Caspase Cleavage of Influenza A Virus M2 Disrupts M2-LC3 Interaction and Regulates Virion Production

Core Concepts

Caspase cleavage of the influenza A virus M2 protein disrupts its interaction with LC3, leading to altered M2 trafficking and reduced virion production.

Abstract

The content describes how the influenza A virus (IAV) Matrix 2 (M2) protein interacts with the autophagy-related protein LC3 through a conserved LC3-interacting region (LIR) motif. This interaction is important for the efficient budding and production of IAV virions. The key findings are: M2 is cleaved by caspases, predominantly caspase-6, at a specific 82SAVD85 motif. This cleavage disrupts the M2-LC3 interaction by removing the LIR motif. Caspase cleavage of M2 impairs its trafficking to the plasma membrane, which is important for virion assembly and budding. An IAV mutant expressing a permanently truncated M2 (lacking the LIR motif) exhibits reduced virion production and attenuated viral titers. These results highlight how the host protease machinery can dynamically regulate the M2-LC3 interaction to modulate IAV exit and virion production in response to the host cell state.

Stats

The ratio of cleaved M2 to full-length M2 was significantly reduced in ΔCASP6 cells compared to wild-type cells. Treatment of IAV-infected cells with a caspase-6 inhibitor (Z-VEID-FMK) significantly reduced the abundance of cleaved M2. Infection with an IAV mutant expressing M2D85A, which cannot be cleaved by caspases, abolished the appearance of the lower molecular weight M2 band. Infection with the M2Δ86-97 mutant, lacking the LIR motif, led to a significant decrease in LC3B lipidation compared to wild-type M2. The M2Δ86-97 mutant exhibited reduced M2 localization to the plasma membrane compared to wild-type M2 and the M2D85A mutant. Purified virions containing the M2Δ86-97 mutant had a lower ratio of M2 to other viral proteins compared to the M2D85A mutant. The M2Δ86-97 mutant virus exhibited a significantly decreased viral titer compared to wild-type M2.

Quotes

"Caspase cleavage of M2 must provide an evolutionary advantage for the virus despite attenuation observed in the permanently truncated M2Δ86-97 mutant." "We speculate that caspase cleavage of M2 removes the LIR motif to enable a switch between filamentous and non-filamentous budding in response to depletion of cellular resources."

Key Insights Distilled From

Caspase cleavage of Influenza A virus M2 disrupts M2-LC3 interaction and regulates virion production

by Beale,R., Fi... at www.biorxiv.org 04-04-2024

https://www.biorxiv.org/content/10.1101/2024.04.04.588074v1

Deeper Inquiries

How might the regulation of M2-LC3 interaction by caspase cleavage impact the pathogenicity and transmission of different influenza A virus strains

The regulation of M2-LC3 interaction by caspase cleavage can have significant implications for the pathogenicity and transmission of different influenza A virus strains. Caspase cleavage of M2 disrupts the M2-LC3 interaction, affecting the transport of M2 to the plasma membrane and its incorporation into virions. This modulation can impact the efficiency of viral budding and release, which are crucial steps in the viral life cycle. Strains of influenza A virus with altered caspase cleavage sites in M2 may exhibit differences in virion production, infectivity, and transmission rates. Strains with enhanced caspase cleavage leading to disrupted M2-LC3 interaction may produce fewer infectious virions, resulting in reduced pathogenicity and transmission. On the other hand, strains with reduced caspase cleavage and intact M2-LC3 interaction may have higher virion production, increased infectivity, and enhanced transmission potential. Therefore, the regulation of M2-LC3 interaction by caspase cleavage can influence the virulence and spread of different influenza A virus strains.

What other host factors or signaling pathways might modulate the M2-LC3 interaction and influence influenza A virus budding and release

Several host factors and signaling pathways may modulate the M2-LC3 interaction, impacting influenza A virus budding and release. One key factor is the autophagy machinery, particularly components involved in the CASM pathway. The interaction between M2 and LC3 is crucial for the relocalization of LC3 to the plasma membrane during viral budding. Modulation of autophagy-related proteins, such as ATG16L1, ATG8s, and V-ATPases, can influence the efficiency of M2-LC3 interaction and subsequent virion production. Additionally, cellular stress responses, immune signaling pathways, and post-translational modifications of M2 or LC3 proteins may also affect the M2-LC3 interaction. For example, activation of stress response pathways like the unfolded protein response (UPR) or interferon signaling pathways could impact the expression or function of proteins involved in the M2-LC3 interaction. Furthermore, kinases, phosphatases, or ubiquitin ligases that target M2 or LC3 for modification could regulate their interaction and influence viral budding and release.

Could the insights gained from this study on influenza A virus be applied to understand the regulation of host-virus interactions in other RNA virus infections

The insights gained from this study on influenza A virus, particularly regarding the regulation of host-virus interactions through caspase cleavage of M2 and modulation of M2-LC3 interaction, could be applied to understand similar mechanisms in other RNA virus infections. Many RNA viruses, including coronaviruses, flaviviruses, and paramyxoviruses, utilize host factors and cellular pathways for their replication, assembly, and release. The interplay between viral proteins and host factors, such as autophagy-related proteins, proteases, and signaling pathways, is crucial for the viral life cycle. By studying how caspase cleavage affects viral protein interactions and virion production in influenza A virus, researchers can explore similar mechanisms in other RNA viruses. Understanding the role of host factors in modulating viral budding and release can provide insights into the pathogenesis, transmission, and potential therapeutic targets for a wide range of RNA virus infections.