Endocrinology, Vol 126, 1783-1785, Copyright © 1990 by Endocrine Society

ARTICLES

The parathyroid hormone-related protein stimulates human osteoblast- like cells to secrete a 9,000 dalton bone-resorbing protein

CA Morris, ME Mitnick, EC Weir, M Horowitz, BL Kreider and KL Insogna
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510.

The mechanism by which parathyroid hormone-related protein (PTH-RP) stimulates bone resorption is not known. Like certain other resorbing agents it may act to release bone-resorbing cytokines from the osteoblast. To examine this hypothesis, we used serum-free conditioned media (CM) from SAOS II cells incubated with 10(-8) M h(1-74) PTH-RP for 48 h. Treated CM contained substantially more bone-resorbing activity (BRA) in the fetal-rat long-bone assay than CM from untreated cells (2.17 +/- 0.21 vs 1.38 +/- 0.16 fold stimulation over basal [f]; p less than 0.05]. After centrifugation and dialysis, 1 liter of treated CM contained a total BRA of 7102 ngeq b(1-34) PTH with a specific activity (SA) of 447 ngeq b(1-34) PTH/mg protein. Treated CM did not stimulate the ROS assay and the cytokines PGE2, TGF-alpha, EGF, GM-CSF and IL-1 were present in low concentrations. The BRA was heat sensitive. Ultrafiltration revealed that 97% of the BRA was in a 3-30 kD fraction. Further purification was achieved by sequential reverse phase HPLC and size exclusion-HPLC (SE-HPLC). A single fraction containing BRA from SE-HPLC was purified 277-fold to a SA of 123,810 ngeq b(1-34) PTH/mg protein and had an apparent MW of 9 kD. SDS-PAGE revealed 4 bands in this SE-HPLC fraction with 1 band at 9 kD unique to that fraction. PTH-RP may cause bone resorption in part by stimulating the release of a 9 kD protein from osteoblasts which is responsible for activating osteoclasts.

This article has been cited by other articles:

				K. Fuller, B. Wong, S. Fox, Y. Choi, and T. J. Chambers TRANCE Is Necessary and Sufficient for Osteoblast-mediated Activation of Bone Resorption in Osteoclasts J. Exp. Med., September 7, 1998; 188(5): 997 - 1001. [Abstract] [Full Text] [PDF]

				H. Fleisch Bisphosphonates: Mechanisms of Action Endocr. Rev., February 1, 1998; 19(1): 80 - 100. [Abstract] [Full Text]

				B. h. Sun, M. Mitnick, C. Eielson, G. Q. Yao, I. Paliwal, and K. Insogna Parathyroid Hormone Increases Circulating Levels of Fibronectin in Vivo: Modulating Effect of Ovariectomy Endocrinology, September 1, 1997; 138(9): 3918 - 3924. [Abstract] [Full Text] [PDF]

				I. A. Nakchbandi, E. E. Weir, K. L. Insogna, W. M. Philbrick, and A. E. Broadus Parathyroid hormone-related protein induces spontaneous osteoclast formation via a paracrine cascade PNAS, June 20, 2000; 97(13): 7296 - 7300. [Abstract] [Full Text] [PDF]