Porcine Hemagglutinating Encephalomyelitis Virus Triggers Neural Autophagy Independently of ULK1.

ABSTRACT

Uncoordinated 51-like kinase 1 (ULK1) is a well-characterized initiator of canonical autophagy under basal or pathological conditions. Porcine hemagglutinating encephalomyelitis virus (PHEV), a neurotropic betacoronavirus (ß-CoV), impairs ULK1 kinase but hijacks autophagy to facilitate viral proliferation. However, the machinery of PHEV-induced autophagy initiation upon ULK1 kinase deficiency remains unclear. Here, the time course of PHEV infection showed a significant accumulation of autophagosomes (APs) in nerve cells in vivo and in vitro. Utilizing ULK1-knockout neuroblastoma cells, we have identified that ULK1 is not essential for productive AP formation induced by PHEV. In vitro phosphorylation studies discovered that mTORC1-regulated ULK1 activation stalls during PHEV infection, whereas AP biogenesis was controlled by AMPK-driven BECN1 phosphorylation. A lack of BECN1 is sufficient to block LC3 lipidation and disrupt recruitment of the LC3-ATG14 complex. Moreover, BECN1 acts as a bona fide substrate for ULK1-independent neural autophagy, and ectopic expression of BECN1 somewhat enhances PHEV replication. These findings highlight a novel machinery of noncanonical autophagy independent of ULK1 that bypasses the conserved initiation circuit of AMPK-mTORC1-ULK1, providing new insights into the interplay between neurotropic ß-CoV and the host. IMPORTANCE The ongoing coronavirus disease 2019 (COVID-19) pandemic alongside the outbreaks of severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) pose Betacoronavirus (ß-CoV) as a global public health challenge. Coronaviruses subvert, hijack, or utilize autophagy to promote proliferation, and thus, exploring the cross talk between ß-CoV and autophagy is of great significance in confronting future ß-CoV outbreaks. Porcine hemagglutinating encephalomyelitis virus (PHEV) is a highly neurotropic ß-CoV that invades the central nervous system (CNS) in pigs, but understanding of the pathogenesis for PHEV-induced neurological dysfunction is yet limited. Here, we discovered a novel regulatory principle of neural autophagy initiation during PHEV infection, where productive autophagosome (AP) biogenesis bypasses the multifaceted regulation of ULK1 kinase. The PHEV-triggered noncanonical autophagy underscores the complex interactions of virus and host and will help in the development of therapeutic strategies targeting noncanonical autophagy to treat ß-CoV disease.