Parathyroid hormone increases thiol proteinase activity by activation of protein kinase C in cultured kidney tubule cells (OK).

Chronic exposure (24 h) to parathyroid hormone (PTH) increases the intracellular proteolytic activity in cultured opossum kidney cells 2-fold at physiological PTH concentrations (10(-12) mol/l). This increase can be blocked by E-64, an inhibitor of thiol proteinases. The phorbol ester TPA mimicks the effect of PTH, whereas the calcium ionophore A23187 reduces the intracellular proteinase activity. Forskolin and dibutyrylic cAMP do not elevate proteinase activity. The protein kinase C inhibitor staurosporine is equally effective in blocking the TPA- and PTH-induced proteinase activity increase. These data indicate that PTH increases the intracellular thiol proteinase activity by an activation of protein kinase C and not by the cAMP dependent way.