Mucins are high-molecular-weight glycoproteins present on all mucosal surfaces. Mucins are characterised by the presence of tandemly repeated amino acid sequences, the mucin domains that contain high amounts of serine and threonine and thus create an attachment point for O-linked glycosylation [].Epiglycanin/mucin-21 (MUC21) is a transmembrane mucin that modulates cell adhesion [, ].
The unusual mucin, epiglycanin, is membrane-bound at the C terminus but has a long region of this tandem-repeat at the N terminus []. It was the first mucin identified to be associated with the malignant behaviour of carcinoma cells []. Mouse Muc21/epiglycanin is thought to be a highly glycosylated molecule, which makes it likely that its function is dependent on its glycoforms. Cells expressing Muc21 are significantly less adherent to each other and to extracellular matrix components than control cells, and this loss of adhesion is mediated by the tandem-repeat portion of Muc21 [].
