[Abstract unavailable

(1999) J. Biol. Chem. 274, 27529 -27535). In the present investigation, we define a second pathway contributing to CREB-dependent up-regulation of Bcl-2 expression as a novel anti-apoptotic function of Akt signaling. To examine the role of Akt on Bcl-2 expression, a series of transient transfections using a luciferase reporter gene driven by the promoter region of Bcl-2 containing a CRE were carried out. Pharmacological inhibition of phosphatidylinositol (PI) 3-kinase, the upstream kinase of Akt, with LY294002 led to a 45% decrease in Bcl-2 promoter activity. The reporter activity was enhanced 2.3-fold by overexpression of active p110 subunit of PI 3-kinase and inhibited 44% by the dominant negative p85 subunit of PI 3-kinase. Cotransfection with 3-phosphoinositide-dependent kinase (PDK1), which is required for the full activation of Akt, resulted in enhanced luciferase activity. Insulin-like growth factor-I-mediated induction of Bcl-2 promoter activity was decreased significantly (p < 0.01) by the dominant negative forms of p85 subunit of PI 3-kinase, PDK1, and Akt. These data indicate that regulation of Bcl-2 expression by IGF-I involves a signaling cascade mediated by PI 3-kinase/PDK1/Akt/CREB. Furthermore, we measured the Bcl-2 mRNA in PC12 cells overexpressing Akt by real-time quantitative reverse transcriptionpolymerase chain reaction using the TaqMan TM fluorogenic probe system. We observed a 2.1-fold increase in Bcl-2 mRNA levels in the Akt cell line compared with control PC12 cells, supporting the observation that enhanced CREB activity by Akt signaling leads to increased Bcl-2 promoter activity and cell survival.The serine threonine kinase Akt/protein kinase B is an important mediator of metabolic as well as survival responses to insulin and growth factors (1). Akt is activated by translocation to plasma membrane when the PI 3-kinase-generated 3-phosphoinositides bind to its pleckstrin homology domain (2). For its full activation it needs to be further phosphorylated by 3-phosphoinositide-dependent kinase1 (PDK1) 1 at Thr-308 and by PDK2 at Ser-473. The metabolic actions of insulin mediated by Akt include stimulation of GLUT4 translocation and activation of glycogen synthase and the glycolytic enzyme 6-phosphofructose-

T1D youth demonstrated IR, impaired functional exercise capacity and cardiovascular dysfunction. The phenotype of IR in T1D youth was unique, suggesting a pathophysiology that is different from T2D, yet may adversely affect long-term cardiovascular outcomes.

Persons with type II diabetes mellitus (DM), even without cardiovascular complications have a decreased maximal oxygen consumption (VO2 max) and submaximal oxygen consumption (VO2) during graded exercise compared with healthy controls. We evaluated the hypothesis that change in the rate of VO2 in response to the onset of constant-load exercise (measured by VO2-uptake kinetics) was slowed in persons with type II DM. Ten premenopausal women with uncomplicated type II DM, 10 overweight, nondiabetic women, and 10 lean, nondiabetic women had a VO2 max test. On two separate occasions, subjects performed 7-min bouts of constant-load bicycle exercise at workloads below and above the lactate threshold to enable measurements of VO2 kinetics and heart rate kinetics (measuring rate of heart rate rise). VO2 max was reduced in subjects with type II DM compared with both lean and overweight controls (P < 0.05). Subjects with type II DM had slower VO2 and heart rate kinetics than did controls at constant workloads below the lactate threshold. The data suggest a notable abnormality in the cardiopulmonary response at the onset of exercise in people with type II DM. The findings may reflect impaired cardiac responses to exercise, although an additional defect in skeletal muscle oxygen diffusion or mitochondrial oxygen utilization is also possible.

Obesity is the result of numerous, interacting behavioral, physiological, and biochemical factors. One increasingly important factor is the generation of additional fat cells, or adipocytes, in response to excess feeding and/or large increases in body fat composition. The generation of new adipocytes is controlled by several "adipocyte-specific" transcription factors that regulate preadipocyte proliferation and adipogenesis. Generally these adipocyte-specific factors are expressed only following the induction of adipogenesis. The transcription factor(s) that are involved in initiating adipocyte differentiation have not been identified. Here we demonstrate that the transcription factor, CREB, is constitutively expressed in preadipocytes and throughout the differentiation process and that CREB is stimulated by conventional differentiation-inducing agents such as insulin, dexamethasone, and dibutyryl cAMP. Stably transfected 3T3-L1 preadipocytes were generated in which we could induce the expression of either a constitutively active CREB (VP16-CREB) or a dominantnegative CREB (KCREB). Inducible expression of VP16-CREB alone was sufficient to initiate adipogenesis as determined by triacylglycerol storage, cell morphology, and the expression of two adipocyte marker genes, peroxisome proliferator activated receptor gamma 2, and fatty acid binding protein. Alternatively, KCREB alone blocked adipogenesis in cells treated with conventional differentiation-inducing agents. These data indicate that activation of CREB was necessary and sufficient to induce adipogenesis. Finally, CREB was shown to bind to putative CRE sequences in the promoters of several adipocyte-specific genes. These data firmly establish CREB as a primary regulator of adipogenesis and suggest that CREB may play similar roles in other cells and tissues.Excess body fat, or obesity, is a major health concern in the United States and other developed nations. It has been estimated that 26% of Americans are overweight (2), with 5 to 14% of men and 7 to 24% of women considered obese depending on the definition employed (2,5,6,12,22,45,57). Similar or even higher estimates for the prevalence of obesity have been reported in other countries (42). Obesity contributes to an increased rate of mortality (20) by virtue of its role in the development of cardiovascular disease, diabetes, pulmonary dysfunction, and gallstones (5, 10, 12).Weight gain and obesity occur when energy intake by an individual exceeds the rate of energy expenditure (23). Energy intake and expenditure are in turn determined by multiple, interacting factors ranging from dietary composition and feeding and exercise habits to physiologic factors and biochemical pathways that modulate lipid and overall energy metabolism (58). At the cellular level obesity was originally considered a hypertrophic disease resulting from an increase in fat cell size or volume (30). However, several studies have demonstrated a hyperplastic component to obesity. For example, sequential biopsies in children indicate that f...