6925

TCF4

E2-2|ITF-2|ITF2|PTHS|SEF-2|SEF2|SEF2-1|SEF2-1A|SEF2-1B|SEF2-1D|TCF-4|bHLHb19;transcription factor 4;TCF4;transcription factor 4

SL3-3 enhancer factor 2|class B basic helix-loop-helix protein 19|immunoglobulin transcription factor 2

18q21.1

protein-coding

BACKGROUND & AIMS: The ubiquitously expressed basic helix-loop-helix transcription factor ITF-2B has an important role in differentiation processes, and its transcription is regulated by beta-catenin. The ITF-2 gene is located in the chromosomal region 18q21; allelic loss of this locus occurs in 70% of colorectal cancers. We analyzed the expression, regulation, and function of ITF-2B in colorectal carcinogenesis. METHODS: The loss-of-heterozygosity (LOH) status of 18q21 and expression of ITF-2B were studied in colorectal carcinomas using polymerase chain reaction-based methods and immunohistochemistry. The biologic effects of ITF-2B were studied in colorectal cancer cells. Reporter gene assays and chromatin immunoprecipitation were utilized to analyze effects of ITF-2B on gene transcription. RESULTS: ITF-2B is strongly expressed in colon adenomas but frequently down-regulated in carcinomas because of LOH at 18q21. ITF-2B induces cell cycle arrest and regulates the expression of p21(Cip1) via newly identified E-boxes in the CDKN1A gene, independently of p53. Loss of ITF-2B expression correlates with loss of p21(Cip1) expression in primary colon carcinomas. CONCLUSIONS: Accumulation of mutations and allelic losses are driving forces of colorectal carcinogenesis. ITF-2B, which is up-regulated during early colorectal carcinogenesis because of loss of adenomatous polyposis coli, is a target for LOH on chromosome 18q, along with deleted in colorectal carcinoma and Smad4. This finding, along with the fact that ITF-2B is a regulator of the key cell cycle inhibitor p21(Cip1), indicates that ITF-2B is a tumor suppressor that has an important function at the adenoma to carcinoma transition.

Loss of heterozygosity (LOH) is a hallmark of cancer and the chromosomal regions 5q, 8p, 17p, and 18q are frequently affected by LOH in colorectal cancer. The ITF2 gene is located on chromosome 18q and we have recently demonstrated that expression of the basic helix-loop-helix (bHLH) transcription factor ITF-2B is affected by LOH. Apart from ITF-2B, the ITF2 gene also encodes the isoform ITF-2A that lacks amino-terminal sequences found in ITF-2B. Analysis of ITF-2A expression in micro-dissected colorectal tumor tissue revealed that ITF-2A expression is frequently lost in colorectal cancers, suggesting that loss of ITF-2A provides cancer cells with a growth advantage. Further studies demonstrated that re-expression of ITF-2A in colon cancer cell lines interferes with cell cycle progression. This data support the notion that the ITF2 gene on chromosome 18q is a tumor suppressor gene.