The tyrosine kinase FRK/RAK participates in cytokine-induced islet cell cytotoxicity

• Published in: Biochemical journal 2004-08, Vol.382 (Pt 1), p.261-268
• Main Authors: Welsh, Michael, Welsh, Charlotte, Ekman, Maria, Dixelius, Johan, Hägerkvist, Robert, Annerén, Cecilia, Akerblom, Björn, Mahboobi, Siavosh, Chandrasekharan, Subhashini, Liu, Edison T
• Format: Article
• Language: English
• Subjects: Animals; b-cell; Cell Death - physiology; Cell Line; cytokine; Cytokines - antagonists & inhibitors; Cytokines - physiology; cytotoxicity; Enzyme Inhibitors - pharmacology; fyn-related kinase (FRK)/RAK; Insecta - cytology; Islets of Langerhans - drug effects; Islets of Langerhans - enzymology; Islets of Langerhans - pathology; Islets of Langerhans - secretion; kinase inhibitor; knockout; Macrophage Activation; MEDICIN; MEDICINE; Mice; Mice, Inbred C57BL; Mice, Knockout; Neoplasm Proteins - antagonists & inhibitors; Neoplasm Proteins - chemistry; Neoplasm Proteins - deficiency; Neoplasm Proteins - physiology; Phosphopeptides - metabolism; Phosphorylation; Protein-Tyrosine Kinases - antagonists & inhibitors; Protein-Tyrosine Kinases - chemistry; Protein-Tyrosine Kinases - deficiency; Protein-Tyrosine Kinases - physiology; RNA Interference - physiology; src-Family Kinases; T-Lymphocytes, Cytotoxic
• ISSN: 0264-6021; 1470-8728; 1470-8728
• DOI: 10.1042/bj20040285

Hallmarks of the inflammatory process in Type I diabetes are macrophage activation, local release of beta-cell-toxic cytokines and infiltration of cytotoxic T lymphocytes. We have observed recently that mice overexpressing active FRK (fyn-related kinase)/RAK (previously named GTK/Bsk/IYK, where GTK stands for gut tyrosine kinase, Bsk for beta-cell Src-homology kinase and IYK for intestinal tyrosine kinase) in beta-cells exhibit increased susceptibility to beta-cell-toxic events, and therefore, we now attempt to find a more precise role for FRK/RAK in these processes. Phosphopeptide mapping of baculovirus-produced mouse FRK/RAK revealed an autophosphorylation pattern compatible with Tyr-394 being the main site. No evidence for in vitro phosphorylation of the C-terminal regulatory sites Tyr-497 and Tyr-504 was obtained, nor was there any indication of in vitro regulation of FRK/RAK kinase activity. Screening a panel of known tyrosine kinase inhibitors for their ability to inhibit FRK/RAK revealed several compounds that inhibited FRK/RAK, with a potency similar to that reported for their ability to inhibit other tyrosine kinases. Cytokine-induced islet toxicity was reduced in islets isolated from FRK/RAK knockout mice and this occurred without effects on the production of nitric oxide. Addition of the nitric oxide inhibitor nitroarginine to FRK/RAK knockout islets exposed to cytokines decreased cell death to a basal level. In normal islets, cytokine-induced cell death was inhibited by the addition of two FRK/RAK inhibitors, SU4984 and D-65495, or by transfection with short interfering RNA against FRK/RAK. It is concluded that FRK/RAK contributes to cytokine-induced beta-cell death, and inhibition of this kinase could provide means to suppress beta-cell destruction in Type I diabetes.