Mechanisms of osteoclastic secretion.

A tight balance between bone resorption by osteoclasts and bone formation by osteoblasts is required for the maintenance of bone mass and integrity. A net increase in bone resorption over formation results in osteoporosis, a disease associated with significantly morbidity and mortality. Following attachment via the integrin alphavbeta3, osteoclasts degrade bone by generation of the ruffled border, the unique resorptive organelle of the cell. The adherent cell then secretes into the subcellular space protons and acidic proteases. We review here the concepts relating to the mechanisms of regulated secretion and provide preliminary data on the role of one protein important for secretion by osteoclasts.