Exendin-4 prevents c-Jun N-terminal protein kinase activation by tumor necrosis factor-alpha (TNFalpha) and inhibits TNFalpha-induced apoptosis in insulin-secreting cells.
Glucagon-like peptide-1 and its analogs may preserve pancreatic beta-cell mass by promoting resistance to cytokine-mediated apoptosis. The mechanisms of TNFalpha-induced apoptosis and of its inhibition by exendin-4 were investigated in insulin-secreting cells. INS-1 and MIN6 insulinoma cells were exposed to 20 ng/ml TNFalpha, with or without pretreatment with 10 nm exendin-4. Treatment with TNFalpha increased c-Jun N-terminal protein kinase (JNK) phosphorylation 2-fold, reduced inhibitor-kappaBalpha (IkappaBalpha) protein content by 50%, induced opposite changes in caspase-3 and Bcl-2 protein content, and increased cellular apoptosis. Moreover, exposure to TNFalpha resulted in increased serine phosphorylation of both insulin receptor substrate (IRS)-1 and IRS-2 and reduced basal and insulin-induced Akt phosphorylation. However, in the presence of a JNK inhibitor, TNFalpha-induced apoptosis was diminished and serine phosphorylation of IRS proteins was prevented. When cells were pretreated with exendin-4, TNFalpha-induced JNK and IRS-1/2 serine phosphorylation was markedly reduced, Akt phosphorylation was increased, caspase-3 and Bcl-2 protein levels were restored to normal, and TNFalpha-induced apoptosis was inhibited by 50%. This was associated with a 2-fold increase in IRS-2 expression levels. A similar ability of exendin-4 to prevent TNFalpha-induced JNK phosphorylation was found in isolated pancreatic human islets. The inhibitory effect of exendin-4 on TNFalpha-induced JNK phosphorylation was abrogated in the presence of the protein kinase A inhibitor H89. In conclusion, JNK activation mediates TNFalpha-induced apoptosis and impairment of the IRS/Akt signaling pathway in insulin-secreting cells. By inhibiting JNK phosphorylation in a PKA-dependent manner, exendin-4 counteracts TNFalpha-mediated apoptosis and reverses the inhibitory events in the IRS/Akt pathway, resulting in promotion of cell survival.
Natalicchio
Annalisa
A
Department of Emergency and Organ Transplantation, Section on Internal Medicine, Endocrinology, Andrology, and Metabolic Diseases, University of Bari, Piazza Giulio Cesare, Bari, Italy.
De Stefano
Francesca
F
Orlando
Maura Roberta
MR
Melchiorre
Mariangela
M
Leonardini
Anna
A
Cignarelli
Angelo
A
Labarbuta
Rossella
R
Marchetti
Piero
P
Perrini
Sebastio
S
Laviola
Luigi
L
Giorgino
Francesco
F
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D045744:Cell Line, Tumor; D004789:Enzyme Activation / Q000187:drug effects; D000077270:Exenatide; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D020672:I-kappa B Proteins / Q000378:metabolism; D015151:Immunoblotting; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism; D007546:Isoquinolines / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000072000:NF-KappaB Inhibitor alpha; D010455:Peptides / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D014688:Venoms / Q000494:pharmacology*
D007004:Hypoglycemic Agents; D020672:I-kappa B Proteins; D055504:Insulin Receptor Substrate Proteins; D007546:Isoquinolines; C000606204:NFKBIA protein, human; D010455:Peptides; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; D014409:Tumor Necrosis Factor-alpha; D014688:Venoms; D000072000:NF-KappaB Inhibitor alpha; D012694:Serine; D000077270:Exenatide; D051057:Proto-Oncogene Proteins c-akt; D048031:JNK Mitogen-Activated Protein Kinases; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide