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Promoter region CpG island methylation status and protein levels of NDRG1 and NDRG2 in laryngeal squamous cell carcinoma
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Abstract:
Objective: To investigate the promoter region CpG island methylation status and protein levels of NDRG1 and NDRG2 in laryngeal carcinoma. Methods: Larynx tumor tissue ( n =45) and normal lung tissue ( n =18) specimens were collected from 45 patients with laryngeal squamous cell carcinoma (LSCC) who underwent surgery in the Department of Head and Neck Surgery, the Fourth Hospital of Hebei Medical University between January, 2010 and December, 2011. The promoter CpG island methylation status and protein levels of NDRG1 and NDRG2 in the collected specimens were quantified by methylation specific polymerase chain reaction and immunohistochemistry, respectively. Results: The methylation level of promoter CpG island was significantly higher in LSCC tissue and in normal larynx tissue for both NDRG1 (66.7% vs 33.3%, P <0.05) and NDRG2 (53.3% vs 22.2%, P <0.05) genes. The proportion of NDRG1 and NDRG2 promoter methylation in LSCC tissue specimens was associated with lymph node metastasis and clinical stage ( P <0.05), but neither with pathological grade and clinical classification of the lesion nor with smoking history, age and sex ( P >0.05). NDRG1 protein was detected in 37.8% (17/45) of LSCC specimens and in 88.9% (16/18) of normal tissue specimens ( P <0.01) and NDRG2 protein in 33.3% (15/45) of LSCC specimens and in 83.3% (15/18) of normal larynx tissue specimens ( P <0.01). Like promoter methylation status, NDRG1 and NDRG2 protein levels in LSCC tissue were associated with lymph node metastasis and clinical stage ( P <0.05), but not with pathological grading and clinical classification of the lesions, smoking history, age and sex ( P >0.05). CpG island methylation in the promoter region was negatively correlated with protein expression for both NDRG1 ( r 1＝-0.713, P <0.01) and NDRG2 ( r 2＝-0.472 , P <0.01) genes. Conclusion: Both NDRG1 and NDRG2 promoters are hypermethylated, resulting in decreased NDRG1 and NDRG2 protein expression, in LSCC tissue. This observation suggests that anti-methylation of CpG island in the promoter region of the NDRG1 and NDRG2 genes may offer a novel therapeutic strategy for LSCC.
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