CD44 is a protein coding gene located on chromosome 11p13. The protein encoded by this gene is a receptor for hyaluronic acid (HA). It is a cell surface glycoprotein(CD44) involved in cell-cell interactions, cell adhesion and migration to sense and respond to changes in the tissue microenvironment (Yoshida T et al. 2012). Transcripts of this gene undergo a complex alternative splicing process that results in many functionally distinct isoforms. The nature of some of these full-length variants is unknown. Alternative splicing is the basis for the structural and functional diversity of this protein and may be related to tumor metastasis.
CD 44, as a hyaluronic acid receptor, can also interact with other ligands such as collagens and matrix metalloproteinases (MMPs). CD44 is involved in a variety of cellular functions, including lymphocyte activation, recirculation and homing, hematopoiesis, and tumor metastasis.
The encoded protein is involved in a variety of cellular functions, including T lymphocyte activation, circulation and homing, hematopoiesis, inflammation, and response to bacterial infection (Funaro A et al. 1994). It binds extracellular matrix components such as hyaluronan/HA, collagen, growth factors, cytokines or proteases via its ectodomain and serves as a platform for signal transduction by assembling protein complexes containing receptor kinases and membrane proteases via its cytoplasmic domain (Midgley AC et al. 2013). These effectors include PKN2 (protein kinase), the RhoGTPases RAC1 and RHOA, Rho kinase (ROCK1+ 2), and phospholipase C. They coordinate signaling pathways that promote calcium mobilization and actin-mediated reorganization of the cytoskeleton, which are important for cell migration and adhesion (Bourguignon LY et al. 2004).