Induction of nuclear factor-kappaB and its downstream genes by TNF-alpha and IL-1beta has a pro-apoptotic role in pancreatic beta cells.
OBJECTIVE
IL-1beta and TNF-alpha contribute to pancreatic beta cell death in type 1 diabetes. Both cytokines activate the transcription factor nuclear factor-kappaB (NF-kappaB), but recent observations suggest that NF-kappaB blockade prevents IL-1beta + IFN-gamma- but not TNF-alpha + IFN-gamma-induced beta cell apoptosis. The aim of the present study was to compare the effects of IL-1beta and TNF-alpha on cell death and the pattern of NF-kappaB activation and global gene expression in beta cells.


METHODS
Cell viability was measured after exposure to IL-1beta or to TNF-alpha alone or in combination with IFN-gamma, and blockade of NF-kappaB activation or protein synthesis. INS-1E cells exposed to IL-1beta or TNF-alpha in time course experiments were used for IkappaB kinase (IKK) activation assay, detection of p65 NF-kappaB by immunocytochemistry, real-time RT-PCR and microarray analysis.


RESULTS
Blocking NF-kappaB activation protected beta cells against IL-1beta + IFNgamma- or TNFalpha + IFNgamma-induced apoptosis. Blocking de novo protein synthesis did not increase TNF-alpha- or IL-1beta-induced beta cell death, in line with the observations that cytokines induced the expression of the anti-apoptotic genes A20, Iap-2 and Xiap to a similar extent. Microarray analysis of INS-1E cells treated with IL-1beta or TNF-alpha showed similar patterns of gene expression. IL-1beta, however, induced a higher rate of expression of NF-kappaB target genes putatively involved in beta cell dysfunction and death and a stronger activation of the IKK complex, leading to an earlier translocation of NF-kappaB to the nucleus.


CONCLUSIONS
NF-kappaB activation in beta cells has a pro-apoptotic role following exposure not only to IL-1beta but also to TNF-alpha. The more marked beta cell death induced by IL-1beta is explained at least in part by higher intensity NF-kappaB activation, leading to increased transcription of key target genes.
Ortis
F
F
Laboratory of Experimental Medicine, Université Libre de Bruxelles (ULB), Route de Lennik, 808-CP-618, 1070, Brussels, Belgium, fortis@ulb.ac.be.
Pirot
P
P
Naamane
N
N
Kreins
A Y
AY
Rasschaert
J
J
Moore
F
F
Théâtre
E
E
Verhaeghe
C
C
Magnusson
N E
NE
Chariot
A
A
Orntoft
T F
TF
Eizirik
D L
DL
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003922:Diabetes Mellitus, Type 1 / Q000276:immunology / Q000473:pathology / Q000503:physiopathology*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects / Q000276:immunology; D051550:I-kappa B Kinase / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D053583:Interleukin-1beta / Q000378:metabolism* / Q000494:pharmacology; D016328:NF-kappa B / Q000235:genetics* / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism* / Q000494:pharmacology
D053583:Interleukin-1beta; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D051550:I-kappa B Kinase