PTH1R-CaSR Cross Talk: New Treatment Options for Breast Cancer Osteolytic Bone Metastases

Table 1

Similarity and difference between PTH and PTHrP.

	PTH	PTHrP
Production	Parathyroid glands	All cells especially tumor cells including breast cancer cells
Protein size	84 amino acids	PTHrP is comprised of 139, 141, or 173 amino acids
Action mechanism	Acts as an endocrine factor	Acts as an endocrine, paracrine, autocrine, or intracrine factor
Binding to receptor	Binding to both PTH1R and PTH2R	Only binding to PTH1R
Nuclear localization sequence	No	Yes, increase of tumor proliferation
Promotion of bone resorption	Yes	Yes
Increase of renal tubular reabsorption of calcium	Yes	Yes
1-α-Hydroxylase	Activates its activity to form 1,25 dihydroxy-vitamin D and then promotes calcium absorption in the intestine	No
Hyperparathyroidism	Primary and secondary hyperparathyroidism	No
Humoral hypercalcemia of malignancy	No, except parathyroid carcinoma	Yes