Mutations of the C-terminal end of cathepsin K affect proenzyme secretion and intracellular maturation

Transfection of the human cathepsin K cDNA into CHO cells results in the ex pression of mature catalytically active 27-kDa protein and in cells secreti ng the 39-kDa proenzyme form. Monensin, which neutralizes the pH of acidic organelles, was found to inhibit intracellular processing of the proenzyme and to stimulate its secretion into the culture medium. Brefeldin A caused alterations in immunofluorescence staining consistent with interference of lysosomal targeting and inhibited both intracellular processing and secreti on of cathepsin K. Inhibition of glycosylation by tunicamycin also abolishe d cathepsin K maturation. Furthermore, the processing of the proenzyme to t he mature form was abolished by a single mutation of the terminal Met(329) to Ala. The triple mutation of Ser(325) Pro(327), and Met(329) (all to Ala) inhibited both maturation and secretion, using either transient or stable expression systems, The results indicate that intracellular maturation and secretion of cathepsin K can he affected differentially by various treatmen ts and by mutations of the C-terminal end of the protein. These results are consistent with the involvement of both the secreted proenzyme and the int racellularly processed enzyme in cathepsin K-mediated processes. (C) 2001 A cademic Press.