TGF-β signaling promotes the expression of proviral circular RNA ciTRAN in HIV-1 infection

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 unclear. We report that HIV-1 Vpr triggers TGF-β signaling, which we linked to the increased expression 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 the SAMD2/3 binding motif is crucial for ciTRAN upregulation. In response to treatment with DNA-damaging agents or the exogenous addition of recombinant TGF-β, the TGF-β-SMAD axis upregulated the expression of ciTRAN as well as the parental SMARCA5 mRNA. Finally, pharmacological targeting of TGF-β signaling or genetic ablation of TGFBR1 can reduce the ability of HIV-1 Vpr to induce the expression of ciTRAN and viral genes. These results offer crucial mechanistic insights into the regulation of ciTRAN expression by TGF-β signaling and suggest a strategy to inhibit circRNA expression during infection by small molecules.