# The ASFV CD2v protein inhibits apoptosis by inducing proteasomal degradation of BimEL via activation of the TPL2-MEK-ERK signaling pathway

## TL;DR

This study shows how the ASFV CD2v protein prevents cell death by activating a signaling pathway that degrades a key pro-apoptotic protein, helping the virus survive and spread.

## Contribution

The study reveals a novel anti-apoptotic mechanism of ASFV involving CD2v-mediated TPL2-MEK-ERK signaling and BimEL degradation.

## Key findings

- CD2v activates the TPL2-MEK-ERK pathway to induce proteasomal degradation of BimEL in infected cells.
- Soluble CD2v can also inhibit apoptosis in uninfected bystander cells through the same signaling pathway.
- CRISPR-Cas9 knockout of CD2v abolishes ERK1/2 activation and BimEL degradation.

## Abstract

African swine fever virus (ASFV) employs sophisticated regulatory strategies to manipulate host cell apoptosis, a process critical for its pathogenesis and immune evasion; however, the mechanisms underlying this process remain incompletely understood. Here, we report a novel mechanism by which the ASFV-encoded envelope protein CD2v suppresses apoptosis by activating the TPL2 (tumor progression locus 2)-MEK (mitogen-activated protein kinase kinase)-ERK (extracellular signal-regulated kinase) signaling axis, leading to proteasomal degradation of the pro-apoptotic protein BimEL in primary porcine alveolar macrophages and wild boar lung (WSL) cells. We further demonstrated that ASFV infection triggers ERK1/2-dependent phosphorylation and degradation of BimEL, a process independent of viral replication and mediated by viral structural components. A targeted screen identified CD2v as the key viral protein driving this pathway. Both the purified extracellular domain of CD2v (Asp17−Tyr206) and virion-associated CD2v activated TPL2-MEK-ERK signaling without requiring internalization into cells, resulting in BimEL downregulation and subsequent suppression of apoptosis. Crucially, CRISPR-Cas9-mediated knockout of CD2v abolished ASFV-induced ERK1/2 activation and consequential BimEL degradation. Furthermore, we discovered that soluble CD2v released from ASFV-infected cells can activate this signaling axis in uninfected bystander cells, thereby inhibiting apoptosis distantly. This paracrine function, alongside its intrinsic role in directly infected cells, enables CD2v to establish a pro-survival microenvironment conducive to viral propagation. Our findings uncover a multifaceted anti-apoptotic mechanism employed by ASFV, expanding the functional repertoire of CD2v and providing new insights into ASFV pathogenesis with potential therapeutic implications.

This study elucidates a distinct mechanism of apoptosis inhibition by African swine fever virus (ASFV), a pathogen that causes a devastating disease in swine. We identify the ASFV CD2v protein as a key suppressor of cell death that operates by hijacking the host TPL2-MEK-ERK signaling pathway to degrade the pro-apoptotic protein BimEL. Importantly, CD2v mediates this effect not only within infected cells but also, in a soluble form, on surrounding uninfected bystander cells. This dual action helps create a protective, pro-survival cellular environment that facilitates viral spread and persistence. Understanding this novel apoptotic suppression mechanism advances our knowledge of ASFV-host interactions and highlights potential new avenues for therapeutic intervention.