Targeted Disruption of the Inhibitor of DNA Binding 4 (Id4) Gene Alters Photic Entrainment of the Circadian Clock

Inhibitor of DNA binding (Id) genes comprise a family of four helix-loop-helix (HLH) transcriptional inhibitors. Our earlier studies revealed a role for ID2 within the circadian system, contributing to input, output, and core clock function through its interaction with CLOCK and BMAL1. Here, we explore the contribution of ID4 to the circadian system using a targeted disruption of the Id4 gene. Attributes of the circadian clock were assessed by monitoring the locomotor activity of Id4-/- mice, and they revealed disturbances in its operation. Id4-mutant mice expressed a shorter circadian period length, attenuated phase shifts in responses to continuous and discrete photic cues, and an advanced phase angle of entrainment under a 12:12 light:dark cycle and under short and long photoperiods. To understand the basis for these properties, suprachiasmatic nucleus (SCN) and retinal structures were examined. Anatomical analysis reveals a smaller Id4-/- SCN in the width dimension, which is a finding consistent with its smaller brain. As a result of this feature, anterograde tracing in Id4-/- mice revealed retinal afferents innovate a disproportionally larger SCN area. The Id4-/- photic entrainment responses are unlikely to be due to an impaired function of the retinal pathways since Id4-/- retinal anatomy and function tested by pupillometry were similar to wild-type mice. Furthermore, these circadian characteristics are opposite to those exhibited by the Id2-/- mouse, suggesting an opposing influence of the ID4 protein within the circadian system; or, the absence of ID4 results in changes in the expression or activity of other members of the Id gene family. Expression analysis of the Id genes within the Id4-/- SCN revealed a time-of-day specific elevated Id1. It is plausible that the increased Id1 and/or absence of ID4 result in changes in interactions with bHLH canonical clock components or with targets upstream and/or downstream of the clock, thereby resulting in abnormal properties of the circadian clock and its entrainment.

Strategies to Inhibit Hepatitis B Virus at the Transcript Level

Approximately 240 million people are chronically infected with hepatitis B virus (HBV), despite four decades of effective HBV vaccination. During chronic infection, HBV forms two distinct templates responsible for viral transcription: (1) episomal covalently closed circular (ccc)DNA and (2) host genome-integrated viral templates. Multiple ubiquitous and liver-specific transcription factors are recruited onto these templates and modulate viral gene transcription. This review details the latest developments in antivirals that inhibit HBV gene transcription or destabilize viral transcripts. Notably, nuclear receptor agonists exhibit potent inhibition of viral gene transcription from cccDNA. Small molecule inhibitors repress HBV X protein-mediated transcription from cccDNA, while small interfering RNAs and single-stranded oligonucleotides result in transcript degradation from both cccDNA and integrated templates. These antivirals mediate their effects by reducing viral transcripts abundance, some leading to a loss of surface antigen expression, and they can potentially be added to the arsenal of drugs with demonstrable anti-HBV activity. Thus, these candidates deserve special attention for future repurposing or further development as anti-HBV therapeutics.

Development of 7SK snRNA Mimics That Inhibit HIV Transcription

The 332-nucleotide small nuclear RNA (snRNA) 7SK is a highly conserved non-coding RNA that regulates transcriptional elongation. By binding with positive transcriptional elongation factor b (P-TEFb) via HEXIM1, 7SK snRNA decreases the kinase activity of P-TEFb and inhibits transcriptional elongation. Additionally, it is reported that 7SK inhibition results in the stimulation of human immunodeficiency virus (HIV)-specific transcription. These reports suggest that 7SK is a naturally occurring functional molecule as negative regulator of P-TEFb and HIV transcription. In this study, we developed functional oligonucleotides that mimic the function of 7SK (7SK mimics) as novel inhibitors of HIV replication. We defined the essential region of 7SK regarding its suppressive effects on transcriptional downregulation using an antisense strategy. Based on the results, we designed 7SK mimics containing the defined region. The inhibitory effects of 7SK mimics on HIV-1 long terminal repeat promoter specific transcription was drastic compared with those of the control mimic molecule. Notably, these effects were found to be more enhanced by co-transfection with Tat-expressing plasmids. From these results, it is indicated that 7SK mimics may have great therapeutic potential for HIV/AIDS treatment.

Regulation of MYB Transcription Factors of Anthocyanin Synthesis in Lily Flowers

Flower color is the decisive factor that affects the commercial value of ornamental flowers. Therefore, it is important to study the regulation of flower color formation in lily to discover the positive and negative factors that regulate this important trait. In this study, MYB transcription factors (TFs) were characterized to understand the regulatory mechanism of anthocyanin biosynthesis in lily. Two R2R3-MYB TFs, LvMYB5, and LvMYB1, were found to regulate anthocyanin biosynthesis in lily flowers. LvMYB5, which has an activation motif, belongs to the SG6 MYB protein subgroup of Arabidopsis thaliana. Transient expression of LvMYB5 indicated that LvMYB5 can promote coloration in Nicotiana benthamiana leaves, and that expression of LvMYB5 increases the expression levels of NbCHS, NbDFR, and NbANS. VIGS experiments in lily petals showed that the accumulation of anthocyanins was reduced when LvMYB5 was silenced. Luciferase assays showed that LvMYB5 can promote anthocyanin synthesis by activating the ANS gene promoter. Therefore, LvMYB5 plays an important role in flower coloration in lily. In addition, the transient expression experiment provided preliminary evidence that LvMYB1 (an R2R3-MYB TF) inhibits anthocyanin synthesis in lily flowers. The discovery of activating and inhibitory factors related to anthocyanin biosynthesis in lily provides a theoretical basis for improving flower color through genetic engineering. The results of our study provide a new direction for the further study of the mechanisms of flower color formation in lilies.

HIV-1 Transcription Inhibitor 1E7-03 Restores LPS-Induced Alteration of Lung Leukocytes' Infiltration Dynamics and Resolves Inflammation in HIV Transgenic Mice

Human immunodeficiency virus (HIV)-infected individuals treated with anti-retroviral therapy often develop chronic non-infectious lung disease. To determine the mechanism of HIV-1-associated lung disease we evaluated the dynamics of lung leukocytes in HIV-1 transgenic (Tg) mice with integrated HIV-1 provirus. In HIV-Tg mice, lipopolysacharide (LPS) induced significantly higher levels of neutrophil infiltration in the lungs compared to wild-type (WT) mice. In WT mice, the initial neutrophil infiltration was followed by macrophage infiltration and fast resolution of leukocytes infiltration. In HIV-Tg mice, resolution of lung infiltration by both neutrophils and macrophages was significantly delayed, with macrophages accumulating in the lumen of lung capillaries resulting in a 45% higher rate of mortality. Trans-endothelial migration of HIV-Tg macrophages was significantly reduced in vitro and this reduction correlated with lower HIV-1 gene expression. HIV-1 transcription inhibitor, 1E7-03, enhanced trans-endothelial migration of HIV-Tg macrophages in vitro, decreased lung neutrophil infiltration in vivo, and increased lung macrophage levels in HIV-Tg mice. Moreover, 1E7-03 reduced levels of inflammatory IL-6 cytokine, improved bleeding score and decreased lung injury. Together this indicates that inhibitors of HIV-1 transcription can correct abnormal dynamics of leukocyte infiltration in HIV-Tg, pointing to the utility of transcription inhibition in the treatment of HIV-1 associated chronic lung disease.

Licochalcone A Inhibits BDNF and TrkB Gene Expression and Hypoxic Growth of Human Tumor Cell Lines

Hypoxic cellular proliferation is a common feature of tumor cells and is associated with tumor progression. Therefore, the inhibition of hypoxic cellular proliferation is expected to regulate malignancy processes. Licochalcone A (LicA) is known to show inhibitory effects on cell growth in normoxia, but it is unclear whether LicA exerts similar effects in hypoxia. Here, we studied the inhibitory activity of LicA in the hypoxic cellular proliferation of tumor cells and its molecular mechanism using human cell lines derived from various tumors including neuroblastoma and colorectal cancer. LicA inhibited cell growth at a 50% inhibitory concentration between 7.0 and 31.1 µM in hypoxia. LicA significantly suppressed hypoxic induction of tropomyosin receptor kinase B (TrkB) gene expression at the transcription level. LicA also downregulated mRNA levels of the TrkB high-affinity ligand brain-derived neurotrophic factor, but not neurotrophin-4, another TrkB ligand, or glyceraldehyde-3-phosphate dehydrogenase, indicating that the inhibitory activity of LicA is selective. Since both LicA-treatment and TrkB-knockdown decreased activation of protein kinase B in hypoxia, LicA exerts its inhibitory effect against hypoxic cell growth through inhibition of the TrkB-AKT axis. These results suggest that LicA has therapeutic potential for malignant tumors including neuroblastoma and colorectal cancer.

Repression of p53-mediated transcription by MDM2: a dual mechanism

The oncoprotein MDM2 binds to the activation domain of the tumor suppressor p53 and inhibits its ability to stimulate transcription. This same region of p53 is able to bind several basal transcription factors that appear to be important for the transactivation function of p53. It has therefore been suggested that MDM2 acts to inhibit p53 by concealing its activation domain from the basal machinery. Here we present data suggesting that MDM2 possesses an additional inhibitory function. Our experiments reveal that in addition to a p53-binding domain, MDM2 also contains an inhibitory domain that can directly repress basal transcription in the absence of p53. By fusing portions of MDM2 to a heterologous DNA-binding domain to allow p53-independent promoter recruitment, we have localized this inhibitory domain to a region encompassing amino acids 50-222 of MDM2. Furthermore, the function of this inhibitory domain does not require the presence of either TFIIA or the TAFs. Of the remaining basal factors, both the small subunit of TFIIE and monomeric TBP are bound by the MDM2 inhibitory domain. It is possible that MDM2 inhibits the ability of the preinitiation complex to synthesize RNA through one of these interactions. Our results are consistent with a model in which MDM2 represses p53-dependent transcription by a dual mechanism: a masking of the activation domain of p53 through a protein-protein interaction that additionally serves to recruit MDM2 to the promoter where it directly interferes with the basal transcription machinery.