LncRNA ZNNT1 induces p53 degradation by interfering with the interaction between p53 and the SART3-USP15 complex.

Mammalian genomes encode large number of long noncoding RNAs (lncRNAs) that play key roles in various biological processes, including proliferation, differentiation, and stem cell pluripotency. Recent studies have addressed that some lncRNAs are dysregulated in human cancers and may play crucial roles in tumor development and progression. Here, we show that the lncRNA ZNNT1 is required for the proliferation and tumorigenicity of colon cancer cells with wild-type p53. ZNNT1 knockdown leads to decreased ubiquitination and stabilization of p53 protein. Moreover, we demonstrate that ZNNT1 needs to interact with SART3 to destabilize p53 and to promote the proliferation and tumorigenicity of colon cancer cells. We further show that SART3 is associated with the ubiquitin-specific peptidase USP15 and that ZNNT1 may induce p53 destabilization by inhibiting this interaction. These results suggest that ZNNT1 interferes with the SART3-USP15 complex-mediated stabilization of p53 protein and thereby plays important roles in the proliferation and tumorigenicity of colon cancer cells. Our findings suggest that ZNNT1 may be a promising molecular target for the therapy of colon cancer.

UHRF1-KAT7-mediated regulation of TUSC3 expression via histone methylation/acetylation is critical for the proliferation of colon cancer cells.

The epigenetic factor UHRF1 regulates transcription by modulating DNA methylation and histone modification, and plays critical roles in proliferation, development, and tumorigenesis. Here, we show that Wnt/c-Myc signaling upregulates UHRF1, which in turn downregulates TUSC3, a candidate tumor suppressor gene that is frequently deleted or downregulated in several cancers. We also show that UHRF1-mediated downregulation of TUSC3 is required for the proliferation of colon cancer cells. Furthermore, we demonstrate that UHRF1 suppresses TUSC3 expression by interacting with methylated H3K14 and thereby suppressing the acetylation of H3K14 by the histone acetyltransferase KAT7. Our study provides evidence for the significance of UHRF1-KAT7-mediated regulation of histone methylation/acetylation in the proliferation of tumor cells and in a diverse set of biological processes controlled by Wnt/c-Myc signaling.

The RNA-binding protein Mex-3B plays critical roles in the development of steroid-resistant neutrophilic airway inflammation.

While most asthma can be treated with steroids, about 10%, called severe asthma, is refractory to steroids. It has recently been shown that in a subgroup of severe asthma cases, neutrophils that infiltrate into the airways play an important role in inflammation. However, the mechanisms underlying this increased neutrophil infiltration are not well understood. Here, using a mouse model of steroid-resistant neutrophilic inflammation, we show that mice deficient for the RNA-binding protein Mex-3B have significantly less neutrophil infiltration in the airways than wild-type mice. We further demonstrate that Mex-3B post-transcriptionally upregulates CXCL2, a chemokine that induces neutrophil chemotaxis and migration. Moreover, we show that treatment with either anti-CXCL2 antibody or anti-Mex-3B antisense oligonucleotide suppresses neutrophilic allergic airway inflammation. These results suggest that Mex-3B-mediated induction of CXCL2 is crucial for steroid-resistant neutrophilic allergic airway inflammation. Our findings suggest new strategies for therapeutic intervention in steroid-resistant severe asthma.

The RNA Binding Protein Mex-3B Is Required for IL-33 Induction in the Development of Allergic Airway Inflammation.

Allergic airway inflammation is one of the primary features of allergic asthma. Interleukin-33 (IL-33) is recognized as a key pro-inflammatory cytokine that mediates allergic airway inflammation, and its expression is elevated in this condition, but little is known about the regulatory mechanisms underlying IL-33 induction. Here, we show that the RNA binding protein Mex-3B plays a critical role in the induction of IL-33 in the development of allergic airway inflammation. We generated Mex3b(-/-) mice and found that they develop significantly less airway inflammation than wild-type mice due to reduced induction of IL-33. Furthermore, we show that Mex-3B directly upregulates IL-33 expression by inhibiting miR-487b-3p-mediated repression of IL-33. Moreover, we show that inhalation of an antisense oligonucleotide targeting Mex-3B suppresses allergic airway inflammation. Our data identify a signaling pathway that post-transcriptionally regulates IL-33 expression and suggest that Mex-3B could be a promising molecular target for the treatment of allergic asthma.

ATF6α stimulates cholesterogenic gene expression and de novo cholesterol synthesis.

The activating transcription factor 6α (ATF6α) is a sensor of the endoplasmic reticulum stress response that regulates the expression of genes involved in the unfolded protein response. Here we found that forced expression of a constitutively active form of ATF6α, ATF6(N), stimulated the expression of cholesterogenic genes, including 3-hydroxy-3-methyl-glutaryl (HMG)-CoA reductase, HMG-CoA synthase, and squalene synthase, and de novo cholesterol synthesis in hepatoma Huh-7 cells. An ATF6α mutant lacking the DNA-binding domain ATF6(N)ΔbZip failed to show these effects. Luciferase assays indicated that ATF6(N) overexpression stimulated the promoter activities of HMG-CoA reductase, HMG-CoA synthase, and squalene synthase. Chromatin immunoprecipitation assays revealed that ATF6(N) interacted with the promoter region of the HMG-CoA synthase gene. Collectively, these results indicate that ATF6α can regulate de novo cholesterol synthesis through stimulation of cholesterogenic gene expression.

Ecdysone receptor (EcR) suppresses lipid accumulation in the Drosophila fat body via transcription control.

Lipid metabolism drastically changes in response to the environmental factors in metazoans. Lipid is accumulated at the food rich condition, while mobilized in adipocyte tissue in starvation. Such lipid mobilization is also evident during the pupation of the insects. Pupation is induced by metamorphosis hormone, ecdysone via ecdysone receptor (EcR) with lipid mobilization, however, the molecular link of the EcR-mediated signal to the lipid mobilization remains elusive. To address this issue, EcR was genetically knocked-down selectively in 3rd instar larva fat body of Drosophila, corresponding to the adipocyte tissues in mammalians, that contains adipocyte-like cells. In this mutant, lipid accumulation was increased in the fat body. Lipid accumulation was also increased when knocked-down of taiman, which served as the EcR co-activator. Two lipid metabolism regulatory factor, E75B and adipose (adp) as well as cell growth factor, dMyc, were found as EcR target genes in the adipocyte-like cells, and consistently knock-down of these EcR target genes brought phenotypes in lipid accumulation supporting EcR function. These findings suggest that EcR-mediated ecdysone signal is significant in lipid metabolism in insects.

Epigenetic silencing of core histone genes by HERS in Drosophila.

Cell cycle-dependent expression of canonical histone proteins enables newly synthesized DNA to be integrated into chromatin in replicating cells. However, the molecular basis of cell cycle-dependency in the switching of histone gene regulation remains to be uncovered. Here, we report the identification and biochemical characterization of a molecular switcher, HERS (histone gene-specific epigenetic repressor in late S phase), for nucleosomal core histone gene inactivation in Drosophila. HERS protein is phosphorylated by a cyclin-dependent kinase (Cdk) at the end of S-phase. Phosphorylated HERS binds to histone gene regulatory regions and anchors HP1 and Su(var)3-9 to induce chromatin inactivation through histone H3 lysine 9 methylation. These findings illustrate a salient molecular switch linking epigenetic gene silencing to cell cycle-dependent histone production.

Glutamine stimulates the gene expression and processing of sterol regulatory element binding proteins, thereby increasing the expression of their target genes.

Here we show that the larger the amount of glutamine added to the medium, the more the expression of genes related to lipid homeostasis is promoted by the activation of sterol regulatory element binding proteins (SREBPs) at the transcriptional and post-translational levels in human hepatoma HepG2 cells. Glutamine increases the mRNA levels of several SREBP targets, including SREBP-2. The gene expression of SREBP-1a, a predominant form of SREBP-1 in most cultured cells and a target of the general transcription factor Sp1, is significantly augmented by glutamine via an increased binding of Sp1 to the SREBP-1a promoter. In contrast, the increased expression of SREBP targets including SREBP-2 is due to stimulation of the processing of SREBP proteins by glutamine. It is also shown that glutamine accelerates SREBP processing through increased transport of the SREBP/SREBP cleavage-activating protein complex from the endoplasmic reticulum to the Golgi apparatus. The processing of activating transcription factor 6 is activated by the same proteases as SREBPs in the Golgi in response to endoplasmic reticulum stress and is not induced by glutamine. Taken together, these results clearly demonstrate that glutamine brings about not only the induction of SREBP-1a transcription but also the stimulation of SREBP processing, thereby facilitating the gene expression of SREBP targets in cultured cells.