IDENTIFICATION OF A SPECIFIC RECEPTOR FOR INTERSTITIAL COLLAGENASE ONOSTEOBLASTIC CELLS

We have previously shown that the rat osteoblastic cell line UMR 106-0 1 responds to parathyroid hormone treatment by secreting interstitial collagenase. Secreted collagenase reaches a maximal concentration 12-2 4 h after parathyroid hormone stimulation, but then declines to undete ctable levels by 96 h. Neither spontaneous nor cell-mediated extracell ular degradation could account for this disappearance, since the enzym e maintained stability in both fresh and conditioned media. Instead, a cell-mediated binding mechanism was suggested by the rapid and satura ble removal of exogenous purified rat collagenase at 37 degrees C. Bin ding studies using I-125-collagenase at 4 degrees C indicated a satura ble receptor of a single class and 12,000 receptors per cell (K-d = 5 x 10(-9) M). A time course revealed specific receptor-mediated binding within 10 min and equilibrium by 60 min, while dissociation experimen ts further demonstrated reversibility, The kinetics of I-125-collagena se binding are characterized by the association (k(1) = 4 x 10(6) M(-1 ) min(-1)) and dissociation (k(-1) = 2 x 10(-3) min(-1)) rate constant s. The receptor was shown to be specific for rat collagenase since a h ost of related and unrelated proteins failed to compete for binding. I nternalization studies revealed maximal intracellular accumulation at 30 min and complete degradation by 90 min, suggesting this receptor fu nctions in these osteoblastic cells to eliminate extracellular collage nase.