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

Abstract

Autophagy 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.

Ubiquitin-Dependent And Independent Signals In Selective Autophagy

“…In addition, endogenous nucleotide 8-nitroguanosine 3 0 ,5 0 -cyclic monophosphate (8-nitro-cGMP) has been shown to promote antibacterial autophagy. 8-Nitro-cGMP modifies bacterial proteins by S-guanylation, which triggers their subsequent K63-ubiquitination and autophagic removal of the labeled bacteria [75]. Furthermore, Salmonella-containing endosomes are subjected to ubiquitination, which recruits the autophagic machinery via the direct interaction of Ub with Atg16L, a component of the Atg12-Atg5-Atg16L complex [76] that conjugates LC3/GABARAP-like proteins to PE and thus incorporates them into autophagosomes.…”

Strategies to increase nitric oxide signalling in cardiovascular disease

“…The product of sGC activation, cGMP, can also be oxidized and nitrated to form nitrocGMP 53 . Interestingly, nitrocGMP has a longer halflife and different biological activity to cGMP, including the modification of protein function via Sguanylation 53 with resulting specific effects, for example, on immune function 54 .…”

Nitric oxide in liver diseases

“…A number of target molecules for S-guanylation have been identified [67]. One remarkable finding was the role of 8-nitro-cGMP in autophagy in macrophages [68]. 8-nitro-cGMP bound to cysteine residues (i.e., S-guanylation) of invading bacteria such as group A streptococcus.…”