[Molecular basis of HIV-1 latency - Part II: HIV-1 reactivation and therapeutic implications]

Epigenetic regulation of HIV-1 latency: focus on polycomb group (PcG) proteins

HIV-1 latency allows the virus to persist until reactivation, in a transcriptionally silent form in its cellular reservoirs despite the presence of effective cART. Such viral persistence represents a major barrier to HIV eradication since treatment interruption leads to rebound plasma viremia. Polycomb group (PcG) proteins have recently got a considerable attention in regulating HIV-1 post-integration latency as they are involved in the repression of proviral gene expression through the methylation of histones. This epigenetic regulation plays an important role in the establishment and maintenance of HIV-1 latency. In fact, PcG proteins act in complexes and modulate the epigenetic signatures of integrated HIV-1 promoter. Key role played by PcG proteins in the molecular control of HIV-1 latency has led to hypothesize that PcG proteins may represent a valuable target for future HIV-1 therapy in purging HIV-1 reservoirs. In this regard, various small molecules have been synthesized or explored to specifically block the epigenetic activity of PcG. In this review, we will highlight the possible therapeutic approaches to achieve either a functional or sterilizing cure of HIV-1 infection with special focus on histone methylation by PcG proteins together with current and novel pharmacological approaches to reactivate HIV-1 from latency that could ultimately lead towards a better clearance of viral latent reservoirs.

Heat Shock Factor 1 Mediates Latent HIV Reactivation

HSF1, a conserved heat shock factor, has emerged as a key regulator of mammalian transcription in response to cellular metabolic status and stress. To our knowledge, it is not known whether HSF1 regulates viral transcription, particularly HIV-1 and its latent form. Here we reveal that HSF1 extensively participates in HIV transcription and is critical for HIV latent reactivation. Mode of action studies demonstrated that HSF1 binds to the HIV 5'-LTR to reactivate viral transcription and recruits a family of closely related multi-subunit complexes, including p300 and p-TEFb. And HSF1 recruits p300 for self-acetylation is also a committed step. The knockout of HSF1 impaired HIV transcription, whereas the conditional over-expression of HSF1 improved that. These findings demonstrate that HSF1 positively regulates the transcription of latent HIV, suggesting that it might be an important target for different therapeutic strategies aimed at a cure for HIV/AIDS.

[CTIP2, a multifunctional protein: cellular physiopathology and therapeutic implications]

The transcription factor CTIP2 (BCL11B) is a multifunctional protein involved in numerous cell physiological processes. To date, many molecular mechanisms underlying this process have been discovered, which highlighted the importance of the epigenetic regulation of genes and the regulation of the elongation factor P-TEFb. Furthermore studies of the deregulation of CTIP2 showed the association of CTIP2 to numerous pathologies including cancer and cardiac hypertrophy. A better comprehension of the physiopathology of these diseases might lead to the design of therapeutical strategies intending to prevent CTIP2 deregulation. Moreover, CTIP2 and its associated proteins constitute potential targets in strategies aiming to reduce and/or purge HIV-1 cell reservoirs.

[Misregulation of P-TEFb activity: pathological consequences]

P-TEFb stimulates transcription elongation by phosphorylating the carboxy-terminal domain of RNA pol II and antagonizing the effects of negative elongation factors. Its cellular availability is controlled by an abundant non coding RNA, conserved through evolution, the 7SK RNA. Together with the HEXIM proteins, 7SK RNA associates with and sequesters a fraction of cellular P-TEFb into a catalytically inactive complex. Active and inactive forms of P-TEFb are kept in a functional and dynamic equilibrium tightly linked to the transcriptional requirement of the cell. Importantly, cardiac hypertrophy and development of various types of human malignancies have been associated with increased P-TEFb activity, consequence of a disruption of this regulatory equilibrium. In addition, the HIV-1 Tat protein also releases P-TEFb from the 7SK/HEXIM complex during viral infection to promote viral transcription and replication. Here, we review the roles played by the 7SK RNP in cancer development, cardiac hypertrophy and AIDS.

[Infection of semen-producing organs by HIV and role in virus dissemination]

Despite semen being the main vector of human immunodeficiency virus (HIV) dissemination worldwide, the origin of the virus in this bodily fluid remains unknown. Of particular significance is the persistence of virus release in the semen of a subset of HIV-infected men under antiretroviral therapy, who otherwise show an undetectable blood viral load. It is therefore considered critical to identify the sources of virus shedding in semen for the more efficient control of HIV transmission. Our recent findings indicate HIV infection of several semen-producing organs, including the testis (which represents a pharmacological sanctuary for several antiretroviral drugs). This reinforces phylogenetic observations suggesting that the free viral particles and infected cells contaminating semen are produced within the male genital tract. The fact that HIV replicates within the male genital organs raises several questions: Is one or several of the male genital tract organs responsible for the persistence of HIV in semen despite efficient antiviral therapies? What is the nature of HIV interactions with spermatozoa and testicular germ cells? Recent results established that semen from HIV negative men modifies HIV infectivity: does the seminal fluid from HIV+ men enhance or inhibit the efficiency of HIV sexual transmission?