Endocrinology, Vol 136, 3260-3266, Copyright © 1995 by Endocrine Society

ARTICLES

Down-regulation of the receptor for parathyroid hormone (PTH) and PTH- related peptide by transforming growth factor-beta in primary fetal rat osteoblasts

JW Jongen, EC Willemstein-Van Hove, JM Van der Meer, MP Bos, H Juppner, GV Segre, AB Abou-Samra, JH Feyen and MP Herrmann-Erlee
Laboratory of Cell Biology and Histology, University of Leiden, The Netherlands.

We studied the effects of transforming growth factor-beta 2 (TGF beta 2) on the level of PTH/PTH-related peptide-(PTHrP) receptor messenger RNA (mRNA), PTHrP binding, and PTH-stimulated cAMP accumulation in cultured osteoblasts derived from fetal rat calvariae (ROB). When ROB were pretreated with TGF beta 2 at concentrations ranging from 1-100 pM for 24 h, dose-dependent decreases in the level of PTH/PTHrP receptor mRNA, PTHrP binding, and PTH-stimulated cAMP accumulation were observed. For the PTH/PTHrP receptor mRNA level and PTH-stimulated cAMP accumulation, the half-maximal effective concentration was approximately 4 pM. For the inhibition of PTHrP binding, the half- maximal effective concentration was much higher. A 50% decrease in both PTH/PTHrP receptor mRNA level and PTH-stimulated cAMP accumulation was obtained when ROB were treated with 100 pM TGF beta 2 for 4 h. A comparable decrease in PTHrP binding was only observed after 24 h of incubation with 100 pM TGF beta 2. Actinomycin D induced a rapid decrease in the PTH/PTHrP receptor mRNA level (70% after 4 h), indicating a half-life for the receptor mRNA of 2-3 h. Under the same conditions, PTHrP binding and PTH-stimulated cAMP accumulation did not change. When ROB were treated with cycloheximide for the same period, only a small decrease in PTHrP binding (20%) was observed, suggesting that PTH/PTHrP receptors do not have a rapid turnover. Cycloheximide also reduced PTH-stimulated cAMP production; after coincubation of cycloheximide with TGF beta 2, this inhibition was smaller than that in ROB cultures treated with TGF beta 2 exclusively. From these observations we conclude that TGF beta 2 induces a decrease in steady state levels of PTH/PTHrP receptor mRNA that results in decreased PTHrP receptor binding. The PTH-stimulated cAMP accumulation is at least to some extent independent of the PTH/PTHrP receptor availability. Furthermore, there is a high turnover of PTH/PTHrP receptor mRNA, whereas turnover of the receptor protein is much slower. Finally, protein synthesis is required for TGF beta 2-induced desensitization of cAMP responsiveness to PTH.

This article has been cited by other articles:

				S. Yano, T. Yamaguchi, I. Kanazawa, N. Ogawa, K. Hayashi, M. Yamauchi, and T. Sugimoto The uraemic toxin phenylacetic acid inhibits osteoblastic proliferation and differentiation: an implication for the pathogenesis of low turnover bone in chronic renal failure Nephrol. Dial. Transplant., November 1, 2007; 22(11): 3160 - 3165. [Abstract] [Full Text] [PDF]

				B.-Y. Liu, P.-W. Wu, F. R. Bringhurst, and J.-T. Wang Estrogen Inhibition of PTH-Stimulated Osteoclast Formation and Attachment in Vitro: Involvement of Both PKA and PKC Endocrinology, February 1, 2002; 143(2): 627 - 635. [Abstract] [Full Text] [PDF]

				E. A. Gonzalez The role of cytokines in skeletal remodelling: possible consequences for renal osteodystrophy Nephrol. Dial. Transplant., July 1, 2000; 15(7): 945 - 950. [Full Text] [PDF]

				T. Morimoto, J. R. Head, P. C. MacDonald, and M. L. Casey Thrombospondin-1 Expression in Human Myometrium before and during Pregnancy, before and during Labor, and in Human Myometrial Cells in Culture Biol Reprod, October 1, 1998; 59(4): 862 - 870. [Abstract] [Full Text]