APOBEC3B Promotes SARS-CoV-2 Through Activation of PKR/eIF2⍺ and AMPD2 Dysregulation.

APOBEC3B (A3B) has been implicated in host-virus interactions, but its role in SARS-CoV-2 infection is unclear. Here, we demonstrate that A3B is overexpressed in bronchoalveolar lavage fluid (BALF) cells from severe COVID-19 patients compared to those with mild disease. A3B knockdown in Caco-2 cells significantly reduces SARS-CoV-2 infectivity, likely through attenuation of the PKR-mediated integrated stress response, a pathway proposed to promote SARS-CoV-2. Single-cell RNA sequencing (scRNA-seq) data suggest that BALF cells from severe COVID-19 patients exhibit a repressed state for cellular translation, potentially mediated by eIF2α phosphorylation. However, in A549-ACE2 cells, SARS-CoV-2 does not activate PKR, but A3B knockdown still reduces SARS-CoV-2 infectivity, suggesting an alternative mechanism of action in different cellular contexts. To further investigate A3B's role in severe COVID-19, we employed Geneformer, a transformer-based machine learning model, which predicted that A3B knockout would perturb AMPD2 (adenosine monophosphate deaminase 2), a key enzyme in purine metabolism and immune regulation. We validated this prediction using bulk RNA-seq and clinical scRNA-seq data, confirming that AMPD2 expression is downregulated in severe COVID-19 but restored upon A3B knockdown. Together, these findings suggest that A3B plays a proviral role in SARS-CoV-2 infection by modulating translational control and immune regulatory networks, warranting further studies to elucidate the underlying mechanistic details.