[A parathyroid hormone related protein (PTHrP) implicated in hypercalcemia associated with malignancy: research of the PTHrP for novel hormonal tumor marker].

A cDNA complementary to the parathyroid hormone related protein (PTHrP), the humoral hypercalcemia factor in malignancy, was recently isolated and sequenced. PTHrP expression in human carcinomas was examined (determined) by Northern blot hybridization, Southern blot hybridization and radioimmunoassay (RIA). Expression of PTHrP mRNA was detected in three out of four lung squamous cell carcinomas, two out of ten breast carcinomas and the one adenosquamous carcinoma of the maxilla. No clinical hypercalcemia was found in these PTHrP mRNA positive carcinomas. No expression of PTHrP was detected in normal human or rat tissues. In Southern blot hybridization, no amplification of PTHrP gene was found in PTHrP positive cases. An insertion in one allele of promotor region of the gene was identified in one PTHrP positive lung squamous cell carcinoma. The serum level of PTHrP was examined using human PTHrP (1-34) RIA in lung carcinomas. We found no correlation between the level of PTHrP and clinical hypercalcemia or the histopathological diagnosis. We discuss some problems of the PTHrP assay as a novel tumor marker for malignancies. A new RIA assay study using recombinant human PTHrP expressed in Escherichia coli is also reported.