An NAD⁺-dependent novel transcription factor controls stage conversion in <i>Entamoeba</i>.

Abstract

Developmental switching between life-cycle stages is a common feature among parasitic pathogens to facilitate disease transmission and pathogenesis. The protozoan parasite <i>Entamoeba</i> switches between invasive trophozoites and dormant cysts, but the encystation process remains poorly understood despite being central to amoebic biology. We identify a transcription factor, Encystation Regulatory Motif-Binding Protein (ERM-BP), that regulates encystation. Down-regulation of ERM-BP decreases encystation efficiency resulting in abnormal cysts with defective cyst walls. We demonstrate that direct binding of NAD⁺ to ERM-BP affects ERM-BP conformation and facilitates its binding to promoter DNA. Additionally, cellular NAD⁺ levels increase during encystation and exogenous NAD⁺ enhances encystation consistent with the role of carbon source depletion in triggering <i>Entamoeba</i> encystation. Furthermore, ERM-BP catalyzes conversion of nicotinamide to nicotinic acid, which might have second messenger effects on stage conversion. Our findings link the metabolic cofactors nicotinamide and NAD⁺ to transcriptional regulation via ERM-BP and provide the first mechanistic insights into <i>Entamoeba</i> encystation.