**4. Regulation expression of NK cell receptors and their ligands as potential therapeutics for cancer**

The mechanisms of regulation the gene expression, which requires signalling cascades for transducing and integrating regulatory cues to determine which genes are expressed, are obligatory for tumorigenesis, tumor progression and metastasis (Bhalla, 2005; Samarakoon et al., 2009; Stein et al., 2010). Transcriptional gene regulations, particularly in transcriptional factors and epigenetic level, affect several aspects of tumor cell biology, including cell growth, proliferation, phenotype, differentiation, DNA repair, and cell death. NK cells are the major effector lymphocytes of innate immune system that defend against many forms of viral infections and tumor growth without prior sensitizations, by the interaction of inhibitory and activating receptors with corresponding ligands on the target cells. This raises the strong possibility that regulation expression of NK cell receptors on NK cells and their ligands on tumor cells may be an effective treatment strategy for malignant tumors. This treatment strategy, as mentioned above, including activation and suppression of the transcription factors and promoter activity, modification the DNA methylation in the underlying DNA code, and rearrangement the acetylation and methylation of protein in histone posttranslational level, leads to the induced or suppressed expression of NK cells

Transcription Regulation and Epigenetic

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autoimmune diseases.

**6. Acknowledgment** 

**7. References** 

Control of Expression of Natural Killer Cell Receptors and Their Ligands 437

CD84, and NTB-A) (Sidorenko and Clark, 2003; Engel et al., 2003; Morra et al., 2001), are not well understood. More research is needed into other regulated stages of gene expression, such as posttranscriptional modification, RNA transport, translation, and mRNA degradation. Investigation of the regulatory mechanisms of NK-cell receptors and their ligands might aid in the design of therapy against cancer, infection, inflammation, or

This work was supported by grants from the Natural Science Foundation of China (No. 90713033), the National 973 Basic Science Program of China (No. 2007CB815800) and the Important National Science & Technology Specific Projects of China (No. 2008ZX10002-008).

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Fig. 1. Transcription regulation and epigenetic control of KIR and NKG2 receptors and their ligands. A dendrogram representing the relatedness of different KIR and NKG2 receptors (blue) and their ligands (green) to each other, and the extent of the sequence relatedness between two genes is shown by the distance of the lines (Raulet, 2003). The left oval shows the gene regulation in transcription factor level, while the right oval shows the gene regulation in epigenetic level, and the overlapping part shows the co-regulation.
