Induction of apoptosis by the proteasome inhibitor MG132 in human HCC cells: Possible correlation with specific caspase-dependent cleavage of beta-catenin and inhibition of beta-catenin-mediated transactivation.
Proteasome inhibitors, like MG132, can exert cell growth inhibitory and apoptotic effects in different tumor types. The apoptotic mechanism of these compounds involves the activation of the effector caspases. beta-catenin, also an oncogene, represents one of the substrates of these proteases, but the consequences of its cleavage are poorly understood. We investigated its function during apoptosis induced by MG132 in three hepatocellular carcinoma (HCC) cell lines, endowed (HepG2 and HuH-6) or not (HA22T/VGH) with activating mutations of beta-catenin. Induction of apoptosis was associated with cell growth inhibition, accumulation of the cells at the G(2)/M phases of the cell cycle, as well as with fragmentation of beta-catenin (but not of alpha- or gamma-catenin) in all the cell lines. The cleavage of beta-catenin was inhibited by the caspase inhibitors Z-VAD-fmk and Z-DEVD-fmk. Fragmented beta-catenin was found in the nuclei of the treated cells. Analyses through the reporter plasmid pTOPflash showed that MG132 significantly reduces Tcf transcriptional activity in the cells. This was associated with a decrease in the mRNA expression of survivin and c-myc, which are target genes of the APC/beta-catenin/Tcf signaling. Nevertheless, Z-VAD-fmk or Z-DEVD-fmk did not reverse the MG132 effects on Tcf transcriptional activity, suggesting that the compound may affect this activity also by other mechanisms. Overall, the present study supports the therapeutic potential of the proteasome inhibitors in HCC.
Cervello
Melchiorre
M
Istituto di Biomedicina e Immunologia Molecolare 'Alberto Monroy', C.N.R., I-90146 Palermo, Italy. cervello@ibim.cnr.it
Giannitrapani
Lydia
L
La Rosa
Marzia
M
Notarbartolo
Monica
M
Labbozzetta
Manuela
M
Poma
Paola
P
Montalto
Giuseppe
G
D'Alessandro
Natale
N
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism* / Q000473:pathology*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D051180:Desmoplakins; D016195:G2 Phase / Q000187:drug effects; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D007976:Leupeptins / Q000494:pharmacology*; D051821:Lymphoid Enhancer-Binding Factor 1; D008869:Microtubule-Associated Proteins / Q000235:genetics; D009363:Neoplasm Proteins; D009842:Oligopeptides / Q000494:pharmacology; D010446:Peptide Fragments / Q000096:biosynthesis / Q000378:metabolism; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D000077022:Survivin; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects*; D051178:alpha Catenin; D051176:beta Catenin; D051185:gamma Catenin
D000590:Amino Acid Chloromethyl Ketones; C107489:BIRC5 protein, human; C495273:CTNNA1 protein, human; C495270:CTNNB1 protein, human; D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D051180:Desmoplakins; D051034:Inhibitor of Apoptosis Proteins; C495292:JUP protein, human; D007976:Leupeptins; D051821:Lymphoid Enhancer-Binding Factor 1; C489427:MYC protein, human; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D009842:Oligopeptides; D010446:Peptide Fragments; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D000077022:Survivin; D015534:Trans-Activators; D014157:Transcription Factors; D051178:alpha Catenin; C110772:benzoylcarbonyl-aspartyl-glutamyl-valyl-aspartyl-fluoromethyl ketone; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D051176:beta Catenin; D051185:gamma Catenin; C063261:acetylleucyl-leucyl-norleucinal; D020169:Caspases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde