Mucins — large extracellular proteins that are heavily glycosylated with complex oligosaccharides — establish a selective molecular barrier at the epithelial surface and engage in morphogenetic signal transduction. Alterations in mucin expression or glycosylation accompany the development of cancer and influence cellular growth, differentiation, transformation, adhesion, invasion and immune surveillance. Mucins are used as diagnostic markers in cancer, and are under investigation as therapeutic targets for cancer.

Mucins in cancer: Protection and control of the cell surface

Molecular cloning and expression of human Tumor-associated Polymorphic Epithelial Mucin

Gastrointestinal mucus is the first line of defence against bac-teria; the organization of this protective system varies markedly along the digestive tract. In this Review, the authors provide an overview of the mucus system and discuss the role of mucus in health and disease.

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The gastrointestinal mucus system in health and disease

Considerable advances have been made in recent years in our understanding of the biochemistry of mucin-type glycoproteins. This class of compounds is characterized mainly by a high level of O-linked oligosaccharides. Initially, the glycoproteins were solely known as the major constituents of mucus. Recent studies have shown that mucins from the gastrointestinal tract, lungs, salivary glands, sweat glands, breast, and tumor cells are structurally related to high-molecular-weight glycoproteins, which are produced by epithelial cells as membrane proteins. During mucin synthesis, an orchestrated sequence of events results in giant molecules of Mr 4 to 6 x 10(6), which are stored in mucous granules until secretion. Once secreted, mucin forms a barrier, not only to protect the delicate epithelial cells against the extracellular environment, but also to select substances for binding and uptake by these epithelia. This review is designed to critically examine relations between structure and function of the different compounds categorized as mucin glycoproteins.

Mucin-type glycoproteins.

Cell surface mucins are large transmembrane glycoproteins involved in diverse functions ranging from shielding the airway epithelium against pathogenic infection to regulating cellular signaling and transcription. Although hampered by the relatively recent characterization of cell surface mucins and the difficulties inherent in working with molecules of their size, numerous studies have placed the tethered mucins in the thick of normal and diseased lung physiology. This review focuses on the three best-characterized cell surface mucins expressed in the respiratory tract: MUC1, MUC4, and MUC16.

Wen Ning Qi

Papers

Cloning and sequencing of a human pancreatic tumor mucin cDNA.