A NOVEL LIGAND FOR CD44 IS SULFATED PROTEOGLYCAN

We report herein identification of a novel ligand for CD44, a cell sur face glycoprotein implicated in tumor metastasis, lymphocyte different iation and homing. A mouse T cell line CTLL-2 transfected with cDNA en coding a hemopoietic form of mouse CD44 exhibited a new self-adhesive phenotype, forming large aggregates. The aggregation was blocked by an ti-CD44 mAb but little affected by hyaluronidase, indicating the invol vement of CD44 and its non-hyaluronate ligand in the cell aggregation. The ability to induce CD44-dependent aggregation was observed in cult ure supernatants of CTLL-2 and its CD44 transfectants. Immunoprecipita tion analysis using a CD44 - Ig chimeric molecule indicated that CTLL- 2 and its transfectants synthesized a macromolecule (gp600) which boun d specifically to CD44. gp600 was readily labeled with radioactive sul fate and treatment of gp600 with chondroitinase 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 su lfate glycosaminoglycan side chains. However, when binding of CD44 was tested in vitro to chondroitinase-sensitive purified glycosaminoglyca ns, such as chondroitin-4-sulfate, chondroitin-6-sulfate and dermatan sulfate, no binding was demonstrable, suggesting either that a novel t ype of chondroitinase-sensitive glycosaminoglycan is recognized by CD4 4 or that association of the glycosaminoglycan with a core protein is required for recognition by CD44.