Aberrant methylation and loss expression of RKIP is associated with tumor progression and poor prognosis in gastric cardia adenocarcinoma

Raf kinase inhibitory protein (RKIP) has been identified as a member of a novel class of molecules which implicated in cancer progression and suppress the metastatic spread of tumors. The aim of this study was to investigate the promoter methylation and expression of RKIP, determine the prognostic significance of RKIP in gastric cardia adenocarcinoma (GCA). MSP approach and immunohistochemistry methods were used respectively to examine methylation status and protein expression of RKIP in GCA tissues. The frequency of RKIP methylation in GCA tumor tissues (62.1 %) was significantly higher than that in corresponding normal tissues (4.1 %) and was associated with TNM stage, histological differentiation, depth of invasion, LN metastasis, distant metastasis or recurrence, and upper gastrointestinal cancers (UGIC) family history. Positive staining of RKIP in GCA tumor tissues (34.5 %) was significantly decreased than that in corresponding normal tissues (84.1 %) and was associated with RKIP methylation. RKIP may act as a tumor suppressor gene in GCA by regulation of the Raf-1/MEK/ERK signaling pathway. GCA patients in stage III and IV, with positive UGIC family history, and hypermethylation and down-expression of RKIP were most likely to develop metastatic disease and also showed the worse survival. RKIP methylation in GCA was an independent prognostic marker for survival using multivariate Cox regression analysis (P = 0.04). In all, aberrant hypermethylation of RKIP may be one of the mechanisms that lead to loss or down expression of the gene in GCA especially in individuals with UGIC family history. Additionally, hypermethylation and loss of RKIP expression may be used as a marker to predict clinical outcome of GCA.