Mucin-21 (MUC21)

Mucin-21 (MUC21) is a membrane-associated, highly O-glycosylated mucin predominantly expressed on squamous epithelia, where it helps protect against physical and chemical injury by forming part of the epithelial mucous barrier. MUC21 features a polymorphic tandem-repeat domain rich in serine and threonine, extensive O-glycosylation, a transmembrane domain, and a cytoplasmic tail. Its expression renders cells resistant to apoptosis through glycosylation-dependent mechanisms, requiring the full-length protein for full protective effect; both extracellular and cytoplasmic domains are necessary, and specific glycoforms are essential for maximal antiapoptotic activity. MUC21 serves as an anti-adhesive molecule, potentially contributes to immune evasion, and is abnormally upregulated in various carcinomas, most notably incohesive-type lung adenocarcinoma, suggesting use as a cancer biomarker. No specific drugs targeting MUC21 are currently listed, though it represents an emerging potential therapeutic and diagnostic target in oncology.

Other names

MUC21Mucin-21C6orf205UNQ697/PRO1342bCX31G15.2Epiglycaninmucin-21MUC-21epiglycaninKMQK697

Not drug-mediated; resistance to apoptosis is conferred by glycosylated full-length MUC21 altering epithelial cell susceptibility to injury and therapy.