2007 Fiscal Year Final Research Report Summary
Regulation of CREB by LKB1-SIK-TORC signaling cascade
| Project/Area Number |
17390093
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Pathological medical chemistry
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| Research Institution | Tezukayama University (2006-2007)
Osaka University (2005) |
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Principal Investigator |
OKAMOTO Mitsuhiro Tezukayama University, Faculty of Contemporary Human Life Science, Professor (90028613)
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| Co-Investigator(Kenkyū-buntansha) |
TAKEMORI Hiroshi National Institute of Biomedical Innovation, Laboratory of Cell Signaling and Metabolism, Chief Investigator (90273672)
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| Project Period (FY) |
2005 – 2007
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| Keywords | Salt-inducible kinase / Cyclic AMP / CREB / TORC / Protein kinase / LKB1 / Steroid hormone / Transcription coactivator |
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| Research Abstract |
A transcription factor cyclic AMP-responsive element (CRE)-binding protein (CREB) is known to be activated by the PKA-dependent phosphorylation at Ser133. Our recent findings have suggested the Ser133-independent activation mechanism of CREB. By binding to the basic leucine zipper domain of CREB, a novel CREB-specific coactivator named transducer of regulated CREB activity (TORC) upregulates CREB activity. And salt-inducible kinase (SIK) phosphorylates TORC, inducing its nuclear export, and, as a result, represses CREB activity. Here we attempted to investigate how the SIK-TORC-CREB signaling cascade operates at the cellular level and at the animal level. Our results are summarized as follows:
(1) Because LKB1 was shown to be an upstream kinase of SIK, we used LKB1-defective HeLa cells to further elucidate TORC-dependent CREB activation. In the absence of LKB1, SIK was not able to phosphorylate TORC, and as a result CREB was in a constitutively activated state. Overexpression of LKB1 in HeLa cells improved the CRE-dependent transcription in a regulated manner.
(2) The inactivation of kinase cascades by 10 nM staurosporine in LKB1-positive HEK293 cells also induced unregulated, constitutively activated, CRE activity. Treatment with staurosporine completely inhibited SIK kinase activity without any significant effect on the phosphorylation level at the LKB1-phosphorylatable site in SIK or the activity of AMPK, another target of LKB1.
(3) The results suggest that at the cellular level, LKB1 and its downstream SIK play an important role in silencing CREB activity via the phosphorylation of TORC, and such silencing may be indispensable for the regulated activation of CREB.
(4) SIK2-gene-disrupted mice have been developed. Preliminary findings suggest that their TORC-CREB signaling cascade seems to be functioning normally because SIK1 and SIK3, SIK isoforms other than SIK2, compensate the function of SIK2 in these mice.
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Research Products
(24 results)
