9.B.87.1.31
CD44 of 742 aas and 2 TMSs, N- and C-terminal. It is a cell-surface receptor that plays a role in cell-cell interactions, cell adhesion and migration, helping the cells to sense and respond to changes in the tissue microenvironment (Crosby et al. 2009, Yoshida et al. 2012). It participates thereby in a wide variety of cellular functions including the activation, recirculation and homing of T-lymphocytes, hematopoiesis, inflammation and response to bacterial infection (Funaro et al. 1994). CD44 enhances Na⁺/H⁺ exchanger isoform-1 (NHE1) activity, causing ECM remodeling and tumor invasion (Suleiman et al. 2018). Transmembrane proteins, CD51/61 and CD44 facilitate cell adhesion, and are commonly found on the surfaces of cancer cells (Mori et al. 2023). It may play a role in osteoporosis (Wu et al. 2023). CD44 regulates Epac1-mediated beta-adrenergic-receptor-induced Ca²⁺-handling abnormalities implicated in cardiac arrhythmias (Chan et al. 2023).  CD44 is a single-chain transmembrane receptor that exists in multiple forms due to alternative mRNA splicing and post-translational modifications. CD44 is the main cell surface receptor for hyaluronan as well as other extracellular matrix molecules, cytokines, and growth factors that play important roles in physiological processes (such as hematopoiesis and lymphocyte homing) and the progression of various diseases, the predominant one being cancer (Skandalis 2023).  The CD44 intracellular domain interacts with various cytoplasmic effectors regulating cell-trafficking machinery, signal transduction pathways, the transcriptome, and vital cell metabolic pathways (Skandalis 2023).