The APC tumor suppressor promotes transcription-independent apoptosis in vitro.
The APC tumor suppressor is found in nonproliferating epithelial cells of the colonic crypts and is mutated in most colorectal tumors. To understand the function of APC in normal epithelium and how its loss leads to tumor formation, we tested whether APC is a mediator of apoptosis using an in vitro assay that monitors caspase-3-mediated cleavage of lamin B protein or a colorimetric substrate in a cell-free Xenopus egg extract. Recombinant APC protein accelerates apoptosis-associated caspase activity independently of ongoing transcription and protein synthesis. Conversely, the addition of mutant APC and immunodepletion of Xenopus APC decelerates apoptosis-associated caspase activity. Acceleration of apoptosis by APC is abolished by the caspase-8 inhibitor Z-IETD-FMK, demonstrating that caspase-8 is an essential component of APC-mediated apoptosis. These results suggest that the induction of apoptosis may be one role of APC in tumor suppression and that this mechanism is independent of beta-catenin-mediated effects on transcription.
Steigerwald
Kira
K
Department of Genetics, Biochemistry and Microbiology, University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
Behbehani
Gregory K
GK
Combs
Kelly A
KA
Barton
Michelle Craig
MC
Groden
Joanna
J
D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D053148:Caspase 3; D053181:Caspase 8; D061945:Caspase Inhibitors; D020169:Caspases / Q000502:physiology; D002457:Cell Extracts / Q000737:chemistry; D045304:Cytochromes c / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000502:physiology; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D005260:Female; D006801:Humans; D034921:Lamin Type B / Q000378:metabolism; D051379:Mice; D008928:Mitochondria / Q000502:physiology; D009154:Mutation / Q000235:genetics; D009842:Oligopeptides / Q000494:pharmacology; D010063:Ovum / Q000737:chemistry; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology; D014158:Transcription, Genetic; D014981:Xenopus; D029867:Xenopus Proteins; D051176:beta Catenin
D025601:Adenomatous Polyposis Coli Protein; C495266:CTNNB1 protein, Xenopus; C495270:CTNNB1 protein, human; C495267:CTNNB1 protein, mouse; D061945:Caspase Inhibitors; D002457:Cell Extracts; D003598:Cytoskeletal Proteins; D034921:Lamin Type B; D009842:Oligopeptides; D015534:Trans-Activators; D029867:Xenopus Proteins; C403753:benzyloxycarbonyl-isoleucyl-glutamyl-threonyl-aspartic acid fluoromethyl ketone; D051176:beta Catenin; D045304:Cytochromes c; C505407:CASP3 protein, human; C505530:CASP8 protein, human; C505409:Casp3 protein, mouse; C505526:Casp8 protein, mouse; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases