EXPRESSION OF GELATINASE-A, A MEDIATOR OF EXTRACELLULAR-MATRIX REMODELING, BY TRACHEAL GLAND SEROUS CELLS IN CULTURE AND IN-VIVO

Tracheal gland morphogenesis and gland hypertrophy in disease involve the penetration of epithelial cells into the submucosa, a process that requires digestion of the basal lamina and the surrounding extracellu lar matrix. We observed that bovine tracheal gland cells invaded colla gen substrates and were inhibited from doing so in the presence of a m etalloproteinase inhibitor GM6001. The gland cells, but not bovine tra cheal surface epithelial cells, secreted a 72-kDa metalloproteinase. T he purified enzyme could be activated with 4-aminophenylmercuric aceta te and converted to an active 65-kDa form that was far more effective in degrading denatured collagen (gelatin) than nondenatured type I and IV collagens and was ineffective in degrading intact interstitial col lagen fibers. At 25 degrees C, the initial rate of degradation of acid -solubilized type I collagen was approximately 50 mg of type I collage n cleaved per min per mg of enzyme, whereas acid-solubilized type IV c ollagen was degraded at approximately 250 mg cleaved per min per mg of enzyme. In contrast, at the same temperature, heat-denatured type I c ollagen was degraded 1000-fold more rapidly, while heat-denatured type IV collagen was cleaved 50-fold more rapidly, The activity of the enz yme was maximal at pH 7-8 and was completely abolished by the metallop roteinase inhibitors EDTA and 1,10-phenanthroline. In immunoblots, the enzyme was recognized by an antibody directed against human gelatinas e A, the 72-kDa gelatinase. The purified enzyme disrupted the distribu tion pattern of type IV collagen in the gland basal lamina, as well as of interstitial collagen in the underlying stromal tissue, as shown i n tissue sections by immunocytochemistry. Using an antibody directed a gainst the purified enzyme, we also showed by immunocytochemistry that the gelatinase was present in tracheal tissue and was specifically lo cated at the periphery of some tracheal gland acini. Northern blots sh owed higher concentrations of gelatinase A mRNA in glands than in epit helium microdissected from adult cow tracheas, These data indicate tha t gelatinase A is a specialized product of the tracheal gland epitheli al cell, a cell type normally invasive as part of its developmental pr ogram; the enzyme may play an important role in normal gland developme nt and disease-associated hypertrophy.