Multiple Forms of Mouse PG-M, a Large Chondroitin Sulfate Proteoglycan Generated by Alternative Splicing

Abstract

We have isolated and sequenced cDNA clones that encode the core protein of PG-M-like proteoglycan produced by cultured mouse aortic endothelial cells (Morita, H., Takeuchi, T., Suzuki, S., Maeda, K., Yamada, K., Eguchi, G., and Kimata, K. (1990) Biochem. J. 265, 61-68). A homology search of the cDNA sequence has suggested that the core protein is a mouse equivalent of chick PG-M(V1), one of the alternatively spliced forms of the PG-M core protein, which may correspond to human versican. Northern blot analysis revealed three mRNA species of 10, 9, and 8 kilobases (kb) in size. The analysis of PG-M mRNA species in embryonic limb buds and adult brain revealed the presence of other mRNA species with different sizes; the one with the largest size (12 kb) was found in embryonic limb buds, and the ones with smaller sizes of 7.5 and 6.5 kb were in adult brain. Sequencing of cDNA clones for the smaller forms in the adult brain showed that they were different from PG-M(V1) in encoding the second chondroitin sulfate attachment domain (CS alpha) alone. Occurrence of the PCR products striding over the junction of the first and second chondroitin sulfate attachment domains suggested that a mRNA of 12 kb in size corresponded to a transcript without the alternative splicing (PG-M(V0)). It is likely, therefore, that multiforms of the PG-M core protein may be generated by alternative usage of either or both of the two different chondroitin sulfate attachment domains (alpha and beta) and that molecular forms of PG-M may vary from tissue to tissue by such an alternative splicing.

The interaction of versican with its binding partners

“…In this respect, G3 is similar to the selectin family [25] except that the lectican G3 domains contain only one complement binding protein-like subdomain, while selectins contain at least two. Alternative splicing of mRNA encoding GAG chain binding regions generates at least four isoforms of versican named V0, V1, V2 and V3 with molecular weight of the core proteins of about 370 kDa, 263 kDa, 180 kDa, and 74 kDa, respectively [2,[26][27][28]. Each contains different lengths of the GAG binding region with an accompanying variation in number of attached GAG chains (Fig.…”

“…V1 isoform contains CSβ domain, and V2 isoform contains CSα domain. Versican V3 is solely composed of the G1 and G3 domains, lacking all potential GAG attachment sites [27]. In versican, the number of GAG side chains per length of the GAG-binding regions is rather constant.…”

A Human-specific Polymorphism in the Coding Region of the Aggrecan Gene

“…The G3 domain of aggrecan has been shown to have lectin-like activity (29), and the similar domain of the related aggrecan family member versican has been reported to bind a variety of matrix molecules, most notably tenascin-R (30) and heparin sulfate (31). While the GAG attachment domain of versican does not show the same type of conserved repeat sequence as aggrecan and is unlikely to vary in repeat number, it does undergo alternative splicing, producing molecules with varied spacing between G1 and G3 domains (32,33). Variation in spacing between binding domains might be expected to have disruptive effects on tissue architecture, if the ligands are relatively fixed in position.…”

Versican Mediates Mesenchymal-Epithelial Transition

“…The chondroitin sulfate (CS)-attachment domains present in the middle region are divided into two alternatively spliced domains named CS␣ and CS␤. Alternative splicing of versican generates at least four versican isoforms: V0, V1, V2, and V3 (Ito et al, 1995;Zako et al, 1997;Lemire et al, 1999). Different numbers of CS chains are observed in the V0, V1, and V2 versican isoforms.…”