| Co-Investigator(Kenkyū-buntansha) |
MACHIDE Mitsuru Osaka University, Graduate School of Medicine, Assistant Professor, 医学系研究科, 助手 (90346198)
KOSHIMIZU Uichi Osaka University, Graduate School of Medicine, Assistant Professor, 医学系研究科, 助手 (50281126)
NAKAMURA Toshikazu Osaka University, Graduate School of Medicine, Professor, 医学系研究科, 教授 (00049397)
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| Research Abstract |
HGF is involved in regeneration of various tissues, including the liver. HGF exerts its biological activities in injured tissue-specific manner, whereas mechanisms involved in the injured tissue-specific responsiveness/activation of the c-Met remain unknown. Elucidation of injured tissue-specific c-Met activation is expected to lead to understanding of fundamental mechanisms of tissue regeneration and homeostasis. This research focused to elucidate regulatory mechanisms for c-Met receptor function in signal transduction and their significance in tissue regeneration and homeostasis.
1.Regulation of cellular responsiveness associated with c-Met Ser985 phosphorylation :
We found that 1) c-Met receptor tyrosine phosphorylation/activation upon HGF-stimulus is regulated with a reciprocal manner to c-Met Ser985 phosphorylation, 2) c-Met Ser985 phosphorylation is bidirectionally regulated by PKC and PP2A (protein phosphatase-2A), i.e., it is phosphorylated by PKC instead dephosphorylated by PP2A
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, and 3) c-Met Ser985 phosphorylation is induced oxidative stress of cells these cells wherein c-Met Ser985 is phosphorylated are incapable of responding to extracellular HGF-stimulus. In addition, c-Met Ser985 phosphorylation is regulated through cell-cell adhesiveness in hepatocytes in primary culture, suggesting that change in cell-cell adhesiveness in response to tissue and cellular injury may affect Ser985 phosphorylation, thereby regulating cellular responsiveness to HGF.
2.Analysis of physiological significance of c-Met receptor juxtamembrane region including Ser985 through transgenic mice :
The juxtamembrane region of the c-Met receptor contains Ser985 and is considered to be negative regulatory domain for HGF-dependent tyrosine phosphorylation. To elucidate physiological significance of the negative regulation of c-Met receptor function, we planned to prepare genetically modified mice (knock-in mice) wherein mutated c-Met receptor deleted with the juxtamembrane (Δjxt-c-Met) is expressed, instead of full-length c-Met. ES cells having knock-in constract were selected and chimeric mice were obtained.
3.In vivo injured tissue-specific activation of c-Met and its relationship to Ser985 phosphorylation:
c-Met receptor tyrosine phosphorylation was induced in the injured liver 24-48 hr after CC14-administration in mice, whereas c-Met receptor was not activated in intact organs. Instead, c-Met Ser985 was phosphorylated in intact liver, whereas it was dephosphorylated 24-48 hr after liver injury. Thus, c-Met Ser985 and c-Met tyrosine phosphorylation is reciprocally regulated in response to tissue injury, suggesting that Ser985 phosphorylation is a mechanism responsible for injured tissue-specific modification of the c-Met receptor function.
4.Discussion :
Ser985 phosphorylation mediated by activation of PKC and PP2A is likely to play a role in the regulation of c-Met receptor activation and cellular responsiveness to HGF, which depend on the extracellular environment and stimuli. Further studies on regulatory mechanisms responsible for c-Met receptor activation through juxtamembrane domain and Ser985 phosphorylation will provide even further understanding of the HGF-c-Met system in development, tissue regeneration, and tumorigenesis. Less
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