Repression of the Desmocollin 2 Gene Expression in Human Colon Cancer Cells Is Relieved by the Homeodomain Transcription Factors Cdx1 and Cdx2

Abstract

Desmosomes are intracellular junctions that provide strong cell-cell adhesion in epithelia and cardiac muscle. Their disruption causes several human diseases and contributes to the epithelial-to-mesenchymal transition observed in cancer. Desmocollin 2 (DSC2) is a cadherin superfamily member and a critical component of desmosomes found in intestinal epithelium. However, the mechanism regulating DSC2 gene expression in intestinal cells is not known. Cdx1 and Cdx2 are homeodomain transcription factors that regulate intestine-specific gene expression. Cdx expression in the past has been associated with the induction of desmosomes. We now show that the DSC2 gene is a transcriptional target for Cdx1 and Cdx2. Colon cancer cell lines retaining Cdx2 expression typically express DSC2. Restoration of Cdx expression in Colo 205 cells induced DSC2 mRNA and protein and the formation of desmosomes. The 5 ¶-flanking region of the DSC2 promoter contains two consensus Cdx-binding sites. Electrophoretic mobility shift assays show that Cdx1 and Cdx2 bind these sites in vitro, and chromatin immunoprecipitation confirmed Cdx2 binding in vivo. DSC2 promoter truncations established that these regions are Cdx responsive. The truncations also identify a region of the promoter in which potent transcriptional repressors act. This repressor activity is relieved by Cdx binding. We conclude that the homeodomain transcription factors Cdx1 and Cdx2 regulate DSC2 gene expression in intestinal epithelia by reversing the actions of a transcriptional repressor. The regulation of desmosomal junctions by Cdx contributes to normal intestinal epithelial columnar morphology and likely antagonizes the epithelial-to-mesenchymal transition necessary for the metastasis of colon cancer cells in humans.

Intestine-specific transcription factor Cdx2 induces E-cadherin function by enhancing the trafficking of E-cadherin to the cell membrane

“…One challenge to understanding how Cdx2 regulates E-cadherin function has been the absence of an obvious transcriptional mechanism. Several cell-cell adhesion proteins have been identified as transcriptional targets for Cdx2 (12,23,39). Despite the suggestion from one early study that E-cadherin expression was regulated by Cdx2 (28), we found no evidence for this in studies of several colon cancer cell lines (11,12,25).…”

“…The homeodomain transcription factor Cdx2 is required for intestinal differentiation and columnar morphogenesis (11)(12)(13)25). Cdx2 has been suggested to be a tumor suppressor (4,6) or to have tumor suppressor properties (16,17,19) in the colon.…”

“…In previous studies, we demonstrated that Cdx2 expression in colon cancer cells limits cell proliferation and promotes the adoption of a columnar, polarized cell morphology with apical microvilli (17,18,25,31,43,44). Cdx2 expression appears to modulate the activity of tight, adherens, and desmosomal junctions (11,12,25).…”

“…Cdx2 regulates the intestine-specific expression of a number of genes (8,12,22,23,44). Cdx2 has also been suggested to be a tumor suppressor in the colon (4,6) or to have colon tumor-inhibitory properties (16,17,19); however, the full extent of Cdx2's antitumor effects has yet to be elucidated.…”

“…More recently, we demonstrated that the desmocollin-2 gene, a component of desmosomes, is also a transcriptional target for Cdx2 (12). Adherens junction regulation by Cdx2 is less well understood.…”