NAD⁺-Dependent Deacetylase Hst1p Controls Biosynthesis and Cellular NAD⁺ Levels in Saccharomyces cerevisiae

Abstract

Nicotine adenine dinucleotide (NAD⁺) performs key roles in electron transport reactions, as a substrate for poly(ADP-ribose) polymerase and NAD⁺-dependent protein deacetylases. In the latter two processes, NAD⁺ is consumed and converted to ADP-ribose and nicotinamide. NAD⁺ levels can be maintained by regeneration of NAD⁺ from nicotinamide via a salvage pathway or by de novo synthesis of NAD⁺ from tryptophan. Both pathways are conserved from yeast to humans. We describe a critical role of the NAD⁺-dependent deacetylase Hst1p as a sensor of NAD⁺ levels and regulator of NAD⁺ biosynthesis. Using transcript arrays, we show that low NAD⁺ states specifically induce the de novo NAD⁺ biosynthesis genes while the genes in the salvage pathway remain unaffected. The NAD⁺-dependent deacetylase activity of Hst1p represses de novo NAD⁺ biosynthesis genes in the absence of new protein synthesis, suggesting a direct effect. The known Hst1p binding partner, Sum1p, is present at promoters of highly inducible NAD⁺ biosynthesis genes. The removal of HST1-mediated repression of the NAD⁺ de novo biosynthesis pathway leads to increased cellular NAD⁺ levels. Transcript array analysis shows that reduction in cellular NAD⁺ levels preferentially affects Hst1p-regulated genes in comparison to genes regulated with other NAD⁺-dependent deacetylases (Sir2p, Hst2p, Hst3p, and Hst4p). In vitro experiments demonstrate that Hst1p has relatively low affinity toward NAD⁺ in comparison to other NAD⁺-dependent enzymes. These findings suggest that Hst1p serves as a cellular NAD⁺ sensor that monitors and regulates cellular NAD⁺ levels.

ACKNOWLEDGMENTS

We are grateful to D. Gottschling, L. Guarente, and J. Rine for plasmids and yeast strains, members of the Gottschling and Simon laboratories for valuable discussions, and E. Foss, D. Gottschling, F. van Leeuwen, and S. Parkhurst for comments on the manuscript.

This work was supported by a National Heart, Lung and Blood Institute grant (HL04211) and Ellison Medical Foundation Award (to A.B.) and a National Cancer Institute grant (CA78746, to J.S.).