The copper-sensing transcription factor Mac1, the histone deacetylase Hst1, and nicotinic acid regulate de novo NAD+ biosynthesis in budding yeast

Abstract

) is an essential metabolite involved in various cellular biochemical processes. The regulation of NAD metabolism is incompletely understood. Here, using budding yeast (Saccharomyces cerevisiae), we established an NAD intermediate-specific genetic system to identify factors that regulate the de novo branch of NAD biosynthesis. We found that a mutant strain (mac1) lacking Mac1, a copper-sensing transcription factor that activates copper transport genes during copper deprivation, exhibits increases in quinolinic acid (QA) production and NAD levels. Similar phenotypes were also observed in the hst1 strain, deficient in the NAD -dependent histone deacetylase Hst1, which inhibits de novo NAD synthesis by repressing BNA gene expression when NAD is abundant. Interestingly, the mac1 and hst1 mutants shared a similar NAD metabolism-related gene expression profile, and deleting either MAC1 or HST1 de-repressed the BNA genes. ChIP experiments with the BNA2 promoter indicated that Mac1 works with Hst1-containing repressor complexes to silence BNA expression. The connection of Mac1 and BNA expression suggested that copper stress affects de novo NAD synthesis, and we show that copper stress induces both BNA expression and QA production. Moreover, nicotinic acid inhibited de novo NAD synthesis through Hst1-mediated BNA repression, hindered the reuptake of extracellular QA, and thereby reduced de novo NAD synthesis. In summary, we have identified and characterized novel NAD homeostasis factors. These findings will expand our understanding of the molecular basis and regulation of NAD metabolism.