More than 33 million people in the world live with HIV. Treatment with highly active antiretroviral therapy (HAART) has been successful, but therapy is not curative. HIV can establish a state of latency in individual T cells, and HIV is persistently produced in HIV patient, despite undetectable viral loads. The latent HIV reservoir is a major hurdle preventing the eradication and cure of HIV-1. Lifelong HAART is required, because the virus rebounds if HAART is stopped;however, prolonged HAART is costly and associated with various toxicities. Therefore, finding a way to eradicate latent HIV-1 has become an important goal. Acetylation of histone is involved in HIV latency through effects on chromatin structure, a process controlled by two families of enzymes: histone acetyl-transferases (HAT), and histone deacetylases (HDAC). It has been demonstrated that HDAC activation limits HIV-1 transcription, and HAT activation favors HIV-1 transcription. HDAC inhibitors (HDACi) are able to induce HIV-1 transcription in models of HIV latency. We have found that acitretin can induce HIV-1 transcription in HIV latent cell lines and CD4 T cells from HAART suppressed HIV patients. acitretin is a retinoic acid, which can activate HAT. Retinoic acid (RA) receptor RAR and RXR are nuclear retinoid receptors which act as transcription factors. In response to RA binding, RAR/RXR undergo conformational changes and co-activate HAT to recruit mediators into the RNA Pol II complex to initiate gene transcription. RA also upregulates interferon (IFN) regulator factor -1 (IRF-1) expression and IRF-1 is highly expressed in activated, but not in resting, CD4 T cells. IRF-1 is required for full NF-kb transcriptional activity at the HIV-1LTR, and is also required for efficient HIV replication. IRF-1 also can interact with HAT, such as p300/CBP (cAMP-responsive-element-binding factor (CREB)-binding protein) to evoke HIV transcription from the LTR in the absence of Tat. RA can also increase p300/CBP expression;p300/CBP acetylates HIV-Tat on a nucleosome (nuc) assembled HIV proviral DNA to increase transcription of HIV-1. In preliminary studies, we found that acitretin alone is a weak activator o HIV-1 transcription compare to suberoylanilide hydroxamic acid (SAHA) (HDACi), or the phorbol ester, prostratin, but acts synergistically with SAHA or prostratin to greatly induce HIV expression from latently infected cells. Acitretin treatment increases RXR, IRF-1 and p300 expression but does not induce polyclonal activation of CD4 T cells as measured by gene expression and cell surface immunophenotyping for markers of T cell activation. We propose this R21 project to define acitretin as a new drug for use in combination treatment to reduce the latent HIV reservoir.
The aims of this project are to characterize mechanisms of acitretin activation of HIV-1 transcription in cell lines latently infected with HIV (Aim1) and to define thein vitro activity of acitretin alone and in combination with HDACi or phorbol esters for inducing vira transcription and clearance of CD4 T cells carrying HIV from HIV patients on suppressive HAART (Aim2) as the first steps in the development of a novel strategy for HIV eradication.
This project addresses acitretin activation of the HIV LTR to reverse HIV latency in CD4 T cells from HAART treated, virally suppressed, HIV patients. We will investigate mechanisms of action such as induction of IRF-1, p300/CBP, and recruitment and binding of positive transcription elongation factor b (p-TEFb) to the latent HIV promoter by acitretin used alone or in combination with other drugs. Next we will assess the ability of acitretin, alone or combined with SAHA or prostratin, to induce HIV expression from CD4 T cells obtained from on- HAART HIV patients and the result of such viral induction on cell clearance and death from cytotoxic effects. The results of this project will be directly relevant to development of a novel strategy for the potential eradication of HIV.
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