Project description:Under feeding conditions, increases in circulating glucose concentrations trigger the release of glucagon-like peptide (GLP-1) from intestinal L cells. GLP-1 promotes insulin secretion and pancreatic beta cell viability in part via triggering of the beta cell GLP-1 receptor and subsequent induction of the cAMP signaling pathway, leading to the protein kinase A (PKA) mediated phosphorylation of CREB and induction of CREB target genes. By contrast with the acute effects of this pathway on immediate early CREB target genes, which attenuate the cAMP-CREB response, sustained exposure of beta cells to GLP-1 agonist (exenatide-4; Ex-4) or adenyl cyclase activator (Forskolin; FSK) stimulates the expression of beta cell specific CREB target genes with delayed kinetics. In a proteomic screen for transcriptional co-regulators that mediate the long-term effects of GLP-1, we identified Med14, a backbone subunit of the Mediator complex. Exposure to either Ex-4 or FSK stimulates Med14 phosphorylation at Ser983, corresponding to a conserved PKA recognition site (RRXS) that is located within an intrinsically disordered region of Med14. Phosphorylation of Med14 is essential for maintenance of enhancers that drive induction of beta cell-specific and diabetes-linked genes. Mutation of Med14 at Ser983 to alanine decreased beta cell numbers and repressed growth factor signaling in primary mouse islets. Our work reveals how phosphorylation of a general transcription factor in response to GLP-1 analogs triggers a broad genomic response with salutary effects on beta cell function.
Project description:Under feeding conditions, increases in circulating glucose concentrations trigger the release of glucagon-like peptide (GLP-1) from intestinal L cells. GLP-1 promotes insulin secretion and pancreatic beta cell viability in part via triggering of the beta cell GLP-1 receptor and subsequent induction of the cAMP signaling pathway, leading to the protein kinase A (PKA) mediated phosphorylation of CREB and induction of CREB target genes. By contrast with the acute effects of this pathway on immediate early CREB target genes, which attenuate the cAMP-CREB response, sustained exposure of beta cells to GLP-1 agonist (exenatide-4; Ex-4) or adenyl cyclase activator (Forskolin; FSK) stimulates the expression of beta cell specific CREB target genes with delayed kinetics. In a proteomic screen for transcriptional co-regulators that mediate the long-term effects of GLP-1, we identified Med14, a backbone subunit of the Mediator complex. Exposure to either Ex-4 or FSK stimulates Med14 phosphorylation at Ser983, corresponding to a conserved PKA recognition site (RRXS) that is located within an intrinsically disordered region of Med14. Phosphorylation of Med14 is essential for maintenance of enhancers that drive induction of beta cell-specific and diabetes-linked genes. Mutation of Med14 at Ser983 to alanine decreased beta cell numbers and repressed growth factor signaling in primary mouse islets. Our work reveals how phosphorylation of a general transcription factor in response to GLP-1 analogs triggers a broad genomic response with salutary effects on beta cell function.
Project description:Under feeding conditions, increases in circulating glucose concentrations trigger the release of glucagon-like peptide (GLP-1) from intestinal L cells. GLP-1 promotes insulin secretion and pancreatic beta cell viability in part via triggering of the beta cell GLP-1 receptor and subsequent induction of the cAMP signaling pathway, leading to the protein kinase A (PKA) mediated phosphorylation of CREB and induction of CREB target genes. By contrast with the acute effects of this pathway on immediate early CREB target genes, which attenuate the cAMP-CREB response, sustained exposure of beta cells to GLP-1 agonist (exenatide-4; Ex-4) or adenyl cyclase activator (Forskolin; FSK) stimulates the expression of beta cell specific CREB target genes with delayed kinetics. In a proteomic screen for transcriptional co-regulators that mediate the long-term effects of GLP-1, we identified Med14, a backbone subunit of the Mediator complex. Exposure to either Ex-4 or FSK stimulates Med14 phosphorylation at Ser983, corresponding to a conserved PKA recognition site (RRXS) that is located within an intrinsically disordered region of Med14. Phosphorylation of Med14 is essential for maintenance of enhancers that drive induction of beta cell-specific and diabetes-linked genes. Mutation of Med14 at Ser983 to alanine decreased beta cell numbers and repressed growth factor signaling in primary mouse islets. Our work reveals how phosphorylation of a general transcription factor in response to GLP-1 analogs triggers a broad genomic response with salutary effects on beta cell function.
Project description:Under feeding conditions, increases in circulating glucose concentrations trigger the release of glucagon-like peptide (GLP-1) from intestinal L cells. GLP-1 promotes insulin secretion and pancreatic beta cell viability in part via triggering of the beta cell GLP-1 receptor and subsequent induction of the cAMP signaling pathway, leading to the protein kinase A (PKA) mediated phosphorylation of CREB and induction of CREB target genes. By contrast with the acute effects of this pathway on immediate early CREB target genes, which attenuate the cAMP-CREB response, sustained exposure of beta cells to GLP-1 agonist (exenatide-4; Ex-4) or adenyl cyclase activator (Forskolin; FSK) stimulates the expression of beta cell specific CREB target genes with delayed kinetics. In a proteomic screen for transcriptional co-regulators that mediate the long-term effects of GLP-1, we identified Med14, a backbone subunit of the Mediator complex. Exposure to either Ex-4 or FSK stimulates Med14 phosphorylation at Ser983, corresponding to a conserved PKA recognition site (RRXS) that is located within an intrinsically disordered region of Med14. Phosphorylation of Med14 is essential for maintenance of enhancers that drive induction of beta cell-specific and diabetes-linked genes. Mutation of Med14 at Ser983 to alanine decreased beta cell numbers and repressed growth factor signaling in primary mouse islets. Our work reveals how phosphorylation of a general transcription factor in response to GLP-1 analogs triggers a broad genomic response with salutary effects on beta cell function.
Project description:Obesity and its co-morbidities, such as diabetes and hypertension, can significantly reduce a person’s quality of life and place huge pressure on healthcare resources. When we eat a meal our gut and brain release hormones to control the amount of food and fluid we ingest to prevent overeating. One of these hormones is called glucagon-like peptide 1 (GLP-1) and is released from intestinal cells in response to food intake, but also produced and released in the brain. Drug analogues of GLP-1 are already in use in the clinic to treat both diabetes and obesity. The aim of this work was to obtain fundamental knowledge about a GLP-1 receptor population in nerve terminals of the posterior pituitary gland. We have investigated the pharmacological actions of GLP-1 using a selective receptor agonist called liraglutide, a drug that is approved for diabetes and obesity treatment in humans. Our work has focussed on the phosphoproteome of the neurointermediate lobe (posterior pituitary + intermediate lobe) of the rat pituitary gland 30 minutes after intraperitoneal injection of liraglutide (100 µg/kg) compared to vehicle controls (n = 6 animals per group). New understanding of this GLP-1 receptor population is essential for our knowledge of current treatments of diabetes and obesity that use stable peptide analogues in humans.
Project description:We find that GLP-1 signaling-activated PKA directly phosphorylates menin at serine 487 residue, relieving menin mediated suppression of insulin expression in beta cells and islets of diabetic GK rat. Mechanistically, GLP-1-induced PKA activation leads to menin Ser487 phosphorylation, and phosphorylated menin gains increased binding affinity to cytoskeleton proteins such as beta actin and myosin. Sequestration of Ser487 phosphorylated menin from the Ins1 gene promoter leads to reduced binding of menin-associating repressive epigenetic regulators such as SUV39H1 and HDAC1 at the locus, resulting in increased Ins1 transcription. Our results have linked GLP-1 signaling to physiologically suppression of menin function in repressing insulin expression, and uncovered a potential step to modulate menin phosphorylation to improve T2D therapy.