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Extracellular-regulated kinase 1/2, Jun N-terminal kinase, and c-Jun are involved in NF-kappa B-dependent IL-6
L M Tuyt1, W H Dokter, K Birkenkamp
1Division of Hematology, Department of Medicine, University of Groningen, The Netherlands.
Abstract:
In the present study we investigated the possible involvement of the mitogen-activated protein kinase family members extracellular-regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK) in mediating IL-6 gene expression in human monocytes, in particular their role in enhancing NF-kappa B activity. Freshly isolated monocytes treated with the protein phosphatase inhibitor okadaic acid secreted high levels of IL-6 protein, which coincided with enhanced binding activity of NF-kappa B as well as with phosphorylation and activation of the ERK1/2 and JNK proteins. The ERK pathway-specific inhibitor PD98059 inhibited IL-6 secretion from monocytes. Transient overexpression of inactive mutants of either Raf-1 or JNK1 showed that both pathways were involved in kappa B-dependent IL-6 promoter activity. By using PD98059, we demonstrated that the Raf1/MEK1/ERK1/2 pathway did not affect the DNA binding of NF-kappa B but, rather, acted at the level of transcriptional activity of NF-kappa B. Interestingly, it was shown that NF-kappa B-mediated gene transcription, both in the context of the IL-6 promoter as well as on its own, was dependent on both serine kinase activity and interaction with c-Jun protein. We conclude that okadaic acid-induced IL-6 gene expression is at least partly mediated through the ERK1/2 and JNK pathway-dependent activation of NF-kappa B transcriptional capacity. Our results suggest that the JNK pathway may regulate NF-kappa B-mediated gene transcription through its phosphorylation and activation of c-Jun.
Insights
Mitogen-activated protein kinase pathways, including extracellular-regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK), activate NF-kappa B transcriptional capacity, driving IL-6 gene expression in human monocytes.
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- Interleukin-6 (IL-6) is a key cytokine involved in immune responses and inflammation.
- NF-kappa B is a crucial transcription factor regulating the expression of numerous genes, including IL-6.
- Mitogen-activated protein kinase (MAPK) pathways, such as ERK and JNK, are implicated in cellular signaling.
Purpose of the Study:
- To investigate the role of ERK1/2 and JNK pathways in IL-6 gene expression in human monocytes.
- To elucidate the involvement of these MAPK pathways in modulating NF-kappa B activity.
- To determine the specific mechanisms by which ERK1/2 and JNK influence IL-6 transcription.
Main Methods:
- Human monocytes were treated with okadaic acid to induce IL-6 secretion.
- NF-kappa B binding activity, ERK1/2, and JNK phosphorylation/activation were assessed.
- Specific inhibitors (PD98059) and dominant-negative mutants (Raf-1, JNK1) were used to probe pathway involvement.
- IL-6 promoter activity and NF-kappa B-mediated transcription were analyzed.
Main Results:
- Okadaic acid treatment increased IL-6 secretion, NF-kappa B activity, and ERK1/2/JNK activation.
- Inhibition of the ERK pathway (PD98059) reduced IL-6 secretion.
- Both ERK and JNK pathways were essential for NF-kappa B-dependent IL-6 promoter activity.
- The ERK1/2 pathway enhanced NF-kappa B transcriptional activity, not DNA binding.
- NF-kappa B transcription required serine kinase activity and c-Jun interaction, with JNK potentially phosphorylating c-Jun.
Conclusions:
- Okadaic acid-induced IL-6 expression is partly mediated by ERK1/2 and JNK pathways activating NF-kappa B transcriptional capacity.
- The JNK pathway may regulate NF-kappa B-mediated transcription via c-Jun phosphorylation and activation.
- These findings highlight the intricate crosstalk between MAPK signaling and NF-kappa B in controlling IL-6 production.