Epigenetic activation of the TUSC3 gene as a potential therapy for XMEN disease

Abstract

"X-linked MAGT1 deficiency with increased susceptibility to EBV infection and N-linked glycosylation defect" (XMEN) disease is a rare combined immunodeficiency (CID) caused by loss of function mutations in the magnesium transporter 1 (MAGT1) gene. MAGT1 deficiency impairs magnesium transport and the N-glycosylation of a panel of proteins, which subsequently abolishes the expression of key immune receptors such as Natural-Killer Group 2, member D (NKG2D). These effects induce immune system abnormalities, chronic EBV infection and neoplasia. Recent research shows that MAGT1 and tumor candidate suppressor 3 (TUSC3) share high sequence and functional similarity. We sought to investigate the feasibility of activating TUSC3 expression to provide a potential therapeutic strategy for XMEN disease. The expression profiles of MAGT1 and TUSC3 were analyzed using multiple databases, RT‒PCR, and western blot. The effects of decitabine and panobinostat on the regulation of TUSC3 expression were explored in both MAGT1 knock-out (KO)/patient-derived lymphocytes and MAGT1 KO hepatocytes. Although TUSC3 is widely expressed, it is undetectable specifically in the immune system and liver, consistent with the main diseased tissues in XMEN patients. CRISPR/Cas9-mediated KO of MAGT1 in the NKL cell line successfully mimicked the phenotypes of XMEN patient-derived lymphocytes, and exogenous expression of TUSC3 rescued the deficiencies in KO NKL cells. Using this in vitro model, we identified two epigenetic drugs, decitabine and panobinostat, by screening. Combination treatment using these two drugs significantly upregulated TUSC3 expression and rescued the immune and liver abnormalities. Epigenetic activation of TUSC3 expression constitutes an effective therapeutic strategy for XMEN disease.