Understandinly the function of the hepatitis B virus X protein (HBx) is fundamental to elucidating the Underlying mechanisms of hepatitis and hepatocarcinogenesis caused by hepatitis B virus (HBV) infection. We identified heat shock protein 60 (Hsp60) as a novel cellular target of HBx by the combination of affinity Purification and mass spectrometry. Physical interaction between HBx and Hsp60 was confirmed by standard immunoprecipitation and immunoblot methods. Analysis of HBx deletion constructs showed that amino acids 88-117 of HBx were responsible for the binding to Hsp60. Confocal laser microscopy demionstrated that HBx and Hsp60 colocalized in mitochondria. Furthermore, terminal deoxynucleotidyl transferase-mediated dUTP end labeling (TUNEL) revealed that the introduction of Hsp60 into cells facilitated HBx-induced apoptosis. These findings Suggest the importance of the molecular chaperon protein Hsp60 to the function of HBV viral proteins. (C) 2004 Elsevier Inc. All rights reserved.