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ABSTRACT: Radiotherapy is the most widely used therapeutic modality in brain metastasis; however, it only provides palliation due to inevitable tumor recurrence. Resistance of tumor cells to ionizing radiation is a major cause of treatment failure. A critical unmet need in oncology is to develop rationale driven approaches that can enhance the efficacy of radiotherapy against metastatic tumor. Utilizing in vivo orthotopic primary tumor and brain metastasis models that recapitulate clinical situation of the patients with metastatic breast cancer, we investigated a molecular mechanism through which metastatic tumor cells acquire resistance to radiation. Recent studies have demonstrated that the hepatocyte growth factor (HGF)-c-Met pathway is essential for the pathologic development and progression of many human cancers such as proliferation, invasion and resistance to anticancer therapies. In this study, c-Met signaling activity as well as total c-Met expression was significantly upregulated in both breast cancer cell lines irradiated in vitro and ex vivo radio-resistant cells derived from breast cancer brain metastatic xenografts. To interrogate the role of c-Met signaling in radioresistance of brain metastasis, we evaluated the effects on tumor cell viability, clonogenicity, sensitivity to radiation, and in vitro/in vivo tumor growth after targeting c-Met by small-hairpin RNA (shRNA) or small-molecule kinase inhibitor (PF-2341066). Although c-Met silencing or radiation alone demonstrated a modest decrease in clonogenic growth of parental breast cancers and brain metastatic derivatives, combination of two modalities showed synergistic antitumor effects resulting in significant prolongation of overall survival in tumor-bearing mice. Taken together, optimizing c-Met targeting in combination with radiation is critical to enhance the effectiveness of radiotherapy in the treatments of brain metastasis.Laboratory Investigation advance online publication, 4 February 2013; doi:10.1038/labinvest.2012.180.
Laboratory Investigation 02/2013; · 3.64 Impact Factor
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ABSTRACT: Background
Glioblastoma (GBM) is the most lethal and common type of primary brain tumor. Recent evidence suggests that a subpopulation of GBM cells (glioblastoma stem cells [GSCs]) is critical for tumor progression, invasion, and therapeutic resistance. We and others have demonstrated that MET, a receptor tyrosine kinase, positively regulates the stemness phenotype and radioresistance of GSCs. Here, we interrogated the downstream effector pathways of MET signaling in GSCs.Methods
We have established a series of GSCs and xenograft tumors derived from freshly dissociated specimens from patients with GBM and characterized a subpopulation enriched with MET activation (MET(high/+)). Through global expression profiling and subsequent pathways analysis, we identified signaling pathways that are enriched in MET(high/+) populations, one of which is Wnt/β-catenin signaling pathway. To determine molecular interaction and the biological consequences of MET and Wnt/β-catenin signaling, we used pharmacological and shRNA-mediated genetic inhibition and performed various molecular and cellular analyses, including flow cytometry, immunohistochemistry, and clonogenicity assays.ResultsWe found that Wnt/β-catenin signaling is highly active in MET(high/+) cells, compared with bulk tumor cells. We also showed that Wnt/β-catenin signaling activities in GBM are directly modulated by the addition of ligand-mediated MET activation or MET inhibition. Furthermore, the ectopic expression of active-β-catenin (S37A and S45Y) rescued the phenotypic effects caused by MET inhibition.Conclusion
These data suggest that Wnt/β-catenin signaling is a key downstream effector of MET signaling and contributes to the maintenance of GSC and GBM malignancy.
Neuro-Oncology 12/2012; · 5.72 Impact Factor
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ABSTRACT: Primary lung tumors, breast tumors, and melanoma metastasize mainly in the brain where therapy is limited to surgery and radiation. To investigate the molecular basis of brain metastases, we isolated brain-trophic metastatic MDA-MB-435-LvBr2 (LvBr2) cells via left ventricle (LV) injection of MDA-MB-435 cells into immunodeficiency (NOD/SCID) mice. Whereas parent MDA-MB-435 cells displayed an elongated morphology, LvBr2 cells were round and displayed an aggregated distribution. LvBr2 cells expressed lower β-catenin levels and higher heterogeneous nuclear ribonucleoprotein C1/C2 (hnRNPC) levels than parental cells. Since microRNAs are known to play an important role in cancer progression including metastasis, we screened microRNAs expressed specifically in brain metastases. MicroRNA-146a was almost undetectable in LvBr2 cells and highly expressed in the parental cells. Overexpression of miR-146a increased β-catenin expression and suppressed the migratory and invasive activity of LvBr2 cells. The miR-146a-elicited decrease in hnRNPC in turn lowered the expression of MMP-1, uPA, and uPAR and inhibited the migratory and invasive activity of LvBr2 cells. Taken together, our findings indicate that miR-146a is virtually absent from brain metastases and can suppress their metastatic potential including their migratory and invasive activities associated with upregulation of β-catenin and downregulation of hnRNPC.
Molecules and Cells 09/2012; 34(3):329-34. · 2.18 Impact Factor
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Kyeung Min Joo,
Juyoun Jin,
Eunhee Kim, Kang Ho Kim,
Yonghyun Kim,
Bong Gu Kang,
Youn-Jung Kang,
Justin D Lathia,
Kwang Ho Cheong,
Paul H Song,
Hyunggee Kim,
Ho Jun Seol,
Doo-Sik Kong,
Jung-Il Lee,
Jeremy N Rich,
Jeongwu Lee,
Do-Hyun Nam
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ABSTRACT: Glioblastomas multiforme (GBM) contain highly tumorigenic, self-renewing populations of stem/initiating cells [glioblastoma stem cells (GSC)] that contribute to tumor propagation and treatment resistance. However, our knowledge of the specific signaling pathways that regulate GSCs is limited. The MET tyrosine kinase is known to stimulate the survival, proliferation, and invasion of various cancers including GBM. Here, we identified a distinct fraction of cells expressing a high level of MET in human primary GBM specimens that were preferentially localized in perivascular regions of human GBM biopsy tissues and were found to be highly clonogenic, tumorigenic, and resistant to radiation. Inhibition of MET signaling in GSCs disrupted tumor growth and invasiveness both in vitro and in vivo, suggesting that MET activation is required for GSCs. Together, our findings indicate that MET activation in GBM is a functional requisite for the cancer stem cell phenotype and a promising therapeutic target.
Cancer Research 05/2012; 72(15):3828-38. · 7.86 Impact Factor
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Kyeung Min Joo,
Juyoun Jin,
Bong Gu Kang,
Se Jeong Lee, Kang Ho Kim,
Heekyoung Yang,
Young-Ae Lee,
Yu Jin Cho,
Yong-Seok Im,
Dong-Sup Lee,
Do-Hoon Lim,
Dong Hyun Kim,
Hong-Duck Um,
Sang-Hun Lee,
Jung-Ii Lee,
Do-Hyun Nam
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ABSTRACT: Radiation therapy is an indispensable therapeutic modality for various brain diseases. Though endogenous neural stem cells (NSCs) would provide regenerative potential, many patients nevertheless suffer from radiation-induced brain damage. Accordingly, we tested beneficial effects of exogenous NSC supplementation using in vivo mouse models that received whole brain irradiation. Systemic supplementation of primarily cultured mouse fetal NSCs inhibited radiation-induced brain atrophy and thereby preserved brain functions such as short-term memory. Transplanted NSCs migrated to the irradiated brain and differentiated into neurons, astrocytes, or oligodendrocytes. In addition, neurotrophic factors such as NGF were significantly increased in the brain by NSCs, indicating that both paracrine and replacement effects could be the therapeutic mechanisms of NSCs. Interestingly, NSCs also differentiated into brain endothelial cells, which was accompanied by the restoration the cerebral blood flow that was reduced from the irradiation. Inhibition of the VEGF signaling reduced the migration and trans-differentiation of NSCs. Therefore, trans-differentiation of NSCs into brain endothelial cells by the VEGF signaling and the consequential restoration of the cerebral blood flow would also be one of the therapeutic mechanisms of NSCs. In summary, our data demonstrate that exogenous NSC supplementation could prevent radiation-induced functional loss of the brain. Therefore, successful combination of brain radiation therapy and NSC supplementation would provide a highly promising therapeutic option for patients with various brain diseases.
PLoS ONE 01/2012; 7(2):e25936. · 4.09 Impact Factor
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Yonghyun Kim, Kang Ho Kim,
Jeena Lee,
Young-Ae Lee,
Misuk Kim,
Se Jeong Lee,
Kernyu Park,
Heekyoung Yang,
Juyoun Jin,
Kyeung Min Joo,
Jeongwu Lee,
Do-Hyun Nam
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ABSTRACT: Glioblastoma (GBM) patients have dismal median survival even with the most rigorous treatments currently available. Radiotherapy is the most effective non-surgical therapy for GBM patients; however, patients succumb due to tumor recurrence within a year. To develop a curative therapeutic approach, we need to better understand the underlying molecular mechanism of radiation resistance in GBM. Towards this goal, we developed an in vivo orthotopic GBM model system that mimics the radiation response of human GBM, using both established-GBM cell line and patient-derived freshly dissociated GBM specimen. In-vivo ionizing radiation (IR) treatment prolonged the survival of mice with intracranical tumor derived from U373MG, but failed to prevent tumor recurrence. U373MG and GBM578 cells isolated after in-vivo IR (U373-IR and 578-IR) were more clonogenic and enriched with stem cell-like characteristics, compared with mock-treated control tumor cells. Transcriptomic analyses and quantitative real-time reverse-transcription PCR analyses using these matched GBM cells before and after radiation treatment revealed that Wnt pathways were preferentially activated in post-IR GBM cells. U373-IR cells and 578-IR were enriched with cells positive for both active β-catenin (ABC) and Sox2 population, and this subpopulation was further increased after additional in-vitro radiation treatment, suggesting that radiation resistance of GBM is mediated due, in part, to the activation of stem cell-associated pathways including Wnt. Finally, pharmacological and siRNA inhibition of Wnt pathway significantly decreased the survival and clonogenicity of GBM cells and reduced their ABC(+)/Sox2(+) population. Together, these data suggest that Wnt activation is a molecular mechanism to confer GBM radioresistance and an important therapeutic target.
Laboratory Investigation 11/2011; 92(3):466-73. · 3.64 Impact Factor
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Ho Jun Seol,
Juyoun Jin,
Dong-Ho Seong,
Kyeung Min Joo,
Wonyoung Kang,
Heekyoung Yang,
Jandi Kim,
Chul Soo Shin,
Yonghyun Kim, Kang Ho Kim,
Doo-Sik Kong,
Jung-Ii Lee,
Karen S Aboody,
Hong Jun Lee,
Seung U Kim,
Do-Hyun Nam
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ABSTRACT: Neural stem cells (NSCs) led to the development of a novel strategy for delivering therapeutic genes to tumors. NSCs expressing rabbit carboxyl esterase (F3.CE), which activates CPT-11, significantly inhibited the growth of MDA-MB-435 cells in the presence of CPT-11. F3.CE cells migrated selectively into the brain metastases located in the opposite hemisphere. The treatment also significantly decreased tumor volume in immune-deficient mice bearing MDA-MB-435 tumors when F3.CE cells were transplanted into the contralateral hemisphere. The survival rate was significantly prolonged with the treatment with F3.CE and CPT-11. This strategy may be considered as an effective treatment regimen for brain metastases.
Cancer letters 07/2011; 311(2):152-9. · 4.86 Impact Factor
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Kang Ho Kim,
Hae Yong Yoo,
Kyeung Min Joo,
Yong Jung,
Juyoun Jin,
Yonghyun Kim,
Su Jin Yoon,
Seung Ho Choi,
Ho Jun Seol,
Woong Yang Park,
Do Hyun Nam
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ABSTRACT: Radiation is the most useful treatment modality for cancer patients. It initiates a series of signal cascades such as DNA damage response (DDR) signaling for repairing damaged DNA, arresting the cell cycle, and inducing cell death. Until now, few genes have been found to be regulated by radiation, which explains the molecular mechanisms of cellular responses to radiation. Although the transcriptional changes caused by radiation have been widely investigated, little is known about the direct evidence for the transcriptional control of DDR-related genes. Here, we examined the radiosensitivity of two non-small cell lung cancer cell lines (H460 and H1299), which have different p53 status. We monitored the time-dependent changes of 24 DDR-related gene expressions via microarray analysis. Based on the basal expression levels and temporal patterns, we further classified 24 DDR-related genes into four subgroups. Then, we also addressed the protein levels of several DDR-related genes such as TopBP1, Chk1 and Chk2, confirming the results of microarray analysis. Together, these results indicate that the expression patterns of DDR-related genes are associated with radiosensitivity and with the p53 statuses of H460 and H1299, which adds to the understanding of the complex biological responses to radiation.
Experimental and Molecular Medicine 06/2011; 43(7):419-26. · 2.48 Impact Factor
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ABSTRACT: Liver X receptor (LXR), a sterol-activated nuclear hormone receptor, has been implicated in cholesterol and fatty acid homeostasis via regulation of reverse cholesterol transport and de novo fatty acid synthesis. LXR is also involved in immune responses, including anti-inflammatory action and T cell proliferation. In this study, we demonstrated that activated LXR suppresses cell cycle progression and proliferation in certain cell types. Stimulation of LXR with synthetic ligand T0901317 or GW3965 inhibited cell growth rate and arrested the cell cycle at the G1/S boundary in several cells, such as RWPE1, THP1, SNU16, LNCaP, and HepG2. However, LXR ligands did not exhibit antiproliferative activity in PC3, HEK293, or HeLa cells. Interestingly, activated LXR-mediated cell cycle arrest is closely correlated with the lipogenic gene expression and triacylglyceride accumulation. In accordance with these findings, suppression of FAS via small-interference RNA (siRNA) partially alleviated the antiproliferative effect of LXR activation in RWPE1 cells. Together, these data suggest that LXR activation with its ligands inhibits cell proliferation and induces G1/S arrest through elevated lipogenic activity, thus proposing a novel effect of activated LXR on cell cycle regulation.
The Journal of Lipid Research 12/2010; 51(12):3425-33. · 5.56 Impact Factor
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A Young Kim,
Yun Sok Lee, Kang Ho Kim,
Jae Ho Lee,
Hee Kyu Lee,
Su-Hwa Jang,
Seong-Eun Kim,
Gha Young Lee,
Joo-Won Lee,
Sung-Ae Jung,
Hee Yong Chung,
Sunjoo Jeong,
Jae Bum Kim
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ABSTRACT: In obesity, dysregulation of adipocytokines is involved in several pathological conditions including diabetes and certain cancers. As a member of the adipocytokines, adiponectin plays crucial roles in whole-body energy homeostasis. Recently, it has been reported that the level of plasma adiponectin is reduced in several types of cancer patients. However, it is largely unknown whether and how adiponectin affects colon cancer cell growth. Here, we show that adiponectin suppresses the proliferation of colon cancer cells including HCT116, HT29, and LoVo. In colon cancer cells, adiponectin attenuated cell cycle progression at the G(1)/S boundary and concurrently increased expression of cyclin-dependent kinase inhibitors such as p21 and p27. Adiponectin stimulated AMP-activated protein kinase (AMPK) phosphorylation whereas inhibition of AMPK activity blunted the effect of adiponectin on the proliferation of colon cancer cells. Furthermore, knockdown of adiponectin receptors such as AdipoR1 and AdipoR2 relieved the suppressive effect of adiponectin on the growth of colon cancer cells. In addition, adiponectin repressed the expression of sterol regulatory element binding protein-1c, which is a key lipogenic transcription factor associated with colon cancers. These results suggest that adiponectin could inhibit the growth of colon cancer cells through stimulating AMPK activity.
Molecular Endocrinology 05/2010; 24(7):1441-52. · 4.54 Impact Factor
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ABSTRACT: Liver X receptor (LXR) is a ligand-activated transcription factor that plays important roles in cholesterol and lipid homeostasis. However, ligand-induced posttranslational modification of LXR is largely unknown. Here, we show that ligand-free LXRalpha is rapidly degraded by ubiquitination. Without ligand, LXRalpha interacts with an ubiquitin E3-ligase protein complex containing breast and ovarian cancer susceptibility 1 (BRCA1)-associated RING domain 1 (BARD1). Interestingly, LXR ligand represses ubiquitination and degradation of LXRalpha, and the interaction between LXRalpha and BARD1 is inhibited by LXR ligand. Consistently, T0901317, a synthetic LXR ligand, increased the level of LXRalpha protein in liver. Moreover, overexpression of BARD1/BRCA1 promoted the ubiquitination of LXRalpha and reduced the recruitment of LXRalpha to the target gene promoters, whereas BARD1 knockdown reversed such effects. Taken together, these data suggest that LXR ligand prevents LXRalpha from ubiquitination and degradation by detaching BARD1/BRCA1, which might be critical for the early step of transcriptional activation of ligand-stimulated LXRalpha through a stable binding of LXRalpha to the promoters of target genes.
Molecular Endocrinology 02/2009; 23(4):466-74. · 4.54 Impact Factor
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ABSTRACT: Sterol regulatory element binding protein-1c (SREBP-1c) is a basic helix-loop-helix (bHLH) homodimeric transactivator, which induces itself and several lipogenic enzymes, notably fatty acid synthase (FAS). We demonstrated that hypoxia-inducible factor (HIF) represses the SREBP-1c gene by inducing Stimulated with retinoic acid (Stra)13/Differentiated embryo chondrocyte 1(DEC1) and its isoform, DEC2. Stra13/DEC1 and DEC2 are bHLH homodimeric transcription repressors. We found that both Stra13 and DEC2 inhibit SREBP-1c-induced transcription by competing with SREBP-1c for binding to the E-box in the SREBP-1c promoter and/or by interacting with SREBP-1c protein. DEC2 is instantly and temporarily induced in acute hypoxia, while Stra13 is induced in prolonged hypoxia. This expression profile reflects the finding that Stra13 represses DEC2, thus maintains low level of DEC2 in prolonged hypoxia. DEC2-siRNA restores the hypoxic repression but Stra13-siRNA fails to do so, suggesting that DEC2 is the major initiator of hypoxic repression of SREBP-1c, whereas Stra13 substitutes for DEC2 in prolonged hypoxia. Our findings imply that Stra13 and DEC2 are the mediators to repress SREBP-1c gene in response to hypoxia. By doing so, HIF and its targets, Stra13 and DEC2 reduce the ATP consuming anabolic lipogenesis prior to the actual decrease of ATP acting as a feed-forward mechanism.
Nucleic Acids Research 11/2008; 36(20):6372-85. · 8.03 Impact Factor
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ABSTRACT: Liver X receptor (LXR)alpha and LXRbeta play important roles in fatty acid metabolism and cholesterol homeostasis. Although the functional roles of LXR in the liver, intestine, fat, and macrophages are well established, its role in pancreatic beta-cells has not been clearly defined. In this study, we revealed that chronic activation of LXR contributes to lipotoxicity-induced beta-cell dysfunction. We observed significantly elevated expression of LXR in the islets of diabetic rodent models, including fa/fa ZDF rats, OLETF rats, and db/db mice. In primary pancreatic islets and INS-1 insulinoma cells, activation of LXR with a synthetic ligand, T0901317, stimulated expression of the lipogenic genes ADD1/SREBP1c, FAS, and ACC and resulted in increased intracellular lipid accumulation. Moreover, chronic LXR activation induced apoptosis in pancreatic islets and INS-1 cells, which was synergistically promoted by high glucose conditions. Taken together, we suggest lipid accumulation caused by chronic activation of LXR in beta-cells as a possible cause of beta-cell lipotoxicity, a key step in the development of type 2 diabetes.
Diabetes 07/2007; 56(6):1534-43. · 8.29 Impact Factor
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ABSTRACT: In adipocytes, oxidative stress and chronic inflammation are closely associated with metabolic disorders, including insulin resistance, obesity, cardiovascular disease, and type 2 diabetes. However, the molecular mechanisms underlying these metabolic disorders have not been thoroughly elucidated. In this report, we demonstrate that overexpression of glucose-6-phosphate dehydrogenase (G6PD) in adipocytes stimulates oxidative stress and inflammatory responses, thus affecting the neighboring macrophages. Adipogenic G6PD overexpression promotes the expression of pro-oxidative enzymes, including inducible nitric oxide synthase and NADPH oxidase, and the activation of nuclear factor-kappaB (NF-kappaB) signaling, which eventually leads to the dysregulation of adipocytokines and inflammatory signals. Furthermore, secretory factors from G6PD-overexpressing adipocytes stimulate macrophages to express more proinflammatory cytokines and to be recruited to the adipocytes; this would cause chronic inflammatory conditions in the adipose tissue of obesity. These effects of G6PD overexpression in adipocytes were abolished by pretreatment with NF-kappaB inhibitors or antioxidant drugs. Thus, we propose that a high level of G6PD in adipocytes may mediate the onset of metabolic disorders in obesity by increasing the oxidative stress and inflammatory signals.
Diabetes 12/2006; 55(11):2939-49. · 8.29 Impact Factor
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ABSTRACT: Liver X receptors (LXRs) are nuclear hormone receptors that behave as lipid sensors of cellular cholesterol and fatty acid. Although LXR activation can alleviate hypercholesterolemia by inducing cholesterol efflux, it also results in undesirable effects of fatty acid synthesis, resulting in hepatic steatosis and hyperlipidemia. Therefore, it is critical to identify LXRalpha inhibitory agents that would repress fatty acid synthesis and hepatic lipid accumulation. In current study, screening of plant extracts used for traditional oriental medicine resulted in the identification of two candidates demonstrating selective LXRalpha inhibitory activity. These were whole leaf methanol extracts of Parthenocissua tricuspidata (MEH184) and Euscaphis japonica (MEH185). Both MEH184 and MEH185 decreased transcriptional activity of LXRalpha and the expression of LXRalpha target genes, such as FAS and ADD1/SREBP1c. Additionally, MEH184 and MEH184 significantly reduced lipogenesis and adipocyte differentiation. Together, the data imply that MEH184 and MEH185 possess selective antagonistic properties on LXRalpha to downregulate lipogenesis.
Biochemical and Biophysical Research Communications 11/2006; 349(2):513-8. · 2.48 Impact Factor
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ABSTRACT: Chronic inflammation is closely associated with metabolic disorders such as obesity and type 2 diabetes, however, the underlying mechanism is unclear. Toll-like receptors (TLRs) play a key role in innate immune response as well as inflammatory signals. Here, we observed that mRNA level of TLR4 was induced during adipocyte differentiation and remarkably enhanced in fat tissues of obese db/db mice. In addition, activation of TLR4 with either LPS or free fatty acids stimulated NFkappaB signaling and expression of inflammatory cytokine genes, such as TNFalpha and IL-6 in 3T3-L1 adipocytes. Furthermore, we discovered that TLR4 activation in 3T3-L1 adipocytes provoked insulin resistance. Taken together, these results suggest that activation of TLR4 in adipocyte might be implicated in the onset of insulin resistance in obesity and type 2 diabetes.
Biochemical and Biophysical Research Communications 09/2006; 346(3):739-45. · 2.48 Impact Factor
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Ernest U Do,
Eun Bae Jo,
Gyu Choi,
Long Zhu Piao,
Jaekyoon Shin,
Min-Duk Seo,
Su-Jin Kang,
Bong-Jin Lee, Kang Ho Kim,
Jae Bum Kim,
Su-il Kim
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ABSTRACT: We have developed fluorescence polarization (FP) assays of human melanocortin 4 receptor (MC4R) in 384-well microtiter plates using TAMRA-NDP-MSH as a tracer. The rank order of potency of agonists and antagonists agrees well relative to the published assays: SHU9119>MTII>NDP alphaMSH>alphaMSH. We have screened libraries of Korean plant extracts and frog peptide analogues in search of MC4R ligands using FP assays and cell-based CRE luciferase reporter assays. We report that FLGFLFKVASK, FLGWLFKVASK, FLGALFKWASK, and FLGWLFKWASK are the peptide analogues, which bind to human MC4R receptor with good affinity in vitro. FLGWLFKVASK and FLGWLFKWASK stimulated CRE-driven reporter gene via MC4R. In luciferase reporter assays, they possess the pharmacological and functional profiles of full agonists. We demonstrate the interaction of MC4R with 11-residue antimicrobial peptides derived from the Korean frog, Rana rugosa. The results suggest that MC4R interacts promiscuously with bioactive analogues of antimicrobial peptide, gaegurin-5.
Biochemical and Biophysical Research Communications 06/2006; 343(4):1094-100. · 2.48 Impact Factor
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ABSTRACT: Specific cell type differentiation is driven by programmed regulation of gene expression, which is the result of coordinated modulation of the transcription machinery and chromatin-remodeling factors. We present evidence here that the down-regulation of histone deacetylases is an important process during adipocyte differentiation. In 3T3-L1 cells, histone hyperacetylation was selectively induced at the promoter regions of adipogenic genes during adipocyte differentiation. Interestingly, this was accompanied by a dramatic decrease in the expression level of several histone deacetylases including HDAC1, -2, and -5 and a reduction in overall histone deacetylase enzyme activity. Inhibition of histone deacetylase activity using sodium butyrate resulted in stimulation of adipogenic gene expression and adipocyte differentiation. Consistently, HDAC1 knock-down promoted adipogenesis whereas HDAC1 overexpression attenuated adipocyte differentiation in 3T3-L1 cells. Together, these results suggest that the regulation of not only adipogenic transcription factors, but also chromatin-modifying enzymes is crucial for the execution of bona fide adipogenesis.
Journal of Biological Chemistry 04/2006; 281(10):6608-15. · 4.77 Impact Factor
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ABSTRACT: Oxygen is the most important factor for the appropriate regulation of multiple energy homeostasis and cell differentiation. Although hypoxia-induced signaling cascades have been intensively studied, the molecular mechanism by which hypoxic signals suppress adipocyte differentiation is unclear. Here, we demonstrated that repression of adipocyte differentiation by hypoxia and HIF1alpha- or Stra13-overexpression was not associated with HDACs. Furthermore, HDACs did not affect inhibitory effect of Stra13 on PPARgamma promoter activity, although the hypoxia-induced suppression of adipogenesis was accompanied with reduced acetylation of histone H3 and H4 at the PPARgamma promoter. Instead, we revealed that hypoxic circumstances biphasically activated AMPK and concomitantly blocked clonal expansion of preadipocytes, which is an indispensable step for early phase of adipocyte differentiation. Taken together, these results suggest that hypoxic condition attenuates adipocyte differentiation by inhibition of PPARgamma expression in a HDAC-independent manner and by activation of AMPK which impairs clonal expansion phase.
Biochemical and Biophysical Research Communications 09/2005; 333(4):1178-84. · 2.48 Impact Factor
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ABSTRACT: Glucose-6-phosphate dehydrogenase (G6PD) produces cellular NADPH, which is required for the biosynthesis of fatty acids and cholesterol. Although G6PD is required for lipogenesis, it is poorly understood whether G6PD in adipocytes is involved in energy homeostasis, such as lipid and glucose metabolism. We report here that G6PD plays a role in adipogenesis and that its increase is tightly associated with the dysregulation of lipid metabolism and insulin resistance in obesity. We observed that the enzymatic activity and expression levels of G6PD were significantly elevated in white adipose tissues of obese models, including db/db, ob/ob, and diet-induced obesity mice. In 3T3-L1 cells, G6PD overexpression stimulated the expression of most adipocyte marker genes and elevated the levels of cellular free fatty acids, triglyceride, and FFA release. Consistently, G6PD knockdown via small interfering RNA attenuated adipocyte differentiation with less lipid droplet accumulation. Surprisingly, the expression of certain adipocytokines such as tumor necrosis factor alpha and resistin was increased, whereas that of adiponectin was decreased in G6PD overexpressed adipocytes. In accordance with these results, overexpression of G6PD impaired insulin signaling and suppressed insulin-dependent glucose uptake in adipocytes. Taken together, these data strongly suggest that aberrant increase of G6PD in obese and/or diabetic subjects would alter lipid metabolism and adipocytokine expression, thereby resulting in failure of lipid homeostasis and insulin resistance in adipocytes.
Molecular and Cellular Biology 07/2005; 25(12):5146-57. · 5.53 Impact Factor
