Increased cytokine-induced cytotoxicity of pancreatic islet cells from transgenic mice expressing the Src-like tyrosine kinase GTK.
BACKGROUND
The loss of beta cells in type 1 diabetes may involve protein kinases because they control cell growth, differentiation, and survival. Previous studies have revealed that GTK, a Src-like protein tyrosine kinase expressed in beta cells (also named Bsk/Iyk), regulates multiple responses including growth and survival of rat insulinoma cells (RINm5F) and differentiation of neuronal PC12 cells. In the present study, we have generated a transgenic mouse expressing a kinase active GTK mutant (GTK-Y504F) under the control of the rat insulin I promoter to establish a role of GTK in beta cells.


METHODS
Control and GTK-transgenic CBA mice were used for determination of in vivo glucose tolerance and the relative insulin-positive area. Isolated islets from both groups were cultured in the absence and presence of cytokines and insulin secretion, viability and protein expression were assessed.


RESULTS
The beta-cell mass of GTK-transgenic mice was increased as a consequence of a larger pancreas and an increased relative beta-cell area. Islets isolated from the transgenic animals exhibited an enhanced glucose-induced insulin release and reduced viability in response to cytokines that could not be explained by higher levels of nitric oxide (NO) compared with control islets. Extracellular signal-regulated kinase (ERK) 1/2, p38 mitogen-activated protein kinase (MAPK), c-Jun NH2-terminal kinase (JNK), and Akt were all activated by cytokines, but GTK-transgenic islets contained higher basal levels of phosphorylated ERK1/2 and lower basal levels of phosphorylated p38 compared with the control islets. The total amount of activated MAPKs was, however, higher in the cytokine-stimulated transgenic islets compared with the control islets due to increased levels of phospho-ERK1/2. Moreover, the proline-rich tyrosine kinase (PYK) 2 (also named RAFTK/CAK beta/CADTK) levels were elevated in response to a 24-hr exposure to cytokines in control islets but not in the GTK-transgenic islets.


CONCLUSIONS
These results suggest that although GTK increases the beta-cell mass, it also enhances islet cell death in response to cytokines and may thus be involved in the beta-cell damage in type 1 diabetes.
Annerén
C
C
Department of Medical Cell Biology, Uppsala University, Sweden. cecilia.anneren@medcellbiol.uu.se
Welsh
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M
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002470:Cell Survival / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D016207:Cytokines / Q000502:physiology*; D005260:Female; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000254:growth & development* / Q000502:physiology*; D048031:JNK Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D008297:Male; D051379:Mice; D008808:Mice, Inbred CBA; D008822:Mice, Transgenic; D019950:Mitogen-Activated Protein Kinase 1 / Q000187:drug effects; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000187:drug effects; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects; D009154:Mutation; D009929:Organ Size; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt; D048051:p38 Mitogen-Activated Protein Kinases
D016207:Cytokines; D007328:Insulin; D011518:Proto-Oncogene Proteins; C100882:gtk kinase; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases