Heinen CD, Goss KH, Cornelius JR, Babcock GF, Knudsen ES, Kowalik T, Groden J. The APC tumor suppressor controls entry into S-phase through its ability to regulate the cyclin D/RB pathway.
Gastroenterology 2002;
123:751-63. [PMID:
12198702 DOI:
10.1053/gast.2002.35382]
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Abstract
BACKGROUND & AIMS
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.
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