2007 Fiscal Year Final Research Report Summary
Elucidation of tumor suppressor function of Birt-Hogg-Dube syndrome gene(BHD)
| Project/Area Number |
18590380
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Experimental pathology
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| Research Institution | Juntendo University |
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Principal Investigator |
KOBAYASHI Toshiyuki Juntendo University, Grad. Sch. Med., Associate Professor (40260070)
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| Project Period (FY) |
2006 – 2007
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| Keywords | BHDsyndrome / FnipL / mTOR / AMPK / Tsc2 / Fnip 1 |
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| Research Abstract |
In this study, a novel Bhd product (Flcn)-binding protein (Fnipl-like protein = FnipL) was identified by homology search and its binding with Flcn and AMPK was characterized. The interaction between FnipL and Flcn may be mediated mainly by the C-terminal domains of each proteins as well as Flcn-Fnipl interaction. Ectopically expressed Flcn was localized mainly in the nucleus. Co-transfection analysis revealed that Hen is localized to the cytoplasm by FnipL or Fnipl. A deletion of carboxy-terminal Flcn-binding domain in FnipL cancelled cytoplasmic localization of Flcn, suggesting that the Fnip proteins regulate localization of Flcn through the complex formation. By the employment of siRNA, a decrease in S6K1 phosphorylation in the BHD-suppressed cell was observed. A decrease in S6K1 phosphorylation in FNIPL- or FN/P/ -suppressed cells was also observed. These results suggest that Flcn-FnipL and Flcn-Fnipl complexes positively regulate S6K1 phosphorylation. We also analyzed phosphorylation of Flcn. Phosphorylation of Flcn was suppressed by rapamycin-treatment or expression of Tsc2 in the Tsc2-deficient renal carcinoma cells. Forced expression of Rheb in 293 cells induced Flcn phosphorylation. Conversely, RNAi-mediated inhibition of raptor reduced Flcn phosphorylation. These results suggest that Tsc2-mTOR pathway regulates Flcn phosphorylation. By site-directed mutagenesis and mass spectrometry revealed that a serine residue in the amino-terminal region is a major phosphorylation site. However phosphorylation of this site was thought to be not regulated by Tsc2-mTOR. Several other candidate phosphorylation sites were identified. Together, in this study, reciplocal functional relationship between Flcn and mTOR has been revelead as a clue to elucidate the molecular mechanism of carcinogenesis associated with BHD-deficiency.
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