Poster Presentation Abstracts

Glucose transporter 4 (GLUT4) is the major insulin-responsible glucose transporter expressed in muscle and adipose tissue and plays an important role in whole body glucose homeostasis. In the basal state, GLUT4 is sequestrated in several intracellular compartments, one of which has come to be known as insulin-responsive compartment (IRC). The IRC is a tissue specific compartment that is a target of insulin signaling cascade, however, its precise nature is unclear. Here, we report a novel mechanism to regulate IRC and glucose transport in adipocytes. First, we investigated the intracellular localization of p34 in adipocytes, and found that p34 was localized in the perinuclear region and exhibited the partial co-localization with GLUT4 at basal condition. Next, we show that p34 can bind syntaxin6, a Qc-SNARE, localized at trans-Golgi area. Third, we determined the role of p34 on insulin stimulated glucose transport in p34 silenced cells. P34 knockdown by siRNA decrease insulin responsive glucose uptake by 20%. These data suggested that p34 may have a role on GLUT4 entry into IRC and regulate GLUT4-recycling required for proper glucose transport. Cytokines such as interleukin-1 beta (IL-1b) stimulate iNOS expression and nitrite (NO) overproduction leading to the b-cell damage. Meanwhile, glucagon-like peptide-1 (GLP-1) and its potent analog exendin-4 (EX-4) were well known for b-cell proliferation. However, the protective mechanisms of GLP-1 in b-cells exposed to cytokines were not fully elucidated. Therefore, the effects of EX-4 on the IL-1b-induced iNOS gene expression were investigated employing RINm5F b-cells. EX-4 inhibited IL-1b-induced iNOS protein expression and NO production. However, Northern blot and promoter analyses showed that EX-4 failed to inhibit IL-1b-induced iNOS mRNA expression and iNOS promoter activity. By electrophoretic mobility shift assay (EMSA), EX-4 did not alter the binding activity of NF-jB to the iNOS promoter. Consistent with the EMSA result, EX-4 did not inhibit nuclear translocation of p65. We also tested the effect of EX-4 on iNOS mRNA stability. Actinomycin D chase experiments showed that EX-4 did not affect the decay rate of iNOS mRNA and the promoter assay using the construct containing 3'-untranslated region of iNOS showed that EX-4 did not alter the stability of iNOS mRNA. Meanwhile, forskolin significantly inhibited IL-1b-induced iNOS protein, which was reversed by H-89, a protein kinase A (PKA) inhibitor. Moreover, EX-4 pretreatment restored IL-1b-induced decrease in cAMP toward control level. Additionally, cycloheximide chase study demonstrated that EX-4 significantly accelerated iNOS protein degradation. We, therefore, concluded that EX-4 inhibited …