Seungmae Seo

Mechanistic Role for a Novel Glucocorticoid-KLF11 (TIEG2) Protein Pathway in Stress-induced Monoamine Oxidase A Expression

Background: The function of KLF11/TIEG2 under stressful conditions is undefined. Results: KLF11 increases brain MAO expression through its promoter and a chromatin partner, which can be enhanced by stress. Conclusion: This is the first elucidation of mechanisms underlying stress-induced KLF11-MAO up-regulation. Significance: This novel KLF11-MAO pathway may play an important role in stress-related brain disorders. Chronic stress is a risk factor for psychiatric illnesses, including depressive disorders, and is characterized by increased blood glucocorticoids and brain monoamine oxidase A (MAO A, which degrades monoamine neurotransmitters). This study elucidates the relationship between stress-induced MAO A and the transcription factor Kruppel-like factor 11 (KLF11, also called TIEG2, a member of the Sp/KLF- family), which inhibits cell growth. We report that 1) a glucocorticoid (dexamethasone) increases KLF11 mRNA and protein levels in cultured neuronal cells; 2) overexpressing KLF11 increases levels of MAO A mRNA and enzymatic activity, which is further enhanced by glucocorticoids; in contrast, siRNA-mediated KLF11 knockdown reduces glucocorticoid-induced MAO A expression in cultured neurons; 3) induction of KLF11 and translocation of KLF11 from the cytoplasm to the nucleus are key regulatory mechanisms leading to increased MAO A catalytic activity and mRNA levels because of direct activation of the MAO A promoter via Sp/KLF-binding sites; 4) KLF11 knockout mice show reduced MAO A mRNA and catalytic activity in the brain cortex compared with wild-type mice; and 5) exposure to chronic social defeat stress induces blood glucocorticoids and activates the KLF11 pathway in the rat brain, which results in increased MAO A mRNA and enzymatic activity. Thus, this study reveals for the first time that KLF11 is an MAO A regulator and is produced in response to neuronal stress, which transcriptionally activates MAO A. The novel glucocorticoid-KLF11-MAO A pathway may play a crucial role in modulating distinct pathophysiological steps in stress-related disorders.

Sequence-specific Recruitment of Heterochromatin Protein 1 via Interaction with Krüppel-like Factor 11, a Human Transcription Factor Involved in Tumor Suppression and Metabolic Diseases

Background: Chromatin remodeling mechanisms utilized by Krüppel-like factor proteins remain poorly defined. Results: Krüppel-like factor 11 directly recruits heterochromatin protein 1α to promoters in a sequence-specific manner. Conclusion: Coupling to heterochromatin protein 1 α and its histone methyltransferase underlies Krüppel-like factor-mediated gene expression and tumor suppression. Significance: This data advances our understanding of how chromatin-mediated mechanisms achieve these functions with increased specificity for target genes. Heterochromatin protein 1 (HP1) proteins are “gatekeepers” of epigenetic gene silencing that is mediated by lysine 9 of histone H3 methylation (H3K9me). Current knowledge supports a paradigm whereby HP1 proteins achieve repression by binding to H3K9me marks and interacting to H3K9 histone methyltransferases (HMTs), such as SUV39H1, which methylate this residue on adjacent nucleosomes thereby compacting chromatin and silencing gene expression. However, the mechanism underlying the recruitment of this epigenetic regulator to target gene promoters remains poorly characterized. In the current study, we reveal for the first time a mechanism whereby HP1 is recruited to promoters by a well characterized Krüppel-like transcription factor (KLF), in a sequence-specific manner, to mediate complex biological phenomena. A PXVXL HP1-interacting domain identified at position 487–491 of KLF11 mediates the binding of HP1α and KLF11 in vitro and in cultured cells. KLF11 also recruits HP1α and its histone methyltransferase, SUV39H1, to promoters to limit KLF11-mediated gene activation. Indeed, a KLF11ΔHP1 mutant derepresses KLF11-regulated cancer genes, by inhibiting HP1-SUV39H1 recruitment, decreasing H3K9me3, while increasing activation-associated marks. Biologically, impairment of KLF11-mediated HP1-HMT recruitment abolishes tumor suppression, providing direct evidence that HP1-HMTs act in a sequence-specific manner to achieve this function rather than its well characterized binding to methylated chromatin without intermediary. Collectively, these studies reveal a novel role for HP1 as a cofactor in tumor suppression, expand our mechanistic understanding of a KLF associated to human disease, and outline cellular and biochemical mechanisms underlying this phenomenon, increasing the specificity of targeting HP1-HMT complexes to gene promoters.

Krüppel-like Factor 11 Differentially Couples to Histone Acetyltransferase and Histone Methyltransferase Chromatin Remodeling Pathways to Transcriptionally Regulate Dopamine D2 Receptor in Neuronal Cells

Background: Chromatin-mediated events utilized by Krüppel-Like factors in neurons remain undefined. Results: Krüppel-Like factor 11 couples to antagonistic chromatin pathways (p300 versus heterochromatin protein 1) to regulate the dopamine D2 receptor gene. Conclusion: This is the first description of mechanisms underlying Krüppel-like factor-mediated functions in neurons. Significance: This knowledge expands our understanding of chromatin-mediated mechanisms that influence homeostasis in highly specialized cells. The importance of Krüppel-like factor (KLF)-mediated transcriptional pathways in the biochemistry of neuronal differentiation has been recognized relatively recently. Elegant studies have revealed that KLF proteins are important regulators of two major molecular and cellular processes critical for neuronal cell differentiation: neurite formation and the expression of neurotransmitter-related genes. However, whether KLF proteins mediate these key processes in a separate or coordinated fashion remains unknown. Moreover, knowledge on the contribution of chromatin dynamics to the biochemical mechanisms utilized by these proteins to perform their function is absent. Here we report the characterization of two antagonistic, chromatin-mediated mechanisms by which KLF11, also known as TIEG2 (transforming growth factor-β-inducible early gene 2) and MODY VII (maturity onset diabetes of the young VII), regulates transcription of the fopamine D2 receptor (Drd2) gene. First, KLF11 activates transcription by binding to a distinct Sp-KLF site within the Drd2 promoter (−98 to −94) and recruiting the p300 histone acetyltransferase. Second, Drd2 transcriptional activation is partially antagonized by heterochromatin protein 1 (HP1), the code reader for histone H3 lysine 9 methylation. Interestingly, KLF11 regulates neurotransmitter receptor gene expression in differentiating neuronal cell populations without affecting neurite formation. Overall, these studies highlight histone methylation and acetylation as key biochemical mechanisms modulating KLF-mediated neurotransmitter gene transcription. These data extend our knowledge of chromatin-mediated biochemical events that maintain key phenotypic features of differentiated neuronal cells.

Epigenetics: a promising paradigm for better understanding and managing pain.

UNLABELLED Epigenetic regulation of gene expression is a rapidly growing area of research. Considering the longevity and plasticity of neurons, the studies on epigenetic pathways in the nervous system should be of special interest for both epigeneticists and neuroscientists. Activation or inactivation of different epigenetic pathways becomes more pronounced when the cells experience rapid changes in their environment, and such changes can be easily caused by injury and inflammation, resulting in pain perception or distortion of pain perception (eg, hyperalgesia). Therefore, in this regard, the field of pain is at an advantage to study the epigenetic pathways. More importantly, understanding pain from an epigenetics point of view would provide a new paradigm for developing drugs or strategies for pain management. In this review, we introduce basic concepts of epigenetics, including chromatin dynamics, histone modifications, DNA methylation, and RNA-induced gene silencing. In addition, we provide evidence from published studies suggesting wide implication of different epigenetic pathways within pain pathways. PERSPECTIVE This article provides a brief overview of epigenetic pathways for gene regulation and highlights their involvement in pain. Our goal is to expose the readers to these concepts so that pain-related phenotypes can be investigated from the epigenetic point of view.

Functional impact of Aurora A-mediated phosphorylation of HP1γ at serine 83 during cell cycle progression.

BackgroundPrevious elegant studies performed in the fission yeast Schizosaccharomyces pombe have identified a requirement for heterochromatin protein 1 (HP1) for spindle pole formation and appropriate cell division. In mammalian cells, HP1γ has been implicated in both somatic and germ cell proliferation. High levels of HP1γ protein associate with enhanced cell proliferation and oncogenesis, while its genetic inactivation results in meiotic and mitotic failure. However, the regulation of HP1γ by kinases, critical for supporting mitotic progression, remains to be fully characterized.ResultsWe report for the first time that during mitotic cell division, HP1γ colocalizes and is phosphorylated at serine 83 (Ser83) in G2/M phase by Aurora A. Since Aurora A regulates both cell proliferation and mitotic aberrations, we evaluated the role of HP1γ in the regulation of these phenomena using siRNA-mediated knockdown, as well as phosphomimetic and nonphosphorylatable site-directed mutants. We found that genetic downregulation of HP1γ, which decreases the levels of phosphorylation of HP1γ at Ser83 (P-Ser83-HP1γ), results in mitotic aberrations that can be rescued by reintroducing wild type HP1γ, but not the nonphosphorylatable S83A-HP1γ mutant. In addition, proliferation assays showed that the phosphomimetic S83D-HP1γ increases 5-ethynyl-2´-deoxyuridine (EdU) incorporation, whereas the nonphosphorylatable S83A-HP1γ mutant abrogates this effect. Genome-wide expression profiling revealed that the effects of these mutants on mitotic functions are congruently reflected in G2/M gene expression networks in a manner that mimics the on and off states for P-Ser83-HP1γ.ConclusionsThis is the first description of a mitotic Aurora A-HP1γ pathway, whose integrity is necessary for the execution of proper somatic cell division, providing insight into specific types of posttranslational modifications that associate to distinct functional outcomes of this important chromatin protein.

Phenotypic characterization of mice carrying homozygous deletion of KLF11, a gene in which mutations cause human neonatal and MODY VII diabetes

We have previously shown that amino acid changes in the human Kruppel-Like Factor (KLF) 11 protein is associated with the development of maturity onset diabetes of the young VII, whereas complete inactivation of this pathway by the -331 human insulin mutation causes neonatal diabetes mellitus. Here, we report that Klf11-/- mice have decreased circulating insulin levels, alterations in the control of blood glucose and body weight, as well as serum dyslipidemia, but do not develop diabetes. Functional assays using ex vivo liver tissue sections demonstrate that Klf11-/- mice display increased insulin sensitivity. Genome-wide experiments validated by pathway-specific quantitative PCR arrays reveal that the Klf11-/- phenotype associates to alterations in the regulation of gene networks involved in lipid metabolism, in particular those regulated by peroxisome proliferator-activated receptor-γ. Combined, these results demonstrate that the major phenotype given by the whole-body deletion of Klf11 in mouse is not diabetes but increased insulin sensitivity, likely due to altered transcriptional regulation in target tissues. The absence of diabetes in the Klf11-/- mouse either indicates an interspecies difference for the role of this transcription factor in metabolic homeostasis between mouse and humans, or potentially highlights the fact that other molecular factors can compensate for its absence. Nevertheless, the data of this study, gathered at the whole-organism level, further support a role for KLF11 in metabolic processes like insulin sensitivity, which regulation is critical in several forms of diabetes.