TCF4 and CDX2, major transcription factors for intestinal function, converge on the same cis-regulatory regions

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• Wnt ligands are crucial signaling molecules in many mammalian tissues, including the intestinal epithelium.
• Constitutive Wnt signaling in the intestine is linked to cancer development.
• Mechanisms for achieving tissue-specific responses from ubiquitous signaling pathways remain incompletely understood.

Purpose of the Study:

• To investigate the role of the intestine-restricted transcription factor CDX2 in regulating Wnt signaling.
• To identify cis-regulatory regions bound by CDX2 and TCF4 in colonic cells.
• To understand how ubiquitous signaling pathways achieve tissue-specific outcomes.

Main Methods:

• Genome-wide analysis of DNA cis-regulatory regions bound by CDX2 in colonic cells.
• Identification of overrepresented sequences binding TCF4, a Wnt signaling effector.
• Chromatin immunoprecipitation to confirm TCF4 and CDX2 co-occupancy at regulatory sites.
• Analysis of the association between co-occupancy, intestine-specific gene expression, and colorectal cancer risk variants (e.g., rs6983267).

Main Results:

• CDX2-bound regions showed significant overrepresentation of TCF4 binding sequences.
• CDX2 and TCF4 were frequently co-occupied at regulatory sites, often in close proximity.
• A colorectal cancer risk-associated region (rs6983267 within a MYC enhancer) was among the co-occupied sites.
• CDX2 loss reduced TCF4 binding, indicating CDX2's role in directing TCF4 to specific sites.
• Co-occupancy correlated with intestine-specific gene expression.

Conclusions:

• CDX2 plays a critical role in directing TCF4 binding within intestinal cells, thereby mediating Wnt signaling specificity.
• Co-occupancy of regulatory regions by tissue-restricted and signal-effector transcription factors represents a general mechanism for achieving tissue-specific gene expression from ubiquitous pathways.
• This mechanism has implications for understanding both normal intestinal function and colorectal cancer pathogenesis.