p16INK4a hypermethylation and p53, p16 and MDM2 protein expression in Esophageal Squamous Cell Carcinoma

Cancerous tissues and the adjacent normal tissue obtained from 50 ESCC patients were assessed with Methylation-Specific-PCR to examine the methylation status of p16. The expression of p16, p53 and MDM2 proteins was detected by immunohistochemical staining.Abnormal expression of p16 and p53, but not MDM2, was significantly higher in the tumoral tissue. p53 was concomitantly accumulated in ESCC tumor along with MDM2 overexpression and p16 negative expression. Aberrant methylation of the p16INK4a gene was detected in 31/50 (62%) of esophageal tumor samples, while two of the adjacent normal mucosa were methylated (P < 0.001). p16INK4a aberrant methylation was significantly associated with decreased p16 protein expression (P = 0.033), as well as the overexpression of p53 (P = 0.020).p16 hypermethylation is the principal mechanism of p16 protein underexpression and plays an important role in ESCC development. It is associated with p53 protein overexpression and may influence the accumulation of abnormally expressed proteins in p53-MDM2 and p16-Rb pathways, suggesting a possible cross-talk of the involved pathways in ESCC development.Esophageal cancer is the fifth leading cause of cancer-related deaths in Iran [1]. It is also considered the second most common type of cancer in both males and females in Golestan province of northeastern Iran (Age Standardized Rate: 22.57 in males and 19.89 in females in 105 persons/year) (unpublished data). This region is located in the "Esophageal Cancer Belt," stretching from China westward through central Asia to northern Iran, where there is a high incidence of Esophageal Squamous Cell Carcinoma (ESCC)[2,3]. Although several environmental risk factors are proposed for ESCC, the specific underlying genetic alterations have not been well defined for this region to date [3,4].Several genetic and epigenetic alterations are involved in esophageal carcinogenesis [5-7]. Investigation of alterations in oncogenes and tumor suppressor genes impli