Description: CD44 is a cell membrane associated, polymorphic glycoprotein with apparent molecular weights ranging from 85 kDa to 250 kDa. CD44 isoforms participate in a wide variety of cell-cell or cell-matrix interactions including lymphocyte homing, establishment of B and T cell immune responses, tumor metastases formation and inflammation.
Three isoform categories of the CD44 molecule have been identified:
1) an 80-90 kDa isoform, the so-called standard form named CD44std, which is widely distributed on several hematopoietic and nonhemato-poietic cells including all subsets of leukocytes, monocytes, erythrocytes, many types of epithelium, mesenchymal elements like fibroblasts, smooth muscle cells and glial cells of the central nervous system,
2) a medium size category of 110-160 kDa which is weakly expressed on epithelial cells and highly expressed in some carcinomas and
3) a category which includes very large isoforms of 250 kDa covalently modified by the addition of chondroitin sulfate.
These bigger isoforms of CD44 arise by alternative splicing of one or more "variant" exons (v2-v10) into the extracellular part of the 90kDa constant form molecule. Compared to the standard CD44, all larger isoforms are expressed in a much more restricted fashion, only in a few normal tissues or on the surface of certain tumor cells. Some splice variants of CD44 play important and distinct roles in tumor metastasis.
CD44 is known to interact with the ezrin family (ERM family) members and form a complex that plays diverse roles within both normal and abnormal cells, particularly cancer cells. CD44 and ezrin and their respective complex have properties suggesting that they may be important in the process of tumour-endothelium interactions, cell migrations, cell adhesion, tumour progression and metastasis. Determination of sCD44std will provide more detailed insight into different pathological modifications during cancer and other diseases.