A Complex Comprising Phosphatidylinositol 4-Kinase IIIβ, ACBD3, and Aichi Virus Proteins Enhances Phosphatidylinositol 4-Phosphate Synthesis and Is Critical for Formation of the Viral Replication Complex

Abstract

Phosphatidylinositol 4-kinase III␤ (PI4KB) is a host factor required for the replication of certain picornavirus genomes. We previously showed that nonstructural proteins 2B, 2BC, 2C, 3A, and 3AB of Aichi virus (AiV), a picornavirus, interact with the Golgi protein, acyl-coenzyme A binding domain containing 3 (ACBD3), which interacts with PI4KB. These five viral proteins, ACBD3, PI4KB, and the PI4KB product phosphatidylinositol 4-phosphate (PI4P) colocalize to the AiV RNA replication sites (J. Sasaki et al., EMBO J. 31:754 -766, 2012). We here examined the roles of these viral and cellular molecules in the formation of AiV replication complexes. Immunofluorescence microscopy revealed that treatment of AiV polyprotein-expressing cells with a small interfering RNA targeting ACBD3 abolished colocalization of the viral 2B, 2C, and 3A proteins with PI4KB. A PI4KB-specific inhibitor also prevented their colocalization. Virus RNA replication increased the level of cellular PI4P without affecting that of PI4KB, and individual expression of 2B, 2BC, 2C, 3A, or 3AB stimulated PI4P generation. These results suggest that the viral protein/ACBD3/PI4KB complex plays an important role in forming the functional replication complex by enhancing PI4P synthesis. Of the viral proteins, 3A and 3AB were shown to stimulate the in vitro kinase activity of PI4KB through forming a 3A or 3AB/ACBD3/PI4KB complex, whereas the ACBD3-mediated PI4KB activation by 2B and 2C remains to be demonstrated. IMPORTANCEThe phosphatidylinositol 4-kinase PI4KB is a host factor required for the replication of certain picornavirus genomes. Aichi virus, a picornavirus belonging to the genus Kobuvirus, forms a complex comprising one of the viral nonstructural proteins 2B, 2BC, 2C, 3A, and 3AB, the Golgi protein ACBD3, and PI4KB to synthesize PI4P at the sites for viral RNA replication. However, the roles of this protein complex in forming the replication complex are unknown. This study showed that virus RNA replication and individual viral proteins enhance the level of cellular PI4P, and suggested that the viral protein/ACBD3/PI4KB complex plays an important role in forming a functional replication complex. Thus, the present study provides a new example of modulation of cellular lipid metabolism by viruses to support the replication of their genomes.

Phosphatidylinositol 4-kinases: Function, structure, and inhibition

“…Although, Arf1 and GBF1 seem to be involved in the membrane recruitment and activation of PI4K IIIβ in uninfected cells they are presumed to participate on this process also during the enteroviral infections [90]. Work on Aichi virus led to conclusion that Golgi adaptor protein ACBD3 is the cellular mediator of interaction between 3A protein and PI4K IIIβ [74,104] but details regarding the recruitment of the IIIβ enzyme by enteroviruses are conflicting. siRNA against ACBD3 was reported to both lower and increase the replication of the poliovirus [105,107] but not of the CVB3 or rhinovirus [108,109], which is surprising as the 3A proteins of these enteroviruses are rather similar and their 3A proteins interact with ACBD3 [105].…”

“…The anti-Poliovirus and anti-Coxsackievirus B3 (CVB3) activity of several compounds was linked with their PI4K IIIβ inhibitory activity [102,103]. Sasaki and colleagues showed that this enzyme is also essential in the life cycle of another picornavirus, the Aichi virus (Kobuvirus) and that the virus hijacks PI4K IIIβ through the Golgi residing ACBD3 protein [74,104]. Greninger and colleagues showed that PI4K IIIβ recruitment through the interaction with ACBD3 protein is common to many picornaviruses and suggested that the IIIβ enzyme might be target for a broad anti-picornavirus therapy [105,106].…”

Type III phosphatidylinositol 4 kinases: structure, function, regulation, signalling and involvement in disease

“…The underlying mechanism for viral hijacking of PI4KIIIβ is complex and not fully understood. In a subset of enteroviral infections 3A activates the guanine exchange factor Golgi-specific brefeldin A-resistance guanine nucleotide exchange factor 1 (GBF1) for Arf1, leading to activation of PI4KIIIβ [46]. In a number of picornaviruses, including both poliovirus and aichivirus, 3A activation of PI4KIIIβ appears to be mediated by interactions with ACBD3 [43,45,47,48].…”

Ligand binding to the ACBD6 protein regulates the acyl-CoA transferase reactions in membranes

“…HNF4 ␣ ( 11 ), sterol regulatory element-binding protein (SREBP) 1 ( 12 ), plant AtEBP ( 13 ), and several viral proteins ( 3,(14)(15)(16)(17)(18). Plant ACBP members are also implicated in a multitude of function such as embryogenesis and resistance to various stresses ( 4,5,11 ).…”