PUB - Publikationen an der Universität Bielefeld

**Abstract**
HIV-1 infection establishes a reservoir of long-lived cells with integrated proviral DNA that can persist despite antiretroviral therapy (ART). The mechanisms governing the transcriptional regulation of the provirus are complex and incompletely understood. Here, we investigated the role of histone H3 citrullination, a post-translational modification catalyzed by protein-arginine deiminase type-4 (PADI4), in HIV-1 transcription and latency. We found that PADI4 inhibition by GSK484 reduced HIV-1 transcription after T cell activation inex vivocultures of CD4 T cells from viremic and ART treated people living with HIV-1 (PLWH). The effect was more pronounced in the viremic group. Using cell models of HIV-1 latency, we showed that PADI4-mediated citrullination of histone H3 occurred at the HIV-1 promoter upon T cell stimulation which facilitated proviral transcription. Citrullination of the H3R8 residue prevented heterochromatin formation. We also demonstrated that HIV-1 preferentially integrated into genomic regions marked by H3 citrullination and that proviruses in H3 citrullinated chromatin were more transcriptionally active and less prone to latency than those in non-citrullinated chromatin. Our data reveal a novel mechanism of HIV-1 transcriptional regulation by PADI4 and H3 citrullination and suggest a potential therapeutic target for reducing the size of the latent reservoir, as an approach to cure.

**Highlights**

The PADI4 enzyme stimulates HIV-1 transcription during T cell activation.

PADI4 citrullinates histone H3 at the HIV-1 promoter upon T cell activation and inhibiting PADI4 reduces HIV-1 reactivation inex vivoCD4 T cells from people living with HIV-1.

H3cit is mostly found at gene promoters, and productive HIV-1 proviruses are more likely than latent or reactivatable proviruses, to integrate in chromatin susceptible for citrullination.

H3cit prevents latency establishment by interfering with the binding of HP1α to H3K9me3.