| Project/Area Number |
07044250
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| Research Category |
Grant-in-Aid for international Scientific Research
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| Allocation Type | Single-year Grants |
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| Section | Joint Research |
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
MINATO Nagahiro Kyoto University, Faculty of Medicine, Professor, 医学研究科, 教授 (40137716)
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| Co-Investigator(Kenkyū-buntansha) |
MARUTA Hiroshi Ludwing Institute for Cancer Research, Melbourne branch Senior Investigator, 主任研究員
KUBOTA Hiroshi Kyoto University, Faculty of Medicine Asistant, 医学研究科, 助手 (80263094)
HATTORI Masakazu Kyoto University, Faculty of Medicine Assistant, 医学研究科, 助手 (40211479)
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| Project Period (FY) |
1995
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| Project Status |
Completed (Fiscal Year 1995)
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| Budget Amount *help |
¥4,800,000 (Direct Cost: ¥4,800,000)
Fiscal Year 1995: ¥4,800,000 (Direct Cost: ¥4,800,000)
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| Keywords | Ran binding / nuclear protein / processing / cell cycle progression / Ran / RCC-1 system / PEST / leucine zipper motif |
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| Research Abstract |
We have cloned a novel cDNA (Spa-1), specifically induced to express in the lymphoid cells following the mitogenic stimulation. Spa-1 encodes a nuclear protein possessing a human Rap1 GTPase activating protein-related domain (GRD) at N-terminus followed by unique sequence containing a number of PEST sequences and leucine zipper-like motif at its C-terminus. Indeed, a fusion protein of N-terminal GRD exhibited GAP activity for Rap1 in vitro, and rather surprisingly also for Ran which is so far the only small GTPase known to be present in the nuclei. Using thorNIH3T3 fibroblasts stably transfected with Spa-1 cDNA, it was indicated that ectopic overexpression of Spa-1 protein in the arrested G1 phase by serum starvation resulted in the catastrophic cell death during the following S phase, suggesting that Spa-1 protein was involved in the negative regulation of cell cylce progression. In the present stydy, we investigated the behavior of Spa-1 protein in the lymphocytes, in which the protein is normally induced rather selectively. We first provide suggestive evidences that the 68 kDa Spa-1 protein found in the nuclei of normal proliferating lymphocytes is derived from the cytosolic full-length 85 kDa Spa-1 protein by posttranslational processing at the C-terminal portion resulting in the deletion of LZ motif. Comparative experiments using a full-length Spa-1 cDNA and C-termically trancated form of it indicated that the protein from the latter but not the former preferentially translocated into the nuclei, bound to Ran-GTP, and suppressed the colony formation of normal NIH3T3. These results suggest that the nuclear form of Spa-1 in the lymphoid cells is involved in the negative regulation of normal lymphocyte proliferation possibly as a distinct member of Ran/RCC-1 system.
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