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. Author manuscript; available in PMC: 2015 Jan 27.
Published in final edited form as: Clin Chest Med. 2008 Mar;29(1):1–v. doi: 10.1016/j.ccm.2007.12.001

Figure 5.

Figure 5

The effect of hypermethylation of tumor-suppressor gene promoters. CpG islands are regions of the gene rich in cytosine-guanine dinucleotides. Most CpG islands are found in the proximal promoter region of nearly half of all genes in the mammalian genome and are normally unmethylated. In the human genome, methylation (Me) occurs only at CpG islands. Hypermethylation of the promoter regions of tumor suppressor genes occurs early in the development of lung cancer and silences the transcription of the gene. Silencing by hypermethylation affects genes involved in all aspects of normal cell function and is a critical trigger for malignant transformation and cancer progression.