IGF2 DMR0 Methylation, Loss of Imprinting, and Patient Prognosis in Esophageal Squamous Cell Carcinoma

Abstract

Insulin like growth factor 2 gene (IGF2) is normally imprinted. Loss of imprinting (LOI) of IGF2 in humans is associated with an increased risk of cancer and is controlled by CpG-rich regions known as differentially methylated regions (DMRs). Specifically, the methylation level at IGF2 DMR0 is correlated with IGF2 LOI and is a suggested surrogate marker for IGF2 LOI. A relationship between IGF2 DMR0 hypomethylation and poor prognosis has been shown in colorectal cancer. However, to our knowledge, no study has examined the relationships among the IGF2 DMR0 methylation level, LOI, and clinical outcome in esophageal squamous cell carcinoma (ESCC). The IGF2 imprinting status was screened using ApaI polymorphism, and IGF2 protein expression was evaluated by immunohistochemistry with 30 ESCC tissue specimens. For survival analysis, IGF2 DMR0 methylation was measured using a bisulfite pyrosequencing assay with 216 ESCC tissue specimens. Twelve (40 %) of 30 cases were informative (i.e., heterozygous for ApaI), and 5 (42 %) of 12 informative cases displayed IGF2 LOI. IGF2 LOI cases exhibited lower DMR0 methylation levels (mean 23 %) than IGF2 non-LOI cases (37 %). The IGF2 DMR0 methylation level was significantly associated with IGF2 protein expression. Among 202 patients eligible for survival analysis, IGF2 DMR0 hypomethylation was significantly associated with higher cancer-specific mortality. The IGF2 DMR0 methylation level in ESCC was associated with IGF2 LOI and IGF2 protein expression. In addition, IGF2 DMR0 hypomethylation was associated with a shorter survival time, suggesting its potential role as a prognostic biomarker.