Epithelial Mucin Genes

Abstract

The last seven years have been exciting in the world of mucin biology. Molecular analyses of mucin genes and deduced protein structures have provided insight into structural features of mucins and tools with which to examine expression, secretion, and glycosylation, thereby enabling a better understanding of the role of mucins in normal physiological processes and in disease. Functional studies are in progress both in vitro using cDNAs and cell lines and in vivo utilizing mutant mice in which a particular mucin gene has been inactivated or overexpressed. These studies should help determine whether the functions of mucins are restricted to protection and lubrication, or if they are involved in the adhesion of tumor cells to other cells or tissue components or in modulation of the immune system.

Sialomucin complex at the rat ocular surface: a new model for ocular surface protection

“…SMC is similar to MUC1 in that both are expressed in a number of normal secretory epithelial tissues, including the lactating mammary gland, trachea and uterus [10,21,22]. Both proteins are found as heterodimeric complexes containing a transmembrane subunit [19,27].…”

“…Both proteins are found as heterodimeric complexes containing a transmembrane subunit [19,27]. In addition, SMC and MUC1 can be found in both membrane and soluble forms ; the latter lack the C-terminal and transmembrane domains [10,21]. The soluble form of MUC1 may be generated either by alternative RNA splicing [28] or by proteolytic cleavage [29].…”

“…Both MUC1 and SMC have been shown to disrupt cell-cell and cell-matrix interactions and to provide resistance to cell killing by natural killer cells [30]. However, SMC is uniquely expressed in some tissues where MUC1 is not detected, such as the colon and small intestine [10,21]. In addition, the transmembrane subunit ASGP-2 contains two epidermal growth factor (EGF)-like domains which contain all of the consensus residues found in EGF-like regions of proteins possessing growth factor activity ( Figure 1) [23], and has been shown to act as a ligand for the receptor tyrosine kinase ErbB-2 [22,31].…”

“…Because of its large extended structure and cell surface location, MUC1 has been assigned a number of possible functions. In normal and tumour tissue MUC1 may create a barrier to cell-cell interactions, reduce the adhesion of macromolecules to the cell surface, and provide resistance to natural killer and cytotoxic T-cell killing [10]. Several different mucins have been reported in ocular tissues, and it was once thought that all ocular mucin was produced by conjunctival goblet cells.…”

Biochemical analysis of a bladder-cancer-associated mucin: structural features and epitope characterization

“…The central domain of the mucin polypeptide is composed of a variable number of tandem repeats which are rich in serine, threonine and proline residues and may or may not be separated by domains rich in hydrophobic residues [10,12]. The abundance of serine and threonine residues in these domains provides the backbone necessary for the bulk glycosylation of mucins through Oglycosylation of these residues [13].…”