Ectopic activation of lymphoid high mobility group-box transcription factor TCF-1 and overexpression in colorectal cancer cells.
Physical interaction between the lymphoid high mobility group (HMG)-box architectural transcription factors TCF/LEF and beta-catenin is associated with translocation of the heteromeric complex to the nucleus and regulation of target gene expression. Since formation of molecular complexes among beta-catenin, E-cadherin, p300apc and TCF/LEF depends on balanced expression of these constituents, we investigated the biosynthesis of TCF-1 in colorectal cancer. Here we report detailed analyses of activation and overexpression of lymphoid transcription factor TCF-1 in human colorectal cancer-derived cell lines. Northern blot analyses revealed considerable steady-state expression levels of TCF-1 mRNA of normal size. Genomic rearrangement of the 5' flanking region of the TCF-1 gene was excluded as a cause of ectopic expression. By contrast, CAT-reporter constructs depending on a 515-bp T-cell-regulated TCF-1 genomic upstream region were significantly activated in epithelial tumor cells. RT-PCR analyses revealed a heterogeneic population of mRNA isoforms due to alternative splicing in the TCF-1 gene. On Western blots of colorectal cancer cells, the TCF-1-specific monoclonal antibody 7H3 detected a similar heterogeneous spectrum of TCF-1 specific polypeptide chains. Interestingly, overexpression of TCF-1-specific splice forms correlated with the metastatic behavior of the analyzed cells and with overproduction of lymphoid tyrosine protein kinase p56(lck). We conclude that ectopic expression of the HMG-box factor TCF-1 is associated with late events in tumor progression.
Mayer
K
K
Institute of Human Genetics, University Erlangen-Nuremberg, Erlangen, Germany.
Hieronymus
T
T
Castrop
J
J
Clevers
H
H
Ballhausen
W G
WG
D017398:Alternative Splicing; D015152:Blotting, Northern; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D018450:Disease Progression; D006367:HeLa Cells; D006801:Humans; D051821:Lymphoid Enhancer-Binding Factor 1; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D051822:T Cell Transcription Factor 1; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; D051821:Lymphoid Enhancer-Binding Factor 1; D012334:RNA, Neoplasm; D051822:T Cell Transcription Factor 1; C497576:TCF7 protein, human; D014157:Transcription Factors