Profilin2 is required for filamentous actin formation induced by human parainfluenza virus type 2

Human parainfluenza virus type 2 V protein inhibits mitochondrial apoptosis pathway through two ways

Paramyxoviruses are reported to block apoptosis for their replication, but the mechanisms remain unclear. Furthermore, regulation of mitochondrial apoptosis by paramyxoviruses has been hardly reported. We investigated whether and how human parainfluenza virus type 2 (hPIV-2) counteracts apoptosis. Infection of recombinant hPIV-2 carrying mutated V protein showed higher caspase 3/7 activity and higher cytochrome c release from mitochondria than wild type hPIV-2 infection. This indicates that V protein controls mitochondrial apoptosis pathway. hPIV-2 V protein interacted with Bad, an apoptotic promoting protein, and this interaction inhibited the binding of Bad to Bcl-XL. V protein also bound to 14-3-3ε, which was essential for inhibition of 14-3-3ε cleavage. Our data collectively suggest that hPIV-2 V protein has two means of preventing mitochondrial apoptosis pathway: the inhibition of Bad-Bcl-XL interaction and the suppression of 14-3-3ε cleavage. This is the first report of the mechanisms behind how paramyxoviruses modulate mitochondrial apoptosis pathways.

Screening and identification of cyprinid herpesvirus 2 (CyHV-2) ORF55-interacting proteins by phage display

BACKGROUND

Cyprinid herpesvirus 2 (CyHV-2) is a pathogenic fish virus belonging to family Alloherpesviridae. The CyHV-2 gene encoding thymidine kinase (TK) is an important virulence-associated factor. Therefore, we aimed to investigate the biological function of open reading frame 55 (ORF55) in viral replication.

METHODS

Purified CyHV-2 ORF55 protein was obtained by prokaryotic expression, and the interacting peptide was screened out using phage display. Host interacting proteins were then predicted and validated.

RESULTS

ORF55 was efficiently expressed in the prokaryotic expression system. Protein and peptide interaction prediction and dot-blot overlay assay confirmed that peptides identified by phage display could interact with the ORF55 protein. Comparing the peptides to the National Center for Biotechnology Information database revealed four potential interacting proteins. Reverse transcription quantitative PCR results demonstrated high expression of an actin-binding Rho-activating protein in the latter stages of virus-infected cells, and molecular docking, cell transfection and coimmunoprecipitation experiments confirmed that it interacted with the ORF55 protein.

CONCLUSION

During viral infection, the ORF55 protein exerts its biological function through interactions with host proteins. The specific mechanisms remain to be further explored.

Human Parainfluenza Virus Type 2 V Protein Modulates Iron Homeostasis

Intracellular iron concentration is tightly controlled for cell viability. It is known to affect the growth of several viruses, but the molecular mechanisms are not well understood. We found that iron chelators inhibit growth of human parainfluenza virus type 2 (hPIV-2). Furthermore, infection with hPIV-2 alters ferritin localization from granules to a homogenous distribution within cytoplasm of iron-stimulated cells. The V protein of hPIV-2 interacts with ferritin heavy chain 1 (FTH1), a ferritin subunit. It also binds to nuclear receptor coactivator 4 (NCOA4), which mediates autophagic degradation of ferritin, so-called ferritinophagy. V protein consequently interferes with interaction between FTH1 and NCOA4. hPIV-2 growth is inhibited in FTH1 knockdown cell line where severe hPIV-2-induced apoptosis is shown. In contrast, NCOA4 knockdown results in the promotion of hPIV-2 growth and limited apoptosis. Our data collectively suggest that hPIV-2 V protein inhibits FTH1-NCOA4 interaction and subsequent ferritinophagy. This iron homeostasis modulation allows infected cells to avoid apoptotic cell death, resulting in effective growth of hPIV-2.IMPORTANCE hPIV-2 V protein interferes with interaction between FTH1 and NCOA4 and inhibits NCOA4-mediated ferritin degradation, leading to the inhibition of iron release to the cytoplasm. This iron homeostasis modulation allows infected cells to avoid apoptotic cell death, resulting in effective growth of hPIV-2.

Inhibition of Cavin3 Degradation by the Human Parainfluenza Virus Type 2 V Protein Is Important for Efficient Viral Growth

Cavin proteins have important roles in the formation of caveolae in lipid raft microdomains. Pulse-chase experiments of cells infected with human parainfluenza virus type 2 (hPIV-2) showed decreased proteasomal degradation of Cavin3. Overexpression of hPIV-2 V protein alone was sufficient to inhibit Cavin3 degradation. Immunoprecipitation analysis revealed that V protein bound to Cavin3. Trp residues within C-terminal region of V protein, as well as the N-terminal region of Cavin3, are important for V–Cavin3 interaction. Cavin3 knockdown suppressed hPIV-2 growth without affecting its entry, replication, transcription, or translation. Higher amounts of Cavin3 were observed in V protein-overexpressing cells than in control cells in lipid raft microdomains. Our data collectively suggest that hPIV-2 V protein binds to and stabilizes Cavin3, which in turn facilitates assembly and budding of hPIV-2 in lipid raft microdomains.

Common and unique mechanisms of filamentous actin formation by viruses of the genus Orthorubulavirus

We previously found that infection with human parainfluenza virus type 2 (hPIV-2), a member of the genus Orthorubulavirus, family Paramyxoviridae, causes filamentous actin (F-actin) formation to promote viral growth. In the present study, we investigated whether similar regulation of F-actin formation is observed in infections with other rubulaviruses, such as parainfluenza virus type 5 (PIV-5) and simian virus 41 (SV41). Infection with these viruses caused F-actin formation and RhoA activation, which promoted viral growth. These results indicate that RhoA-induced F-actin formation is important for efficient growth of these rubulaviruses. Only SV41 and hPIV-2 V and P proteins bound to Graf1, while the V and P proteins of PIV-5, mumps virus, and hPIV-4 did not bind to Graf1. In contrast, the V proteins of these rubulaviruses bound to both inactive RhoA and profilin 2. These results suggest that there are common and unique mechanisms involved in regulation of F-actin formation by members of the genus Orthorubulavirus.