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)-bo x architectural transcription factors TCF/LEF and beta-catenin is asso ciated with translocation of the heteromeric complex to the nucleus an d regulation of target gene expression. Since formation of molecular c omplexes among beta-catenin, E-cadherin, p300(apc) and TCF/LEF depends on balanced expression of these constituents, we investigated the bio synthesis of TCF-1 in colorectal cancer. Here we report detailed analy ses of activation and overexpression of lymphoid transcription factor TCF-1 in human colorectal cancer-derived cell lines. Northern blot ana lyses revealed considerable steady-state expression levers of TCF-1 mR NA of normal size. Genomic rearrangement of the 5' flanking region of the TCF-1 gene was excluded as a cause of ectopic expression. By contr ast, CAT-reporter constructs depending on a 515-bp T-cell-regulated TC F-1 genomic upstream region were significantly activated in epithelial tumor cells. RT-PCR analyses revealed a heterogeneic population of mR NA isoforms due to alternative splicing in the TCF-1 gene. On Western blots of colorectal cancer cells, the TCF-1-specific monoclonal antibo dy 7H3 detected a similar heterogeneous spectrum of TCF-1 specific pol ypeptide chains. Interestingly, overexpression of TCF-1-specific splic e 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 ass ociated with late events in tumor progression. (C) 1997 Wiley-Liss, In c.