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  • Title: SEK1/MKK4-mediated SAPK/JNK signaling participates in embryonic hepatoblast proliferation via a pathway different from NF-kappaB-induced anti-apoptosis.
    Author: Watanabe T, Nakagawa K, Ohata S, Kitagawa D, Nishitai G, Seo J, Tanemura S, Shimizu N, Kishimoto H, Wada T, Aoki J, Arai H, Iwatsubo T, Mochita M, Watanabe T, Satake M, Ito Y, Matsuyama T, Mak TW, Penninger JM, Nishina H, Katada T.
    Journal: Dev Biol; 2002 Oct 15; 250(2):332-47. PubMed ID: 12376107.
    Abstract:
    Mice lacking the stress-signaling kinase SEK1 die from embryonic day 10.5 (E10.5) to E12.5. Although a defect in liver formation is accompanied with the embryonic lethality of sek1(-/-) mice, the mechanism of the liver defect has remained unknown. In the present study, we first produced a monoclonal antibody specifically recognizing murine hepatoblasts for the analysis of liver development and further investigated genetic interaction ofsek1 with tumor necrosis factor-alpha receptor 1 gene (tnfr1) and protooncogene c-jun, which are also responsible for liver formation and cell apoptosis. The defective liver formation in sek1(-/-) embryos was not protected by additionaltnfr1 mutation, which rescues the embryonic lethality of mice lacking NF-kappaB signaling components. There was a progressive increase in the hepatoblast cell numbers of wild-type embryos from E10.5 to E12.5. Instead, impaired hepatoblast proliferation was observed in sek1(-/-) livers from E10.5, though fetal liver-specific gene expression was normal. The impaired phenotype in sek1(-/-) livers was more severe than in c-jun(-/-) embryos, and sek1(-/-) c-jun(-/-) embryos died more rapidly before E8.5. The hepatoblast proliferation required no hematopoiesis, since liver development was not impaired in AML1(-/-) mice that lack hematopoietic functions. Stimulation of stress-activated protein kinase/c-Jun N-terminal kinase by hepatocyte growth factor was attenuated in sek1(-/-) livers. Thus, SEK1 appears to play a crucial role in hepatoblast proliferation and survival in a manner apparently different from NF-kappaB or c-Jun.
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