The intracellular pyrimidine 5'-nucleotidase NT5C3A is a negative epigenetic factor in interferon and cytokine signaling.

The enzyme pyrimidine 5'-nucleotidase (NT5C3A), which mediates nucleotide catabolism, was previously thought to be restricted to blood cells. We showed that expression of the gene encoding NT5C3A was induced by type I interferons (IFNs) in multiple cell types and that NT5C3A suppressed cytokine production through inhibition of the nuclear factor κB (NF-κB) pathway. NT5C3A expression required both an intronic IFN-stimulated response element and the IFN-stimulated transcription factor IRF1. Overexpression of NT5C3A, but not of its catalytic mutants, suppressed IL-8 production by HEK293 cells. Whereas knockdown of NT5C3A enhanced tumor necrosis factor (TNF)-stimulated IL-8 production, it reduced the IFN-mediated suppression of Il8 expression. Overexpression of NT5C3A increased the abundance of NAD+ and the activation of the sirtuins SIRT1 and SIRT6, which are NAD+-dependent deacetylases. NT5C3A-stimulated sirtuin activity resulted in deacetylation of histone H3 and the NF-κB subunit RelA (also known as p65), both of which were associated with the proximal region of the Il8 promoter, thus repressing the transcription of Il8 Together, these data identify an anti-inflammatory pathway that depends on the catalytic activity of NT5C3A and functions as a negative feedback regulator of inflammatory cytokine signaling.