MUCIN GENE STRUCTURE AND EXPRESSION - PROTECTION VS ADHESION

The cloning of mucin cDNAs brought about by the application of molecul ar biology and molecular analyses constitutes a major step in understa nding mucin structure and function. Here two classes of mucins are des cribed: epithelium-associated and endothelium/leukocyte-associated muc ins, which have thus far been described separately in the literature. The epithelial mucins are generally believed to play a role in cytopro tection. The endothelial and leukocyte class of mucins are adhesion mo lecules involved in lymphocyte homing and lymphocyte activation or are part of the adhesion cascade that plays a role in the initiation of i nflammation. Mucins in general contain many threonine and serine resid ues, which are extensively O-glycosylated. Due to this profound glycos ylation, mucins have a filamentous conformation. By virtue of their ex tended filamentous, and often negatively charged, structure, mucins ca n act as a barrier protecting the cell. However, when an opposing cell has specific receptors for mucins, adhesion can override the barrier function. Therefore, mucins may be powerful two-edged swords: they are both protective and adhesive.