Effects of Foot-and-Mouth Disease Virus Nonstructural Proteins on the Structure and Function of the Early Secretory Pathway: 2BC but Not 3A Blocks Endoplasmic Reticulum-to-Golgi Transport

Abstract

Infection of cells by picornaviruses leads to the generation of intracellular membrane vesicles. The expression of poliovirus (PV) 3A protein causes swelling of the endoplasmic reticulum (ER) and inhibition of protein trafficking between the ER and the Golgi apparatus. Here, we report that the nonstructural proteins of a second picornavirus, foot-and-mouth disease virus (FMDV), also perturb the secretory pathway. FMDV proteins 3A, 2B, 2C, and 2BC expressed alone in cells were recovered from crude membrane fractions, indicating membrane association. Immunofluorescence microscopy showed that 3A was located in a reticular structure and 2B was located in the ER, while 2C was located in both the ER and the bright punctate structures within the Golgi apparatus. 2BC gave punctate cytoplasmic staining and also caused accumulation of ER proteins in large vesicular structures located around the nuclei. The effect of the FMDV proteins on the trafficking of the vesicular stomatitis virus glycoprotein (G protein) from the ER to the cell surface was determined. Unlike its PV counterpart, the 3A protein of FMDV did not prevent trafficking of the G protein to the cell surface. Instead, surface expression of the G protein was blocked by 2BC, with retention of the G protein in a modified ER compartment staining for 2BC. The results suggest that the nonstructural proteins of different picornaviruses may vary in their ability to perturb the secretory pathway. Since FMDV 2BC can block the delivery of proteins to the cell surface, it may, as shown for PV 3A, play a role in immune evasion and contribute to the persistent infections observed in ruminants.It has been known for several years that the secretory pathway is disrupted in cells infected with picornaviruses (3, 11, 13-15, 31, 38, 48). This is characterized by the appearance of large numbers of membrane vesicles in the cytoplasm. In the case of poliovirus (PV) infection, the membrane vesicles are thought to originate from the endoplasmic reticulum (ER), either from COPII-coated vesicles that move proteins from the ER to the Golgi apparatus or from double-membraned vacuoles that extend from the ER during autophagy (6,37,43). Several studies suggest that the rearranged membranes are utilized during virus replication (7,10,40,43). Viral proteins responsible for replication and newly synthesized viral RNA are, for example, associated with these membranes, and membrane fractions isolated from infected cells can synthesize viral RNA in vitro (6,44,47). A link between a functioning secretory pathway and virus replication has also been provided by the observation that brefeldin A (BFA), a drug that blocks ER-to-Golgi transport by preventing the formation of transport vesicles, blocks replication of PV (23, 28). The membrane rearrangements seen within infected cells are caused by the nonstructural proteins encoded by the P2 and P3 regions of the genome. Studies on the activity of individual PV proteins and the membranes they modify have implicated a role for the nonstructural proteins ...

Mitochondrial genomes are retained by selective constraints on protein targeting

“…2). Mistargeting of these mt-encoded proteins to the ER resulted in the formation of aberrant honeycomb structures, as previously observed during viral infections (31). This finding suggests that mistargeting of mitochondrial proteins to the ER affects the morphology of the cell.…”

Inhibition of Protein Trafficking by Coxsackievirus B3: Multiple Viral Proteins Target a Single Organelle

“…on May 10, 2018 by guest http://jvi.asm.org/ data have suggested that not all picornavirus 3A proteins directly target this organelle (20), and our observation of Golgi disruption suggested-but did not prove-that the CVB3 3A protein might traffic beyond the ER. Thus, we used our anti-3A polyclonal antiserum to determine the localization of 3A in transfected cells.…”

“…For several picornaviruses, most notably poliovirus type 1, it has been proposed that the 3A protein is responsible for this phenomenon, specifically blocking anterograde trafficking from the endoplasmic reticulum (ER) to the Golgi (12). Major histocompatibility complex class I transport inhibition has also been observed for foot-and-mouth-disease virus (28), and it has been proposed that the 2BC protein from this virus, rather than 3A, inhibits ER-to-Golgi trafficking (20). Interestingly, both the 2B and 3A proteins of coxsackievirus B3 (CVB3) have been shown to inhibit protein secretion (35,37), but the exact mechanism behind this phenomenon is not known.…”

Subcellular localization and live-cell imaging of the Helicoverpa armigera stunt virus replicase in mammalian and Spodoptera frugiperda cells

“…Biochemical analysis of cells expressing the poliovirus 2C protein demonstrates that several host-cell membranes, including lysosomes, ER, Golgi apparatus and endosomes, contribute to virus-induced vesicles (Schlegel et al, 1996). When expressed alone in cells, foot-and-mouth disease virus non-structural proteins 2B and 2C are found in association with ER and Golgi membranes (Moffat et al, 2005). Flock House virus, which is related structurally to the tetraviruses, replicates its RNA in association with the outer mitochondrial membrane in infected Drosophila cells (Miller et al, 2001).…”