Autophagy is a highly regulated self-degradative mechanism required at a basal level for intracellular clearance and recycling of cytoplasmic contents. Upon intracellular pathogen invasion, autophagy can be induced as an innate immune mechanism to control infection. Nevertheless, pathogens have developed strategies to avoid or hijack autophagy for their own benefit. The molecular pathways inducing autophagy in response to infection remain poorly documented. We report here that the engagement of CD46, a ubiquitous human surface receptor able to bind several different pathogens, is sufficient to induce autophagy. CD46-Cyt-1, one of the two C-terminal splice variants of CD46, is linked to the autophagosome formation complex VPS34/Beclin1 via its interaction with the scaffold protein GOPC. Measles virus and group A Streptococcus, two CD46-binding pathogens, induce autophagy through a CD46-Cyt-1/GOPC pathway. Thus, upon microorganism recognition, a cell surface pathogen receptor can directly trigger autophagy, a critical step to control infection.

Autophagy is a conserved degradative pathway used as a host defense mechanism against intracellular pathogens. However, several viruses can evade or subvert autophagy to insure their own replication. Nevertheless, the molecular details of viral interaction with autophagy remain largely unknown. We have determined the ability of 83 proteins of several families of RNA viruses (Paramyxoviridae, Flaviviridae, Orthomyxoviridae, Retroviridae and Togaviridae), to interact with 44 human autophagy-associated proteins using yeast two-hybrid and bioinformatic analysis. We found that the autophagy network is highly targeted by RNA viruses. Although central to autophagy, targeted proteins have also a high number of connections with proteins of other cellular functions. Interestingly, immunity-associated GTPase family M (IRGM), the most targeted protein, was found to interact with the autophagy-associated proteins ATG5, ATG10, MAP1CL3C and SH3GLB1. Strikingly, reduction of IRGM expression using small interfering RNA impairs both Measles virus (MeV), Hepatitis C virus (HCV) and human immunodeficiency virus-1 (HIV-1)-induced autophagy and viral particle production. Moreover we found that the expression of IRGM-interacting MeV-C, HCV-NS3 or HIV-NEF proteins per se is sufficient to induce autophagy, through an IRGM dependent pathway. Our work reveals an unexpected role of IRGM in virus-induced autophagy and suggests that several different families of RNA viruses may use common strategies to manipulate autophagy to improve viral infectivity.

The results indicate that T-cell depletion is achieved rapidly and primarily in peripheral lymphoid tissues at high ATG dosage. Short ATG treatments could therefore be clinically evaluated when major peripheral T-cell depletion is required.