The VTI1A-TCF4 colon cancer fusion protein is a dominant negative regulator of Wnt signaling and is transcriptionally regulated by intestinal homeodomain factor CDX2

<div><p>Sequencing of primary colorectal tumors has identified a gene fusion in approximately 3% of colorectal cancer patients of the <i>VTI1A</i> and <i>TCF7L2</i> genes, encoding a VTI1A-TCF4 fusion protein containing a truncated TCF4. As dysregulation of the Wnt signaling pathway is associated with colorectal cancer development and progression, the functional properties and transcriptional regulation of the VTI1A-TCF4 fusion protein may also play a role in these processes. Functional characteristics of the VTI1A-TCF4 fusion protein in Wnt signaling were analyzed in NCI-H508 and LS174T colon cancer cell lines. The NCI-H508 cell line, containing the <i>VTI1A</i>-<i>TCF7L2</i> fusion gene, showed no active Wnt signaling, and overexpression of the VTI1A-TCF4 fusion protein in LS174T cells along with a Wnt signaling luciferase reporter plasmid showed inhibition of activity. The transcriptional regulation of the <i>VTI1A-TCF4</i> fusion gene was investigated in LS174T cells where the activity of the <i>VTI1A</i> promoter was compared to that of the <i>TCF7L2</i> promoter, and the transcription factor CDX2 was analyzed for gene regulatory activity of the <i>VTI1A</i> promoter through luciferase reporter gene assay using colon cancer cell lines as a model. Transfection of LS174T cells showed that the <i>VTI1A</i> promoter is highly active compared to the <i>TCF7L2</i> promoter, and that CDX2 activates transcription of <i>VTI1A</i>. These results suggest that the VTI1A-TCF4 fusion protein is a dominant negative regulator of the Wnt signaling pathway, and that transcription of <i>VTI1A</i> is activated by CDX2.</p></div