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Cell Death Differ. 2014 Aug;21(8):1313-24. doi: 10.1038/cdd.2014.53. Epub 2014 May 2.

JunB protects β-cells from lipotoxicity via the XBP1-AKT pathway.

Author information

1
Laboratory of Experimental Medicine and ULB Center of Diabetes Research, Université Libre de Bruxelles, Brussels, Belgium.
2
Department of Endocrinology and Metabolism, University of Pisa, Pisa, Italy.
3
1] Laboratory of Experimental Medicine and ULB Center of Diabetes Research, Université Libre de Bruxelles, Brussels, Belgium [2] Division of Endocrinology, Erasmus Hospital, Université Libre de Bruxelles, Brussels, Belgium.

Abstract

Diets rich in saturated fats may contribute to the loss of pancreatic β-cells in type 2 diabetes. JunB, a member of the activating protein 1 (AP-1) transcription factor family, promotes β-cell survival and mediates part of the beneficial effects of GLP-1 agonists. In this study we interrogated the molecular mechanisms involved in JunB-mediated β-cell protection from lipotoxicity. The saturated fatty acid palmitate decreased JunB expression, and this loss may contribute to β-cell apoptosis, as overexpression of JunB protected cells from lipotoxicity. Array analysis of JunB-deficient β-cells identified a gene expression signature of a downregulated endoplasmic reticulum (ER) stress response and inhibited AKT signaling. JunB stimulates XBP1 expression via the transcription factor c/EBPδ during ER stress, and forced expression of XBP1s rescued the viability of JunB-deficient cells, constituting an important antiapoptotic mechanism. JunB silencing inhibited AKT activation and activated the proapoptotic Bcl-2 protein BAD via its dephosphorylation. BAD knockdown reversed lipotoxic β-cell death potentiated by JunB siRNA. Interestingly, XBP1s links JunB and AKT signaling as XBP1 knockdown also reduced AKT phosphorylation. GLP-1 agonists induced cAMP-dependent AKT phosphorylation leading to β-cell protection against palmitate-induced apoptosis. JunB and XBP1 knockdown or IRE1 inhibition decreased AKT activation by cAMP, leading to β-cell apoptosis. In conclusion, JunB modulates the β-cell ER stress response and AKT signaling via the induction of XBP1s. The activation of the JunB gene network and the crosstalk between the ER stress and AKT pathway constitute a crucial defense mechanism by which GLP-1 agonists protect against lipotoxic β-cell death. These findings elucidate novel β-cell-protective signal transduction in type 2 diabetes.

PMID:
24786832
PMCID:
PMC4085537
DOI:
10.1038/cdd.2014.53
[Indexed for MEDLINE]
Free PMC Article

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