Tumor suppressive role of the antimicrobial lectin REG3A targeting the O-GlcNAc glycosylation pathway.

Abstract

Antimicrobial proteins of the REG3 family provide a first line of protection against infections and transformed cells. Their expression is inducible by inflammation, which makes their role in cancer biology less clear, since an immune- inflammatory context may preexist or coexist with cancer, as occurs in hepatocellular carcinoma (HCC). The aim of this study is to clarify the role of REG3A in liver carcinogenesis and to determine whether carbohydrate-binding functions are involved. This study provides evidence of the suppressive role of REG3A in HCC by reducing O-GlcNAcylation in two mouse models of HCC, in vitro cell studies, and in clinical samples. REG3A expression in hepatocytes significantly reduces global O- GlcNAcylation and O-GlcNAcylation of c-MYC in preneoplastic and tumor livers and markedly inhibits HCC development in REG3A-c-MYC double transgenic mice and in mice exposed to diethylnitrosamine (DEN). REG3A modifies O-GlcNAcylation without altering the expression or activity of OGT, OGA, or GFAT. Reduced O-GlcNAcylation was consistent with decreased levels of UDP-GlcNAc in pre-cancerous and cancerous livers. This effect is linked to the ability of REG3A to bind Glc and Glc-6P, suggested by a REG3A mutant unable to bind Glc and Glc- 6P and alter O-GlcNAcylation. Importantly, cirrhotic patients with high hepatic REG3A expression had lower levels of O-GlcNAcylation and longer cancer-free survival than REG3A- negative cirrhotic livers. REG3A helps fight liver cancer by reducing O-GlcNAcylation. This study suggests a new paradigm for the regulation of O-GlcNAc signalling in cancer-related pathways through interactions with the carbohydrate-binding function of REG3A.