Two forms of parathyroid hormone-like adenylate cyclase-stimulating protein derived from tumors associated with humoral hypercalcemia of malignancy

Abstract

Tumors associated with humoral hypercalcemia of malignancy (HHM) contain parathyroid hormone-like adenylate cyclase-stimulating proteins (hACSPs). We previously purified a 17,000 MW hACSP from an HHM-associated breast carcinoma. This report describes the characterization of hACSPs from three additional HHM-associated tumors: two typical HHM-associated tumors (squamous carcinomas) and a third unusual tumor type (pheochromocytoma). Each tumor was extracted in acid-urea/ethanol-sodium chloride, and adenylate cyclase-stimulating activity (ACSA) was examined following reverse-phase and size-exclusion HPLC and isoelectric focusing. Each tumor contained a high molecular weight form of ACSA which co-eluted with the 17,000 molecular weight breast carcinoma hACSP in each of the three separation procedures. Each also contained a lower molecular weight form(s) of ACSA (6,000-9,000 molecular weight). Both forms were inhibited by Nle8,18Tyr34bPTH(3-34) amide. The high molecular weight form was not changed to the lower molecular weight form by a reducing agent. Some HHM-associated tumors contain two forms of hACSP, one with a molecular weight of 17,000 and another with a molecular weight of 6,000-9,000, which appears to be an amino-terminal cleavage product of the larger protein.