Abstract
Ryudocan is a type I integral membrane heparan sulfate proteoglycan, which was originally cloned from rat microvascular endothelial cells as an important molecule maintaining blood fluidity. We purified rat ryudocan as well as rat syndecan, which had an apparent molecular sizes of 30kDa and 50kDa of the core proteins established by SDS gel electrophoresis, respectively. We cloned the cDNAs encoded the core proteins for rat ryudocan and rat syndecan. Both of the deduced amino acids residues of rat ryudocan and syndecan had homologous transmembrane and intracellular domains, but very distinct extracellular regions. Now, ryudocan is known to be one of the syndecan family members. We also cloned the human ryudocan cDNA, of which the gene localizes on the chromosome 20q 12. Purified endogenous ryudocan as well as expressed epitope-tagged ryudocan bore anticoagulantly active heparan sulfate (HSact) and/or inactive heparan sulfate (HSinact). HSact and HSinact have molecular sizes of about 25-30kDa with the same overall composition of monosaccharides except that HSact exhibits more glucuronsyl 3-O-sulfated glucosamines than HSinact. Increased intracellular levels of stably expressing epitope-tagged ryudocan probably act by saturating the capacity of components which regulate HSact production by coordinating the function of biosynthetic enzymes. Moreover, stably expressing epitope-tagged ryudocan showed the production of the following multiple isoforms: pure HS-ryudocan, various HS/CS-hybrids, and pure CS-ryudocan. The production of multiple isoforms of ryudocan may serve to expand the functional versatility of this cell surface component and allow it to participate in many different biological processes.
