Homeobox protein CDX2 reduces Cox-2 transcription by inactivating the DNA-binding capacity of nuclear factor-kappaB.
BACKGROUND
While cyclooxygenase-2 (COX-2) is not normally expressed by epithelial cells lining the human colon, COX-2 protein is aberrantly overexpressed in premalignant adenomatous polyps and carcinomas of the human colon. On the other hand, Cdx2 has been identified as a colonic tumor-suppressor gene, besides its role in cell differentiation. However, the relationship between CDX2 attenuation and COX-2 overexpression in colorectal carcinoma has not been established. Here, we investigated the mechanistic link between CDX2 downregulation and COX-2 upregulation.


METHODS
Gene expression was examined by immunoblotting, reverse transcription-polymerase chain reaction, and promoter analysis. Promoter transactivation was quantified by using a luciferase construct. DNA binding of nuclear factor-kappaB (NF-kappaB) was examined by electromobility shift analysis.


RESULTS
CDX2 decreased expression of COX-2 mRNA and protein at the transcriptional level in the human colon cancer Caco-2 cell line. Though p50/p65 NF-kappaB translocated into nucleus in the presence of CDX2, CDX2 interacted with p50/p65 NF-kappaB and impeded the formation of an NF-kappaB-DNA complex, required for promotion of Cox-2 transcription.


CONCLUSIONS
The results indicate that CDX2 inhibits transcription of Cox-2 by interfering with the binding of NF-kappaB on the NF-kappaB binding site.
Mutoh
Hiroyuki
H
Department of Medicine, Division of Gastroenterology, Jichi Medical University, 3311-1 Yakushiji, Shimotsuke, 329-0431, Japan.
Hayakawa
Hiroko
H
Sakamoto
Hirotsugu
H
Sugano
Kentaro
K
D001665:Binding Sites / Q000235:genetics; D014408:Biomarkers, Tumor / Q000096:biosynthesis / Q000235:genetics; D000071616:CDX2 Transcription Factor; D018938:Caco-2 Cells; D051546:Cyclooxygenase 2 / Q000235:genetics* / Q000378:metabolism; D004273:DNA, Neoplasm / Q000235:genetics* / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D017930:Genes, Reporter / Q000235:genetics; D006367:HeLa Cells; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D016328:NF-kappa B / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic / Q000235:genetics
D014408:Biomarkers, Tumor; D000071616:CDX2 Transcription Factor; C491270:CDX2 protein, human; D004273:DNA, Neoplasm; D018398:Homeodomain Proteins; D016328:NF-kappa B; D051546:Cyclooxygenase 2