Expression and characterization of minican, a recombinant syndecan-1 with extensively truncated core protein.

Syndecan-1 is an integral membrane heparan sulfate/chondroitin sulfate proteoglycan, involved in the control of cell growth and differentiation. The biological activities of syndecan-1 involve interactions with a variety of extracellular ligands, such as growth factors and matrix components, that are mainly mediated by the heparan sulfate moieties. The expression of syndecan-1 is downregulated in various malignant tumors, and low levels of expression appear to correlate with poor prognosis of some cancer types. On the other hand, the extracellular portion of syndecan-1 (ectodomain) has been demonstrated to inhibit the proliferation of various cancer cells in culture, suggesting that proteoglycan-like molecules should be studied further with regard to their antitumor activities. We have expressed, in CHO cells, a truncated syndecan-1 ectodomain ("minican") harboring domains for glycosaminoglycan attachment and antibody recognition. Analysis of recombinant minican indicates that it shares some of the biochemical and biological characteristics attributed to syndecan-1 ectodomain. Minican was thus substituted with heparan sulfate chains and bound to extracellular matrix proteins as well as fibroblast growth factors. Notably, minican inhibited the proliferation of S115 mouse mammary carcinoma cells and the effect seemed to involve inhibition of the Ras/Erk signaling pathway. Our data suggest that recombinant syndecan-1 with a minimal protein component is biologically active. This information may provide useful in further design of proteoglycan-like antitumor molecules.