Abstract
We have identified a novel ligand for CD44, a cell surface glycoprotein implicated in tumor metastasis and lymphocyte homing. When the mouse T cell line CTLL-2 was transfected with cDNA encoding a hemopoietic form of mouse CD44, CTLL-2 cells exhibited a new self-adhesive phenotype, forming large aggregates. The aggregation was blocked by neutralizing anti CD44 monoclonal antibody but unaffected by hyaluronidase, indicating the involvement of CD44 and its non-hyaluronate ligand in the cell aggregation. The ability to induce CD44-dependent aggregation was found in culture supernatants of CTLL-2 and its CD44 transfectants. The use of CD44-immunoglobulin chimeric protein revealed that CTLL-2 and its transfectants synthesized a large-molecular weight protein (gp600) which bound specifically to CD44. The gp600 was readily labeled with radioactive sulfate, and treatment of gp600 with chondroitinase ABC or ACII generated a lower molecular weight species (18-22 kDa), suggesting that gp600 consists of a small core protein with chondroitin sulfate glycosaminoglycan side chains. However, binding of CD44 to glycosaminoglycans such as chondroitin 4-sulfate, chondroitin 6-sulfate, and dermatan sulfate was undetectable, suggesting either that a novel chondroitin-type glycosaminoglycan is recognized by CD44 or that a particular configuration of the glycosaminoglycan is required for recognition by CD44.
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