Mucin 1, cell surface-associated (MUC1) or polymorphic epithelial mucin (PEM) is a membrane-bound protein that is a member of the mucin family. Mucins are heavily glycosylated proteins that give the mucosa viscous gel-forming properties, and contribute to the structural organization of secretory epithelia. The mucosa serves as a physical barrier to protect the epithelium from harsh environments such as low pH and microbial infections. Cell surface associated mucins, such as Mucin-1 (Muc-1), are important components of the mucosal barrier that exist at the interface of the apical surface between secreted mucins and the cell surface. In addition to the mucus-type functions of its extracellular mucin domain, Muc-1 is a transmembrane protein with a cytoplasmic tail that is a known target of multiple kinases that has been shown to participate in normal and oncogenic signaling.Muc-1 is overexpressed and aberrantly glycosylated in many cancers, where it has been documented to play an important role in inflammation and tumor progression.Muc-1 is also expressed on many non-epithelial cell types including leukocytes, where its function is less well characterized. It has been documented that Muc-1 controls inflammation resulting from Helicobacter pylori infection by suppressing activation of the NLRP3 inflammasome. Knockout of Muc-1 also results in aberrant expansion of myeloid derived suppressor cells from the bone marrow.