The hsp90-related Protein TRAP1 Is a Mitochondrial Protein with Distinct Functional Properties

Abstract

The hsp90 family of molecular chaperones was expanded recently due to the cloning of TRAP1 and hsp75 by yeast two-hybrid screens. Careful analysis of the human TRAP1 and hsp75 sequences revealed that they are identical, and we have cloned a similar protein from Drosophila. Immunofluorescence data show that human TRAP1 is localized to mitochondria. This mitochondrial localization is supported by the existence of mitochondrial localization sequences in the amino termini of both the human and Drosophila proteins. Due to the striking homology of TRAP1 to hsp90, we tested the ability of TRAP1 to function as an hsp90-like chaperone. TRAP1 did not form stable complexes with the classic hsp90 co-chaperones p23 and Hop (p60). Consistent with these observations, TRAP1 had no effect on the hsp90-dependent reconstitution of hormone binding to the progesterone receptor in vitro, nor could it substitute for hsp90 to promote maturation of the receptor to its hormonebinding state. However, TRAP1 is sufficiently conserved with hsp90 such that it bound ATP, and this binding was sensitive to the hsp90 inhibitor geldanamycin. In addition, TRAP1 exhibited ATPase activity that was inhibited by both geldanamycin and radicicol. Thus, TRAP1 has functions that are distinct from those of hsp90.

TRAP1 regulation of mitochondrial life or death decision in cancer cells and mitochondria-targeted TRAP1 inhibitors

“…Thus, though they are homologous to each other, TRAP1 in the mitochondrial microenvironment could have different cellular functions from cytosolic Hsp90, due to the potential differential distribution of interactors, such as clients and regulators of the chaperone located inside and outside of the mitochondria. TRAP1 does not interact with the co-chaperones or the client proteins of Hsp90 in vitro, which further implies the regulation and function of TRAP1 in mitochondria are different from those of Hsp90 (14). A pool of Hsp90 is also found inside mitochondria in various cancer cells and some normal mouse tissues (16), and is likely to be modulated differentially from cytosolic Hsp90 for the same reason.…”

“…The N domain contains an ATP binding site and is the most conserved region between Hsp90 and TRAP1 (12,13). Both chaperones have ATPase activities and are inhibitable by a prototype Hsp90 inhibitor, geldanamycin, at a comparable working concentration (14). This indicates that Hsp90-targeted drugs designed to occupy the ATP pocket in the Hsp90 N domain can also inhibit the TRAP1 chaperone function in vitro.…”

“…However, subsequent careful analyses of the TRAP1 cDNA sequence and subcellular localization using biochemical and microscopic techniques have proven the existence of a mitochondrial targeting sequence at its N-terminal end and mitochondrial accumulation of the protein (14).…”

TRAP1 and the proteasome regulatory particle TBP7/Rpt3 interact in the endoplasmic reticulum and control cellular ubiquitination of specific mitochondrial proteins

“…1,2 Through an mRNA-differential display analysis between oxidant-adapted and control osteosarcoma cells, our group identified, among other proteins, TRAP1, whose expression was highly induced upon oxidant adaptation. 3 Furthermore, TRAP1 showed antioxidant and antiapoptotic functions, 4 while an involvement of this mitochondrial (MITO) chaperone in the multi-drug resistance of human colorectal carcinoma (CRC) cells was also established.…”

Mitochondrial DNA variability modulates mRNA and intra-mitochondrial protein levels of HSP60 and HSP75: experimental evidence from cybrid lines

“…In these cells we analyzed the expression of two heat shock protein genes, HSP60 and HSP75, at both basal and heat stress conditions. HSP60 (Cpn60) and HSP75 (TRAP1) are mitochondrial chaperones that assist, in both stressed and non-stressed cells, in the folding, unfolding, or disaggregating of proteins either imported from the cytosol or synthesized within mitochondria (HSP60) (Cheng et al 1989;Frydman 2001;Itoh et al 2002;Saibil 2008) and in the reallocation of cytosolic protein into mitochondria (HSP75) (Felts et al 2000;Mokranjac and Neupert 2005). In addition to its chaperone activity, HSP60 has welldocumented anti-or pro-apoptotic roles (Arya et al 2007;Chandra et al 2007) as well as immunoregulatory properties (Habich and Burkart 2007;Pockley et al 2008).…”