Abstract
Parathyroid hormone (PTH)-related protein (PTHrP) seems to affect bone resorption by interaction with bone cytokines, among them interleukin-6 (IL-6). Recent studies suggest that nuclear factor (NF)-kappaB activation has an important role in bone resorption. We assessed whether the N-terminal fragment of PTHrP, and its C-terminal region, unrelated to PTH, can activate NF-kappaB, and its relationship with IL-6 gene induction in different rat and human osteoblastic cell preparations. Here we present molecular data demonstrating that both PTHrP (1-36) and PTHrP (107-139) activate NF-kappaB, leading to an increase in IL-6 mRNA, in these cells. Using anti-p65 and anti-p50 antibodies, we detected the presence of both proteins in the activated NF-kappaB complex. This effect induced by either the N- or C-terminal PTHrP domain in osteoblastic cells appears to occur by different intracellular mechanisms, involving protein kinase A or intracellular Ca(2+)/protein kinase C activation, respectively. However, the effect of each peptide alone did not increase further when added together. Our findings lend support to the hypothesis that the C-terminal domain of PTHrP, in a manner similar to its N-terminal fragment, might stimulate bone resorption. These studies also provide further insights into the putative role of PTHrP as a modulator of bone remodeling.
Highlights
Nancy, is produced in a broad spectrum of normal tissues, including bone [1]
Statistical significance was determined by either t test or analysis of variance, when appropriate. Both N- and C-terminal PTHrP Domains Increase IL-6 mRNA through nuclear factor (NF)-B Activation in UMR 106 Cells—We first examined the putative role of nuclear factor B (NF-B) activation on the induction of IL-6 gene expression by N- and C-terminal PTHrP in UMR 106 cells
We found that each peptide, at 100 nM, induced an increase of IL-6 mRNA within 1 h, and this effect was abolished by 25 M pyrrolidinedithiocarbamate and 1 M dexamethasone, two NF-B inhibitors [27, 33], in these cells (Fig. 1)
Summary
Nancy, is produced in a broad spectrum of normal tissues, including bone [1]. PTHrP is emerging as an autocrine/ paracrine regulator of cell growth and differentiation in many of these tissues [1, 2]. This effect induced by either the N- or C-terminal PTHrP domain in osteoblastic cells appears to occur by different intracellular mechanisms, involving protein kinase A or intracellular Ca2؉/protein kinase C activation, respectively.
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