvironment (Emre and Imhof 2014; Lau 2016; Li et al. 2015). Lately, two papers brought new insights in the field of hepatocellular carcinoma and pancreatic cancer with opposing consequences, which well resumes the opposing effects of CCN1 in the context of cancer.

In the model of hepatocarcinogen diethylnitrosamine delivery, hepatocytes die from DNA damage. Consequently, a mechanism of hepatocyte proliferation is initiated to counteract the cell loss. However, stimulation may promote the proliferation of mutated hepatocyte, thus favoring cancerogenesis. The absence of CCN1 worsened hepatocarcinoma development, as observed in hepatocyte-specific Ccn1-deficient mice. To be more precise, CCN1 impaired epidermal growth factor receptor-dependent hepatocyte proliferation by inducing ROS production and activating p53. The action of CCN1 was mediated by integrin α6β1, as Ccn1DM/DM mice replicated the phenotype of hepatocyte-specific Ccn1-deficient mice with decreased p53 activity (Chen et al. 2016).

In another recent study, CCN1 was reported to sustain pancreatic cancer development in the model of Rip-Tag mice, which exhibit anarchic proliferation of insulin-producing β-cells. Specific overexpression of CCN1 in these cells resulted in bigger tumors. In addition they were more invasive and more vascularized. The effect of CCN1 occurred through integrin α6β1, stimulating both invasion and adhesion capabilities. All these effects could be suppressed by blocking angiogenesis with anti-VEGFR2 antibody treatment (Huang et al. 2016).

Inflammation and Immune System

CCN1 is able to support adhesion and migration of leukocytes (Emre and Imhof 2014). Short-term treatment with CCN1 increased actin polymerization and migratory capabilities of human leukocytes in vitro (Lobel et al. 2012). However, longer stimulation inhibited leukocyte migration through the downregulation of PI3Kγ, p38, and Akt phosphorylation. Therefore, locally produced CCN1 may first stimulate the recruitment of leukocytes into the injured tissue and then favor their attachment and immobilization (Lobel et al. 2012). However, despite its upregulation upon viral or bacterial infections (Emre and Imhof 2014), few are known about CCN1 in inflammation.

Endothelium-bound CCN1 was reported to provide a molecular support for the patrolling behavior of Ly6Clow monocytes both in the steady state and in Toll-like receptor 7/8 (TLR7/8)-mediated inflammation of mesenteric veins. Although CCN1 was from endothelial origin in the steady state, endothelium-bound CCN1 was released by platelets within minutes of vascular inflammatory stimulation. Blocking CCN1 inhibited the early recruitment of Ly6Clow monocytes to the luminal side of the endothelium that were in charge of the arrival and extravasation of neutrophils. In fact CCN1 was necessary for Ly6Clow monocytes to commit to a meticulous patrolling of the endothelial wall (Imhof et al. 2016).

Another important area of research for CCN1 concerns rheumatoid arthritis where it is considered as a pro-inflammatory molecule (Xu et al. 2016). Indeed, high levels of CCN1 in synovial tissue macrophages were correlated with the inflammatory score in rheumatoid arthritis. Moreover, CCN1 activated Th17 cells, sustained the proliferation of fibroblast-like synoviocytes, and stimulated the expression of inflammatory cytokines, including TNF-α, IFN-γ, IL-6, IL-8, IL-12, and IL-17 (Zhang et al. 2009; Zhu et al. 2013). Interestingly, CCN1-dependent IL-8 induction was responsible for neutrophil infiltration (Zhu et al. 2013). Anti-CCN1 treatment managed to limit neutrophil infiltration and dampen inflammation in the murine model of collagen-induced arthritis (Xu et al. 2016; Zhu et al. 2013).

In addition to its function in inflammatory conditions, the importance of CCN1 was demonstrated in the function of the thymus. Thymic epithelial cells (TEC), components of thymic stroma, are essential for the production of T cells within the thymus. CCN1, which is highly expressed in TEC in normal thymus of mice, induced the proliferation of TEC in an autocrine/paracrine manner through the activation of Akt signaling leading to the expansion of the thymic stromal compartment. Engraftment of CYR61-overexpressing thymic lobes into athymic nude mice drastically boosts the yield of thymic output via expansion of TEC. This increases the space for the recruitment of circulating hematopoietic progenitors and the development of T cells (Amir-Moazami and Emre 2016; Emre et al. 2013).


CCN1/CYR61 is a very interesting molecule. Being an extracellular matrix protein, it bridges cell surface integrins to matrix proteins such as collagen, laminin, fibronectin, and so on. Therefore, it affects many cellular functions with sometimes opposing effects, depending on the cell type and the local cellular environment, from cell proliferation to cell senescence through cytokine production and cell migration. Its functions are of main importance in the resolution of wound healing and in the setup of an appropriate inflammatory response.


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© Springer International Publishing AG 2018

Authors and Affiliations

  1. 1.Department of Pathology and ImmunologyUniversity of GenevaGenevaSwitzerland