[Cathepsin cysteine proteinases in the lung]

Proteolytic enzymes play an important role during remodeling and digestion of extracellular matrix proteins. An overproduction of extracellular matrix or insufficient extracellular matrix digestion may result in fibrosis. Enhanced proteolytic activity or an insufficient inhibitory potential could be followed by emphysema development. Since the first reports showed an emphysema induction in rats after intratracheal application of the cysteine protease papain, a number of proteolytic enzymes involved in the remodeling of the extracellular matrix of the lung were discovered. Most of them are cysteine-, metallo-, serine- or aspartic proteases. In this paper some new findings concerning the expression, function and regulation of the activity of papain-like cysteine proteases in the process of tissue destruction and remodeling in the lung are reviewed. The functional relationship between cathepsins and other proteolytic enzymes are discussed.