Global m6A methylation and gene expression patterns in human microglial HMC3 cells infected with HIV-1

The OLR1/NF-κB feedback loop exacerbates HIV-1 Tat-induced microglial inflammatory response and neuronal apoptosis

Oxidized low density lipoprotein receptor 1 (OLR1), a type II integral membrane glycoprotein, is involved in multiple neurological diseases. However, the roles and mechanisms of OLR1 in HIV-associated neurocognitive disorder (HAND) remain unclear. In the central nervous system, Transactivator of transcription (Tat) induces inflammatory response in microglia, thereby leading to neuronal apoptosis. In the present study, we demonstrated that OLR1 expression was upregulated during ectopic expression of Tat or soluble Tat stimulus in BV-2 microglial cells. Moreover, OLR1 signaling was proved to facilitate Tat-triggered inflammatory response and alleviated the microglia-derived conditioned media-mediated HT-22 neural cells apoptosis in a NF-κB-dependent manner. Conversely, Tat augmented OLR1 expression via NF-κB signaling pathway. Finally, in mouse models, we determined that silencing of OLR1 significantly ameliorated Tat‑induced neuroinflammation and hippocampal neuronal death. Taken together, our study clarifies the potential role of the OLR1/NF-κB feedback loop in Tat-induced microglial inflammatory response and neuronal apoptosis, which could be a novel therapeutic target for relief of HAND.

Single-base m6A epitranscriptomics reveals novel HIV-1 host interaction targets in primary CD4+ T cells

N 6-methyladenosine (m6A) is the most prevalent cellular mRNA modification and plays a critical role in regulating RNA stability, localization, and gene expression. m6A modification plays a vital role in modulating the expression of viral and cellular genes during HIV-1 infection. HIV-1 infection increases cellular RNA m6A levels in many cell types, which facilitates HIV-1 replication and infectivity in target cells. However, the function of m6A modification in regulating HIV-1 infection of primary CD4+ T cells remains unclear. Here, we demonstrate that HIV-1 infection of Jurkat CD4+ T cells and primary CD4+ T cells promotes the interaction between the m6A writer complex subunits methyltransferase-like 3 and 14 (METTL3/METTL14). Using single-base m6A-specific RNA sequencing, we identified several differentially m6A-modified cellular mRNAs, including perilipin 3 (PLIN3), during HIV-1 infection in primary CD4+ T cells. Interestingly, HIV-1 infection increased PLIN3 mRNA level by enhancing its stability, but PLIN3 protein level was decreased. Knocking down PLIN3 in primary CD4+ T cells reduced HIV-1 production but enhanced virion infectivity. In contrast, in Jurkat cells, PLIN3 mRNA and protein expression levels were unaffected by HIV-1 infection, and knocking out PLIN3 did not impact HIV-1 production or infectivity. These results indicate that the interplay between HIV-1 and PLIN3 is cell-type specific and only observed in primary CD4+ T cells. Overall, our results highlight the importance of m6A RNA modification in HIV-1-infected primary CD4+ T cells and suggest its significance as a regulatory mechanism in HIV-1 infection.

When animal viruses meet N6-methyladenosine (m6A) modifications: for better or worse?

N6-methyladenosine (m6A) is a prevalent and dynamic RNA modification, critical in regulating gene expression. Recent research has shed light on its significance in the life cycle of viruses, especially animal viruses. Depending on the context, these modifications can either enhance or inhibit the replication of viruses. However, research on m6A modifications in animal virus genomes and the impact of viral infection on the host cell m6A landscape has been hindered due to the difficulty of detecting m6A sites at a single-nucleotide level. This article summarises the methods for detecting m6A in RNA. It then discusses the progress of research into m6A modification within animal viruses' infections, such as influenza A virus, porcine epidemic diarrhoea virus, porcine reproductive, and respiratory syndrome virus. Finally, the review explores how m6A modification affects the following three aspects of the replication of animal RNA viruses: the regulation of viral genomic RNA function, the alteration of the m6A landscape in cells after viral infection, and the modulation of antiviral immunity through m6A modification. Research on m6A modifications in viral RNA sheds light on virus-host interactions at a molecular level. Understanding the impact of m6A on viral replication can help identify new targets for antiviral drug development and may uncover novel regulatory pathways that could potentially enhance antiviral immune responses.

Epitranscriptomic m6A modifications during reactivation of HIV-1 latency in CD4+ T cells

Despite effective antiretroviral therapy reducing HIV-1 viral loads to undetectable levels, the presence of latently infected CD4+ T cells poses a major barrier to HIV-1 cure. N6-methyladenosine (m6A) modification of viral and cellular RNA has a functional role in regulating HIV-1 infection. m6A modification of HIV-1 RNA can affect its stability, translation, and splicing in cells and suppresses type-I interferon induction in macrophages. However, the function of m6A modification in regulating HIV-1 latency reactivation remains unknown. We used the Jurkat T cell line-derived HIV-1 latency model (J-Lat cells) to investigate changes in m6A levels of cellular RNA in response to latency reversal. We observed a significant increase in m6A levels of total cellular RNA upon reactivation of latent HIV-1 in J-Lat cells. This increase in m6A levels was transient and returned to steady-state levels despite continued high levels of viral gene expression in reactivated cells compared to control cells. Upregulation of m6A levels occurred without significant changes in the protein expression of m6A writers or erasers that add or remove m6A, respectively. Knockdown of m6A writers in J-Lat cells significantly reduced HIV-1 reactivation. Treatment with an m6A writer inhibitor reduced cellular RNA m6A levels, along with a reduction in HIV-1 reactivation. Furthermore, using m6A-specific sequencing, we identified cellular RNAs that are differentially m6A-modified during HIV-1 reactivation in J-Lat cells. Knockdown of identified m6A-modified RNA validates these results with an established primary CD4+ T cell model of HIV-1 latency. These results show the importance of m6A RNA modification in HIV-1 latency reversal.

IMPORTANCE

RNA m6A modification is important for regulating gene expression and innate immune responses to HIV-1 infection. However, the functional significance of m6A modification during HIV-1 latency reactivation is unknown. To address this important question, in this study, we used established cellular models of HIV-1 latency, m6A-specific sequencing at single-base resolution, and functional assays. We demonstrate that HIV-1 latency reversal leads to increased levels of cellular m6A modification, correlates with cellular m6A levels, and is dependent on the catalytic activity of the m6A methyltransferase enzyme. We also identified cellular genes that are differentially m6A-modified during HIV-1 reactivation, as well as the sites of m6A within HIV-1 RNA. Our novel findings point toward a significant role for m6A modification in HIV-1 latency reversal.

The Functions of N-methyladenosine (m6A) Modification on HIV-1 mRNA

In recent years, there has been a growing interest in the study of RNA modifications, with some researchers focusing specifically on the connection between these modifications and viruses, as well as the impact they have on viral mRNA and its functionality. The most common type of RNA chemical modification is m6A, which involves the addition of a methyl group covalently to the N6 position of adenosine. It is a widely observed and evolutionarily conserved RNA modification. The regulation of m6A modification primarily involves methyltransferases (writers) and demethylases (erasers) and is mediated by m6A-binding proteins (readers). In HIV-1, m6A sites are predominantly located in the 5' untranslated region (5'UTR) and 3' untranslated region (3'UTR). Additionally, m6A modifications are also present in the RRE RNA of HIV-1. This review provides a detailed account of the effects of these m6A modifications on HIV-1 functionality.

Functional Impacts of Epitranscriptomic m6A Modification on HIV-1 Infection

Epitranscriptomic RNA modifications play a crucial role in the posttranscriptional regulation of gene expression. N6-methyladenosine (m6A) is the most prevalent internal modification of eukaryotic RNA and plays a pivotal role in RNA fate. RNA m6A modification is regulated by a group of cellular proteins, methyltransferases (writers) and demethylases (erasers), which add and remove the methyl group from adenosine, respectively. m6A modification is recognized by a group of cellular RNA-binding proteins (readers) that specifically bind to m6A-modified RNA, mediating effects on RNA stability, splicing, transport, and translation. The functional significance of m6A modification of viral and cellular RNA is an active area of virology research. In this review, we summarize and analyze the current literature on m6A modification of HIV-1 RNA, the multifaceted functions of m6A in regulating HIV-1 replication, and the role of viral RNA m6A modification in evading innate immune responses to infection. Furthermore, we briefly discuss the future directions and therapeutic implications of mechanistic studies of HIV-1 epitranscriptomic modifications.