Schematic representation of the CD44 gene and its encoded proteins.

The extracellular domain and cytoplasmic tail of CD44 isoforms vary in size as the result of alternative splicing. The alternatively spliced exons are indicated by open boxes. The human v1 exon contains a stop codon. In the model of the protein, all putative glycosylation sites are indicated: O-glycosylation (open circles); N-glycosylation (closed circles); chondroitin sulfate (open squares); heparan sulfate (HS) (rod). As indicated, the HS-binding site in exon v3 has the ability to bind growth factors, including hepatocyte growth factor/scatter factor (HGF/SF) and fibroblast growth factor (FGF). In addition, the hyaluronate-binding sites (double line), the disulfide bonds (S-S), the ankyrin binding site (. . . . .), the Ezrin-binding site (– – –), the phosphorylation sites (P), and the putative interaction site for the src-family kinase p56^lckare indicated. aa, aminoacid; TM, transmembrane.