Hsp72 chaperone function is dispensable for protection against stress-induced apoptosis
In addition to its role as a molecular chaperone, heat shock protein 72 (Hsp72) protects cells against a wide range of apoptosis inducing stresses. However, it is unclear if these two roles are functionally related or whether Hsp72 inhibits apoptosis by a mechanism independent of chaperone activity. The N-terminal adenosine triphosphatase domain, substrate-binding domain and the C-terminal EEVD regulatory motif of Hsp72 are all essential for chaperone activity. In this study, we show that Hsp72 mutants with a functional substrate-binding domain but lacking chaperone activity retain their ability to protect cells against apoptosis induced by heat and tumor necrosis factor alpha. In contrast, a deletion mutant lacking a functional substrate-binding domain has no protective capacity. The ability of the Hsp72 substrate-binding domain to inhibit apoptosis independent of the regulatory effects of the adenosine triphosphate-binding domain indicates that the inhibition of apoptosis may involve a stable binding interaction with a regulatory substrate rather than Hsp72 chaperone activity.
KeywordsHsp72 Functional analysis Apoptosis Chaperone activity
This study was supported by a grant from the NIH/NCI CA81421. The authors wish to acknowledge the kind gifts of reagents from Dr. R. Morimoto, Dr. Lois Greene, Dr. C. Hunt, Dr. S. Jane, Dr. W. Welch, Dr. P. Darcy, and Dr. N. Hoogenraad and technical assistance from Ms. C. Restall.
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