The APC tumor suppressor controls entry into S-phase through its ability to regulate the cyclin D/RB pathway.
OBJECTIVE
APC gene mutation is an early alteration in most colorectal tumors. In an attempt to determine its role in tumor development, we asked whether reintroducing wild-type APC into colorectal cancer cells with mutant APC affected cell cycle progression.


METHODS
Using transient transfection, a plasmid containing the APC complementary DNA and DNA encoding the green fluorescent protein was expressed in SW480 cells. In addition, several other constructs were co-expressed with APC to determine their combined effects.


RESULTS
We report that colorectal cancer cell lines transfected with wild-type APC arrest in the G(1)- phase of the cell cycle and that this arrest is abrogated by cotransfecting constitutively active beta-catenin or cyclin D1 and cMYC together. This APC-induced cell cycle arrest involves the disruption of beta-catenin-mediated transcription and depends on components of the G(1)/S regulatory machinery, as overexpression of E1a or E2F-1, -2, or -3 overrides the G(1) arrest. Consistent with this, APC transfection inhibits RB phosphorylation and reduces levels of cyclin D1.


CONCLUSIONS
Our results suggest that APC functions upstream of RB in the G(1)/S regulatory pathway, cyclin D1 and cMYC affect APC-mediated arrest equivalently to oncogenic beta-catenin, and most colon tumors disrupt control of G(1)/S progression by APC mutation.
Howard Hughes Medical Institute, Department of Molecular Genetics, University of Cincinnati College of Medicine, Ohio 45267-0524, USA.
Christopher D
CD
Heinen
Kathleen Heppner
KH
Goss
James R
JR
Cornelius
George F
GF
Babcock
Erik S
ES
Knudsen
Timothy
T
Kowalik
Joanna
J
Groden
D017502:Adenovirus E2 Proteins / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D019938:Cyclin D1 / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000494:pharmacology; D004338:Drug Combinations; D016193:G1 Phase / Q000502:physiology; D017491:Genes, APC / Q000502:physiology*; D016147:Genes, Tumor Suppressor / Q000502:physiology*; D006801:Humans; D009857:Oncogenes / Q000502:physiology; D010766:Phosphorylation; D016271:Proto-Oncogene Proteins c-myc / Q000494:pharmacology; D016160:Retinoblastoma Protein / Q000378:metabolism*; D016196:S Phase / Q000502:physiology*; D015534:Trans-Activators / Q000235:genetics / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D014407:Tumor Cells, Cultured; D051176:beta Catenin
D017502:Adenovirus E2 Proteins; C495270:CTNNB1 protein, human; D003598:Cytoskeletal Proteins; D004338:Drug Combinations; D016271:Proto-Oncogene Proteins c-myc; D016160:Retinoblastoma Protein; D015534:Trans-Activators; D051176:beta Catenin; D019938:Cyclin D1