Induction of Interleukin-8 Synthesis Integrates Effects on Transcription and mRNA Degradation from at Least Three Different Cytokine- or Stress-Activated Signal Transduction Pathways

Abstract

A hallmark of inflammation is the burst-like formation of certain proteins, initiated by cellular stress and proinflammatory cytokines like interleukin 1 (IL-1) and tumor necrosis factor, stimuli which simultaneously activate different mitogen-activated protein (MAP) kinases and NF-κB. Cooperation of these signaling pathways to induce formation of IL-8, a prototype chemokine which causes leukocyte migration and activation, was investigated by expressing active and inactive forms of protein kinases. Constitutively active MAP kinase kinase 7 (MKK7), an activator of the stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) pathway, induced IL-8 synthesis and transcription from a minimal IL-8 promoter. Furthermore, MKK7 synergized in both effects with NF-κB-inducing kinase (NIK). Activation of the IL-8 promoter by either of the kinases required functional NF-κB and AP-1 sites. While NIK and MKK7 did not affect degradation of IL-8 mRNA, an active form of MKK6, which selectively activates p38 MAP kinase, induced marked stabilization of the transcript and further increased IL-8 protein formation induced by NIK plus MKK7. Consistently, the MAP kinase kinase kinase MEKK1, which can activate NF-κB, SAPK/JNK, and p38 MAP kinases, most potently induced IL-8 formation. These results provide evidence that maximal IL-8 gene expression requires the coordinate action of at least three different signal transduction pathways which cooperate to induce mRNA synthesis and suppress mRNA degradation.

ACKNOWLEDGMENTS

This work was supported by grants Kr1143/2-1, SFB 244/B15, and SFB 244/B18 from the Deutsche Forschungsgemeinschaft to H.H. and M.K.

We thank Hermann Bujard for providing plasmids pUHD10-3 and pUHC13-3 and HeLa cells expressing the tet transactivator protein, J. R. Woodgett for his gift of expression plasmid for GST-Jun, and Jeremy Saklatvala for providing antiserum SAK14 against NIK and for helpful discussions. We gratefully acknowledge the skillful technical assistance of Birgit Ritter.