BPIFB3 Regulates Autophagy and Coxsackievirus B Replication through a Noncanonical Pathway Independent of the Core Initiation Machinery

Enteroviruses require autophagy to facilitate the formation of autophagosome (AP)-like double-membrane vesicles that provide the scaffolding for RNA replication. Here, we identify bactericidal/permeability-increasing protein (BPI) fold-containing family B, member 3 (BPIFB3) as a gene whose silencing greatly enhances coxsackievirus B (CVB) replication and induces dramatic alterations in the morphology of CVB-induced replication organelles. We show that BPIFB3 is associated with the endoplasmic reticulum (ER), and its silencing by RNA interference enhances basal levels of autophagy and promotes increased autophagy during CVB replication. Conversely, overexpression of BPIFB3 inhibits CVB replication, dramatically alters the morphology of LC3B-positive vesicles, and suppresses autophagy in response to rapamaycin. In addition, we found that, whereas silencing of core autophagy components associated with the initiation of APs in control cells suppressed CVB replication, silencing of these same components had no effect on CVB-induced autophagy or viral replication in cells transfected with BPIFB3 small interfering RNA. Based on these results, taken together, this study reports on a previously uncharacterized regulator of enterovirus infection that controls replication through a noncanonical pathway independent from the core autophagy initiation machinery.