The tyrosine kinase FRK/RAK participates in cytokine-induced islet cell cytotoxicity.
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.
Welsh
Michael
M
Department of Medical Cell Biology, Uppsala University, 75123, Uppsala, Sweden. michael.welsh@medcellbiol.uu.se
Welsh
Charlotte
C
Ekman
Maria
M
Dixelius
Johan
J
Hägerkvist
Robert
R
Annerén
Cecilia
C
Akerblom
Björn
B
Mahboobi
Siavosh
S
Chandrasekharan
Subhashini
S
Liu
Edison T
ET
D000818:Animals; D016923:Cell Death / Q000502:physiology; D002460:Cell Line; D016207:Cytokines / Q000037:antagonists & inhibitors / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007313:Insecta / Q000166:cytology; D007515:Islets of Langerhans / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology*; D008262:Macrophage Activation; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000172:deficiency / Q000502:physiology*; D010748:Phosphopeptides / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000172:deficiency / Q000502:physiology*; D034622:RNA Interference / Q000502:physiology; D013602:T-Lymphocytes, Cytotoxic; D019061:src-Family Kinases
D016207:Cytokines; D004791:Enzyme Inhibitors; D009363:Neoplasm Proteins; D010748:Phosphopeptides; D011505:Protein-Tyrosine Kinases; C490512:Frk protein, mouse; D019061:src-Family Kinases