Yoo-Wook Kwon

Negative regulation of hypoxia inducible factor-1α by necdin

Hypoxia‐inducible factor 1 (HIF‐1) is a master transcription factor that mediates cellular and systemic homeostatic responses to reduce O2 availability, such as erythropoiesis, angiogenesis, and glycolysis. Using the yeast two‐hybrid screening system, we found that the oxygen dependent degradation (ODD) domain of HIF‐1α interacts with necdin, a growth suppressor. The interaction of necdin with HIF‐1α was confirmed using coimmunoprecipitation with the overexpressed HIF‐1α. Biological effect of necdin on HIF‐1α showed that necdin reduces the transcriptional activity of HIF‐1 under hypoxia. Moreover, necdin decreased the level of the HIF‐1α protein, but not that of mRNA, implying a possibility of necdin‐mediated HIF‐1α degradation. Furthermore, necdin has an anti‐angiogenic activity in the tube formation assay and CAM assay, which might be due to the downregulation of HIF‐1α. Collectively, these results suggest that necdin can be a novel negative regulator of HIF‐1α stability via the direct interaction.

Blood-brain barrier interfaces and brain tumors

In the developing brain, capillaries are differentiated and matured into the blood-brain barrier (BBB), which is composed of cerebral endothelial cells, astrocyte end-feet, and pericytes. Since the BBB regulates the homeostasis of central nervous system (CNS), the maintenance of the BBB is important for CNS function. The disruption of the BBB may result in many brain disorders including brain tumors. However, the molecular mechanism of BBB formation and maintenance is poorly understood. Here, we summarize recent advances in the role of oxygen tension and growth factors on BBB development and maintenance, and in BBB dysfunction related with brain tumors.

Pustular psoriasis and the Kobner phenomenon caused by allergic contact dermatitis from zinc pyrithione-containing shampoo.

Zinc pyrithione is a shampoo ingredient that has been shown to be safe and effective for dandruff and scalp psoriasis. It is thought to decrease the cell turnover rate in hyperproliferative dermatoses such as psoriasis, and also has fungistatic and antimicrobial activity, although its exact mode of action is unknown. In psoriasis, external factors, such as trauma, infection and drugs, may provoke aggravated manifestations of psoriatic skin lesions. Rarely, irritant or allergic mechanisms are likely causes of psoriatic flare and Köbnerization. A patient had had stable psoriasis for 25 years and no any other skin disease. Within 20 days, she developed an aggravated scaly erythematous patch on the scalp, where a shampoo had been applied, and simultaneously developed pustular psoriasis on both forearms. Patch testing showed a relevant sensitization to zinc pyrithione, and we observed symptomatic aggravation by provocation testing with zinc pyrithione shampoo. We report a rare case of psoriasis aggravated by the induction of allergic contact dermatitis from zinc pyrithione after using antidandruff shampoo.

FOXO1 impairs whereas statin protects endothelial function in diabetes through reciprocal regulation of Krüppel-like factor 2

AIMSnKrüppel-like factor 2 (KLF2) is implicated as a key molecule maintaining endothelial function. This study was designed to evaluate the reciprocal regulation of KLF2 by the forkhead transcription factor FOXO1, and the 3-hydroxy-3-methylglutaryl coenzymexa0A reductase inhibitor atorvastatin, in hyperglycaemic conditions.nnnMETHODS AND RESULTSnExposure of human umbilical vein endothelial cells to 30 mM glucose activated FOXO1 and suppressed KLF2. These effects were reversed by FOXO1 small interfering RNA. Adenoviral transfection of constitutively active FOXO1 suppressed KLF2 expression. Interestingly, atorvastatin inhibited FOXO1 by increasing phosphorylation and also by inhibiting nuclear localization and replenished KLF2 in high-glucose conditions. This effect of atorvastatin was attenuated by mevalonate. Chromatin immunoprecipitation analysis demonstrated that glucose increased whereas atorvastatin decreased FOXO1 binding to the promoter region of the KLF2 gene. In the vessels of Otsuka Long-Evans Tokushima Fatty rats, animal models of type 2 diabetes, FOXO1 was activated and KLF2 was suppressed, and this was reversed by atorvastatin treatment. The arteries from Otsuka Long-Evans Tokushima Fatty rats showed impairment of endothelium-dependent vasodilatation, and both atorvastatin and KLF2 gene therapies restored it.nnnCONCLUSIONSnSuppression of KLF2 by FOXO1 may be a plausible mechanism of diabetic endothelial dysfunction. High-glucose-induced, FOXO1-mediated KLF2 suppression was reversed by atorvastatin, suggesting that intensive statin treatment could be a therapeutic option in diabetic vascular dysfunction.

PPARγ modulates vascular smooth muscle cell phenotype via a protein kinase G-dependent pathway and reduces neointimal hyperplasia after vascular injury

Vascular smooth muscle cells (VSMCs) undergo phenotypic changes in response to vascular injury such as angioplasty. Protein kinase G (PKG) has an important role in the process of VSMC phenotype switching. In this study, we examined whether rosiglitazone, a peroxisome proliferator-activated receptor (PPAR)-γ agonist, could modulate VSMC phenotype through the PKG pathway to reduce neointimal hyperplasia after angioplasty. In vitro experiments showed that rosiglitazone inhibited the phenotype change of VSMCs from a contractile to a synthetic form. The platelet-derived growth factor (PDGF)-induced reduction of PKG level was reversed by rosiglitazone treatment, resulting in increased PKG activity. This increased activity of PKG resulted in phosphorylation of vasodilator-stimulated phosphoprotein at serine 239, leading to inhibited proliferation of VSMCs. Interestingly, rosiglitazone did not change the level of nitric oxide (NO) or cyclic guanosine monophosphate (cGMP), which are upstream of PKG, suggesting that rosiglitazone influences PKG itself. Chromatin immunoprecipitation assays for the PKG promoter showed that the activation of PKG by rosiglitazone was mediated by the increased binding of Sp1 on the promoter region of PKG. In vivo experiments showed that rosiglitazone significantly inhibited neointimal formation after balloon injury. Immunohistochemistry staining for calponin and thrombospondin showed that this effect of rosiglitazone was mediated by modulating VSMC phenotype. Our findings demonstrate that rosiglitazone is a potent modulator of VSMC phenotype, which is regulated by PKG. This activation of PKG by rosiglitazone results in reduced neointimal hyperplasia after angioplasty. These results provide important mechanistic insight into the cardiovascular-protective effect of PPARγ.

Identification of the early and late responder genes during the generation of induced pluripotent stem cells from mouse fibroblasts

Background The generation of induced pluripotent stem cell (iPSC), a substitute for embryonic stem cell (ESC), requires the proper orchestration of a transcription program at the chromatin level. Our recent approach for the induction of pluripotent stem cells from fibroblasts using protein extracts from mouse ESCs could overcome the potential tumorigenicity risks associated with random retroviral integration. Here, we examine the epigenetic modifications and the transcriptome of two types of iPSC and of partially reprogrammed iPSCs (iPSCp) generated independently from adult cardiac and skin fibroblasts to assess any perturbations of the transcription program during reprogramming. Results The comparative dissection of the transcription profiles and histone modification patterns at lysines 4 and 27 of histone H3 of the iPSC, iPSCp, ESC, and somatic cells revealed that the iPSC was almost completely comparable to the ESC, regardless of their origins, whereas the genes of the iPSCp were dysregulated to a larger extent. Regardless of the origins of the somatic cells, the fibroblasts induced using the ESC protein extracts appear to be completely reprogrammed into pluripotent cells, although they show unshared marginal differences in their gene expression programs, which may not affect the maintenance of stemness. A comparative investigation of the iPSCp generated by unwanted reprogramming showed that the two groups of genes on the pathway from somatic cells to iPSC might function as sequential reprogramming-competent early and late responders to the induction stimulus. Moreover, some of the divergent genes expressed only in the iPSCp were associated with many tumor-related pathways. Conclusions Faithful transcriptional reprogramming should follow epigenetic alterations to generate induced pluripotent stem cells from somatic cells. This genome-wide comparison enabled us to define the early and late responder genes during the cell reprogramming process to iPSC. Our results indicate that the cellular responsiveness to external stimuli should be pre-determined and sequentially orchestrated through the tight modulation of the chromatin environment during cell reprogramming to prevent unexpected reprogramming.