EXPRESSION AND SECRETION OF PARATHYROID HORMONE-RELATED PROTEIN BY A HUMAN CANCER CELL-LINE

The regulation of expression of parathyroid hormone-related protein (PTHRP) mRNA by protein kinase C and cyclic-AMP-dependent pathways was studied in a human lung cancer cell line (BEN). PTHRP mRNA was increased by agents which activate protein kinase C, but not by those which activate cyclic-AMP-dependent pathways. Activators of both second messenger pathways stimulated a dose-dependent increase in the accumulation of PTHRP in conditioned medium assayed using sensitive region-specific immunoassays for PTHRP1-34 and 1-86. Calcitonin had a dose-dependent effect on the accumulation of PTHRP in culture medium which may be mediated via cyclic AMP. Varying the calcium concentration from 0-2.5 mM had no effect on peptide secretion over 20 h, while short-term incubation (30 min) with ionomycin (2.5-75 mu g/ml) significantly increased PTHRP immunoreactivity in the medium.