The six hyaluronidase-like genes in the human and mouse genomes

Mucins are the principal organic constituents of mucus, the slimy visco-elastic material that coats all mucosal surfaces. Compelling evidence suggests that they play an integral role in non-immune protection of the oral cavity. Specific protective functions include: 1) protection against desiccation and environmental insult, 2) lubrication, and 3) antimicrobial effects against potential pathogens. Biosynthesis of mucin is regulated by both intrinsic ("cooperative sequential specificity") and extrinsic ("structural modulation") controls. These controls form the basis by which mucin's structure can be modified to meet a dynamically changing biological need.

Role of salivary mucins in the protection of the oral cavity

Hyaluronan is a negatively charged, high molecular weight glycosaminoglycan found predominantly in the extracellular matrix. Intracellular locations for hyaluronan have also been documented in cytoplasm, nucleus, and nucleolus. The polymer has an extraordinarily high rate of turnover in vertebrate tissues. The focus here is to formulate a metabolic pathway for hyaluronan degradation using all available data, including the recently acquired information on the hyaluronidase gene family. Such a catabolic scheme has defied explication up to now. In somatic tissues, stepwise processing occurs, from the extracellular high molecular weight space filling, antiangiogenic approximately 107-kDa polymer, to intermediate sized highly angiogenic, inflammatory, and immune-stimulating fragments, and ultimately to tetrasaccharides that are antiapoptotic and potent inducers of heat-shock proteins. It is proposed that the high molecular weight extracellular polymer is tethered to the cell surface by the combined efforts of hyaluronan receptors and hyaluronidase-2 (Hyal-2). The hyaluronan is cleaved to a 20-kDa intermediate-sized fragment, the limit product of Hyal-2 digestion. These fragments are delivered to endosomal- and ultimately lysosomal-like structures. Further catabolism occurs there by Hyal-1, coordinated with the activity of two lysosomal beta-exoglycosidases, beta-glucuronidase and beta-N-acetyl-glucosaminidase. A membrane-associated mini-organelle is postulated, the hyaluronasome, in which coordinated synthetic and catabolic enzyme reactions occur. The hyaluronasome can respond to the physiological states of the cell by a series of membrane-bound and soluble hyaluronan-associated receptors, binding proteins, and cofactors that trigger enzymatic events and signal transduction pathways. These in turn can be modulated by the amounts and sizes of the hyaluronan polysaccharides generated in the catabolic cascade. Most of these highly dynamic interactions remain to be determined. It is also proposed that malignant cells can commandeer some of these interactions for facilitating tumor growth and spread.

Miriam De Salegui

Papers

Preparation and properties of porcine submaxillary mucins.

The existence of an acid-active hyaluronidase in serum.