Coexistence of high levels of apoptotic signaling and inhibitor of apoptosis proteins in human tumor cells: implication for cancer specific therapy.
It is well known that dysfunction of the apoptotic pathway confers apoptosis resistance and results in a low sensitivity of human cancer cells to therapeutic agents. A novel strategy to overcome the resistance is to target the apoptotic pathway directly. To identify molecular targets in the apoptotic pathway that are differentially regulated in cancer and normal cells, we have examined the levels of apoptotic effectors and inhibitors in human tumor and normal cell lines as well as in cancer and normal tissues. These include three pancreatic cancer lines (BXPC-3, MIA PaCa-2, and Panc-1), four breast cancer cell lines (MDA-MB-231, MDA-MB-435, MDA-MB-361, and MCF-7), and colon carcinoma line (SW620). Additionally, breast carcinoma tissue specimens were examined. Compared with normal human fibroblast and mammary epithelial cell lines, we detected high basal levels of caspase-3 and caspase-8 activities and active caspase-3 fragments in the tumor cell lines and cancer tissues in the absence of apoptotic stimuli. Furthermore, the tumor cells expressed high levels of survivin and XIAP, two members of the inhibitor of apoptosis (IAP) protein family. When the activity of these IAPs was blocked by expression of dominant-negative mutant survivin (survivinT34A) and XIAP-associated factor 1, respectively, apoptosis was induced in tumor but not normal cell lines. Moreover, down-regulation of both survivin and XIAP significantly enhanced tumor-cell apoptosis as compared with inhibition of either survivin or XIAP alone. These results suggest that up-regulated IAP expression counteracts the high basal caspase-3 activity observed in these tumor cells and that apoptosis in tumor cells but not normal cells can be induced by blocking IAP activity. Therefore, IAPs are important molecular targets for the development of cancer-specific therapeutic approaches.
Yang
Lily
L
Department of Surgery and Winship Cancer Institute, Emory University School of Medicine, Atlanta, Georgia 30322, USA. Lyang02@emory.edu
Cao
Zehong
Z
Yan
Hui
H
Wood
William C
WC
D048868:Adaptor Proteins, Signal Transducing; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D061945:Caspase Inhibitors; D020169:Caspases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D015536:Down-Regulation; D015972:Gene Expression Regulation, Neoplastic; D015316:Genetic Therapy; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D014176:Protein Biosynthesis; D011506:Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D000077022:Survivin; D051636:X-Linked Inhibitor of Apoptosis Protein
D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C107489:BIRC5 protein, human; D061945:Caspase Inhibitors; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D011506:Proteins; D000077022:Survivin; D051636:X-Linked Inhibitor of Apoptosis Protein; C417551:XAF1 protein, human; C496866:XIAP protein, human; D020169:Caspases