THE MECHANISMS AND REGULATION OF PROCATHEPSIN-L SECRETION FROM OSTEOCLASTS IN BONE-RESORPTION

The secretion mechanisms of cathepsin L from osteoclasts in the proces s of bone resorption were investigated. The increases in bone pit numb ers formed take place by PTH addition in parallel with the increases o f cathepsin L and/or L-like proteinase activities in the culture mediu m of bone cells, and these were suppressed by the addition of calciton in. The Z-Phe-Arg-MCA hydrolysing activity increased in the medium thr ough the effect of PTH is considered to be a kind of procathepsin L by Western blotting analysis, and was suppressed by calcitonin addition. Furthermore, monensin inhibited not only the PTH-induced pit formatio n, but also cysteine proteinase activity in osteoclasts. Therefore, th e procathepsin L excreted might be transferred from endothelial reticu lum via Golgi and/or via lysosomes.