Gene structure
The transcribed region of the CYR61 genomic locus spans ~3,2 kb, with 5 exons interspaced by 4 introns. The first exon encodes the 5 untranslated region of the mRNA and followed by sequences encoding the protein secretory signal peptide. The remaining 4 exons each encode a discrete CYR61 domain, and the last exon also contains the mRNA 3 untranslated sequence (OBrien et al., 1990). The 2 kb DNA upstream of the transcription start site contains sufficient information as the Cyr61 promoter to drive accurate expression in transgenic mice both during embryonic development and in adult wound healing (Latinkic et al., 2001). Since each CYR61 domain is encoded by a discrete exon, it was hypothesized that CYR61 arose through an exon-shuffling mechanism (Brigstock, 1999; Lau and Lam, 1999).

SNP
rs3753794 and rs3753793 (r2= 0.77) were associated plasma HDL-cholesterol levels (p= 0.016 and p= 0.008) (Bouchard et al., 2007).
rs954353, located 1,8 kb upstream of CYR61, is linked to susceptibility to colorectal cancer (Fernández-Rozadilla et al., 2010).

The CYR61 promoter is a TATA-box promoter containing binding sites for many transcription factors including AP1, ATF, E2F, HNF3b, NF1, NFkB, SP1, and SRF, and 2 poly(CA) stretches that may form Z-DNA structure. CYR61 transcription is highly responsive to induction by serum growth factors, cytokines, hormones (angiotensin II, estrogen, vitamin D3), and environmental perturbations including UV irradiation, hypoxia, and mechanical stress. During mouse embryo development Cyr61 is highly expressed in cardiovascular, neuronal, and skeletal systems. In adulthood CYR61 is induced at sites of inflammation and wound repair, and de-regulated in many forms of cancer.
Internal ribosome entry site: CYR61 mRNA contains a highly conserved, guanine-cytosine (GC)-rich region of approximately 200 bp near the 5-end of the open reading frame which serves as an internal ribosome entry site (Mukudai et al., 2010). It may facilitate CYR61 production in stressful conditions such as during viral infection (Johannes et al., 1999).
Alternative splicing: hypoxia during breast carcinogenesis may promote a shift of CYR61 alternative splicing to promote CYR61 production. In normal breast tissue most CYR61 RNA transcript contains intron-3, which does not produce CYR61 protein. In cancerous tissues that often suffer hypoxia, intron-3 is spliced out, resulting in mature CYR61 mRNA and a higher level of CYR61 production (Hirschfeld et al., 2009; Hirschfeld et al., 2011).
3-UTR: CYR61 3UTR contains 5 copies of AU-rich element (ARE) in the 3-UTR, which causes RNA instability (Leng et al., 2002). In addition, CYR61 mRNA 3-UTR contains a microRNA-155 target site. In preeclampsia where placental miR-155 level is high, CYR61 mRNA is reduced due to targeted degradation by miR-155 (Zhang et al., 2010).

None identified yet.

CYR61 is a secreted protein located in the extracellular matrix and on cell surface (Yang and Lau, 1991), and regulates diverse cellular activity including cell adhesion, migration, proliferation, apoptosis, senescence, and differentiation (Lau, 2011). It binds to and acts through cell surface integrin receptors, with heparan sulfate proteoglycans (HSPGs) as coreceptors in some contexts (Chen and Lau, 2009; Lau, 2011). Cell adhesion to CYR61 as a substrate induces activation of various signaling molecules including Rac1, FAK, the MAP kinases ERK1/ERK2, and transcription factors such as NFκB (Chen et al., 2001a; Bai et al., 2010). CYR61 is a strong inducer of intracellular reactive oxygen species (ROS) through multiple cellular sources including NADPH Oxidase, 5-lipoxygenase, sphingomyelinase, and the mitochondria; accumulation of ROS mediates Cyr61-promoted apoptosis and cellular senescence (Chen CC et al., 2007; Jun and Lau, 2010b; Juric et al., 2012).
Targeted Cyr61 deletion in mice is embryonic lethal due to cardiac atrioventricular septal defects, impaired placentation, and compromised blood vessel integrity (Mo et al., 2002; Mo and Lau, 2006). Consistently, CYR61 induces pro-angiogenic activity in endothelial cells in culture and neovascularization in vivo (Babic et al., 1998; Fataccioli et al., 2002; Leu et al., 2002).
In adulthood Cyr61 expression is strongly associated with inflammation and wound repair (Lau, 2011). In particular, Cyr61 plays a critical role in the resolution of fibrosis during wound healing by inducing cellular senescence in myofibroblasts (Jun and Lau, 2010b). In inflammation, CYR61 is critical for TNFα-mediated apoptosis in vivo, and can enhance the cytotoxicity of other TNF family cytokines including LTα, FasL, and TRAIL (Chen CC et al., 2007; Franzen et al., 2009; Juric et al., 2009). Finally, CYR61 expression is de-regulated in most human chronic inflammatory diseases including rheumatoid arthritis, diabetic retinopathy and nephropathy, atherosclerosis, and many cancers (Lau, 2011).

Domain structure, receptor binding sites, and interacting proteins
Full-length CYR61 precursor is 381 amino acids in length, with aa 1-24 being the secretory signal peptide. The calculated molecular size for mature CYR61 is 39,4 kDa, and on SDS-PAGE it migrates as a ~40 kDa protein band. CYR61 contains unusually high cysteine content (37 cysteines in the processed protein), in addition, all cysteines are completely conserved among CCN1, CCN2, CCN3, and CCN4.
CYR61 is a direct ligand of several integrin receptors, including αvβ3, αvβ5, αIIbβ3, αMβ2, and α6β1, and has strong binding for cell surface HSPGs (Kireeva et al., 1998; Jedsadayanmata et al., 1999; Chen et al., 2000; Grzeszkiewicz et al., 2002; Schober et al., 2002). Cyr61 binds preferentially to particular integrins in a cell-type specific manner, and this interaction mediates many activities of CYR61.
Proteins of the CCN protein family consists of four structural domains (Holbourn et al., 2008). The first CYR61 domain has sequence homologies to insulin-like growth factor binding protein (IGFBP), although CYR61 does not bind IGFs. The second domain is homologous to the von Willebrand Factor type C repeat (vWC). It has a functional integrin αvβ3 binding site with the sequence NCKHQCTCIDGAVGCIPLCP from aa 116 to 135 (Chen et al., 2004). A point mutation substituting the center aspartic acid residue to alanine (D125A mutation) eliminates the binding activity. Consistent with the notion that CYR61 induces angiogenesis through direct binding to integrin αvβ3, the D125A mutation in Cyr61 effectively abrogates its angiogenic activity (Chen et al., 2004).
Following the vWC-domain is a hinge-region that does not seem to have a particular 3d structure, and its aa sequence is not conserved among the CCN-family members.
The third domain has homology to thrombospondin type 1 repeat (TSR). It contains an integrin α6β1 binding site called T1 with the sequence TTSWSQCSKS from aa 231-240 (Leu et al., 2003).
The fourth domain (CT) has homology to the cysteine-knot motif, and has two binding sites to integrin α6β1 and HSPGs called H1 (aa 278-295, YSSLKKGKKCSKTKKSPE) and H2 (aa 302-314, SSVKKYRPKYCGS), each contributes to heparin binding and integrin α6β1/HSPGs-mediated fibroblast cell adhesion (Chen et al., 2000). The H2 site also overlaps a binding site for integrin αMβ2 and can mediate monocyte cell adhesion (Schober et al., 2002).
The domains of CYR61 may function independently. A mutant CYR61 protein with the CT-domain deleted is unable to induce fibroblast cell adhesion, but still able to activate αv integrin-mediated activities, including cell migration, and potentiate bFGF-induced cell proliferation (Grzeszkiewicz et al., 2001). Similarly, a CYR61 mutant protein (DM) with disrupted integrin α6β1/HSPGs-binding sites is defective for CYR61 supported fibroblast functions, but can still promoting αv integrin-mediated angiogenic activities (Chen et al., 2004). The N-terminal half of CYR61 alone, which contains domains 1 and 2, can bind purified integrin αvβ3 and mediate endothelial cell adhesion (Chen et al., 2004). Mixing CYR61-D125A (mutated in the αv integrin binding site), with CYR61-DM (mutated in the α6β1/HSPG binding sites) can reconstitute wild-type CYR61 function to synergize with TNFα and induce fibroblast apoptosis (Chen CC et al., 2007).

The CYR61 gene is located in human chromosome 1p22.3, within the region of a susceptibility gene locus for atrioventricular septal defects (AVSD; 1p21-1p31) (Sheffield et al., 1997). Targeted disruption of Cyr61 in mice results in severe atrioventricular septal defects (AVSD). Furthermore, Cyr61 haploinsufficiency results in delayed formation of the ventricular septa in embryos and persistent ostium primum atrial septal defects (ASD) in ≈20% of adults (Mo and Lau, 2006).