An antisense transcript induced by Wnt/beta-catenin signaling decreases E2F4.
Wnt signaling induces the nuclear accumulation of beta-catenin and transcription of specific target genes via the DNA-binding proteins TCF/Lef. Although all known beta-catenin target genes encode proteins, genome-wide RNA profiling studies indicate that many transcripts do not have this capability. Transcription factor-binding sites associated with these noncoding transcripts can be identified using unbiased techniques such as serial analysis of chromatin occupancy (SACO). We used this method to identify a beta-catenin-regulated antisense RNA expressed in HCT116 colorectal carcinoma cells, a cellular model of activated beta-catenin signaling. Genomic signature tags designating putative beta-catenin-binding sites mapped to the 3'-untranslated region (3'-UTR) of the E2F4 gene. We showed that both beta-catenin and TCF4 bind to the E2F4 3'-UTR site in vivo, inducing expression of an E2F4 antisense transcript. LiCl, which mimics Wnt signaling, also induced expression of the E2F4 antisense transcript and decreased E2F4 protein levels. This effect was blocked by a cDNA expressing the E2F4 3'-UTR sense strand. The antisense-mediated decrease in E2F4 protein was reflected by reduced E2F4 association with specific target genes, including CCNA2, CDC2, PCNA, and Rad54. We propose that Wnt/beta-catenin signaling may contribute to colorectal carcinogenesis by reducing the level of the E2F4 cell cycle repressor via an antisense mechanism.
Yochum
Gregory S
GS
Vollum Institute, Division of Biostatistics, Department of Public Health and Preventative Medicine, OHSU Cancer Institute, Oregon Health and Science University, Portland 97239, USA. yochumg@ohsu.edu
Cleland
Ryan
R
McWeeney
Shannon
S
Goodman
Richard H
RH
D016375:Antisense Elements (Genetics); D015179:Colorectal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D018076:DNA, Complementary; D050704:E2F4 Transcription Factor / Q000235:genetics* / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D045325:HCT116 Cells; D006801:Humans; D011401:Promoter Regions, Genetic / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D051820:TCF Transcription Factors / Q000378:metabolism; D058118:Transcription Factor 7-Like 2 Protein; D051153:Wnt Proteins / Q000378:metabolism*; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
D016375:Antisense Elements (Genetics); C495270:CTNNB1 protein, human; D018076:DNA, Complementary; D050704:E2F4 Transcription Factor; C493762:E2F4 protein, human; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; D058118:Transcription Factor 7-Like 2 Protein; D051153:Wnt Proteins; D051176:beta Catenin