Biological and diagnostic role of cathepsin D.

Biosynthesis, posttranslating modifications, intracellular transport and activation of procathepsin D are discussed. Active cathepsin D evokes degradation of cellular and extracellular proteins and it also activates proenzymes, prohormones and growth factors and inactivates their active forms. Impairment of lysosomes in hypoxia or necrosis evokes transition of cathepsin D to cytosol and body fluids. Increase of cathepsin D content in cytosol also evokes enhancement of the synthesis rate observed among others, in neoplastic tissues and regenerating organs. Increase of cathepsin D content and activity in cytosol and blood serum is of essential diagnostic and prognostic importance in some pathologic conditions.