MicroRNA-155 Reinforces HIV Latency.

The presence of a small number of infected but transcriptionally dormant cells currently thwarts a cure for the more than 35 million individuals infected with HIV. Reactivation of these latently infected cells may result in three fates: 1) cell death due to a viral cytopathic effect, 2) cell death due to immune clearance, or 3) a retreat into latency. Uncovering the dynamics of HIV gene expression and silencing in the latent reservoir will be crucial for developing an HIV-1 cure. Here we identify and characterize an intracellular circuit involving TRIM32, an HIV activator, and miR-155, a microRNA that may promote a return to latency in these transiently activated reservoir cells. Notably, we demonstrate that TRIM32, an E3 ubiquitin ligase, promotes reactivation from latency by directly modifying IκBα, leading to a novel mechanism of NF-κB induction not involving IκB kinase activation.

Dynamic roles for NF-κB in HTLV-I and HIV-1 retroviral pathogenesis.

Viruses and hosts are involved in a continuing 'arms race'. The body deploys multiple defenses; however, viruses utilize generally superior and more rapidly evolving tactics for negating host immune surveillance and viral clearance. In the case of the two major pathogenic human retroviruses, human immunodeficiency virus-1 (HIV-1) and human T-lymphotrophic virus-I (HTLV-I), the nuclear factor-κB (NF-κB) transcription factor plays a key role in the host's anti-viral responses involving both the innate and adaptive arms of the immune response. Similarly, these retroviruses capably exploit NF-κB for their replication, spread, and pathogenic functions. In this review, we discuss the dynamic and intimate interplay that occurs between NF-κB and the HTLV-I and HIV-1 retroviral pathogens.

Acute ischaemic stroke during short-term travel to high altitude.

This is a case report of a young healthy adult who had acute cerebral infarcts after a short-term visit to high-altitude area. He developed acute onset of right-sided limb weakness and right hemianopia a few hours after arrival at an altitude of 3600 m by train. He was initially treated for high-altitude cerebral oedema but later computed tomography and magnetic resonance imaging confirmed ischaemic infarcts in the medial left occipital lobe and left thalamus. Subsequent investigations, including laboratory tests and imaging including an echocardiogram, revealed no culpable predisposing factors.

Myocyte enhancer factor 2 acetylation by p300 enhances its DNA binding activity, transcriptional activity, and myogenic differentiation.

Myocyte enhancer factor 2 (MEF2) family proteins are key transcription factors controlling gene expression in myocytes, lymphocytes, and neurons. MEF2 proteins are known to be regulated by phosphorylation. We now provide evidence showing that MEF2C is acetylated by p300 both in vitro and in vivo. In C2C12 myogenic cells, MEF2 is preferentially acetylated in differentiating myocytes but not in undifferentiated myoblasts. Several major acetylation sites are mapped to the transactivation domain of MEF2C, some of which are fully conserved in other MEF2 members from several different species. Mutation of these lysines affects MEF2 DNA binding and transcriptional activity, as well as its synergistic effect with myogenin in myogenic conversion assays. When introduced into C2C12 myoblasts, the nonacetylatable MEF2C inhibits myogenic differentiation. Thus, in addition to phosphorylation, MEF2 activity is also critically regulated by acetylation during myogenesis.

Keratin 6a reorganization for ubiquitin-proteasomal processing is a direct antimicrobial response.

Skin and mucosal epithelia deploy antimicrobial peptides (AMPs) to eliminate harmful microbes. We reported that the intermediate filament keratin 6a (K6a) is constitutively processed into antimicrobial fragments in corneal epithelial cells. In this study, we show that K6a network remodeling is a host defense response that directly up-regulates production of keratin-derived AMPs (KAMPs) by the ubiquitin-proteasome system (UPS). Bacterial ligands trigger K6a phosphorylation at S19, S22, S37, and S60, leading to network disassembly. Mutagenic analysis of K6a confirmed that the site-specific phosphorylation augmented its solubility. K6a in the cytosol is ubiquitinated by cullin-RING E3 ligases for subsequent proteasomal processing. Without an appreciable increase in K6a gene expression and proteasome activity, a higher level of cytosolic K6a results in enhanced KAMP production. Although proteasome-mediated proteolysis is known to produce antigenic peptides in adaptive immunity, our findings demonstrate its new role in producing AMPs for innate immune defense. Manipulating K6a phosphorylation or UPS activity may provide opportunities to harness the innate immunity of epithelia against infection.

Calcium/calcineurin synergizes with prostratin to promote NF-κB dependent activation of latent HIV.

Attempts to eradicate HIV have been thwarted by the persistence of a small pool of quiescent memory CD4 T cells that harbor a transcriptionally silent, integrated form of the virus that can produce infectious virions following an anamnestic immune response. Transcription factors downstream of T-cell receptor activation, such as NF-κB/Rel and nuclear factor of activated T cells (NFAT) transcription members, are considered important regulators of HIV transcription during acute HIV infection. We now report studies exploring their precise role as antagonists of HIV latency using cell and primary CD4 T cell models of HIV-1 latency. Surprisingly, RNA interference studies performed in J-Lat CD4 T cells suggested that none of the NFATs, including NFATc1, NFATc2, NFATc3, and NFAT5, played a key role in the reactivation of latent HIV. However, cyclosporin A markedly inhibited the reactivation response. These results were reconciled when calcium signaling through calcineurin was shown to potentiate prostratin induced activation of NF-κB that in turn stimulated the latent HIV long terminal repeat (LTR). Similar effects of calcineurin were confirmed in a primary CD4 T cell model of HIV latency. These findings highlight an important role for calcineurin in NF-κB-dependent induction of latent HIV transcription. Innovative approaches exploiting the synergistic actions of calcineurin and prostratin in the absence of generalized T-cell activation merit exploration as a means to attack the latent viral reservoir.

NF-κB/Rel: agonist and antagonist roles in HIV-1 latency.

PURPOSE OF REVIEW: To discuss recent advances in our understanding of the diverse roles of NF-κB/Rel family members in HIV-1 latency. RECENT FINDINGS: Various NF-κB/Rel family members can reinforce maintenance of HIV-1 latency. For example, p50 recruits histone deacetylase 1 to the HIV-1 long terminal repeat promoting chromatin condensation and reduced RNA Pol II recruitment. Low-level NF-κB activation during homeostatic proliferation of memory CD4 T cells induced by IL-7 and TCR signaling or OX40 action promotes expression of antiapoptotic gene targets such as BCL2 and BCLXL. Additionally, the IκB kinase phosphorylates FOXO3a transcription factor, blocking its induction of proapoptotic genes. These combined effects promote memory CD4 T-cell survival, thus maintaining the latent reservoir. Conversely, when the nontumorigenic phorbol ester prostratin is combined with histone deacetylase inhibitors, potent synergistic activation of latent HIV-1 occurs involving nuclear expression of NF-κB. SUMMARY: These recent findings highlight both the antagonistic and agonistic effects of the NF-κB signaling pathway on HIV-1 latency. Synergistic inducers might be useful for flushing of latent virus from reservoirs in infected patients. The ultimate, albeit lofty, goal is to achieve full viral eradication. However, a more reasonable goal might be a functional cure where patients experience a drug-free remission.

Functional characterization of an amino-terminal region of HDAC4 that possesses MEF2 binding and transcriptional repressive activity.

Like the full-length histone deacetylase (HDAC) 4, its amino terminus (amino acids 1-208) without the carboxyl deacetylase domain is also known to effectively bind and repress myocyte enhancer factor 2 (MEF2). Within this repressive amino terminus, we further show that a stretch of 90 amino acids (119-208) displays MEF2 binding and repressive activity. The same region is also found to associate specifically with HDAC1 which is responsible for the repressive effect. The amino terminus of HDAC4 can associate with the DNA-bound MEF2 in vitro, suggesting that it does not repress MEF2 simply by disrupting the ability of MEF2 to bind DNA. In vivo, MEF2 induces nuclear translocation of both the full-length HDAC4 and HDAC4-(1-208), whereas the nuclear HDAC4 as well as HDAC4-(1-208) in turn specifically sequesters MEF2 to distinct nuclear bodies. In addition, we show that MyoD and HDAC4 functionally antagonize each other to regulate MEF2 activity. Combined with data from others, our data suggest that the full-length HDAC4 can repress MEF2 through multiple independent repressive domains.