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

Abstract

Sequencing of primary colorectal tumors has identified a gene fusion in approximately 3% of colorectal cancer patients of the VTI1A and TCF7L2 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 VTI1A-TCF7L2 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 VTI1A-TCF4 fusion gene was investigated in LS174T cells where the activity of the VTI1A promoter was compared to that of the TCF7L2 promoter, and the transcription factor CDX2 was analyzed for gene regulatory activity of the VTI1A promoter through luciferase reporter gene assay using colon cancer cell lines as a model. Transfection of LS174T cells showed that the VTI1A promoter is highly active compared to the TCF7L2 promoter, and that CDX2 activates transcription of VTI1A. These results suggest that the VTI1A-TCF4 fusion protein is a dominant negative regulator of the Wnt signaling pathway, and that transcription of VTI1A is activated by CDX2.

CDX2 expression and perioperative patient serum affects the adhesion properties of cultured colon cancer cells

“…To investigate the role of CDX2 in cell adhesion, the colon cancer cell line LS174T with inducible CDX2 was used. This cell line has previously been used to study the effect of CDX2 on intestinal transcriptional regulation [36][37][38]. Western blotting analysis of the LS174T wild type and LS174T with inducible CDX2 cells was performed to detect CDX2 levels.…”

Identification of recurrent fusion genes across multiple cancer types

“…There is increasing evidence suggesting that gene fusions are some of the key drivers of human cancer development. New gene fusion events have been discovered in prostate cancer 15–17 , breast cancer 23–25 , NSCLC 19,26,27 , colon cancer 28–30 , glioblastoma multiforme 19,31,32 , liver cancer 19,33–35 and ovarian cancer 19,36,37 . Some of these fusion genes appear to play driver roles in the aggressive behaviors of these cancers 19,23,26,31 .…”

Vesicle transport through interaction with t-SNAREs 1a (Vti1a)'s roles in neurons

“…TCF7L2/TC4 is known to co-operate with β-catenin in colorectal carcinogenesis ( Morin et al., 1997 ), but the fusion product lacks the TCF4 β-catenin-binding domain. A more recent analysis has indicated that the Vti1a-TCF4 fusion protein acts as a dominant-negative regulator of Wnt-β-catenin signaling ( Davidsen et al., 2018 ) but the oncogenic role of the fusion protein remains unclear. The genomic region around VTI1A appears rather prone to the production of fusion products.…”

“…Importantly, Vti1a appears to have specific roles in neuronal processes ( Ramirez and Kavalali, 2012 ; Emperador-Melero et al., 2019 ), including neuronal development ( Kunwar et al., 2011 ), non-canonical neurotransmission processes ( Ramirez et al., 2012 ; Emperador-Melero et al., 2018 ), dense core granule secretion ( Walter et al., 2014 ; Emperador-Melero et al., 2018 ), unconventional transport in neuron ( Flowerdew and Burgoyne, 2009 ), and perhaps also brain malignancy ( Kinnersley et al., 2015 ; Wang et al., 2017a , Wang et al., 2017b ; Davidsen et al., 2018 ). In the paragraphs below, Vti1a's involvement in neuronal development, physiology and pathological processes (summarized in Figure 1 ) shall be highlighted and discussed.…”