Parathyroid hormone/parathyroid hormone-related protein receptor expression in nude mice with a transplantable canine apocrine adenocarcinoma (CAC-8) and humoral hypercalcaemia of malignancy.

Abstract

The effect of humoral hypercalcaemia of malignancy (HHM) on parathyroid hormone/parathyroid hormone-related protein (PTH/PTHrP) receptor expression was investigated in nude mice with subcutaneous transplantation of an adenocarcinoma line (CAC-8) which produces PTHrP. Serum calcium and PTHrP concentrations were analysed by colorimetric assay and a two-site IRMA respectively. Mice were hypercalcaemic (3.3 +/- 0.1 mmol/l) compared with non-tumour-bearing control mice (2.1 +/- 0.1 mmol/l) and had elevated serum PTHrP concentrations (30.4 +/- 3.4 pmol/l) compared with nontumour-bearing control mice (0.7 +/- 0.1 pmol/l). Lumbar vertebrae were analysed by histomorphometry. Tumour-bearing mice had a significant (P < 0.01) increase in resorptive perimeter, increased numbers of osteoclasts/mm endosteum and increased endosteal bone-forming perimeter. Total RNA was isolated from calvarium, humerus and kidney and analysed for PTH/PTHrP receptor expression by Northern blot analysis. There was no significant difference between PTH/PTHrP receptor mRNA expression in the kidney and humeri of tumour-bearing mice compared with non-tumour control mice, but a significant increase in PTH/PTHrP receptor expression in calvaria. Kidneys and vertebral bodies were stained for PTH/PTHrP receptor protein by immunohistochemistry. Renal proximal tubules (especially the basolateral regions) and endosteal osteoblasts of control and tumour-bearing mice stained positive for PTH/PTHrP receptor. These results demonstrated that HHM induced by increased serum PTHrP concentrations did not result in down-regulation of PTH/PTHrP receptor mRNA or protein expression in vivo.