Previously, we showed that exposure of human osteoblasts to titanium particles stimulates protein tyrosine phosphorylation (PTP), activates the transcription factor nuclear factor κB (NF-κB), and causes an approximately 50% decrease in the steady-state messenger RNA (mRNA) level of procollagen α1[I]. In this study, we identify three NF-κB binding sites within the human procollagen α1[I] gene promoter, show that titanium particles stimulate their binding of the NF-κB subunits Rel A (p65) and NF-κB1 (p50), and find NF-κB activation correlates with collagen gene suppression by titanium particles in osteoblasts. Protein tyrosine kinase (PTK) inhibitors, which significantly reduce the suppressive effect of titanium particles on collagen gene expression, inhibited NF-κB binding activity showing that titanium particle stimulation of PTK signals in osteoblasts are critical for both NF-κB activation and collagen gene expression. The antioxidant pyrrolidine dithiocarbamate (PDTC), which also inhibits the titanium particle suppression of collagen, abrogated the titanium particle activation of NF-κB, suggesting the involvement of redox signals in NF-κB-mediated collagen gene expression. The RNA polymerase II inhibitor actinomycin D (Act D) decreased procollagen α1[I] mRNA expression and effectively blocked the titanium-induced suppressive effect, suggesting that titanium particles activate a cascade of signals in osteoblasts, which result in a suppression of procollagen α1[I] mRNA. Collectively, these results show that titanium particles can activate NF-κB signaling in osteoblasts and suggest that NF-κB binding to the collagen gene promoter has a functional role in the down-regulation of procollagen α1[I] gene transcription.
- Nuclear factor κB
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Orthopedics and Sports Medicine