Exercise-induced changes in expression and activity of proteins involved in insulin signal transduction in skeletal muscle: Differential effects on insulin-receptor substrates 1 and 2

Level of physical activity is linked to improved glucose homeostasis. We determined whether exercise alters the expression and/or activity of proteins involved in insulin-signal transduction in skeletal muscle. Wistar rats swam 6 h per day for 1 or 5 days. Epitrochlearis muscles were excised 16 h after the last exercise bout, and were incubated with or without insulin (120 nM). Insulin-stimulated glucose transport increased 30% and 50% after 1 and 5 days of exercise, respectively. Glycogen content increased 2- and 4-fold after 1 and 5 days of exercise, with no change in glycogen synthase expression. Protein expression of the glucose transporter GLUT4 and the insulin receptor increased 2-fold after 1 day, with no further change after 5 days of exercise. Insulin-stimulated receptor tyrosine phosphorylation increased 2-fold after 5 days of exercise. Insulin-stimulated tyrosine phosphorylation of insulin-receptor substrate (IRS) 1 and associated phosphatidylinositol (PI) 3-kinase activity increased 2.5- and 3.5-fold after 1 and 5 days of exercise, despite reduced (50%) IRS-1 protein content after 5 days of exercise. After 1 day of exercise, IRS-2 protein expression increased 2.6-fold and basal and insulin-stimulated IRS-2 associated PI 3-kinase activity increased 2.8-fold and 9-fold, respectively. In contrast to IRS-1, IRS-2 expression and associated PI 3-kinase activity normalized to sedentary levels after 5 days of exercise. Insulin-stimulated Akt phosphorylation increased 5-fold after 5 days of exercise. In conclusion, increased insulin-stimulated glucose transport after exercise is not limited to increased GLUT4 expression. Exercise leads to increased expression and function of several proteins involved in insulin-signal transduction. Furthermore, the differential response of IRS-1 and IRS-2 to exercise suggests that these molecules have specialized, rather than redundant, roles in insulin signaling in skeletal muscle.

O artigo 1.228 do Código Civil e os deveres do proprietário em matéria de preservação do meio ambiente

Inclui notas explicativas, bibliográficas e bibliografia

Crystallographic evidence for the action of potassium, thallium, and lithium ions on fructose-1,6-bisphosphatase.

Fructose-1,6-bisphosphatase (Fru-1,6-Pase; D-fructose-1,6-bisphosphate 1-phosphohydrolase, EC 3.1.3.11) requires two divalent metal ions to hydrolyze alpha-D-fructose 1,6-bisphosphate. Although not required for catalysis, monovalent cations modify the enzyme activity; K+ and Tl+ ions are activators, whereas Li+ ions are inhibitors. Their mechanisms of action are still unknown. We report here crystallographic structures of pig kidney Fru-1,6-Pase complexed with K+, Tl+, or both Tl+ and Li+. In the T form Fru-1,6-Pase complexed with the substrate analogue 2,5-anhydro-D-glucitol 1,6-bisphosphate (AhG-1,6-P2) and Tl+ or K+ ions, three Tl+ or K+ binding sites are found. Site 1 is defined by Glu-97, Asp-118, Asp-121, Glu-280, and a 1-phosphate oxygen of AhG-1,6-P2; site 2 is defined by Glu-97, Glu-98, Asp-118, and Leu-120. Finally, site 3 is defined by Arg-276, Glu-280, and the 1-phosphate group of AhG-1,6-P2. The Tl+ or K+ ions at sites 1 and 2 are very close to the positions previously identified for the divalent metal ions. Site 3 is specific to K+ or Tl+. In the divalent metal ion complexes, site 3 is occupied by the guanidinium group of Arg-276. These observations suggest that Tl+ or K+ ions can substitute for Arg-276 in the active site and polarize the 1-phosphate group, thus facilitating nucleophilic attack on the phosphorus center. In the T form complexed with both Tl+ and Li+ ions, Li+ replaces Tl+ at metal site 1. Inhibition by lithium very likely occurs as it binds to this site, thus retarding turnover or phosphate release. The present study provides a structural basis for a similar mechanism of inhibition for inositol monophosphatase, one of the potential targets of lithium ions in the treatment of manic depression.

Domains of transcription factor Sp1 required for synergistic activation with sterol regulatory element binding protein 1 of low density lipoprotein receptor promoter.

Feedback regulation of transcription from the low density lipoprotein (LDL) receptor gene is fundamentally important in the maintenance of intracellular sterol balance. The region of the LDL receptor promoter responsible for normal sterol regulation contains adjacent binding sites for the ubiquitous transcription factor Sp1 and the cholesterol-sensitive sterol regulatory element-binding proteins (SREBPs). Interestingly, both are essential for normal sterolmediated regulation of the promoter. The cooperation by Sp1 and SREBP-1 occurs at two steps in the activation process. SREBP-1 stimulates the binding of Sp1 to its adjacent recognition site in the promoter followed by enhanced stimulation of transcription after both proteins are bound to DNA. In the present report, we have defined the protein domains of Sp1 that are required for both synergistic DNA binding and transcriptional activation. The major activation domains of Sp1 that have previously been shown to be essential to activation of promoters containing multiple Sp1 sites are required for activation of the LDL receptor promoter. Additionally, the C domain is also crucial. This slightly acidic approximately 120-amino acid region is not required for efficient synergistic activation by multiple Sp1 sites or in combination with other recently characterized transcriptional regulators. We also show that Sp1 domain C is essential for full, enhanced DNA binding by SREBP-1. Taken together with other recent studies on the role of Sp1 in promoter activation, the current experiments suggest a unique combinatorial mechanism for promoter activation by two distinct transcription factors that are both essential to intracellular cholesterol homeostasis.

Intersubunit contacts made by tryptophan 120 with biotin are essential for both strong biotin binding and biotin-induced tighter subunit association of streptavidin.

In natural streptavidin, tryptophan 120 of each subunit makes contacts with the biotin bound by an adjacent subunit through the dimer-dimer interface. To understand quantitatively the role of tryptophan 120 and its intersubunit communication in the properties of streptavidin, a streptavidin mutant in which tryptophan 120 is converted to phenylalanine was produced and characterized. The streptavidin mutant forms a tetrameric molecule and binds one biotin per subunit, as does natural streptavidin, indicating that the mutation of tryptophan 120 to phenylalanine has no significant effect on the basic properties of streptavidin. However, its biotin-binding affinity was reduced substantially, to approximately 10(8) M-1, indicating that the contact made by tryptophan 120 to biotin has a considerable contribution to the extremely tight biotin binding by streptavidin. The mutant retained bound biotin over a wide pH range or with the addition of urea up to 6 M at neutral pH. However, bound biotin was efficiently released by the addition of excess free biotin due, presumably, to exchange reactions. Electrophoretic analysis revealed that the intersubunit contact made by tryptophan 120 to biotin through the dimer-dimer interface is the major interaction responsible for the biotin-induced, tighter subunit association of streptavidin. In addition, the mutant has weaker subunit association than natural streptavidin even in the absence of biotin, indicating that tryptophan 120 also contributes to the subunit association of tetramers in the absence of biotin.

Caught in the act: gas and stellar velocity dispersions in a fast Quenching compact star-forming galaxy at z ~ 1.7

We present Keck I MOSFIRE spectroscopy in the Y and H bands of GDN-8231, a massive, compact, star-forming galaxy at a redshift of z ~ 1.7. Its spectrum reveals both Hα and [Nii] emission lines and strong Balmer absorption lines. The Hα and Spitzer MIPS 24 μm fluxes are both weak, thus indicating a low star-formation rate of SFR≲5-10 M_⨀ yr−1. This, added to a relatively young age of ~700 Myr measured from the absorption lines, provides the first direct evidence for a distant galaxy being caught in the act of rapidly shutting down its star formation. Such quenching allows GDN-8231 to become a compact, quiescent galaxy, similar to three other galaxies in our sample, by z ~ 1.5. Moreover, the color profile of GDN-8231 shows a bluer center, consistent with the predictions of recent simulations for an early phase of inside-out quenching. Its line-of-sight velocity dispersion for the gas, σ_LOG^gas = 127 ± 32 km s^−1, is nearly 40% smaller than that of its stars, σ_LOG^* = 215 ± 35 km s^−1. High-resolution hydro-simulations of galaxies explain such apparently colder gas kinematics of up to a factor of ~1.5 with rotating disks being viewed at different inclinations and/or centrally concentrated star-forming regions. A clear prediction is that their compact, quiescent descendants preserve some remnant rotation from their star-forming progenitors.

Letter from George Richards Minot to Daniel Kilham, 1777 December 1

Three-page handwritten letter from Harvard undergraduate George Richards Minot to his friend and Harvard graduate Daniel Kilham, dated December 1, 1777. The letter describes the discipline inflicted upon Minot and seven of his classmates by the Harvard government following a “Thanksgiving frolic,” and the retributions carried out by the students against a Tutor who recommended harsh measures for the accused students. The Early Faculty minutes for 1777 (UAIII 5.5, Volume 4, pages 75-76) describes the students’ crime as “making riotous & tumultuous noises in the Hall…committed in Presence of a number foreigners, & and on a day appointed by Authority for public Thanksgiving.”

Chicago and vicinity, Illinois, 1953 (Image 1 of 3) (Raster Image)

This layer is a georeferenced raster image of the historic, topographic paper map entitled: Chicago and vicinity, Ill.-Ind. : sheet no. 1 of 3 (Evanston), 1953, mapped, edited, and published by the Geological Survey. It was published in 1957. Scale 1:24,000. The source map was compiled from 1:24,000 scale maps of Evanston, Park Ridge, Arlington Heights, Elmhurst, River Forest, and Chicago Loop, 1953 7.5 minute quadrangles. Hydrography from U.S. Lake Survey Charts 75 (1:120,000), 751 (1:60,000), and 752 (1:15,000). This layer is image 1 of 3 total images of the three sheet source map. The image inside the map neatline is georeferenced to the surface of the earth and fit to the Illinois East State Plane Coordinate System NAD27 (in Feet) (Fipszone 1201). All map collar and inset information is also available as part of the raster image, including any inset maps, profiles, statistical tables, directories, text, illustrations, index maps, legends, or other information associated with the principal map. This is a typical topographic map portraying both natural and manmade features. It shows and names works of nature, such as mountains, valleys, lakes, rivers, vegetation, etc. It also identify the principal works of humans, such as roads, railroads, boundaries, transmission lines, major buildings, etc. Relief is shown with standard contour intervals of 5 feet. Depths shown by isolines and soundings. This layer is part of a selection of digitally scanned and georeferenced historic maps from The Harvard Map Collection as part of the Imaging the Urban Environment project. Maps selected for this project represent major urban areas and cities of the world, at various time periods. These maps typically portray both natural and manmade features at a large scale. The selection represents a range of regions, originators, ground condition dates, scales, and purposes.