Browsing by Subject "MAP Kinase Signaling System"
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Item Effects of Glucose and Free Fatty Acids on ERK1/2 in Pancreatic B-Cells(2005-05-04) Arnette Jr., Donald Ervin; Cobb, MelanieDiabetes is a growing problem in the United States. There is a growing occurrence of obesity in the United States, which directly adds to the incidence and occurrence of diabetes. Our lab has previously showed that the extracellular signal-regulated protein kinases (ERKs) 1 and 2 are activated by elevated concentrations of glucose and are involved in insulin transcription. In this study we examine the mechanism by which glucose induces ERK1/2 activity. The effects of free fatty acids on ERK1/2 activity were also examined. In this study a rat insulinoma cell line was used. The rat insulinoma cell line INS-1 is a model system which is commonly used to represent pancreatic ᭣ells. Elevated glucose activates ERK1/2 in INS-1 cells. With the use of several pharmacological agents which interrupt calcium signaling, it was concluded that calcium signaling is involved in glucose-induced ERK1/2 activation. Calmodulin and the calmodulin-dependent phosphatase calcineurin were determined to be required for glucose-induced ERK1/2 activity as well as glucagons-like peptide induced ERK1/2 activity. This activation was also shown to require the release of calcium from intracellular stores. It has been well documented that free fatty acids (FFAs) have negative effects on pancreatic ᭣ells. FFAs have been shown to decrease insulin secretion. The effects ofFFAs on ERK1/2 activity were also examined. Chronic exposure of FFAs causes constitutive activation of ERK1/2 in INS-1 cells. This constitutive activity of ERK1/2 was determined to be protein kinase C (PKC) independent. The FFA-induced ERK1/2 activity resulted in a ERK1/2 nuclear localization pattern that is dramatically different from the usual pattern of ERK1/2 nuclear localization. It has been previously shown that ERK1/2 phosphorylate insulin transcription factors that are required for maximal glucose-induced insulin transcription. This altered ERK1/2 nuclear localization may affect the phosphorylation of these transcription factors, which might explain how chronic exposure to FFAs inhibits insulin transcription.Item Mechanistic Basis of Signal Amplitude Modulation by the Ras Effector IMP(2007-08-08) Chen, Chiyuan; White, Michael A.The RAF/MEK/MAP Kinase signal transduction cascade is the most extensively studied MAPK pathway that mediates diverse cellular responses to environmental cues, and makes a major contribution to Ras-dependent oncogenic transformation. The Ras effector and E3 ligase family member IMP (Impedes Mitogenic signal Propagation) acts as a steady-state resistor within the RAFMEK- ERK kinase module. IMP concentrations are regulated by Ras, through induction of autodegradation, and can modulate signal/response thresholds by directly limiting the assembly of functional KSR1-dependent RAF/MEK complexes. Here, we examine the mechanistic basis of signal amplitude modulation by the Ras effector IMP. We show that the capacity of IMP to inhibit signal propagation through RAF to MEK is a consequence of disrupting assembly of multivalent mitogenic complexes that are required for C-RAF kinase activation and functional coupling of active kinases to downstream substrates. We also study how Ras regulates IMP functions by isolating IMP mutants compromised for Ras interaction and how post-translational modifications such as sumoylation control IMP activities. Finally, we identify some candidate IMP binding proteins to further investigate how IMP impacts cell behaviors through protein-protein interactions and how IMP is modulated by other proteins.