Abstract
A novel variant of human heat-shock cognate protein 70 (HSC70) transcript, named heat-shock cognate protein 54 (HSC54), was identified and characterized. The transcript encodes the protein lacking 153 amino acid residues of HSC70 in a part of the protein-binding and variable domains, resulting in a calculated molecular mass of 53.5 kDa. HSC54 mRNA was detected in all human cells and tissues examined. The protein was also detected in peripheral mononuclear cells and U937 human histiocytic lymphoma cells. Heat treatment of U937 cells up-regulated the expression of HSC54. The chaperoning activity of HSC54 was examined by luciferase renaturation assay. HSC70 recovered the luciferase activity in the presence of reticulocyte lysate as a source of cochaperones. However, HSC54 did not facilitate the recovery of denatured luciferase; besides, HSC54 significantly inhibited the HSC70-mediated chaperoning activity. In pull-down experiments, HSC54 interacted with cochaperones, p60, HSP40, and p48, as HSC70 did. The resonant mirror detection analysis showed that p60 binds to HSC54 with a higher association rate constant than HSC70 with a similar affinity constant. These results suggest that HSC54 is constitutively expressed and also inducible by stress and may function as an endogenous inhibitory regulator of HSC70 by competing the cochaperones.
Footnotes
- Received April 24, 2000.
- Accepted August 31, 2000.
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Send reprint requests to: Dr. Fujiko Tsukahara, Department of Pharmacology, Tokyo Women's Medical University, School of Medicine, 8-1, Kawada-cho, Shinjuku-ku, Tokyo, 162-8666, Japan. E-mail:fuji{at}research.twmu.ac.jp
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The present work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan (Grant 11839025). The nucleotide sequence data reported in this paper will appear in the DDBJ/EMBL/GenBank nucleotide sequence databases with the accession number AB034951.
- The American Society for Pharmacology and Experimental Therapeutics
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