CD44 is a transmembrane glycoprotein that plays a crucial role in cell-cell and cell-matrix interactions. It is widely expressed on various cell types, including endothelial cells, epithelial cells, fibroblasts, and leukocytes. The molecule is composed of an extracellular domain, a transmembrane domain, and an intracellular domain, with the extracellular domain being responsible for binding to ligands such as hyaluronic acid (HA), which is its primary ligand. CD44 is involved in numerous physiological processes, including cell adhesion, migration, proliferation, and immune cell activation. Additionally, it plays a significant role in cancer progression, as it is often overexpressed in cancer cells and contributes to tumor growth, invasion, and metastasis. The diverse functions of CD44 are attributed to its various isoforms, which result from alternative splicing and post-translational modifications.
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