👤 Tamar R Grossman

Recent data indicate that artificial sweeteners (AS) may have deleterious effects on glucose metabolism. The purpose of this study was to compare the effects of AS and the effects of a high fructose diet (HFrD) on glucose metabolism and insulin resistance (IR) in Sprague-Dawley (SD) rats. SD rats were fed either regular chow, chow with saccharin (Sac) (0.1 mg/mL) placed in their water, or HFrD for seven weeks. Glucose, insulin, and triglycerides (Tg) levels were measured upon completion. A homeostatic model assessment (HOMA)-IR index was used to determine insulin resistance. The liver was stained to detect signs of a fatty liver. Hepatic mRNA expression of glucose metabolism regulation genes, Srepb-1c (sterol regulatory element binding protein) and ChREB (α & β) (carbohydrate response element binding protein), as well as other glycolytic and lipogenic genes including glucose-6-phosphatase (G6pc), were considered IR markers. Both HFrD and Sac significantly increased fasting blood glucose levels compare to the control (140 ± 5 and 137 ± 6 vs. 118 ± 3 mg/dL, respectively, Show less

Membrane type 1 metalloprotease (MT1-MMP) is a membrane-anchored, zinc-dependent protease. MT1-MMP is an important mediator of cell migration and invasion, and overexpression of this enzyme has been correlated with the malignancy of various tumor types. Therefore, modulators of MT1-MMP activity are proposed to possess therapeutic potential in numerous invasive diseases. Here we report the inhibition mode of MT1-MMP by LEM-2/15 antibody, which targets a surface epitope of MT1-MMP. Specifically, the crystal structures of Fab LEM-2/15 in complex with the MT1-MMP surface antigen suggest that conformational swiveling of the enzyme surface loop is required for effective binding and consequent inhibition of MT1-MMP activity on the cell membrane. This inhibition mechanism appears to be effective in controlling active MT1-MMP in endothelial cells and at the leading edge of migratory cancer cells. Show less

Protein flexibility is thought to play key roles in numerous biological processes, including antibody affinity maturation, signal transduction, and enzyme catalysis, yet only limited information is available regarding the molecular details linking protein dynamics with function. A single point mutation at the distal site of the endogenous tissue inhibitor of metalloproteinase 1 (TIMP-1) enables this clinical target protein to tightly bind and inhibit membrane type 1 matrix metalloproteinase (MT1-MMP) by increasing only the association constant. The high-resolution X-ray structure of this complex determined at 2 A could not explain the mechanism of enhanced binding and pointed to a role for protein conformational dynamics. Molecular dynamics (MD) simulations reveal that the high-affinity TIMP-1 mutants exhibit significantly reduced binding interface flexibility and more stable hydrogen bond networks. This was accompanied by a redistribution of the ensemble of substrates to favorable binding conformations that fit the enzyme catalytic site. Apparently, the decrease in backbone flexibility led to a lower entropy cost upon formation of the complex. This work quantifies the effect of a single point mutation on the protein conformational dynamics and function of TIMP-1. Here we argue that controlling the intrinsic protein dynamics of MMP endogenous inhibitors may be utilized for rationalizing the design of selective novel protein inhibitors for this class of enzymes. Show less

Cortisol secretion is usually under the control of ACTH. However, cortisol secretion occurs in response to gastric inhibitory polypeptide (GIP) in rare cases of food-dependent Cushing's syndrome (CS). We have investigated whether chronic ACTH stimulation or activation of the ACTH signaling pathway might be associated with GIP receptor (GIPR) expression. RT-PCR analysis and primary culture of hyperplastic adrenals. All patients presented with CS: 20 unilateral adrenal adenomas, five Cushing's disease, one food-dependent CS. RT-PCR revealed GIPR expression in all hyperplastic adrenals studied. No RT-PCR product could be detected in two normal adrenals or 20 hyperfunctioning adrenal adenomas. Primary culture revealed a significant cAMP response to ACTH in all adrenals available for study (EC50, 8.1 x 10(-10) M in normals, 4.7 x 10(-10) M in Cushing's disease, and 4.4 x 10(-10) M in food-dependent disease). However, cultures taken from all four ACTH-dependent and the one food-dependent hyperplastic adrenals studied were also responsive to GIP (EC50 for cAMP, 1.3 x 10(-9) M in Cushing's disease and 4.1 x 10(-10) M in food-dependent disease). Fasting cortisol levels were low in the case of food-dependant Cushing's, rising postprandially as predicted. However, there was no trend toward low fasting or high postprandial cortisol in the other cases, suggesting that the presence of detectable GIPR alone, albeit with definite function in vitro, is not sufficient to cause clinically food-dependent CS. These data are consistent with the hypothesis that chronic ACTH stimulation or constitutive activation of the ACTH signaling pathway may be associated with aberrant GIPR expression, and suggest one mechanism for the pathogenesis of this phenomenon. Show less