Comparative Analysis of 14-3-3 Isoform Expression and Epigenetic Alterations in Colorectal Cancer

Abstract

The 14-3-3 family is a group of intracellular proteins found in all eukaryotic organisms. Humans have 7 isoforms that serve as scaffolds to promote interactions of regulatory phospho-proteins involved in many vital cellular processes. Previous studies have shown that disturbances in native 14-3-3 levels can contribute significantly to the development of various cancers. Our study aims to establish the normal and cancerous expression levels of all 7 isoforms in human colon adenocarcinomas and correlate 14-3-3 expression changes with epigenetic silencing. 14-3-3 mRNA expression levels were established by qRT-PCR analysis. Here we present statistically significant data showing decreased levels of 14-3-3 sigma, eta, and zeta observed among colon adenocarcinomas compared to normal tissue. These data suggest a link between 14-3-3 protein expression levels and the development of colon cancers. To further explore the mechanisms behind 14-3-3 expression changes, we examined the methylation status of sigma, eta, and zeta isoforms in eight selected samples. Our data identifies novel CpG methylation sites in zeta and eta promoters and suggests an epigenetic mechanism for silencing of 14-3-3 sigma and eta isoforms during colon tumorigenesis. To our knowledge, this is the first study to identify silencing of the 14-3-3 eta gene by DNA methylation.