BTB and CNC homology 1 (Bach1) induces lung cancer stem cell phenotypes by stimulating CD44 expression

BACKGROUND

Growing evidence suggests that cancer stem cells (CSCs) are responsible for cancer initiation in tumors. Bach1 has been identified to contribute to several tumor progression, including lung cancer. The role of Bach1 in CSCs remains poorly known. Therefore, the function of Bach1 on lung CSCs was focused currently.

METHODS

The expression of Bach1, CD133, CD44, Sox2, Nanog and Oct4 mRNA was assessed using Real-Time Quantitative Reverse Transcription PCR (RT-qPCR). Protein expression of Bach1, CD133, CD44, Sox2, Nanog, Oct4, p53, BCL2, BAX, p-p38, p-AKT1, c-Fos and c-Jun protein was analyzed by western blotting. 5-ethynyl-29-deoxyuridine (EdU), colony formation, Flow cytometry analysis and transwell invasion assay were carried out to analyze lung cancer cell proliferation, apoptosis and invasion respectively. Tumor sphere formation assay was utilized to evaluate spheroid capacity. Flow cytometry analysis was carried out to isolate CD133 or CD44 positive lung cancer cells. The relationship between Bach1 and CD44 was verified using ChIP-qPCR and dual-luciferase reporter assay. Xenograft tumor tissues were collected for hematoxylin and eosin (HE) staining and IHC analysis to evaluate histology and Ki-67.

RESULTS

The ratio of CD44 + CSCs from A549 and SPC-A1 cells were significantly enriched. Tumor growth of CD44 + CSCs was obviously suppressed in vivo compared to CD44- CSCs. Bach1 expression was obviously increased in CD44 + CSCs. Then, via using the in vitro experiment, it was observed that CSCs proliferation and invasion were greatly reduced by the down-regulation of Bach1 while cell apoptosis was triggered by knockdown of Bach1. Loss of Bach1 was able to repress tumor-sphere formation and tumor-initiating CSC markers. A repression of CSCs growth and metastasis of shRNA-Bach1 was confirmed using xenograft models and caudal vein injection. The direct interaction between Bach1 and CD44 was confirmed by ChIP-qPCR and dual-luciferase reporter assay. Furthermore, mitogen-activated protein kinases (MAPK) signaling pathway was selected and we proved the effects of Bach1 on lung CSCs were associated with the activation of the MAPK pathway. As manifested, loss of Bach1 was able to repress p-p38, p-AKT1, c-Fos, c-Jun protein levels in lung CSCs. Inhibition of MAPK signaling remarkably restrained lung CSCs growth and CSCs properties induced by Bach1 overexpression.

CONCLUSION

In summary, we imply that Bach1 demonstrates great potential for the treatment of lung cancer metastasis and recurrence via activating CD44 and MPAK signaling.

MicroRNA-30c-5p protects against myocardial ischemia/reperfusion injury via regulation of Bach1/Nrf2

MicroRNAs (miRNAs) are critical regulatory factors in myocardial ischemia/reperfusion (I/R) injury. The miRNA miR-30c-5p has been reported as a key mediator in several myocardial abnormalities. However, the precise roles and mechanisms of miR-30c-5p in myocardial I/R injury remain not well-studied. This project aimed to explore the potential function of this miRNA in mediating myocardial I/R injury. Significant induction of miR-30c-5p was observed in myocardial tissue of rats with myocardial I/R injury in vivo and cardiomyocytes with hypoxia/re‑oxygenation (H/R) injury in vitro. Functional studies elucidated that forced expression of miR-30c-5p in rats effectively reduced infarct area, cardiac apoptosis, oxidative stress and inflammation induced by myocardial I/R injury. Moreover, in vitro cardiomyocytes with forced expression of miR-30c-5p were also protected from H/R-induced apoptosis, oxidative stress and inflammation. Importantly, BTB domain and CNC homology 1 (Bach1) was identified as a new target of miR-30c-5p. miR-30c-5p was shown to promote the activation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) via the inhibition of Bach1. The re-expression of Bach1 reversed miR-30c-5p-mediated-cardioprotective effects against myocardial I/R injury in vivo or H/R injury in vitro. Overall, our results demonstrate that forced expression of miR-30c-5p exhibited beneficial effects against myocardial I/R injury through enhancement of Nrf2 activation via inhibition of Bach1. This work reveals a novel molecular mechanism for myocardial I/R injury at the miRNA level and suggests a therapeutic value of miR-30c-5p in treatment of myocardial I/R injury.

Photoexcited CRYPTOCHROME 1 Interacts Directly with G-Protein β Subunit AGB1 to Regulate the DNA-Binding Activity of HY5 and Photomorphogenesis in Arabidopsis

Light and the heterotrimeric G-protein are known to antagonistically regulate photomorphogenesis in Arabidopsis. However, whether light and G-protein coordinate the regulation of photomorphogenesis is largely unknown. Here we show that the blue light photoreceptor cryptochrome 1 (CRY1) physically interacts with the G-protein β subunit, AGB1, in a blue light-dependent manner. We also show that AGB1 directly interacts with HY5, a basic leucine zipper transcriptional factor that acts as a critical positive regulator of photomorphogenesis, to inhibit its DNA-binding activity. Genetic studies suggest that CRY1 acts partially through AGB1, and AGB1 acts partially through HY5 to regulate photomorphogenesis. Moreover, we demonstrate that blue light-triggered interaction of CRY1 with AGB1 promotes the dissociation of HY5 from AGB1. Our results suggest that the CRY1 signaling mechanism involves positive regulation of the DNA-binding activity of HY5 mediated by the CRY1-AGB1 interaction, which inhibits the association of AGB1 with HY5. We propose that the antagonistic regulation of HY5 DNA-binding activity by CRY1 and AGB1 may allow plants to balance light and G-protein signaling and optimize photomorphogenesis.

Identification and characterization of BATF3 as a context-specific coactivator of the glucocorticoid receptor

The ability of the glucocorticoid receptor (GR) to regulate the transcriptional output of genes relies on its interactions with transcriptional coregulators. However, which coregulators are required for GR-dependent activation is context-dependent and can be influenced by the sequence of the DNA bound by GR and by the nature of the GR isoform responsible for the regulation of a gene. Here, we screened for GR-interacting proteins for which the interaction signal differed between two GR isoforms GRα and GRγ. These isoforms diverge by a single amino acid insertion in a domain, the lever arm, which adopts DNA sequence-specific conformations. We identify Basic Leucine Zipper ATF-Like Transcription Factor 3 (BATF3), an AP-1 family transcription factor, as a GR coregulator whose interaction with GR is modulated by the lever arm. Further, a combination of experiments uncovered that BATF3 acts as a gene-specific coactivator of GR whose coactivator potency is influenced by the sequence of the GR binding site. Together, our findings suggest that GR isoform and the sequence of GR binding site influence the interaction of GR with BATF3, which might direct the assembly of gene-specific regulatory complexes to fine-tune the expression of individual GR target genes.

Immunopathogenesis of IBD: Batf as a Key Driver of Disease Activity

BACKGROUND

Inflammatory bowel diseases (IBDs) represent a group of chronic immune-mediated disorders that are influenced by a genetic predisposition and additional environmental triggers. Genome-wide association studies strongly implicate that a number of immune system-related genetic variations are critically contributing to the initiation and promotion of intestinal inflammation. Especially the identification of the strong association of a series of single nucleotide polymorphisms including interleukin (IL)-23R, CCR6, signal transducer and activator of transcription 3 (Stat3) and Stat4 with IBD susceptibility point at a critical involvement of T cells and especially of IL-17a-producing Th17 cells in the immune pathogenesis of IBD. In line with this hypothesis, a series of preclinical studies have unequivocally established that T cells are key drivers of immune-mediated colitis. Interestingly, especially Th17 cells were identified to be highly prevalent in inflamed IBD tissues, a finding that seems to be functionally relevant as genetic inactivation studies in the mouse resulted in almost complete suppression of colitis development.

KEY MESSAGES

While targeting Th17 cell differentiation regulating transcription factors, as retinoic acid-related orphan receptor gamma t (RORγt) is effective in preventing murine colitis, one concern of drugs targeting RORγt in a clinical setting represents the large body of murine data unambiguously demonstrating that additional pathways within and outside the immune system are equally RORγt-dependent increasing the risk of undesirable side effects. The AP1 transcription factor Batf (B cell-activating transcription factor) appears to exclusively regulate pathways within lymphocytes. Importantly, Batf represents a central regulator of Th17 cell development and is strongly upregulated within IBD-affected tissues. Employing 2 acute colitis models, we demonstrate in this study that Batf-expressing T cells are critical drivers of T cell-mediated colitis while in contrast to Stat3 loss of Batf does not affect intestinal epithelial cell homeostasis ex vivo.

CONCLUSIONS

Targeting Batf in IBD emerges as an attractive therapeutic approach disabling colitogenic T cell activities while sparing off-target effects in the intestinal epithelial cell compartment.

The transcription factor BATF modulates cytokine-mediated responses in T cells

The transcription factor BATF (basic leucine zipper transcription factor, ATF-like), belongs to the AP-1 family of transcription factors and has been shown to be predominantly expressed in cells of haematopoietic origin, especially in B and T cells. In studies using Batf-deficient mice, a profound defect in the differentiation of T helper cells type 17 (Th17) and follicular T helper cells (Tfh) was described, as well as an impairment of antibody production with switched isotypes. More recently BATF has been described to influence also Th2 and Th9 responses in models of murine experimental asthma. In CD8(+) T cells BATF has been found associated with anti-viral responses. This review summarizes the role of BATF in CD4(+) T cell subsets and in CD8(+) T cells, with particular focus on this transcription factor in the setting of allergic asthma.

Increasing the affinity of selective bZIP-binding peptides through surface residue redesign

The coiled-coil dimer is a prevalent protein interaction motif that is important for many cellular processes. The basic leucine-zipper (bZIP) transcription factors are one family of proteins for which coiled-coil mediated dimerization is essential for function, and misregulation of bZIPs can lead to disease states including cancer. This makes coiled coils attractive protein-protein interaction targets to disrupt using engineered molecules. Previous work designing peptides to compete with native coiled-coil interactions focused primarily on designing the core residues of the interface to achieve affinity and specificity. However, folding studies on the model bZIP GCN4 show that coiled-coil surface residues also contribute to binding affinity. Here we extend a prior study in which peptides were designed to bind tightly and specifically to representative members of each of 20 human bZIP families. These "anti-bZIP" peptides were designed with an emphasis on target-binding specificity, with contributions to design-target specificity and affinity engineered considering only the coiled-coil core residues. High-throughput testing using peptide arrays indicated many successes. We have now measured the binding affinities and specificities of anti-bZIPs that bind to FOS, XBP1, ATF6, and CREBZF in solution and tested whether redesigning the surface residues can increase design-target affinity. Incorporating residues that favor helix formation into the designs increased binding affinities in all cases, providing low-nanomolar binders of each target. However, changes in surface electrostatic interactions sometimes changed the binding specificity of the designed peptides.

Transcription-independent role of Bach1 in mitosis through a nuclear exporter Crm1-dependent mechanism

The transcriptional repressor Bach1 mediates various stress responses. Despite its role in transcription, Bach1 is predominantly exported to the cytoplasm in a Crm1-dependent manner, but the functional role of its cytoplasmic retention is still unclear. We found that Bach1 was also excluded from mitotic chromatin by a C-terminal cytoplasmic localization sequence dependent and leptomycin B sensitive process. Bach1 depletion resulted in disordered mitotic chromosome alignment, which was rescued by Bach1 mutants lacking the BTB or DNA binding domains, suggesting its transcription-independent mechanism. We thus revealed a novel role of Bach1 in the regulation of mitotic chromosome dynamics.

Heme oxygenase 1 is induced by miR-155 via reduced BACH1 translation in endothelial cells

Heme oxygenase 1 (HO-1) is a stress-inducible enzyme that degrades redox-active heme-producing biliverdin, carbon monoxide, and Fe(2+). It protects cells under various stress conditions and mediates anti-inflammatory and vasodilatory effects in the endothelium. The expression of HMOX1, the HO-1 gene, is highly inducible and its transcriptional regulation is complex. HMOX1 is induced by various proinflammatory stimuli via NF-κB in human endothelial cells, but functional NF-κB-binding elements have not been identified from the human gene. However, the regulation of HMOX1 by the antioxidant-response element is firmly established, with the transcription factor BACH1 serving as a repressor and Nrf2 as an enhancer. miR-155 is one of the TNFα-inducible endothelial microRNAs predicted to bind to the BACH1 mRNA. Oligonucleotides mimicking miR-155 efficiently inhibited BACH1 protein translation, resulting in a concentration-dependent increase in HMOX1 mRNA and protein expression in human umbilical vein endothelial cells. Moreover, endogenous miR-155 was upregulated by TNFα via an NF-κB-dependent mechanism with a subsequent increase in HMOX1 expression. We propose that increased HMOX1 expression in endothelial cells by TNFα results from miR-155-induced repression of BACH1 rather than direct induction of HMOX1 via NF-κB, and that miR-155 is cytoprotective during inflammation by elevating HO-1 expression in endothelial cells.

A small-molecule c-Myc inhibitor, 10058-F4, induces cell-cycle arrest, apoptosis, and myeloid differentiation of human acute myeloid leukemia

OBJECTIVE

The protooncogene c-Myc plays an important role in the control of cell proliferation, apoptosis, and differentiation, and its aberrant expression is frequently seen in multiple human cancers, including acute myeloid leukemia (AML). As c-Myc heterodimerizes with Max to transactivate downstream target genes in leukemogenesis. Inhibition of the c-Myc/Max heterodimerization by the recently identified small-molecule compound, 10058-F4, might be a novel antileukemic strategy.

MATERIALS AND METHODS

HL-60, U937, and NB4 cells and primary AML cells were used to examine the effects of 10058-F4 on apoptosis and myeloid differentiation.

RESULTS

We showed that 10058-F4 arrested AML cells at G0/G1 phase, downregulated c-Myc expression and upregulated CDK inhibitors, p21 and p27. Meanwhile, 10058-F4 induced apoptosis through activation of mitochondrial pathway shown by downregulation of Bcl-2, upregulation of Bax, release of cytoplasmic cytochrome C, and cleavage of caspase 3, 7, and 9. Furthermore, 10058-F4 also induced myeloid differentiation, possibly through activation of multiple transcription factors. Similarly, 10058-F4-induced apoptosis and differentiation could also be observed in primary AML cells.

CONCLUSION

Our study has shown that inhibition of c-Myc/Max dimerization with small-molecule inhibitors affects multiple cellular activities in AML cells and represents a potential antileukemic approach.

Improved low molecular weight Myc-Max inhibitors

Compounds that selectively prevent or disrupt the association between the c-Myc oncoprotein and its obligate heterodimeric partner Max (Myc-Max compounds) have been identified previously by high-throughput screening of chemical libraries. Although these agents specifically inhibit the growth of c-Myc-expressing cells, their clinical applicability is limited by their low potency. We describe here several chemical modifications of one of these original compounds, 10058-F4, which result in significant improvements in efficacy. Compared with the parent structure, these analogues show enhanced growth inhibition of c-Myc-expressing cells in a manner that generally correlates with their ability to disrupt c-Myc-Max association and DNA binding. Furthermore, we show by use of a sensitive fluorescence polarization assay that both 10058-F4 and its active analogues bind specifically to monomeric c-Myc. These studies show that improved Myc-Max compounds can be generated by a directed approach involving deliberate modification of an index compound. They further show that the compounds specifically target c-Myc, which exists in a dynamic and relatively unstructured state with only partial and transient alpha-helical content.

The mitochondrial transcription termination factor mTERF modulates replication pausing in human mitochondrial DNA

The mammalian mitochondrial transcription termination factor mTERF binds with high affinity to a site within the tRNA(Leu(UUR)) gene and regulates the amount of read through transcription from the ribosomal DNA into the remaining genes of the major coding strand of mitochondrial DNA (mtDNA). Electrophoretic mobility shift assays (EMSA) and SELEX, using mitochondrial protein extracts from cells induced to overexpress mTERF, revealed novel, weaker mTERF-binding sites, clustered in several regions of mtDNA, notably in the major non-coding region (NCR). Such binding in vivo was supported by mtDNA immunoprecipitation. Two-dimensional neutral agarose gel electrophoresis (2DNAGE) and 5' end mapping by ligation-mediated PCR (LM-PCR) identified the region of the canonical mTERF-binding site as a replication pause site. The strength of pausing was modulated by the expression level of mTERF. mTERF overexpression also affected replication pausing in other regions of the genome in which mTERF binding was found. These results indicate a role for TERF in mtDNA replication, in addition to its role in transcription. We suggest that mTERF could provide a system for coordinating the passage of replication and transcription complexes, analogous with replication pause-region binding proteins in other systems, whose main role is to safeguard the integrity of the genome whilst facilitating its efficient expression.

A novel E4BP4 element drives circadian expression of mPeriod2

Period2 (Per2) is an essential component of the mammalian clock mechanism and robust circadian expression of Per2 is essential for the maintenance of circadian rhythms. Although recent studies have shown that the circadian E2 enhancer (a non-canonical E-box) accounts for most of the circadian transcriptional drive of mPer2, little is known about the other cis-elements of mPer2 oscillatory transcription. Here, we examined the contribution of E4BP4 to Per2 mRNA oscillation in the cell-autonomous clock. Knockdown experiments of E4BP4 in both Northern blots and real-time luciferase assays suggested that endogenous E4BP4 negatively regulates Per2 mRNA oscillation. Sequence analysis revealed two putative E4BP4-binding sites (termed A-site and B-site) on mammalian Per2 promoter regions. Luciferase assays with mutant constructs showed that a novel E4BP4-binding site (B-site) is responsible for E4BP4-mediated transcriptional repression of Per2. Furthermore, chromatin immunoprecipitation assays in vivo showed that the peak of E4BP4 binding to the B-site on the Per2 promoter almost matched the trough of Per2 mRNA expression. Importantly, real-time luciferase assays showed that the B-site in addition to the E2 enhancer is required for robust circadian expression of Per2 in the cell-autonomous clock. These findings indicated that E4BP4 is required for the negative regulation of mammalian circadian clocks.

Selective inhibition of c-Myc/Max dimerization and DNA binding by small molecules

bZip and bHLHZip protein family members comprise a large fraction of eukaryotic transcription factors and need to bind DNA in order to exert most of their fundamental biological roles. Their binding to DNA requires homo- or heterodimerization via alpha-helical domains, which generally do not contain obvious binding sites for small molecules. We have identified two small molecules, dubbed Mycro1 and Mycro2, which inhibit the protein-protein interactions between the bHLHZip proteins c-Myc and Max. Mycros are the first inhibitors of c-Myc/Max dimerization, which have been demonstrated to inhibit DNA binding of c-Myc with preference over other dimeric transcription factors in vitro. Mycros inhibit c-Myc-dependent proliferation, gene transcription, and oncogenic transformation in the low micromolar concentration range. Our data support the idea that dimeric transcription factors can be druggable even in the absence of obvious small-molecule binding pockets.

HTLV-I basic leucine zipper factor gene mRNA supports proliferation of adult T cell leukemia cells

Human T cell leukemia virus type I (HTLV-I) causes adult T cell leukemia (ATL) in 2-5% of carriers after a long latent period. An HTLV-I encoded protein, Tax, induces proliferation and inhibits apoptosis, resulting in clonal proliferation of infected cells. However, tax gene expression in ATL cells is disrupted by several mechanisms, including genetic changes in the tax gene and DNA methylation/deletion of the 5' long terminal repeat (LTR). Because Tax is the major target of cytotoxic T-lymphocytes in vivo, loss of Tax expression should enable ATL cells to escape the host immune system. The 5' LTR of HTLV-I is frequently hypermethylated or deleted in ATL cells, whereas the 3' LTR remains unmethylated and intact, suggesting the involvement of the 3' LTR in leukemogenesis. Here we show that a gene encoded by the minus strand of the HTLV-I proviral genome, HTLV-I basic leucine zipper factor (HBZ), is transcribed from 3'-LTR in all ATL cells. Suppression of HBZ gene transcription by short interfering RNA inhibits proliferation of ATL cells. In addition, HBZ gene expression promotes proliferation of a human T cell line. Analyses of T cell lines transfected with mutated HBZ genes showed that HBZ promotes T cell proliferation in its RNA form, whereas HBZ protein suppresses Tax-mediated viral transcription through the 5' LTR. Thus, the single HBZ gene has bimodal functions in two different molecular forms. The growth-promoting activity of HBZ RNA likely plays an important role in oncogenesis by HTLV-I.

A credit-card library approach for disrupting protein-protein interactions

Protein-protein interfaces are prominent in many therapeutically important targets. Using small organic molecules to disrupt protein-protein interactions is a current challenge in chemical biology. An important example of protein-protein interactions is provided by the Myc protein, which is frequently deregulated in human cancers. Myc belongs to the family of basic helix-loop-helix leucine zipper (bHLH-ZIP) transcription factors. It is biologically active only as heterodimer with the bHLH-ZIP protein Max. Herein, we report a new strategy for the disruption of protein-protein interactions that has been corroborated through the design and synthesis of a small parallel library composed of 'credit-card' compounds. These compounds are derived from a planar, aromatic scaffold and functionalized with four points of diversity. From a 285 membered library, several hits were obtained that disrupted the c-Myc-Max interaction and cellular functions of c-Myc. The IC50 values determined for this small focused library for the disruption of Myc-Max dimerization are quite potent, especially since small molecule antagonists of protein-protein interactions are notoriously difficult to find. Furthermore, several of the compounds were active at the cellular level as shown by their biological effects on Myc action in chicken embryo fibroblast assays. In light of our findings, this approach is considered a valuable addition to the armamentarium of new molecules being developed to interact with protein-protein interfaces. Finally, this strategy for disrupting protein-protein interactions should prove applicable to other families of proteins.