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Synthesis and Characterization of Novel Volatile Imido-Aminoalkoxide Tantalum Compounds
Park, Bo Keun,Kim, Hyo-Suk,Shin, Su Jung,Min, Jae Ki,Lee, Kang Mun,Do, Youngkyu,Kim, Chang Gyoun,Chung, Taek-Mo American Chemical Society 2012 Organometallics Vol.31 No.23
<P>A novel Ta(V) <SUP>t</SUP>Bu-imido/aminoalkoxide complex, Ta(N<SUP>t</SUP>Bu)(dmamp)<SUB>2</SUB>Cl (<B>1</B>), was synthesized by metathesis reaction between Ta(N<SUP>t</SUP>Bu)Cl<SUB>3</SUB>(py)<SUB>2</SUB> and 2 equiv of Na(dmamp), and subsequent reaction of <B>1</B> with 1 equiv of MeLi gave a new tantalum complex, Ta(N<SUP>t</SUP>Bu)(dmamp)<SUB>2</SUB>Me (<B>2</B>). Compounds <B>1</B> and <B>2</B> have been characterized by IR, <SUP>1</SUP>H and <SUP>13</SUP>C NMR spectroscopy, and microanalytical data. The molecular structure of <B>1</B>, determined by X-ray single crystallography, revealed distorted octahedral geometry. The behavior of compound <B>1</B> in solution was studied by variable-temperature <SUP>1</SUP>H NMR spectra. Thermogravimetric analysis revealed superior thermal properties of <B>2</B> as compared to those of <B>1</B>.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/orgnd7/2012/orgnd7.2012.31.issue-23/om300436p/production/images/medium/om-2012-00436p_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/om300436p'>ACS Electronic Supporting Info</A></P>
PDK4 Deficiency Suppresses Hepatic Glucagon Signaling by Decreasing cAMP Levels
Park, Bo-Yoon,Jeon, Jae-Han,Go, Younghoon,Ham, Hye Jin,Kim, Jeong-Eun,Yoo, Eun Kyung,Kwon, Woong Hee,Jeoung, Nam-Ho,Jeon, Yong Hyun,Koo, Seung-Hoi,Kim, Byung-Gyu,He, Ling,Park, Keun-Gyu,Harris, Robert American Diabetes Association 2018 Diabetes Vol.67 No.10
<P>In fasting or diabetes, gluconeogenic genes are transcriptionally activated by glucagon stimulation of the cAMP-protein kinase A (PKA)-CREB signaling pathway. Previous work showed pyruvate dehydrogenase kinase (PDK) inhibition in skeletal muscle increases pyruvate oxidation, which limits the availability of gluconeogenic substrates in the liver. However, this study found upregulation of hepatic PDK4 promoted glucagon-mediated expression of gluconeogenic genes, whereas knockdown or inhibition of hepatic PDK4 caused the opposite effect on gluconeogenic gene expression and decreased hepatic glucose production. Mechanistically, PDK4 deficiency decreased ATP levels, thus increasing phosphorylated AMPK (p-AMPK), which increased p-AMPK-sensitive phosphorylation of cyclic nucleotide phosphodiesterase 4B (p-PDE4B). This reduced cAMP levels and consequently p-CREB. Metabolic flux analysis showed that the reduction in ATP was a consequence of a diminished rate of fatty acid oxidation (FAO). However, overexpression of PDK4 increased FAO and increased ATP levels, which decreased p-AMPK and p-PDE4B and allowed greater accumulation of cAMP and p-CREB. The latter were abrogated by the FAO inhibitor etomoxir, suggesting a critical role for PDK4 in FAO stimulation and the regulation of cAMP levels. This finding strengthens the possibility of PDK4 as a target against diabetes.</P>
Park, Keun-Gyu,Lee, Kyeong-Min,Seo, Hye-Young,Suh, Ji-Ho,Kim, Hye-Soon,Wang, Li,Won, Kyu-Chang,Lee, Hyoung-Woo,Park, Joong-Yeol,Lee, Ki-Up,Kim, Jung-Guk,Kim, Bo-Wan,Choi, Hueng-Sik,Lee, In-Kyu American Diabetes Association 2007 Diabetes Vol.56 No.2
<P>Prolonged elevations of glucose concentration have deleterious effects on beta-cell function. One of the hallmarks of such glucotoxicity is a reduction in insulin gene expression, resulting from decreased insulin promoter activity. Small heterodimer partner (SHP; NR0B2) is an atypical orphan nuclear receptor that inhibits nuclear receptor signaling in diverse metabolic pathways. In this study, we found that sustained culture of INS-1 cells at high glucose concentrations leads to an increase in SHP mRNA expression, followed by a decrease in insulin gene expression. Inhibition of endogenous SHP gene expression by small interfering RNA partially restored high-glucose-induced suppression of the insulin gene. Adenovirus-mediated overexpression of SHP in INS-1 cells impaired glucose-stimulated insulin secretion as well as insulin gene expression. SHP downregulates insulin gene expression via two mechanisms: by downregulating PDX-1 and MafA gene expression and by inhibiting p300-mediated pancreatic duodenal homeobox factor 1-and BETA2-dependent transcriptional activity from the insulin promoter. Finally, the pancreatic islets of diabetic OLETF rats express SHP mRNA at higher levels than the islets from LETO rats. These results collectively suggest that SHP plays an important role in the development of beta-cell dysfunction induced by glucotoxicity.</P>