Mudit Tyagi George Mason University, Manassas, Virginia, USA CBF-1 induces both establishment and maintenance of HIV latency via recruiting PcG corepressor complex at HIV LTR

Multiple mechanisms are involved in establishing HIV latency Quiescent T cells show an absence of transcription factors such as NF-kB and NF-AT restricting initiation (Nabel, Kinoshita) Quiescent T cells show reduced levels of P-TEFb, limiting transcription elongation and Tat activity (Rice, Karn)

Are there specific repressors of HIV LTR promoter, which are higher in resting T cells than their active counterparts.

A. CBF-1 (mRNA) B. HIV (mRNA) CBF-1 Levels Rapidly Fall after T-cell Activation

CBF-1 plays important role in HIV latency, as its knockdown in latently infected T cells reactivates latent HIV proviruses CBF-1 inhibits HIV transcription by recruiting histone deacetylases (HDAC) containing corepressor complexes CBF-1 facilitates HIV latency in both transformed and primary CD4+ T cells

Scrambled shRNA CBF-1 shRNA Nucleosome-1 (+30 to +134) CBF-1 recruited PcG corepressor complex facilitate HIV latency establishment Input DNA %

Polycomb Group corepressor complex PcG complex carry variety of enzymes known to induce different repressive epigenetic modifications. Thus, PcG complex induce several layers of repressive epigenetic modifications involving both histones and DNA. PcG complex is known to play important role in both inducing and maintaining the silencing of several cellular genes, including transcriptional repression of the endogenous retroviruses and maintaining the long-term silencing of X chromosome.

Scrambled shRNA CBF-1 shRNA Nucleosome-1 (+30 to +134) CBF-1 recruited PcG corepressor complex facilitate HIV latency maintenance too Input DNA %

Luciferase counts Aza-dC (5 uM) + PcG corepressor complex knockdown results in the reactivation of latent HIV proviruses

Conclusions CBF-1 performs its function by recruiting PcG corepressor complex at HIV LTR Like an ideal repressors CBF-1 levels goes down following T cell activation. Multiple chromatin modifying mechanisms are involved in regulating gene expression from latent HIV proviruses CBF-1 is a potent and specific inhibitor of HIV transcription Inhibitors of PcG corepressor complex may play useful role for the induction strategies designed to eradicate latent viral pools in HIV patients.

Acknowledgements Prof. Jonathan Karn