Parathyroid hormone-related protein purified from a human lung cancer cell line

A protein with biological activities similar to parathyroid hormone (PTH) has been purified from serum-free culture medium obtained from a human lung cancer cell line (BEN). A major protein band of 18 kDa was obtained on NaDodSO4/polyacrylamide gels, with faint bands at 35 kDa and 67 kDa. Biological activity was associated only with the 18-kDa band. Amino acid sequence analysis of the material purified by HPLC revealed that 8 of the 16 residues were identical with those of human PTH. Antibody raised to a corresponding synthetic peptide recognized the PTH-related material but showed less than 1% cross-reactivity with human PTH amino-terminal peptides. BEN cells contained PTH DNA, but not PTH messenger RNA, indicating involvement of another gene. The purified PTH-related protein had a specific biological activity approximately equal to 6 times greater than that of bovine PTH(1-34). The PTH-related protein may have a role in the syndrome of humoral hypercalcemia of malignancy.