Departament de Bioquimica i Biologia Molecular, Facultat de Veterinaria, Universitat Autonoma de Barcelona, 08193 Bellaterra, Spain
Posttranslational modifications (PTM): the consensus sequence for chondroitin sulphate attachment sites reveals the number of potential GAG attachment sites: the number of GAG chains attached to the protein core depends on the isoforms since the GAG alpha subdomain bears 12-17 chondroitin sulphate (CS) chains, whereas the GAG beta subdomain bears 5-8 CS chains (Ricciardelli et al., 2009).
Versican belongs to the hyalectan family, characterized by its ability to bind hyaluronan. The overall consensus is that versican together with hyaluronan forms a pericellular matrix that modulates cell proliferation, adhesion and migration in conditions such as in development and wound healing cell. Some of these actions have been ascribed to specific domains in the molecule. Thus, overexpression of versican G1 domain can enhance cell proliferation and reduce cell adhesion (Ang et al., 1999; Zhang et al., 1999). G3 domain has also been involved in several processes like cell proliferation and invasion (Zhang et al., 1998; Yang et al., 2003; Zheng et al., 2004; Yee et al., 2007), and GAG chains have been considered partially responsible for the antiadhesive properties of versican (Yamagata and Kimata, 1994; Sakko et al., 2003).
Cell proliferation. Versican is associated with a proliferative cell phenotype and it is often found in tissues showing elevated proliferation such as in development and in a variety of tumours (Wight, 2002; Ricciardelli et al., 2009). Purified versican added to the culture media in a melanoma cell line induces proliferation (Touab et al., 2002). Silencing experiments with siRNA have lead to the same conclusion in vascular smooth muscle cells (Huang et al., 2006) and preadipocytes (Zizola et al., 2007).
Cell adhesion. Versican is an anti-adhesive substrate (Yamagata and Kimata, 1994). The anti-adhesive role of versican has been also shown in melanoma cells (Touab et al., 2002), prostate carcinoma cells (Sakko et al., 2003) or neural crest cells (Dutt et al., 2006). This inhibitory effect on cell adhesion may be mainly due to the presence of the GAG chains that might create a more hydrated extracellular matrix less suitable for cell adhesion.
Nevertheless, the G3 domain of versican has pro-adhesive properties raising the possibility that different breakdown products might differentially affect cell adhesion (Wu et al., 2002).
Cell migration and invasion. Versican can increase cell motility in embryonic as well as tumour cells. This activity may be mostly associated with its antiadhesive activities. Silencing of V0/V1 versican expression reduces cell migration in wound healing assays in smooth muscle cells (Huang et al., 2006), or in prostate cancer cells, where addition of purified versican to the cells caused an increase in the invasion ability (Ricciardelli et al., 2007). In glioma, treatment of the cells with TGF-beta2 caused an increase in cell migration associated to an increase in versican production (Arslan et al., 2007). In the nervous system and in axonal growth, the V2 splice variant inhibits axonal growth and migration (Schmalfeldt et al., 2000).
Apoptosis. The effect of versican on apoptosis is complex and anti- as well as pro-apoptotic functions have been reported. Overexpression of the V1 versican isoform in cultured fibroblasts increases apoptotic resistance, but cells were also sensitized to a wide range of cytotoxic agents (LaPierre et al., 2007).
Cell differentiation and epithelial-mesenchymal transition (EMT). Versican modulates cell differentiation and morphogenesis, since it is involved in EMT interactions and in mesenchymal cell condensation required for organogenesis. V1 (but not V2) has been shown to trigger MET in fibroblasts by inducing a switch from N-cadherin to E-cadherin and subsequent acquirement of epithelioid phenotype. Silencing of endogenous versican prevents condensation and MET in metanephric mesenchyme (Sheng et al., 2006). Versican is highly expressed in the mesenchymal cell condensation area during development of cartilage, heart, hair follicles and kidney, and in vitro evidences show that versican V0 and V1 isoforms are involved in the process of precartilage mesenchymal condensation and subsequent chondrogenesis (Kamiya et al., 2006). The requirement of versican in development is highlighted by the finding that deficiency of versican in a transgenic mouse model is embryonic lethal, due to defects on cardiac formation, limb mesenchymal aggregation and chondrogenesis (Williams et al., 2005).
Others. In neural cells, versican plays an important role in regulating axonal guidance (Perissinotto et al., 2000). It is also an important molecule in inflammatory processes since it is able to interact with immune cell receptors and chemokines (Hirose et al., 2001).
Only mutations affecting the splicing of exons 7 and 8 have been described associated to Wagner syndrome, a rare disorder belonging to the group of hereditary vitreoretinal degenerations (Miyamoto et al., 2005; Kloeckener-Gruissem et al., 2006).
Daniel Hernández ; Maria José Docampo ; Anna Bassols
Atlas Genet Cytogenet Oncol Haematol. 2010-10-01
Online version: http://atlasgeneticsoncology.org/gene/40173/vcan-(versican)