CD44 in Normal Differentation and Tumor Progression

CD44, also known as HERMES antigen (Jalkanen et al. 1986) or Pgp-1 (Picker et al. 1989), occurs in several isoforms distinguished by primary amino structure and post-translational modification. The different sizes range from an apparent molecular weight of 85 kD to some 250 kD. The smallest form, originally recognized by the HERMES antibody, is the classical CD44 molecule found on many hemapoetic cells such as granulocytes, lymphocytes and macrophages (Flanagan et al. 1989; Jalkanen et al. 1987). Recent cloning and sequencing has shown that larger isoforms carry additional sequences outside the transmembrane region and that the choice of these extra sequences is quite enormous (Stamenkovic et al. 1991; Gunthert et al. 1991; Hofmann et al. 1991). Some ten additional exons can be “inserted”. All CD44 molecules have the remaining portions in common, and possess a large extracellular N-terminus, a transmembrane region and a cytoplasmic tail.