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

## TL;DR

This study reveals how HIV-1 protein Vpr increases a specific circular RNA (ciTRAN) through TGF-β signaling, which may help the virus replicate.

## Contribution

The study identifies a novel mechanism by which HIV-1 Vpr upregulates ciTRAN via TGF-β induction and SMAD2/3 signaling.

## Key findings

- HIV-1 Vpr induces TGF-β production, which upregulates ciTRAN expression.
- SMAD2/3 binds to the SMARCA5 promoter in a Vpr-dependent manner to enhance ciTRAN.
- Blocking TGF-β signaling reduces ciTRAN and viral gene expression.

## Abstract

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.

HIV-1 remains a global challenge, driving the exploration of novel strategies to combat the virus. Emerging evidence suggests that HIV-1 infection is also associated with changes in circular RNA profiles in CD4+ T cells. By an unknown mechanism, the accessory protein Vpr encoded by the primate lentivirus was shown to induce the expression of a SMARCA5-encoded proviral circular RNA ciTRAN (circSMARCA5). Here, we show that HIV-1 Vpr stimulates TGF-β production, orchestrating the upregulation of ciTRAN. Accordingly, the key signaling proteins (SMAD2/3) downstream of TGF-β receptors bind to the SMARCA5 promoter to boost ciTRAN production in the presence of Vpr. The experiments also indicate that treatment with chemotherapeutic DNA damaging agents or exogenous addition of recombinant TGF-β can upregulate ciTRAN. However, blocking the TGF-β signaling pathway by small molecules or depleting its components by genetic means diminished the ability of Vpr to stimulate ciTRAN and the viral gene expression. These findings highlight the TGF-β control of ciTRAN expression and suggest potential ways to block circular RNA expression during HIV-1 infection using small molecules.