JNK3 is abundant in insulin-secreting cells and protects against cytokine-induced apoptosis

Abstract

Aims/hypothesis In insulin-secreting cells, activation of the c-Jun NH 2 -terminal kinase (JNK) pathway triggers apoptosis. Whereas JNK1 and JNK2 are ubiquitously produced, JNK3 has been described exclusively in neurons. This report aims to characterise the expression and role in apoptosis of the three JNK isoforms in insulin-secreting cells exposed to cytokines. Methods Sections of human and mouse pancreases were used for immunohistochemistry studies with isoformspecific anti-JNK antibodies. Human, pig, mouse and rat pancreatic islets were isolated by enzymatic digestion and RNA or protein extracts were prepared. RNA and protein levels were determined by quantitative RT-PCR and western blotting respectively, using JNK-isoform-specific primers and isoform-specific antibodies; activities of the three JNK isoforms were determined by kinase assays following quantitative immunoprecipitation/depletion of JNK3. JNK silencing was performed with small interfering RNAs and apoptotic rates were determined in INS-1E cells by scoring cells displaying pycnotic nuclei. Results JNK3 and JNK2 mRNAs are the predominant isoforms expressed in human pancreatic islets. JNK3 is nuclear while JNK2 is also cytoplasmic. In INS-1E cells, JNK3 knockdown increases c-Jun levels and caspase-3 cleavage and sensitises cells to cytokine-induced apoptosis; in contrast, JNK1 or JNK2 knockdown is protective. Conclusions/interpretation In insulin-secreting cells, JNK3 plays an active role in preserving pancreatic beta cell mass from cytokine attacks. The specific localisation of JNK3 in the nucleus, its recruitment by cytokines, and its effects on key transcription factors such as c-Jun, indicate that JNK3 is certainly an important player in the transcriptional control of genes expressed in insulin-secreting cells.

Coxsackievirus B Tailors the Unfolded Protein Response to Favour Viral Amplification in Pancreatic β Cells

“…JNK1 is the main contributor to cytokine-induced β cell apoptosis [45]. To clarify the role of these isoforms on viral replication, we used previously validated siRNAs targeting JNK1 or JNK2 [24, 45]. These siRNAs knocked down JNK1 and JNK2 protein expression by 55 and 65%, respectively (Fig.…”

“…The siRNAs used were: Allstars Negative Control siRNA (siCTL, Qiagen, Venlo, The Netherlands), and rat JNK1 (siJNK1) [23], rat JNK2 (siJNK2) [24], and rat IRE1α (siIRE1α), all from Invitrogen, Carlsbad, CA, USA [25]. The protocol for siRNA transfection was previously validated using a FITC-coupled siRNA (siGLO Green Transfection Indicator, Thermo Scientific, Chicago, IL, USA).…”

JNK Signaling: Regulation and Functions Based on Complex Protein-Protein Partnerships

“…However, ␤-cells also express JNK3, and this may have protective roles, unlike those prodeath roles described for JNK1 or JNK2 (432). Thus, approaches targeting the JNKs as possible therapeutic strategies will need to consider both tissue-and isoform-specific differences.…”

The Nuclear Translocation of Mitogen-Activated Protein Kinases: Molecular Mechanisms and Use as Novel Therapeutic Target

“…Early studies indicated that these MAPKs, or at least some of their isoforms, are mainly localized in the nucleus of resting cells [70-72], and may be exported out to the cytoplasm upon stimulation [70]. However, it later became clear that in most cells and conditions they do behave similarly to ERK1/2, namely, localized mostly in the cytoplasm of resting cells, and translocate into the nucleus upon stimulation [73, 74].…”