ABSTRACT
Lung cancer is the leading cause of cancer-related mortality in both men and women worldwide. To identify novel factors that contribute to lung cancer pathogenesis, we analyzed a lung cancer database from The Cancer Genome Atlas and found that Krüppel-like Factor 4 (KLF4) expression is significantly lower in patients' lung cancer tissue than in normal lung tissue. In addition, we identified seven missense mutations in the KLF4 gene. KLF4 is a transcription factor that regulates cell proliferation and differentiation as well as the self-renewal of stem cells. To understand the role of KLF4 in the lung, we generated a tamoxifen-induced Klf4 knockout mouse model. We found that KLF4 inhibits lung cancer cell growth and that depletion of Klf4 altered the differentiation pattern in the developing lung. To understand how KLF4 functions during lung tumorigenesis, we generated the K-ras(LSL-G12D/+);Klf4(fl/fl) mouse model, and we used adenovirus-expressed Cre to induce K-ras activation and Klf4 depletion in the lung. Although Klf4 deletion alone or K-ras mutation alone can trigger lung tumor formation, Klf4 deletion combined with K-ras mutation significantly enhanced lung tumor formation. We also found that Klf4 deletion in conjunction with K-ras activation caused lung inflammation. To understand the mechanism whereby KLF4 is regulated during lung tumorigenesis, we analyzed KLF4 promoter methylation and the profiles of epigenetic factors. We found that Class I histone deacetylases (HDACs) are overexpressed in lung cancer and that HDAC inhibitors induced expression of KLF4 and inhibited proliferation of lung cancer cells, suggesting that KLF4 is probably repressed by histone acetylation and that HDACs are valuable drug targets for lung cancer treatment.
Subject(s)
Kruppel-Like Transcription Factors/physiology , Lung Neoplasms/pathology , Neoplastic Stem Cells/physiology , Proto-Oncogene Proteins p21(ras)/genetics , Animals , Carcinogenesis/pathology , Cell Differentiation , Cell Line, Tumor , Gene Expression Regulation, Neoplastic , Gene Silencing , HEK293 Cells , Histone Deacetylase Inhibitors/pharmacology , Humans , Kruppel-Like Factor 4 , Lung/pathology , Lung Neoplasms/genetics , Lung Neoplasms/metabolism , Mice , Mice, Inbred C57BL , Mice, Transgenic , Mutation, Missense , Promoter Regions, Genetic , Tumor Suppressor Proteins/physiologyABSTRACT
The immunosuppressive activity of interleukin-10 (IL-10) makes this cytokine a potentially important clinical tool to reduce inflammatory responses in various diseases. Its efficacy as a therapeutic modality is dependent on the responsiveness of immune cells. We report that macrophages from mice chronically infected with the LP-BM5 retrovirus had a reduced capacity to respond to IL-10 in vitro. The ability of IL-10 to inhibit lipopolysaccharide-induced production of tumor necrosis factor (TNF) alpha and IL-6 was significantly reduced in both alveolar and peritoneal macrophages from infected versus uninfected mice. IL-10 hyporesponsiveness was not related to direct infection by the retrovirus, because bone marrow-derived macrophages infected in vitro with LP-BM5 were as responsive to IL-10 as were uninfected bone marrow-derived macrophages. TNF-alpha appeared to contribute to development of IL-10 hyporesponsiveness, because exposure of normal macrophages to TNF-alpha but not interferon-gamma reduced macrophage responsiveness to IL-10. Reverse transcriptase-PCR and flow cytometry demonstrated normal expression of the alpha and beta chains of the IL-10 receptor in macrophages from infected mice, suggesting that IL-10 hyporesponsiveness is not related to a change in receptor expression. The potential role of reduced IL-10 responsiveness in the chronicity of inflammation in this and other diseases is discussed.
