Fibrillogenic amylin evokes islet beta-cell apoptosis through linked activation of a caspase cascade and JNK1.
Fibrillogenic human amylin elicits pancreatic beta-cell apoptosis that may contribute to development of type-2 diabetes. Here, we demonstrated that activation of a caspase cascade is necessary for induction of apoptosis by fibrillogenic amylin variants in two pancreatic beta-cell lines. Human amylin, as well as truncated 8-37human amylin, evoked sequential activation of caspases-8 and -3, and apoptosis, whereas non-beta-sheet forming and non-fibrillogenic homologs, such as [25,28,29triprolyl]human amylin, did not, implying that the beta-sheet conformer is required for human amylin-induced caspase activation. Significant inhibition of apoptosis was evoked by a selective caspase-1 inhibitor, indicating that caspase-1 is also essential for activation of the caspase cascade. Furthermore, we showed that specific jnk1 antisense oligonucleotides, which suppress phospho-JNK1 expression, effectively decreased human amylin-induced activation of c-Jun. Studies of the interplay between the caspase cascade and the JNK pathway showed that both apoptosis and caspase-3 activation were suppressed by treatment with a JNK inhibitor and by transfection of antisense jnk1 oligonucleotides or antisense-c-jun, whereas a selective inhibitor of caspases-1 and -3 prevented apoptosis but not c-Jun activation. Thus, the JNK1 activation preceded activation of caspases-1 and -3. However, selective JNK inhibition had no effect on caspase-8 activation, and selective caspase-8 inhibition only partially suppressed apoptosis and c-Jun activation, indicating that caspase-8 may partially act upstream of the JNK pathway. Our studies demonstrate a functional interaction of a caspase cascade and JNK1. Fibrillogenic amylin can evoke a JNK1-mediated apoptotic pathway, which is partially dependent and partially independent of caspase-8, and in which caspase-3 acts as a common downstream effector.
Zhang
Shaoping
S
School of Biological Sciences, Faculty of Science, University of Auckland, 3 Symonds St., Level 4.1, Private Bag 92019, Auckland, New Zealand.
Liu
Junxi
J
Dragunow
Michael
M
Cooper
Garth J S
GJ
D000682:Amyloid / Q000737:chemistry*; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D020170:Caspase 1 / Q000378:metabolism; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism*; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D005337:Fibrin / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D007340:Insulinoma / Q000378:metabolism; D058228:Islet Amyloid Polypeptide; D007515:Islets of Langerhans / Q000473:pathology*; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats; D013997:Time Factors
D000682:Amyloid; D004791:Enzyme Inhibitors; D058228:Islet Amyloid Polypeptide; D010455:Peptides; D005337:Fibrin; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C505410:Casp3 protein, rat; C505528:Casp8 protein, rat; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases; D020170:Caspase 1