Defective claudin-7 regulation by Tcf-4 and Sox-9 disrupts the polarity and increases the tumorigenicity of colorectal cancer cells.
Tight junctions have recently emerged as essential signaling regulators of proliferation and differentiation in epithelial tissues. Here, we aimed to identify the factors regulating claudin-7 expression in the colon, and analyzed the consequences of claudin-7 overexpression in colorectal carcinoma (CRC). In healthy human colonic crypts, claudin-7 expression was found to be low in the stem/progenitor cell compartment, where Tcf-4 activity is high, but strong in differentiated and postmitotic cells, where Tcf-4 is inactive. In contrast, claudin-7 was overexpressed in areas with high Tcf-4 target gene levels in CRC samples. In vitro, Tcf-4 was able to repress claudin-7 expression, and the high mobility group-box transcription factor Sox-9 was identified as an essential mediator of this effect. Claudin-7 was strongly expressed in the intestine of Sox-9-deficient mice and in CRC cells with low Sox transcriptional activity. Sox-9 overexpression in these cells reinstated claudin-7 repression, and residual claudin-7 was no longer localized along the basolateral membrane, but was instead restricted to tight junctions. Using HT-29Cl.16E CRC cell spheroids, we found that Sox-9-induced polarization was completely reversed after virus-mediated claudin-7 overexpression. Claudin-7 overexpression in this context increased Tcf-4 target gene expression, proliferation, and tumorigenicity after injection in nude mice. Our results indicate that Tcf-4 maintains low levels of claudin-7 at the bottom of colonic crypts, acting via Sox-9. This negative regulation seems to be defective in CRC, possibly due to decreased Sox-9 activity, and the resulting claudin-7 overexpression promotes a loss of tumor cell polarization and contributes to tumorigenesis.
Darido
Charbel
C
Centre National de la Recherche Scientifique, UMR 5203, Institut de Génomique Fonctionnelle, INSERM U661, Université Montpellier 1, 2, Montpellier, France.
Buchert
Michael
M
Pannequin
Julie
J
Bastide
Pauline
P
Zalzali
Hassan
H
Mantamadiotis
Theo
T
Bourgaux
Jean-François
JF
Garambois
Véronique
V
Jay
Philippe
P
Blache
Philippe
P
Joubert
Dominique
D
Hollande
Frédéric
F
D015153:Blotting, Western; D045744:Cell Line, Tumor; D016764:Cell Polarity / Q000502:physiology*; D057167:Claudins; D015179:Colorectal Neoplasms / Q000235:genetics / Q000473:pathology*; D006609:High Mobility Group Proteins / Q000502:physiology*; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics*; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055758:SOX9 Transcription Factor; D051820:TCF Transcription Factors / Q000502:physiology*; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors / Q000502:physiology*
C473255:CLDN7 protein, human; D057167:Claudins; D006609:High Mobility Group Proteins; D008565:Membrane Proteins; D034741:RNA, Small Interfering; D055758:SOX9 Transcription Factor; C527932:SOX9 protein, human; C527933:Sox9 protein, mouse; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; C544895:Tcf7l2 protein, mouse; D058118:Transcription Factor 7-Like 2 Protein; D014157:Transcription Factors