HIV-1 Vpr orchestrates ciTRAN upregulation through TGF-β induction

Circular RNA (circRNA) expression is widespread in immune cells infected by HIV-1, but the crosstalk between circRNA expression and various cellular signaling pathways remains elusive. Here, we report that HIV-1 Vpr can induce the production of TGF-β during infection, which we linked to the upregulation of ciTRAN, a proviral circRNA encoded by SMARCA5. Consistent with this finding, we observed that the essential intracellular TGF-β receptor signaling component SMAD2/3 was recruited to the SMARCA5 promoter in a Vpr-dependent manner. SMARCA5 promoter analysis and functional assays further revealed that SAMD2/3 binding motif in the SMARCA5 promoter is crucial for ciTRAN upregulation. Notably, in response to treatment with DNA-damaging agents or the exogenous addition of recombinant TGF-β, the TGF-SMAD axis upregulated the expression of ciTRAN as well as the parental SMARCA5 mRNA. Regardless, the QKI protein was necessary for ciTRAN biogenesis. Finally, pharmacological targeting or genetic ablation of TGFBR1 can reduce the ability of Vpr to promote the expression of ciTRAN and viral genes. These results highlight the TGF-β-mediated regulation of ciTRAN expression which may play a role in modulating HIV-1 replication.