title: Anticancer drugs up-regulate HspBP1 and thereby antagonize the prosurvival function of Hsp70 in tumor cells.
abstract: The 70-kDa heat shock protein (Hsp70) is up-regulated in a wide variety of tumor cell types and contributes to the resistance of these cells to the induction of cell death by anticancer drugs. Hsp70 binding protein 1 (HspBP1) modulates the activity of Hsp70 but its biological significance has remained unclear. We have now examined whether HspBP1 might interfere with the prosurvival function of Hsp70, which is mediated, at least in part, by inhibition of the death-associated permeabilization of lysosomal membranes. HspBP1 was found to be expressed at a higher level than Hsp70 in all normal and tumor cell types examined. Tumor cells with a high HspBP1/Hsp70 molar ratio were more susceptible to anticancer drugs than were those with a low ratio. Ectopic expression of HspBP1 enhanced this effect of anticancer drugs in a manner that was both dependent on the ability of HspBP1 to bind to Hsp70 and sensitive to the induction of Hsp70 by mild heat shock. Furthermore, anticancer drugs up-regulated HspBP1 expression, whereas prevention of such up-regulation by RNA interference reduced the susceptibility of tumor cells to anticancer drugs. Overexpression of HspBP1 promoted the permeabilization of lysosomal membranes, the release of cathepsins from lysosomes into the cytosol, and the activation of caspase-3 induced by anticancer drugs. These results suggest that HspBP1, by antagonizing the prosurvival activity of Hsp70, sensitizes tumor cells to cathepsin-mediated cell death.
authors.affiliation: Laboratory of Cell Regulation, Department of Pharmaceutical Sciences, Graduate School of Biomedical Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Tanimura
authors.forename: A-i
authors.initials: AI
authors.lastname: Hirano
authors.forename: Junya
authors.initials: J
authors.lastname: Hashizume
authors.forename: Masahiro
authors.initials: M
authors.lastname: Yasunaga
authors.forename: Takumi
authors.initials: T
authors.lastname: Kawabata
authors.forename: Kei-ichi
authors.initials: K
authors.lastname: Ozaki
authors.forename: Michiaki
authors.initials: M
authors.lastname: Kohno
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001483:Base Sequence; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D002403:Cathepsins / Q000235:genetics / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects / Q000235:genetics; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000235:genetics; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D003600:Cytosol / Q000378:metabolism / Q000473:pathology; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D018869:Heat-Shock Response / Q000187:drug effects / Q000235:genetics; D006801:Humans; D008247:Lysosomes / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D008969:Molecular Sequence Data; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D034622:RNA Interference; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000970:Antineoplastic Agents; D002352:Carrier Proteins; D018840:HSP70 Heat-Shock Proteins; C116331:HSPBP1 protein, human; D002403:Cathepsins; D053148:Caspase 3