Adriamycin enhances proteasome-mediated generation of the proapoptotic processed form of MAGE-A4 in hepatoma cells.
BACKGROUND
Melanoma antigen (MAGE)-A4 is processed to generate a C-terminal fragment with proapoptotic activity. Here we demonstrate that Adriamycin promotes generation of the processed MAGE-A4 by activating the proteasome. The proteasome is known to prevent accumulation of toxic proteins to maintain cellular homeostasis.


RESULTS
Treatment of hepatoma cells expressing MAGE-A4 with a sublethal dose of Adriamycin increased the MAGE-A4 processing and sensitized the cells to Adriamycin-induced apoptosis. The processing of MAGE-A4 was inhibited by the proteasome inhibitors MG115, MG132, lactacystin and epoxamicin. MAGE-A4 was coimmunoprecipitated with the S6 proteasomal ATPase, and present in the fractions containing the proteasome during glycerol gradient centrifugation. Consistent with the notion that the proteasome cleaves MAGE-A4, the 26S proteasome, ubiquitin, and cell lysates were necessary for efficient in vitrocleavage of MAGE-A4.


CONCLUSIONS
The present study suggests that a low dose of Adriamycin increases the proteasome activity, which either maintains cellular homeostasis or leads to apoptosis depending, at least under the present conditions, on the expression of MAGE-A4.
Department of Gastroenterology, Faculty of Medicine, Kinki University, Osakasayama, Japan. sakurai@med.kindai.ac.jp
Toshiharu
T
Sakurai
Masatoshi
M
Kudo
Katsuhiko
K
Itoh
U
U
Ryu
Hiroaki
H
Higashitsuji
Jun
J
Fujita
D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D019556:COS Cells; D006528:Carcinoma, Hepatocellular / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D004317:Doxorubicin / Q000494:pharmacology*; D057809:HEK293 Cells; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D008113:Liver Neoplasms / Q000378:metabolism; D009363:Neoplasm Proteins / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism
D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D007976:Leupeptins; C095204:MAGEA4 protein, human; D009363:Neoplasm Proteins; D025801:Ubiquitin; C089486:carbobenzoxy-leucyl-leucyl-norvalinal; C067713:lactacystin; D004317:Doxorubicin; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D000111:Acetylcysteine