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Interleukin-1 modulates phosphorylation of proteins in human osteoblastic cells
Y M Kang1, Y L Yeh, D T Graves
1Department of Oral Biology, Boston University School of Graduate Dentistry, Massachusetts, USA.
Abstract:
Interleukin-1 (IL-1) is a potent bone resorbing cytokine with diverse biological effects. We previously reported that IL-1 inhibits PDGF-AA-induced biological activities including PDGF-AA-induced tyrosyl phosphorylation. In the present studies, we first investigated and compared the tyrosyl phosphorylation pattern induced by EGF, IGF-1, PDGF-AA, and bFGF in human osteoblastic cells. We then examined the effect of IL-1 on the tyrosyl phosphoproteins induced by each ligand. Immunoblot analyses show that EGF, IGF-1, and PDGF-AA each elicit a different pattern of tyrosyl phosphorylated proteins in normal human osteoblastic cells. IL-1 beta inhibits PDGF-AA induced autophosphorylation by down-regulation of the PDGF-alpha receptor, as demonstrated by immunoprecipitation experiments. For other ligand-induced tyrosyl phosphoproteins, IL-1 beta reduced the intensity of EGF-induced pp55,000, and IGF-1 induced pp185,000 and pp175,000. These experiments indicate that IL-1 inhibits phosphorylation of specific proteins induced by growth factors. By using inhibitors of secondary message pathways, we determined that the inhibitory effect of IL-1 beta on PDGF-AA receptor binding and receptor tyrosyl autophosphorylation was not dependent on protein kinase A, protein kinase C, or the formation of prostaglandins. These data suggest the existence of an alternative pathway that may participate in IL-1 beta signaling.
Insights
Interleukin-1 (IL-1) inhibits specific growth factor-induced protein phosphorylation in human osteoblastic cells. This cytokine impacts signaling pathways, suggesting alternative mechanisms for IL-1 beta
Area of Science:
- Cellular Biology
- Molecular Biology
- Biochemistry
Background:
- Interleukin-1 (IL-1) is a key cytokine involved in bone resorption and cellular signaling.
- Previous research indicated IL-1's inhibitory effect on platelet-derived growth factor (PDGF)-AA-induced activities, including tyrosyl phosphorylation.
- Understanding IL-1's role in osteoblastic cells is crucial for bone biology research.
Purpose of the Study:
- To compare tyrosyl phosphorylation patterns induced by epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), PDGF-AA, and basic fibroblast growth factor (bFGF) in human osteoblastic cells.
- To investigate the inhibitory effects of IL-1 on ligand-induced tyrosyl phosphoproteins.
- To elucidate the signaling pathways involved in IL-1's inhibitory actions.
Main Methods:
- Immunoblot analysis to compare tyrosyl phosphorylation patterns induced by various growth factors.
- Immunoprecipitation experiments to assess PDGF-alpha receptor regulation by IL-1 beta.
- Utilizing inhibitors of secondary messenger pathways (protein kinase A, protein kinase C, prostaglandins) to analyze IL-1 beta's inhibitory mechanism.
Main Results:
- EGF, IGF-1, and PDGF-AA induced distinct tyrosyl phosphorylation profiles in osteoblastic cells.
- IL-1 beta significantly inhibited PDGF-AA-induced autophosphorylation by down-regulating the PDGF-alpha receptor.
- IL-1 beta reduced the intensity of specific phosphoproteins induced by EGF and IGF-1, including pp55,000, pp185,000, and pp175,000.
- The inhibitory effect of IL-1 beta on PDGF-AA signaling was independent of protein kinase A, protein kinase C, and prostaglandin formation.
Conclusions:
- IL-1 exerts specific inhibitory effects on growth factor-induced protein phosphorylation in human osteoblastic cells.
- IL-1 beta down-regulates the PDGF-alpha receptor, impacting PDGF-AA signaling.
- The findings suggest that IL-1 beta may utilize alternative signaling pathways to mediate its effects on osteoblastic cells.