M T Furlong1, P J Morin. 1. Laboratory of Biological Chemistry, Gerontology Research Center, National Institute on Aging, Baltimore, Maryland 21224, USA.
Abstract
OBJECTIVE: The activation of the T cell factor/beta-catenin pathway is a crucial event in colon cancer initiation. A recent report describing the presence of beta-catenin mutations in endometrioid ovarian cancer suggested that the TCF/beta-catenin pathway may be generally activated in ovarian cancer. We therefore undertook to determine the frequency of activation of this pathway in ovarian cancer cell lines using a functional screen. METHODS: We functionally screened a series of ovarian cancer cell lines for the presence of constitutive TCF/beta-catenin-mediated transcriptional activity using a reporter assay. Lines possessing such activity were subjected to mutational and gel-shift analysis, as well as sensitivity to the introduction of dominant-negative TCF or APC alleles. A cDNA harboring a beta-catenin point mutation found in an ovarian cancer line was incorporated into an expression plasmid for functional analysis. RESULTS: Constitutive TCF/beta-catenin transcriptional activity was detected in 21% (4 of 19) of ovarian lines studied, while 32% (6 of 19) exhibited greater than twofold repression. One of the constitutively active lines, UCI107, harbored an activating beta-catenin point mutation, which was shown to be capable of inducing TCF/beta-catenin transcriptional activity in transiently transfected 293 cells. A second active line, SW626, was shown to harbor an inactivating APC mutation and may in fact be of colonic origin. The third and fourth lines harbored neither an APC nor a beta-catenin mutation. Gel-shift analysis, together with the absence of sensitivity to dominant-negative TCF, indicated that the reporter activity exhibited by the latter two cell lines may not be due to a TCF/beta-catenin transcriptional complex. CONCLUSIONS: These results indicate that genuine constitutive activation of the TCF/beta-catenin pathway is infrequent in ovarian cancer, but that constitutive transcriptional repression from TCF sites is more common in this tumor type.
OBJECTIVE: The activation of the T cell factor/beta-catenin pathway is a crucial event in colon cancer initiation. A recent report describing the presence of beta-catenin mutations in endometrioid ovarian cancer suggested that the TCF/beta-catenin pathway may be generally activated in ovarian cancer. We therefore undertook to determine the frequency of activation of this pathway in ovarian cancer cell lines using a functional screen. METHODS: We functionally screened a series of ovarian cancer cell lines for the presence of constitutive TCF/beta-catenin-mediated transcriptional activity using a reporter assay. Lines possessing such activity were subjected to mutational and gel-shift analysis, as well as sensitivity to the introduction of dominant-negative TCF or APC alleles. A cDNA harboring a beta-catenin point mutation found in an ovarian cancer line was incorporated into an expression plasmid for functional analysis. RESULTS: Constitutive TCF/beta-catenin transcriptional activity was detected in 21% (4 of 19) of ovarian lines studied, while 32% (6 of 19) exhibited greater than twofold repression. One of the constitutively active lines, UCI107, harbored an activating beta-catenin point mutation, which was shown to be capable of inducing TCF/beta-catenin transcriptional activity in transiently transfected 293 cells. A second active line, SW626, was shown to harbor an inactivating APC mutation and may in fact be of colonic origin. The third and fourth lines harbored neither an APC nor a beta-catenin mutation. Gel-shift analysis, together with the absence of sensitivity to dominant-negative TCF, indicated that the reporter activity exhibited by the latter two cell lines may not be due to a TCF/beta-catenin transcriptional complex. CONCLUSIONS: These results indicate that genuine constitutive activation of the TCF/beta-catenin pathway is infrequent in ovarian cancer, but that constitutive transcriptional repression from TCF sites is more common in this tumor type.
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