Endogenous Nitrated Nucleotide Is a Key Mediator of Autophagy and Innate Defense against Bacteria

• 8-nitro-cGMP, a nitric oxide downstream mediator, induces autophagy
• Lys63-linked polyubiquitination is essential for 8-nitro-cGMP-induced autophagy
• 8-nitro-cGMP enhances autophagic clearance of intracellular GAS
• 8-nitro-cGMP-modified GAS is selectively ubiquitinated

SummaryAutophagy is a cellular self-catabolic process wherein organelles, macromolecules, and invading microbes are sequestered in autophagosomes that fuse with lysosomes. In this study, we uncover the role of nitric oxide (NO) as a signaling molecule for autophagy induction via its downstream mediator, 8-nitroguanosine 3′,5′-cyclic monophosphate (8-nitro-cGMP). We found that 8-nitro-cGMP-induced autophagy is mediated by Lys63-linked polyubiquitination and that endogenous 8-nitro-cGMP promotes autophagic exclusion of invading group A Streptococcus (GAS) from cells. 8-nitro-cGMP can modify Cys residues by S-guanylation of proteins. We showed that intracellular GAS is modified with S-guanylation extensively in autophagosomes-like vacuoles, suggesting the role of S-guanylation as a marker for selective autophagic degradation. This finding is supported by the fact that S-guanylated bacteria were selectively marked with polyubiquitin, a known molecular tag for selective transport to autophagosomes. These results collectively indicate that 8-nitro-cGMP plays a crucial role in cytoprotection during bacterial infections or inflammations via autophagy upregulation.

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