Unc-51-like kinase 1 (ULK1) regulates bacterial ubiquitylation and p62 recruitment during xenophagic clearance of Listeria monocytogenes.

Abstract

Autophagy is an essential cellular homeostatic process that also serves as an innate immune mechanism against intracellular bacterial pathogens through a highly selective form of autophagy known as xenophagy. Despite advances in understanding how bacteria are targeted for autophagic degradation, the specific regulatory mechanisms that drive the initial steps and ensure bacterial selection remain incompletely defined. Our study uncovers a pivotal role for Unc-51-like kinase 1 (ULK1) in the xenophagic clearance of the intracellular bacterial pathogen Listeria monocytogenes. We observed that ULK1 is essential for the efficient ubiquitylation of bacteria and subsequent recruitment of the autophagic adaptor protein p62 to the bacterial surface. Furthermore, we show that the impact of ULK1 deficiency in these early events-reduction in bacterial ubiquitylation, followed by impaired p62 targeting, results in diminished formation of bacteria-targeted autophagosomes. Notably, phosphorylation of p62 at the S409 residue, which is known to be dependent on ULK1 to enhance its affinity for ubiquitin, is necessary for the recruitment of p62 to the bacterial surface and adequate bacterial clearance, highlighting the regulatory role of ULK1 in this process. These findings unveil a previously unrecognized function of ULK1 in modulating early xenophagy steps, contributing to the autophagic control of intracellular pathogens. Our findings offer new perspectives into the manipulation of ULK1 activity for therapeutic interventions against infectious diseases.IMPORTANCEAutophagy is a vital process in eukaryotic cells that enables them to digest intracellular components, helping them respond to various stresses, including starvation, the accumulation of dysfunctional organelles, and infections. While the autophagic flux has been extensively studied over the past few decades, some key mechanisms remain poorly understood. Our research aimed to clarify one such mechanism: how the autophagic machinery specifically targets intracellular bacteria. We identified a novel role for the protein ULK1 in this process, demonstrating that ULK1 is essential for tagging bacteria with ubiquitin within the cell and recruiting the protein p62. These are critical steps for adequate bacterial clearance. Our results underscore the pivotal role of ULK1 in initiating the cellular defense against bacterial infections. Our findings could pave the way for new therapeutic strategies to enhance the body's capacity to combat bacterial infections.