ATG5 selectively engages virus-tethered BST2/Tetherin in an LC3C-associated pathway

BST2/Tetherin is a restriction factor that reduces HIV-1 dissemination by tethering virus at the cell surface. BST2 also acts as a sensor of HIV-1 budding, establishing a cellular anti-viral state. The HIV-1 Vpu protein antagonizes BST2 antiviral functions, notably by subverting an LC3C-associated pathway, a key cell intrinsic anti-microbial mechanism. Here, we show that ATG5 associates with BST2 and acts as a signaling scaffold to trigger an LC3C-associated pathway induced by HIV-1 infection. This process is initiated at the plasma membrane through the recognition of virus-tethered BST2 by ATG5. ATG5 and BST2 assemble as a complex, independently of the viral protein Vpu and ahead of the recruitment of the ATG protein LC3C. The conjugation of ATG5 with ATG12 is dispensable for this interaction. ATG5 recognizes cysteine-linked homodimerized BST2 and specifically engages phosphorylated BST2 tethering viruses at the plasma membrane, in an LC3C-associated pathway. We also found that this LC3C-associated pathway is used by Vpu to attenuate the inflammatory responses mediated by virion retention. Overall, we highlight that by targeting BST2 tethering viruses, ATG5 acts as a transducer of the LC3C-associated pathway induced by HIV-1 infection. Significance statement The outcome of viral infection in cells is dependent on the balance between host restriction factors and viral countermeasures. BST2/Tetherin is a restriction factor that reduces HIV-1 dissemination by tethering virions at the cell surface. Its action is counteracted by the viral protein Vpu through multiple mechanisms. Here, we describe the initial step of a non-canonical autophagic pathway, called LC3C-associated pathway, subverted by Vpu to counteract BST2 antiviral activities. We found that the autophagic protein ATG5 acts as a transducer by targeting phosphorylated and dimerized virus-tethered BST2 from cell surface to the degradation. Our discovery opens new avenue in the discovery of unconventional functions of ATG5, as an adaptor for receptor at the plasma membrane initiating an unconventional autophagy process. ### Competing Interest Statement The authors have declared no competing interest.