Versican

Function

The role of versican in cell adhesion, migration, and proliferation has been extensively studied. Versican is often considered an anti-adhesion molecule. Considering the large size (>1000 kDa) and hydration capability of versican, it is possible that the interaction of integrins (large family of cell adhesion molecules) with their cell surface receptors is sterically hindered.

Expression of versican is observed in various adult tissues such as blood vessels, skin, and developing heart. Smooth muscle cells of blood vessels, epithelial cells of skin, and the cells of central and peripheral nervous system are a few examples of cell types that express versican physiologically. Versican is involved in development, guiding embryonic cell migration important in the formation of the heart and outlining the path for neural crest cell migration.

N-terminus

The N-terminal of versican has an important role in maintaining the integrity of the ECM by interacting with hyaluronan. Its interactions with link protein has also been studied.

Glycosaminoglycan binding region

The central domain of Versican is decorated with glycosaminoglycans. The structural and functional diversity of Versican is increased by variations in GAG sulfation patterns and the type of GAG chains bound to the core protein. There is a single versican gene, however alternative splicing of its mRNA produces 4 distinct versican isoforms that differ in their potential number of GAG chains. All isoforms have homologous N-terminal (HA binding) and C-terminal (lectin-like) domains. The central domain of versican V0 contains both the GAG-α and GAG-β domains. V1 isoforms has the GAG-β domain, V2 has the GAG-α domain, and V3 is void of any GAG attachment domains, and only consists of the N-terminal and C-terminal globular domains. It is known that the isoforms are differentially expressed in different tissue types. The biological significance of alternative splicing is yet to be determined.

Because of their negatively charged sulfates or carboxyl groups, chondroitin sulfate chains are attracted to various positively charged molecules such as certain growth factors, cytokines, and chemokines. This interaction in the extracellular matrix or on the cell surface is important in the formation of immobilized gradients of these factors, their protection from proteolytic cleavage, and their presentation to specific cell-surface receptors. The binding of versican with leukocyte adhesion molecules L-selectin, P-selectin, and CD44 is also mediated by the interaction of CS chains of versican with the carbohydrate-binding domain of these molecules. Both CD44 and L-selectin have been implicated in leukocyte trafficking. The ability of versican to bind a large panel of chemokines and the biological consequences of such binding has also been examined. Versican can bind specific chemokines through its CS chains and this interaction down-regulates the chemokines function. Recently, in light of results that V1 and V2 isoforms of versican have opposite effects on cell proliferation, glycosaminoglycan domain GAG-β has been implicated in versican-enhanced cell proliferation and versican-induced reduction of cell apoptosis.

C-terminus

The C-terminal of Versican interacts with a variety of molecules in the matrix. One important family of ligands is the tenascin family. For example, The C-lectin domain of versican interacts with tenascin R through its fibronectin type III (FnIII) repeat 3-5 domain in a calcium dependent manner, in vivo. Different tenascin domains interact with a wide range of cellular receptors, including integrins, cell adhesion molecules and members of the syndecan and glypican proteoglycan families. Versican’s C-terminal domain interacts with fibulin-2, a protein whose expression is associated with that of versican in the developing heart. The EGF domain of the C-terminal of versican also binds the EGF-receptor molecule in vivo.

Clinical significance

Versican is a key factor in inflammation through interactions with adhesion molecules on the surfaces of inflammatory leukocytes and interactions with chemokines that are involved in recruiting inflammatory cells.

In the adult central nervous system, versican is found in perineuronal nets, where it may stabilize synaptic connections. Versican can also inhibit nervous system regeneration and axonal growth following an injury to the central nervous system.

Cancer and metastasis

Increased versican expression is often observed in tumor growth in tissues such as breast, brain, ovary, gastrointestinal tract, prostate, and melanoma, sarcoma, and peritoneal mesothelioma. A fifth isoform of versican, V4, that is similar to V1 but with a shortened beta-GAG region, is present and upregulated in human breast cancer.

Versican is required for Lewis lung carcinoma in mice to metastasize to lung, liver and adrenal glands, acting via TLR2 to activate myeloid cells and produce TNF-alpha.

Lung disorders

Versican is increased in the changing tissue extracellular matrix in inflammatory lung disorders such as chronic obstructive pulmonary disease (COPD), asthma and bronchiolitis obliterans syndrome (BOS). Cells (myofibroblasts, macrophages and other inflammatory cells) can migrate more easily through extracellular matrix that has a higher versican content.

Skin disorders

Deposits of versican are not present in normal skin but are found in the reticular dermis during keloid scarring, a condition where scar formation becomes uncontrolled and overgrowth of skin tissue occurs at the site of the wound.

Interactions

Versican has been shown to interact with hyaluronan and a link protein (hyaluronan and proteoglycan link protein 1; HAPLN1).