Cathepsin B contributes to bile salt-induced apoptosis of rat hepatocytes.
OBJECTIVE
Bile salt-induced apoptosis is mediated by a trypsin-like nuclear protease. The aims of this study were to identify this protease and to elucidate its mechanistic role in bile salt-induced hepatocyte apoptosis.


METHODS
Rats, isolated rat hepatocytes, and a rat hepatoma cell line stably transfected with a bile salt transporter (McNtcp.24) were used for this study.


RESULTS
In the bile duct-ligated rat, a threefold increase in apoptosis and a fourfold increase in trypsin-like nuclear protease activity were observed. The nuclear protease activity was purified from bile duct-ligated rats and identified as cathepsin B. Specific, structurally dissimilar cathepsin B inhibitors blocked glycochenodeoxycholate (GCDC)-induced apoptosis in cultured rat hepatocytes. Furthermore, stable transfection of McNtcp.24 cells with the complementary DNA for cathepsin B in the antisense orientation reduced cathepsin B activity and GCDC-induced apoptosis by >75%. Next, cathepsin B cellular localization during apoptosis was determined by immunoblot analysis of nuclear cell fractions, immunocytochemistry, and by determining the compartmentation of expressed cathepsin B fused to green fluorescent protein. All three approaches showed translocation of cathepsin B from the cytoplasm to the nucleus during GCDC-induced apoptosis.


CONCLUSIONS
The data suggest that translocation of cathepsin B from the cytoplasm to the nucleus is a mechanism contributing to bile salt-induced apoptosis of hepatocytes.
Roberts
L R
LR
Mayo Clinic, Rochester, Minnesota 55905, USA.
Kurosawa
H
H
Bronk
S F
SF
Fesmier
P J
PJ
Agellon
L B
LB
Leung
W Y
WY
Mao
F
F
Gores
G J
GJ
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001647:Bile Acids and Salts / Q000633:toxicity*; D001692:Biological Transport; D002401:Cathepsin B / Q000502:physiology*; D002467:Cell Nucleus / Q000201:enzymology; D002478:Cells, Cultured; D008099:Liver / Q000187:drug effects* / Q000473:pathology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley
D001647:Bile Acids and Salts; D002401:Cathepsin B