Oxidative stress induces nucleo-cytoplasmic translocation of pancreatic transcription factor PDX-1 through activation of c-Jun NH(2)-terminal kinase.
Oxidative stress is induced in pancreatic beta-cells under diabetic conditions and causes beta-cell dysfunction. Antioxidant treatment of diabetic animals leads to recovery of insulin biosynthesis and increases the expression of its controlling transcription factor, pancreatic duodenal homeobox-1 (PDX-1), in pancreatic beta-cells. Here, we show that PDX-1 is translocated from the nuclei to the cytoplasm of pancreatic beta-cells in response to oxidative stress. When oxidative stress was charged upon beta-cell-derived HIT-T15 cells, both endogenous PDX-1 and exogenously introduced green fluorescent protein-tagged PDX-1 moved from the nuclei to the cytoplasm. The addition of a dominant negative form of c-Jun NH(2)-terminal kinase (JNK) inhibited oxidative stress-induced PDX-1 translocation, suggesting an essential role of JNK in mediating this phenomenon. Whereas the nuclear localization signal (NLS) in PDX-1 was not affected by oxidative stress, leptomycin B, a specific inhibitor of the classical leucine-rich nuclear export signal (NES), inhibited nucleo-cytoplasmic translocation of PDX-1 induced by oxidative stress. Moreover, we identified an NES at position 82-94 of the mouse PDX-1 protein. Thus, our present results revealed a novel mechanism that negatively regulates PDX-1 function. The identification of the NES, which overrides the function of the NLS in an oxidative stress-responsive, JNK-dependent manner, supports the complicated regulation of PDX-1 function in vivo and may further the understanding of beta-cell pathophysiology in diabetes.
Kawamori
Dan
D
Department of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, Suita City, Osaka, Japan.
Kajimoto
Yoshitaka
Y
Kaneto
Hideaki
H
Umayahara
Yutaka
Y
Fujitani
Yoshio
Y
Miyatsuka
Takeshi
T
Watada
Hirotaka
H
Leibiger
Ingo B
IB
Yamasaki
Yoshimitsu
Y
Hori
Masatsugu
M
D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D018398:Homeodomain Proteins; D007515:Islets of Langerhans / Q000378:metabolism*; D048031:JNK Mitogen-Activated Protein Kinases; D007930:Leucine; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D019913:Nuclear Localization Signals / Q000502:physiology; D018384:Oxidative Stress / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D015534:Trans-Activators / Q000378:metabolism*
D018398:Homeodomain Proteins; D019913:Nuclear Localization Signals; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D007930:Leucine