The Down syndrome candidate dual-specificity tyrosine phosphorylation-regulated kinase 1A phosphorylates the neurodegeneration-related septin 4.

The dual-specific kinase DYRK1A (dual-specificity tyrosine phosphorylation-regulated kinase 1A) is the mammalian orthologue of the Drosophila minibrain (MNB) protein kinase and executes diverse roles in neuronal development and adult brain physiology. DYRK1A is overexpressed in Down syndrome (DS) and has recently been implicated in several neurodegenerative diseases. In an attempt to elucidate the molecular basis of its involvement in cognitive and neurodegeneration processes, we searched for novel proteins interacting with the kinase domain of DYRK1A in the adult mouse brain and identified septin 4 (SEPT4, also known as Pnutl2/CDCrel-2). SEPT4 is a member of the group III septin family of guanosine triphosphate hydrolases (GTPases), which has previously been found in neurofibrillary tangles of Alzheimer disease brains and in alpha-synuclein-positive cytoplasmic inclusions in Parkinson disease brains. In transfected mammalian cells, DYRK1A specifically interacts with and phosphorylates SEPT4. Phosphorylation of SEPT4 by DYRK1A was inhibited by harmine, which has recently been identified as the most specific inhibitor of DYRK1A. In support of a physiological relation in the brain, we found that Dyrk1A and Sept4 are co-expressed and co-localized in neocortical neurons. These findings suggest that SEPT4 is a substrate of DYRK1A kinase and thus provide a possible link for the involvement of DYRK1A in neurodegenerative processes and in DS neuropathologies.

BCL-6: a possible missing link for anti-inflammatory PPAR-delta signalling in pancreatic beta cells.

AIMS/HYPOTHESIS: Inflammatory mediators contribute to pancreatic beta cell death in type 1 diabetes. Beta cells respond to cytokine exposure by activating gene networks that alter cellular metabolism, induce chemokine release (thereby increasing insulitis), and cause apoptosis. We have previously shown by microarray analysis that exposure of INS-1E cells to IL-1beta + IFN-gamma induces the transcription factor peroxisome proliferator-activated receptor (Ppar)-delta and several of its target genes. PPAR-delta controls cellular lipid metabolism and is a major regulator of inflammatory responses. We therefore examined the role of PPAR-delta in cytokine-treated beta cells. MATERIALS AND METHODS: Primary beta cells that had been purified by fluorescence-activated cell sorting and INS-1E cells were cultured in the presence of the cytokines TNF-alpha, IL-1beta, or IL-1beta + IFN-gamma, or the synthetic PPAR-delta agonist GW501516. Gene expression was analysed by real-time PCR. PPAR-delta, monocyte chemoattractant protein (MCP-1, now known as CCL2) promoter and NF-kappaB activity were determined by luciferase reporter assays. RESULTS: Exposure of primary beta cells or INS-1E cells to cytokines induced Ppar-delta mRNA expression and PPAR-delta-dependent CD36, lipoprotein lipase, acyl CoA synthetase and adipophilin mRNAs. Cytokines and the PPAR-delta agonist GW501516 also activated a PPAR-delta response element reporter in beta cells. Unlike immune cells, neither INS-1E nor beta cells expressed the transcriptional repressor B-cell lymphoma-6 (BCL-6). As a consequence, PPAR-delta activation by GW501516 did not decrease cytokine-induced Mcp-1 promoter activation or mRNA expression, as reported for macrophages. Transient transfection with a BCL-6 expression vector markedly reduced Mcp-1 promoter and NF-kappaB activities in beta cells. CONCLUSIONS/INTERPRETATION: Cytokines activate the PPAR-delta gene network in beta cells. This network does not, however, regulate the pro-inflammatory response to cytokines because beta cells lack constitutive BCL-6 expression. This may render beta cells particularly susceptible to propagating inflammation in type 1 diabetes.