Humoral hypercalcemia of malignancy

Area of Science:

• Endocrinology
• Oncology
• Biochemistry

Background:

• Humoral hypercalcemia of malignancy is linked to tumor-produced proteins acting on the parathyroid hormone (PTH) receptor.
• These proteins are immunologically distinct from PTH.

Purpose of the Study:

• To purify and clone the parathyroid hormone-related protein (PTHrP) from a human lung cancer cell line.
• To characterize the biological activity and tissue distribution of PTHrP.

Main Methods:

• Purification and cloning of PTHrP from a human lung cancer cell line.
• Synthesis of a PTHrP(1-34) peptide for bioassays.
• Immunohistochemistry to determine PTHrP tissue distribution.
• Extraction of PTHrP-like activity from ovine placenta and fetal parathyroid tissue.

Main Results:

• Isolated cDNA clones encoding a prepropeptide and a mature 141-amino acid PTHrP.
• PTHrP shares amino-terminal homology with PTH but is immunologically distinct.
• PTHrP(1-34) demonstrated significantly higher potency than PTH(1-34) in stimulating cAMP, plasminogen activity, and adenylate cyclase activation.
• PTHrP(1-34) was more potent in stimulating cAMP and phosphate excretion and reducing calcium excretion in rats.
• PTHrP was detected in squamous cell carcinomas and normal skin keratinocytes, but not in parathyroid tissues or other tumors.
• PTHrP-like activity was found in ovine placenta and fetal parathyroid tissue.

Conclusions:

• PTHrP is a key mediator of humoral hypercalcemia of malignancy.
• PTHrP exhibits distinct biological activities and tissue expression patterns compared to PTH.
• PTHrP may have a physiological role in fetal calcium homeostasis.