Expert review of the joint team of Hu Deqing/Gao Xin revealed the epigenetic and transcriptionary regulation mechanism of HIV latent infection and replication.

Chen Fei (Fudan University) edited by Chen Fei (Fudan University) acquired immunodeficiency syndrome (AIDS) is an infectious disease caused by human immunodeficiency virus (HIV) and has great harm to human health.according to the data statistics of CDC in China, the number of new cases of AIDS and the number of deaths showed an increasing trend year by year. By the end of 2018, there were about 1.25 million people living with AIDS in China.HIV includes two types: HIV-1 and HIV-2, among which HIV-1 is the main pathogen causing AIDS.HIV infects CD4 + T lymphocytes in human body through sexual contact, blood and vertical infection between mother and infant, which damages the immune system of the body and causes various fatal opportunistic infections or malignant tumors.since the discovery and isolation of HIV virus by Fran ó oise Barr é - sinoussi and Luc Montagnier in France in 1983, great progress has been made in the pathogenesis of HIV and ADIS prevention and control methods in the past 30 years, especially the highly active antiretroviral therapy (highly active antiretroviral therapy) proposed by Chinese American scientist he Dayi in 1996, HAART (HAART) therapy makes once fatal aids a chronic disease that most patients can survive for a long time.however, the HIV-1 pre virus latent in the target cells is transcriptionally suppressed and can escape the attack of host immune system and HAART.when HAART treatment is stopped, the provirus will undergo rapid gene transcription activation and replication, resulting in a large number of virus particles in the body of patients and produce AIDS clinical symptoms [1].therefore, latent HIV-1 infection is the most important obstacle to cure AIDS.further study on the molecular mechanism of HIV latent infection and replication can reveal new anti AIDS drug design targets, and it is expected to eradicate latent HIV in patients so as to achieve complete cure of AIDS.HIV belongs to Retroviridae, and its genome is composed of two identical single positive strand RNA. The virus particles contain reverse transcriptase (RT) and integrase (in).under the catalysis of RT, viral genomic RNA was transformed into dsDNA, and then dsDNA was selectively integrated into the host chromatin region with active transcription under the assistance of in and ledgf / p75.proviral gene transcription is driven by long terminal repeat (LTR), and its activity is regulated by many factors such as viral protein, host transcription factors, chromatin modification and structural changes, and RNA polymerase II transcription pause and release.ledgf / p75 is a chromatin modification binding protein containing PWWP domain. In addition to regulating the selective integration of HIV in the host genome by binding in, ledgf / p75 can also be used as a binding factor of multiple protein complexes in cells and participate in the regulation of a variety of biological processes, including chromatin modification, gene transcription, and selective splicing [2-4].pre HIV viruses hijack epigenetic and transcriptional regulation mechanisms in host cells to activate or silence viral gene transcription, thus maintaining its latency and replication.in view of the important role of ledgf / p75 in regulating gene transcription in host cells, does ledgf / p75 affect the replication fate of the integrated provirus in the host cell in addition to regulating the selective integration of HIV? On May 15, 2020, Hu Deqing research group of Tianjin Medical University / State Key Laboratory of Experimental Hematology, in collaboration with Dr. Gao Xin, published the "competition between Paf1 and Mll1 / Compass conferrs the posing function of ledgf / p75 in HIV latency and viral "Reactivation" (the first author is Gao Ru, a doctoral student in 2018) Ledgf / p75 plays an opposite role in the regulation of viral gene transcription in the latent infection and replication activation of HIV pre virus, and reveals the mechanism of its function in transcription extension and chromatin modification depending on Paf1 and Mll1 / Compass complex, respectively. It provides a new understanding of epigenetic and transcriptional regulation mechanism of HIV latent infection and replication, and provides a new understanding of the epigenetic and transcriptional regulation mechanism of HIV latent infection and replication, and provides a new way to clear the host cells The provirus of latent infection provides a potential target for drug intervention.in this study, the authors first used two cell models of HIV latent infection to find that the spontaneous transcriptional activation of the latent pre viral gene occurred after the deletion of ledgf / p75. However, knockdown of ledgf / p75 inhibited the transcriptional activation of viral genes when the authors induced proviral replication in host cells, suggesting that ledgf / p75 has the function of inhibiting and activating viral gene transcription in the latent maintenance and replication of provirus.the expression of ledgf / p75 was decreased, and the viral genes in the active transcription state could not be effectively restored to the transcriptional inhibition state, indicating that ledgf / p75 also plays an important role in the establishment of pre viral latent state. so what mechanism does ledgf / p75 use to inhibit the gene transcription of latent pre virus? By using the methods of affinity purification and multi-dimensional protein identification technology (MudPIT), we found that Paf1 complex can bind to ledgf / p75 and play an important role in the establishment and maintenance of latent HIV infection. However, the deletion of Paf1 complex did not affect the transcriptional activation of viral genes during the replication of provirus. in order to reveal the mechanism of ledgf / p75 and Paf1 inhibiting proviral gene transcription in latent state, the authors used two fluorescence reporting systems, HIV-LTR and GAL4 uas-hiv-ltr respectively, and found that ledgf / p75 and Paf1 directly inhibited the transcription activity of HIV LTR in an interdependent manner, and Paf1's transcriptional inhibition function on LTR required recruitment of ledgf / p75 on LTR. the mammalian Paf1 complex was first isolated and identified by Zhu Bing, a researcher from the Institute of Biophysics, Chinese Academy of Sciences, during his postdoctoral research in Dany Reinberg laboratory [5]. early studies suggested that its function was to promote gene transcription extension by binding with RNA polymerase II. recent studies have found that Paf1 complex can not only promote gene transcription extension, but also play a role in the establishment of RNA polymerase II transcription pause, transcription termination, mRNA poly (a) tailing and selective splicing downstream of gene promoter [6]. one of the most obvious features of latent HIV pre virus LTR is RNA Pol II (RNA Pol II) We found that knockdown of Paf1 and ledgf / p75 could release RNA polymerase II in LTR, which indicated that ledgf / p75 could inhibit viral gene transcription by establishing RNA polymerase II transcription pause on pre viral LTR by Paf1, so as to establish and maintain latent infection of previrus. in order to study the activation mechanism of ledgf / p75 on Pro viral gene transcription during replication, the authors detected the changes of chromatin modification on LTR and found that the level of h3k4me3 increased sharply during the replication of provirus, suggesting that H3K4 methyltransferase may be involved in regulating the transcription activation of previral gene during replication. during the study in Ali shilatifard laboratory, the corresponding author focused on the biochemical mechanism of the establishment of histone H3K4 methylation modification, and systematically revealed the role of compass complex members in the establishment of H3K4 methylation modification in different regions of chromatin [7-9]. subsequently, the authors examined the regulatory effects of compass family members on the transcription of proviral genes during replication, and found that Mll1 / Compass complex is necessary for the establishment and maintenance of viral gene transcription activation. previous studies have found that ledgf / p75 is a binding protein of Mll1 / Compass complex, which can recruit Mll1 fusion protein formed by chromosomal heterotopic to genes related to self-renewal regulation of hematopoietic stem cells, resulting in abnormal transcriptional activation, thus promoting the occurrence of leukemia [3,10]. the authors found that ledgf / 75 plays an important role in the binding of Mll1 / Compass complex to LTR and in the activation of viral gene transcription, indicating that HIV pre viral replication and Mll1 heterotopic protein adopt similar epigenetic mechanisms to promote the occurrence and progress of the disease. The interaction between Paf1 and Mll1 was found to bind to the IBD (integrated binding domain) domain of ledgf / p75 and revealed that their interaction with ledgf / p75 was mutually exclusive. the authors found that Mll1 binding to ledgf / p75 and LTR increased, while Paf1 binding to ledgf / p75 and LTR decreased. so what mechanism makes the binding of ledgf / p75 to Paf1 in latent HIV infection state change to Mll1 binding during replication? Structural biology studies have shown that Mll1 binds to ledgf / p75 in a phosphorylation dependent manner via the IBM (IBD biding motif) motif (11). the authors then analyzed the mass spectrometry data of Mll1 phosphorylation and found that S136, s142 and S153 sites in IBM region could be phosphorylated in vivo. site directed mutagenesis of these three sites showed that their phosphorylation modification played a key role in the competitive binding of Mll1 and Paf1 to ledgf / p75 and LTR. in order to find the kinase that phosphorylates Mll1 during proviral replication, the authors analyzed the mass spectrum data of Mll1 interacting proteins and knocked down the potential kinases that bind to Mll1. It was found that the kinase csnk2-a2 plays an important role in IBM phosphorylation and Mll1 binding to ledgf / p75 and LTR. It was found that NF - κ B could up regulate the expression of csnk2-a2. knockdown of csnk2-a2 expression or interference of its kinase activity can significantly inhibit the transcriptional activation of viral genes during replication. these results indicate that NF - κ B-mediated csnk2-a2 protein expression upregulates phosphorylation of IBM motif, which makes Mll1 competitively bind to ledgf / p75, and establishes h3k4me3 in the chromatin region of ltr; by releasing Paf1 binding to LTR and recruiting Sec complex, the transcription suspended RNA polymerase II can be efficiently extended (productive) In order to enhance the transcription of viral genes. note: the regulatory function and mechanism of ledgf / p75 on viral gene transcription during latent infection and replication of HIV. In general, this study expanded the function of ledgf / p75 from the known regulation of HIV integration in host genome to the transcriptional regulation of viral gene during pre viral incubation and replication, and elaborated the role of transcription extension and epigenetic modification in the regulation of viral gene transcription It provides a new idea and target for drug intervention to eliminate latent HIV in host cells. Hu Deqing, Professor, School of basic medicine, Tianjin Medical University, PI, doctoral supervisor, Tianjin Key Laboratory of epigenetics and State Key Laboratory of experimental hematology. in 2010, he graduated from the Institute of Biophysics, Chinese Academy of Sciences, and then worked at Northwestern University and Stowers Institute for medical research The laboratory conducted postdoctoral research and completed professional training in epigenetics and stem cell biology. at present, he has published several research papers in molecular cell (2013, 2017), nature structure & amp; molecular biology, genes & amp; development, science advances and other journals, with a total of more than 1500 citations, and the highest single citation within 5 yearsThe function and mechanism of epigenetic modification in regulation of latent infection and replication of HIV by ledgf / p75 (science advances, 2020). expert comments on Chen Fei (young researcher of Biomedical Research Institute and Affiliated Cancer Hospital of Fudan University, winner of special excellent award of national excellent self funded international student scholarship, research direction: cancer epigenetics)