Autophagy is emerging as a crucial defense mechanism against bacteria, but the host intracellular sensors responsible for inducing autophagy in response to bacterial infection remain unknown. Here we demonstrated that the intracellular sensors Nod1 and Nod2 are critical for the autophagic response to invasive bacteria. By a mechanism independent of the adaptor RIP2 and transcription factor NF-kappaB, Nod1 and Nod2 recruited the autophagy protein ATG16L1 to the plasma membrane at the bacterial entry site. In cells homozygous for the Crohn's disease-associated NOD2 frameshift mutation, mutant Nod2 failed to recruit ATG16L1 to the plasma membrane and wrapping of invading bacteria by autophagosomes was impaired. Our results link bacterial sensing by Nod proteins to the induction of autophagy and provide a functional link between Nod2 and ATG16L1, which are encoded by two of the most important genes associated with Crohn's disease.

Autophagy, which targets cellular constituents for degradation, is normally inhibited in metabolically replete cells by the metabolic checkpoint kinase mTOR. Although autophagic degradation of invasive bacteria has emerged as a critical host defense mechanism, the signals that induce autophagy upon bacterial infection remain unclear. We find that infection of epithelial cells with Shigella and Salmonella triggers acute intracellular amino acid (AA) starvation due to host membrane damage. Pathogen-induced AA starvation caused downregulation of mTOR activity, resulting in the induction of autophagy. In Salmonella-infected cells, membrane integrity and cytosolic AA levels rapidly normalized, favoring mTOR reactivation at the surface of the Salmonella-containing vacuole and bacterial escape from autophagy. In addition, bacteria-induced AA starvation activated the GCN2 kinase, eukaryotic initiation factor 2α, and the transcription factor ATF3-dependent integrated stress response and transcriptional reprogramming. Thus, AA starvation induced by bacterial pathogens is sensed by the host to trigger protective innate immune and stress responses.

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Highlights d Ultra-deep rRNA-depleted RNA sequencing of 144 localized prostate tumors d Fusion gene profiles differentiate localized from metastatic disease d Widespread RNA circularization events define clinically distinct tumor subtypes d Functional screening reveals pervasive circular isoformspecific essentiality