The Parathyroid Hormone-Related Protein as a Regulator of Normal Tissue Functions

The parathyroid hormone-related protein (PTHrP) was initially identified as a factor secreted by cancer cells causing hypercalcemia in malignant tumors. However, research revealed its physiological roles, including regulating chondrogenesis and cartilage mineralization, with its gene deletion being embryonically lethal in homozygotes. PTHrP was expressed in lactating mammary tissue, secreted into milk, and involved in hair follicle function and epidermal keratinocyte differentiation in the skin. It also acted as a local regulator of smooth muscle tone and was proposed to regulate parturition and placental calcium transport. Evidence suggested additional PTHrP receptors beyond the classic parathyroid hormone receptor.