Parathyroid hormone-related peptide is a downstream target for ras and src activation

Neoplastic transformation may be associated with the development of paraneoplastic syndromes that complicate the management of patients with malignant disease. One of these syndromes, humoral hypercalcemia of malignancy, has been shown to be attributable to increased secretion of a parathyroid hormone-related peptide (PTHrP). The gene encoding PTHrP is expressed at low levels in a growth factor-dependent manner in normal tissues, and the mechanisms underlying selective tumor-associated induction of PTHrP gene expression remain unclear. Here we show that cellular transformation by the EJ-Ha-ras and v-src oncogenes is associated with a marked increase in PTHrP gene expression. Ha-ras- and v-src-transfected NRK 49F cells and ras-transfected RCB 2.2 cell lines secreted increased amounts of immunoreactive PTHrP. Northern blot analysis also demonstrated increased levels of PTHrP mRNA transcripts in oncogene-transfected stable cell lines. No significant change in the half-life of PTHrP mRNA transcripts was detected in Ha-ras- and v-src-transformed cells. In contrast, nuclear run-on assays demonstrated an increased rate of PTHrP gene transcription in oncogene-transformed cells. These observations demonstrate that the gene encoding PTHrP is a downstream target for ras and src, potentially providing a molecular basis for understanding the activation of PTHrP gene expression in malignancy-associated hypercalcemia.