1996 Fiscal Year Final Research Report Summary
Nuclear translocation mechanism of heat shock proteins
| Project/Area Number |
07680790
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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 |
Cell biology
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| Research Institution | Aichi Cancer Center Research Institute |
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Principal Investigator |
OHTSUKA Kenzo Aichi Cancer Center, Lab. Exptl. Radiol., Section Head, 放射線部, 室長 (40150213)
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| Project Period (FY) |
1995 – 1996
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| Keywords | Hsp40 / Hsp70 / nuclear translocation / heat shock / molecular chaperone |
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| Research Abstract |
We recently identified a 40-kDa heat shock protein Hsp40 in mammalian cells. Hsp40 is one of the homologues of bacterial DnaJ heat shock protein. We have already reported that Hsp40 forms complex with Hsp70 in the cytosol and translocates into the nuclei and nucleoli upon heat shock, and that both Hsp40 and Hsc70 bind to the nascent polypetide chains emerging from translating ribosomes and function as molecular chaperons, mediating their correct folding.
We here investigated heat shock-induced nuclear translocation of Hsp40 and Hsp70 in several mamalian cells including human (HeLa), rat (NRK) and Chinese hamster (HA-1). Heat-induced translocation kinetics of Hsp40 is very similar to that of Hsp70 that indicates cotraslocation. Also, both Hsps colocalize in the nucleoli in the same cells, suggesting they work together in repairing heat-denatured proteins.
We next examined biochemical characterization of purified recombinant Hsp40 and Hsc70. The Hsc70 has weak intrinsic ATPase activity. Th
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e ATPase activity is stimulated 2-3 fold by Hsp40. This stimulation effect of Hsp40 is maximum at 45ﾟC,suggesting that Hsc70 and Hsp40 function together as molecular chaperones more efficiently under severe stress conditons. Also, we showed that both Hsc70 and Hsp40 act cooperatively to suppress the aggregation and restore the enzyme activity of denatured protein in an ATP-dependent manner using rhodanese as model protein. However, Hsp4- itself does not have such kind effect.
We tried to establish semi-intact cell system to investigate molecular mechanism of nuclear translocation of Hsps, but the semi-intact cell system did not work well under our experimental conditions. Hsp40 (340 amino acids) has several basic amino acid clusters which might be involved in the nuclear translocation (59-61,157-159,181-182,294-296). Therefore, these basic amino acids were changed to neutral amino acids by site-directed mutagenesis. We are now examining whether these mutant proteins translocate into the nuclei by heat shock Less
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[Publications] Sugito, K., Yamane, M., Hattori, H., Hayashi, Y., Tohnai, I., Ueda, M., Tsuchida, N.and Ohtsuka, K.: "Interaction between hsp70 and hsp40, eukaryotic homologues of Dnak and DnaJ,in human cells expressing mutant-type p53" FEBS Lett.358. 161-164 (1995)
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「研究成果報告書概要(欧文)」より
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[Publications] Kaneko, R., Hattori, H., Hayashi, Y., Tohnai, I., Ueda, M.and Ohtsuka, K.: "Heat-shock protein 40, a novel predictor of thermotolerance in murine cells" Radiat. Res.142. 91-97 (1995)
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[Publications] Yamane, M., Sugito, K., Hattori, H., Hayashi, Y., Tohnai, I., Ueda, M., Nishizawa, K.and Ohtsuka, K.: "Cortranslocation and colocalization of hsp40 (DnaJ) with hsp70 (DnaK) in mammalian cells" Cell Struct. Funct.20. 157-166 (1995)
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[Publications] Terada, K., Ueda, I., Ohtsuka, K., Oda, T., Ichiyama, A.and Mori, M.: "The reguirement of heat shock cognate 70 protein for mitochondrial import varies among precursor proteins and depending on precursor length" Mol. Cell. Biol.16. 6103-6109 (1996)
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