Promoter hypermethylation regulates vitamin D receptor (VDR) expression in colorectal cancer-A study from Kashmir valley

Background: Colorectal carcinogenesis (CRC) is a multistep process, involving both genetic and epigenetic modifications of genes involved in diverse pathways ranging from tumor suppression to DNA mismatch repair.

Purpose: This study was undertaken to assess the role of promoter methylation of vitamin D receptor (VDR) gene, a transcription factor with myriad biological functions, in relation to its expression and clinicopathological parameters.

Methods: Tissue specimens were taken from a total of 75 colorectal cancer cases paired with their normal surrounding epithelium and analyzed by Real-time RT-PCR for assessing the expression profile and MS-PCR for analyzing the promoter methylation status of the VDR gene. Blood sample from the same patients was drawn for vitamin D estimation.

Results: The frequency of promoter methylation in cancerous tissue was 37.33% against 9.33% in normal tissues (p<0.001). The hypermethylated status of VDR promoter showed significantly inverse association with its expression (p=0.008). Furthermore, when compared with the clinical parameters, methylation status of VDR promoter was significantly associated with tumor staging (p=0.008), grading (p<0.001), depth of invasion (p=0.002) and lymph node metastases (p<0.001). Univariate and multivariate analysis indicated patients with increased VDR expression (p<0.001) and decreased methylation status (p=0.012) exhibited longer overall survival. Additionally, serum 25(OH)D₃ levels were not significantly associated with any of the patient characteristics.

Conclusion: Our study, first of its kind from Kashmir, indicated that VDR shows aberrant methylation pattern in CRC with consequent loss in its expression.