LY6G6D is Epigenetically Activated in Classical Colorectal Adenocarcinoma and Hyper-Methylated in Mucinous Subtypes Determining Resistance to FOLFOX Therapeutic Regimens.

Abstract

Background: Colorectal cancer (CRC) represents a significant and ever-increasing societal threat and burden. Activation of Lymphocyte antigen 6G6D could induce anti-tumor specific immunity unique to CRC, but factors regulating its activation remain obscure.Methods: Transcriptome, epigenome and proteomic data from TCGA and independent database were investigated using in silico approaches. Expression of candidate genes was independently validated by immunohistochemistry in CRC tissues. In vitro RNA mediated gene silencing of putative regulators, treatment with MEK and p38 MAPK inhibitors and Bioinformatic prediction were carried out to unveil LY6G6D regulation.Results: LY6G6D is down-regulated in mucinous CRC regardless its anatomic location, while its activation progresses through the classical adenoma-carcinoma sequence. The lack of LY6G6D expression in mucinous CRC involves alterations of secretome-based immune responses. DNA methylation changes in LY6G6D promoter are intimately related to its transcript regulation, epigenomic and different histological subtypes. RNA-mediated gene silencing and chemical inhibition of p38α MAPK as well as DNA methyltransferase DNMT1 knock-down lead to a decrease in LY6G6D expression, supporting that p38a MAPK and DNA methylases mediated LY6G6D regulation. Cancer cells with an intact p38α MAPK stabilize LY6G6D expression allowing effective responses to trametinib, a MEK inhibitor able to exert anti-inflammatory effects. In a metastatic CRC subset, LY6G6D hypermethylation predicts resistance to FOLFOX first-line therapy, supporting the idea that its cancer-specific hypomethylation and consequent activation may be a tissue-specific mechanism of anti-tumor immunity. Conclusions: LY6G6D has the potentiality to be used as a biomarker for patient stratification and immune therapeutic intervention of mucinous versus non-mucinous CRC.