title: Inhibition of proteasome function induced apoptosis in gastric cancer.
abstract: The ubiquitin-proteasome pathway plays a critical role in the degradation of cellular proteins and cell cycle control. Dysregulating the degradation of such proteins should have profound effects on tumor growth and causes cells to undergo apoptosis. The aims of this study are to evaluate the ubiquitin-proteasome pathway in gastric cancer and the potential role of pharmacological inhibition of proteasome on induction of apoptosis in gastric cancer cells. Gastric cancer cell lines AGS (p53 wild-type) and MKN-28 (p53 mutant) were treated with proteasome inhibitor MG132. The results showed that MG132 inhibited cell proliferation in AGS and MKN-28 cells in a time- and dose-dependent manner. The inhibition of cell proliferation was caused by apoptosis which was also time- and dose-dependent. AGS cells were more responsive to MG132 than MKN-28 cells. Induction of apoptosis was preceded by the activation of caspase-3, as measured by a colorimetric caspase-3 cellular activity and Western blotting of the cleavage of caspase-3 and its substrate PARP. Activation of caspase-7 was also exhibited. In addition, z-VAD-fmk, a broad spectrum caspase inhibitor, reversed apoptosis induced by MG132 in AGS and MKN28 cells. Although z-DEVD-fmk, a specific caspase-3 inhibitor, suppressed MG132-induced apoptosis in MKN28 cells, it only partially rescued the apoptotic effect in AGS cells. Caspase-3 activation was the result of release of cytochrome c from mitochondria into the cytosol, as a consequence of upregulation of bax. There were overexpressions of all the proteasome-related proteins p53, p21(waf1) and p27(kip1) at 4 hr after proteasome inhibition which was identified by the accumulation of ubiquitin-tagged proteins. This was accompanied by accumulation of cells at G(1) phase. Our present study suggests that inhibition of proteasome function in gastric cancer cells induces apoptosis and proteasomal inhibitors have potential use as novel anticancer drugs in gastric cancer.
authors.affiliation: Department of Medicine, University of Hong Kong, Hong Kong.
authors.forename: X M
authors.initials: XM
authors.lastname: Fan
authors.forename: B C
authors.initials: BC
authors.lastname: Wong
authors.forename: W P
authors.initials: WP
authors.lastname: Wang
authors.forename: X M
authors.initials: XM
authors.lastname: Zhou
authors.forename: C H
authors.initials: CH
authors.lastname: Cho
authors.forename: S T
authors.initials: ST
authors.lastname: Yuen
authors.forename: S Y
authors.initials: SY
authors.lastname: Leung
authors.forename: M C
authors.initials: MC
authors.lastname: Lin
authors.forename: H F
authors.initials: HF
authors.lastname: Kung
authors.forename: S K
authors.initials: SK
authors.lastname: Lam
mesh_terms: D000230:Adenocarcinoma / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology*; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics; D002455:Cell Division / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016213:Cyclins / Q000096:biosynthesis / Q000235:genetics; D003546:Cysteine Endopeptidases / Q000502:physiology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology*; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors* / Q000502:physiology; D046988:Proteasome Endopeptidase Complex; D013274:Stomach Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology*; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis / Q000235:genetics; D025521:Tumor Suppressor Proteins; D014452:Ubiquitins / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects
chemical_list: C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D009097:Multienzyme Complexes; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D014452:Ubiquitins; D050760:Cyclin-Dependent Kinase Inhibitor p27; C505407:CASP3 protein, human; C505520:CASP7 protein, human; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde