A novel ligand for CD44 is sulfated proteoglycan

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Abstract
We report herein identification of a novel ligand for CD44, a cell surface glycoprotein implicated in tumor metastasis, lymphocyte differentiation and homing. A mouse T cell line CTLL-2 transfected with cDNA encoding a hemopoletic form of mouse CD44 exhibited a new self-adhesive phenotype, forming large aggregates. The aggregation was blocked by antl-CD44 mAb but little affected by hyaluronldase, Indicating the involvement of CD44 and its non-hyaluronate ligand in the cell aggregation. The ability to induce CD44-dependent aggregation was observed in culture supernatants of CTLL-2 and its CD44 transfectants. Immunopreclpltatlon analysis using a CD44 - Ig chlmerlc molecule indicated that CTLL-2 and its transfectants synthesized a macromolecule (gp600) which bound specifically to CD44. gp600 was readily labeled with radioactive sulfate and treatment of gp600 with chondroltlnase ABC or AC II generated a lower molecular weight species (18–22 kDa), suggesting that gp600 consists of a small core protein heavily modified with chondroitin sulfate glycosamlnoglycan side chains. However, when binding of CD44 was tested in vitro to chondroltlnase-sensltlve purified glycosamlnoglycans, such as chondroltln-4-sulfate, chondroltin-6-sulfate and dermatan sulfate, no binding was demonstrable, suggesting either that a novel type of chondroitlnase-sensitive glycosamlnoglycan is recognized by CD44 or that association of trie glycosamlnoglycan with a core protein is required for recognition by CD44.

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