Interleukin-8 (IL-8) is an inflammatory chemokine that has a crucial role in cancer progression through its induction of tumor cell proliferation, recruitment and activation of tumor-infiltrating leukocytes, angiogenesis, and metastasis. The expression of IL-8, as well as expression of many other inflammatory cytokines is regulated at the level of transcription by NF?B. However, studies from our laboratory indicate that the transcriptional regulation of IL-8 differs from the regulation of other NF?B-dependent genes. Specifically, we have found that the nuclear I?B? does not inhibit IL-8 expression in stimulated leukocytes, while it inhibits expression of other NF?B-dependent genes. In addition, our recent data show that the proteasome inhibition that is used as an anti-cancer therapy for its ability to inhibit expression of NF?B-dependent genes actually increases IL-8 expression in metastatic prostate and ovarian cancer cells and in human macrophages. However, the responsible mechanisms are largely unknown. The proposed research addresses the lack of knowledge on the regulation of IL-8 transcription by the proteasome inhibition and by nuclear I?B?. Our long-term goal is to understand the transcriptional mechanisms regulating expression of NF?B-responsive genes. The objective of this proposal is to determine how the proteasome and nuclear I?B? regulate transcription of IL-8, and how this regulation differs from other NF?B-dependent genes. The central hypothesis is that S536 p65 phosphorylation, specificity of the DNA sequence of the NF?B binding site, and/or the transcription factor EGR-1 render IL-8 unresponsive to the inhibition by I?B?, and increase IL-8 expression in response to the proteasome inhibition. Based on our preliminary data, the project will test two mutually non-exclusive models.
In Aim 1, we will test the hypothesis that the IL-8 promoter is occupied predominantly by p65 homodimers phosphorylated on S536, and that the proteasome inhibition increases S536 p65 phosphorylation, resulting in the increased IL-8 transcription.
In Aim 2, we will test the hypothesis that the IL-8 promoter sequence and EGR-1 involvement are responsible for the proteasome inhibition increased IL-8 expression and resistance of IL-8 transcription to I?B? inhibition. We will use metastatic prostate cancer PC-3 cells, ovarian cancer OVCAR-3 cells and stimulated U937 macrophages as models in both Aims. Since IL-8 promotes tumor cell growth, angiogenesis, metastasis, as well as activates leukocytes, understanding its regulation by proteasome and nuclear I?B? may have important clinical implications in cancers and inflammatory disorders characterized by excessive IL-8 expression. In addition, this project will enhance the research environment at St. John's University by providing motivated underprivileged students with numerous opportunities to learn the fundamentals of biomedical research.
This proposal has broad and significant relevance to many types of human cancer as well as inflammatory disorders, due to the fundamental role of interleukin-8 in the regulation of cell survival, proliferation and migration. The completion of th proposed experiments would provide a more thorough understanding of the mechanisms regulating expression of interleukin-8 in metastatic prostate and ovarian cancer cells and in human leukocytes. Since interleukin-8 promotes tumor cell growth, angiogenesis, metastasis, as well as activates leukocytes, understanding its regulation may suggest more effective anti-cancer and anti-inflammatory strategies.
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