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29 THE TRANSCRIPTIONAL REPRESSOR CDP REGULATES PLZF, A NOVEL PUTATIVE REGULATOR OF INTESTINAL EPITHELIAL CELL PROLIFERATION I Fréchette, K Brochu-Gaudreau, C Jones, F Boudreau
BACKGROUND: We recently demonstrated the role of the transcription factor CDP (CCAAT-displacement protein) in colonic repression of SI (sucrase-isomaltase) gene during development. It is well documented that SI gene becomes re-expressed during the first steps of colorectal cancer. However, the role of CDP in the colonic epithelium has not been yet established.
AIM: To gain a better comprehension of CDP intestinal function, we sought to identify additional colonic transcriptional targets of CDP.
METHODS: A microarray analysis utilizing CDP mutant mice was performed by Affymetrix. Expression profile of transcription factors was performed by Western blot. Functional interaction between CDP and gene transcription was determined by EMSA and luciferase assays.
RESULTS: PLZF (Promyelocytic Leukemia Zinc Finger) was identified as being upregulated in the colon of CDP mutant mice. Since PLZF is a transcriptional repressor implicated in the maintenance of stem cells in other systems, we undertook to verify whether CDP could modulate PLZF gene expression. First, we correlated expression of CDP and PLZF in human colorectal cancer cell lines. A Western blot analysis showed weak expression of CDP in cancer cells as compared with normal colonocytes. In contrast, PLZF was expressed in the majority of cancer cells but remained undetectable in normal colonocytes. A computer analysis of the PLZF gene predicted 21 potential interaction sites for CDP. We chose to investigate a 3 kb region upstream to the translation initiation site. EMSA experiments confirmed the presence of five CDP-interacting sites within this region. Cotransfections of 293T cells with a CDP expressing vector and a PLZF-luciferase reporter plasmid resulted in the reduction of PLZF transcriptional activity. Finally, overexpression of CDP in the human colorectal cancer Caco2 cell line resulted in reduction of PLZF expression.
CONCLUSION: Overall, these results suggest that PLZF is a direct target of CDP in the intestinal epithelium. Further studies are ongoing to unravel the biological significance of this genetic interaction in the context of intestinal epithelium maintenance.
Supported by CIHR, CRS, NSERC, FRSQ and CFI