Synthesis of a gene encoding parathyroid hormone-like protein-(1-141): purification and biological characterization of the expressed protein.

PTH-like proteins (PTHLP), which are associated with humoral hypercalcemia of malignancy, have recently been purified. Isolation of their corresponding cDNAs has revealed that they are derived from a single gene. In this report a synthetic gene encoding PTHLP-(1-141), a 141-amino acid protein corresponding to the most abundant PTHLP cDNA detected in human tumors, was expressed in bacteria and purified to homogeneity. Recombinant (r) PTHLP-(1-141) migrates with an aberrantly high mol wt on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, presumably as a result of its unusually basic pI. rPTHLP-(1-141), like PTH, induced hypercalcemia in rats, caused release of 45Ca from fetal rat bones, and stimulated the synthesis of cAMP by rat osteosarcoma cells and canine renal membrane preparations. A comparison of the abilities of rPTHLP-(1-141) and bovine PTH-(1-34) to stimulate cAMP synthesis indicated rPTHLP-(1-141) to be 5-fold more potent in the osteosarcoma assay, while nearly 30-fold less active in the renal membrane adenylate cyclase assay. Although 100-fold less potent than bovine PTH-(1-34) in promoting bone resorption, rPTHLP-(1-141) was a potent calcemic factor in vivo, inducing a rise in serum calcium from 10.4 to 14.5 mg/dl when infused into rats at 1.3 micrograms/h. These results support previous assumptions that PTHLP is the humoral factor responsible for humoral hypercalcemia of malignancy. In addition, they suggest substantial differences between PTHLP and PTH in the regulation of calcium homeostasis.