title: 15-Lipoxygenase-1 transcriptional silencing by DNA methyltransferase-1 independently of DNA methylation.
abstract: Methylation of promoter DNA contributes to transcriptional silencing of various tumor-suppressor genes in cancer. Transcriptional silencing of 15-lipoxygenase-1 (15-LOX-1) promotes tumorigenesis. Methylation of 15-LOX-1 promoter DNA occurs in some cancers, but its mechanistic role in 15-LOX-1 transcriptional silencing is unclear. We examined the mechanistic role of 15-LOX-1 promoter DNA methylation in 15-LOX-1 transcriptional regulation in human colorectal cancers. 15-LOX-1 promoter methylation occurred in colorectal cancer cells in vitro, in 36% of tumor tissue samples of colorectal cancer patients, and in virtually no normal colonic mucosa samples of 50 human subjects with no history of colorectal cancer or polyps. 15-LOX-1 promoter DNA methylation levels, however, did not correlate with 15-LOX-1 expression levels (Spearman's r=0.21; P=0.38). We employed siRNA knockdown and genetic disruption models of DNA methyltransferases (DNMTs) to study the effects of this methylation on 15-LOX-1 expression in colon cancer cells. 15-LOX-1 promoter demethylation was insufficient to reestablish 15-LOX-1 expression. 15-LOX-1 transcription was activated by the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) only after DNMT-1 dissociation from the 15-LOX-1 promoter and without altering 15-LOX-1 promoter DNA methylation. DNMT-1 protein hypomorphism impaired DNMT-1 recruitment to the 15-LOX-1 promoter, which allowed 15-LOX-1 transcription activation by SAHA. DNMT-1 has a direct suppressive role in 15-LOX-1 transcriptional silencing that is independent of 15-LOX-1 promoter DNA methylation.
authors.affiliation: Department of Clinical Cancer Prevention, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030-4009, USA.
authors.forename: Xiangsheng
authors.initials: X
authors.lastname: Zuo
authors.forename: Lanlan
authors.initials: L
authors.lastname: Shen
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Issa
authors.forename: Ofir
authors.initials: O
authors.lastname: Moy
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Morris
authors.forename: Scott M
authors.initials: SM
authors.lastname: Lippman
authors.forename: Imad
authors.initials: I
authors.lastname: Shureiqi
mesh_terms: D001093:Arachidonate 15-Lipoxygenase / Q000235:genetics*; D016022:Case-Control Studies; D015179:Colorectal Neoplasms / Q000201:enzymology / Q000235:genetics*; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000502:physiology*; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000502:physiology; D020868:Gene Silencing; D006801:Humans; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic
chemical_list: D001093:Arachidonate 15-Lipoxygenase; D015254:DNA Modification Methylases; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases