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

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 isoform-specific 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.

Genomic characterization and embryonic expression of the mouse Bigh3 (Tgfbi) gene.

Mutations in human BIGH3 (TGFB1), a gene identified after treatment of an adenocarcinoma cell line with TGF-beta, have been observed in patients with granular Groenouw type I, Reis-Bücklers, Thiel-Behnke, Avellino, and Lattice type I and IIIa, six autosomal dominant corneal dystrophies linked to chromosome 5q. In order to gain insight into the physiological role of this gene, we characterized the genomic structure of the mouse Bigh3 and its expression in murine embryos. The gene spans 30 kb on mouse chromosome 13 and has 17 exons. Embryonic expression of Bigh3 is observed in the mesenchyme of the first and second branchial arches as early as dpc 11.5 and is particularly strong in the mesenchyme of numerous tissues throughout all the development stages. In fetal eye, the expression is first seen at 11.5 dpc in the mesenchyme surrounding the optic stalk, extends toward the sclera and choroid by 14.3 dpc and reaches the cornea by 17.5 dpc. Because the physiological role of BIGH3/Bigh3 is still largely unknown, embryonic expression in organs like heart, vessels, and intestine may help to identify new functions which could be searched for in patients and in knock-out animal models. The characterization of the murine structure is a prerequisite for the making of such models.