Prostaglandin E2 promotes intestinal tumor growth via DNA methylation

Journal name:
Nature Medicine
Volume:
18,
Pages:
224–226
Year published:
DOI:
doi:10.1038/nm.2608
Received
Accepted
Published online

Although aberrant DNA methylation is considered to be one of the key ways by which tumor-suppressor and DNA-repair genes are silenced during tumor initiation and progression, the mechanisms underlying DNA methylation alterations in cancer remain unclear. Here we show that prostaglandin E2 (PGE2) silences certain tumor-suppressor and DNA-repair genes through DNA methylation to promote tumor growth. These findings uncover a previously unrecognized role for PGE2 in the promotion of tumor progression.

At a glance

Figures

  1. PGE2 silences certain tumor-suppressor and DNA-repair genes by enhancing their promoter CGI methylation in human CRC cell lines.
    Figure 1: PGE2 silences certain tumor-suppressor and DNA-repair genes by enhancing their promoter CGI methylation in human CRC cell lines.

    (a) PGE2 increased DNMT1 and DNMT3B protein expression in LS174T, HCA7 and HT-29 cells. (b) A bisulfite PCR sequencing analysis showed that PGE2 increased CGI methylation in the promoters of CNR1 and MGMT in LS174 cells. For the CNR1 promoter, a region (−370 to −160 bp) that contains 24 CpGs was examined. Two representative CpGs are shown. For the MGMT promoter, a region (+27 to +342 bp) that contains 29 CpGs was examined. Six representative CpGs are shown. The stars indicate the locations of CpGs. (c) PGE2 downregulated the expression of CNR1 (also known as CB1) and MGMT at both the protein (top) and mRNA (bottom) levels in LS174T cells. Error bars, s.d. *P < 0.05 (two-tailed unpaired Student's t test). (d) Blockade of PTGER4 attenuated the upregulation of DNMT1 and DNMT3B by PGE2 in LS174T cells. SC, SC19220, a PTGER1 antagonist; AH, AH6809, a PTGER1-3 antagonist; ONO, ONO-AE-208, a PTGER4 antagonist. (e,f) Knockdown of DNMT1 or DNMT3B by shRNAs attenuated the PGE2-induced downregulation of CNR1 (CB1) and MGMT in LS174T cells. The knockdown efficiency was examined by quantitative PCR in two clones (C1 and C2), along with a non-silencing shRNA-transfected control (shCon) (top). Error bars, s.d. *P < 0.05 (two-tailed unpaired Student's t test). CNR1 (CB1) and MGMT protein expression was examined by western blotting in these two clones (C1 and C2) and shCon cells (bottom).

  2. PGE2 promotes intestinal tumor growth through the upregulation of CGI methylation in ApcMin/+ mice.
    Figure 2: PGE2 promotes intestinal tumor growth through the upregulation of CGI methylation in ApcMin/+ mice.

    (a) Treatment of ApcMin/+ mice with PGE2 increased Dnmt1 and Dnmt3b protein expression in colonic tumor epithelial cells. (b,c) PGE2 increased the intestinal polyp number and size in ApcMin/+ mice. Error bars, s.e.m. (n = 7 for each group). *P < 0.05 (Wilcoxon rank-sum test). SI, small intestine. (d) Treatment of three ApcMin/+ mice with PGE2 increased the promoter CGI methylation of Cnr1 and Mgmt in the colonic tumor epithelial cells as compared to three ApcMin/+ mice treated with vehicle. For the Cnr1 promoter, a region (−369 to −34 bp) that contains 35 CpGs was examined. Three representative CpGs are shown. For the Mgmt promoter, a region (−458 to −243 bp) that contains six CpGs was examined. Two representative CpGs are shown. The stars indicate the locations of CpGs. (e) Treatment of ApcMin/+ mice with PGE2 decreased the expression of Cnr1 and Mgmt at both the protein (left) and mRNA levels (middle and right) in colonic tumor epithelial cells. One representative result from three mice is shown. Error bars, s.d. *P < 0.05 (two-tailed unpaired Student's t test). (f) Inhibition of CGI methylation by 5-Aza-dC attenuates PGE2-induced tumor growth in male ApcMin/+ mice. Error bars, s.e.m. (n = 15 for each group; Wilcoxon rank-sum test). (g) Combination treatment with celecoxib and 5-Aza-dC more efficiently inhibited tumor growth than did treatment with either agent alone. Error bars, s.e.m. (n = 12, 14, 14 and 7 for control, 5-Aza-dC, celecoxib and combination treatment, respectively; Wilcoxon rank-sum test). All mice were housed and treated in accordance with protocols approved by the Institutional Animal Care and Use Committee at The University of Texas MD Anderson Cancer Center.

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Affiliations

  1. Department of Cancer Biology, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.

    • Dianren Xia,
    • Dingzhi Wang,
    • Sun-Hee Kim,
    • Hiroshi Katoh &
    • Raymond N DuBois
  2. Department of Gastrointestinal Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.

    • Raymond N DuBois

Contributions

R.N.D., D.W. and D.X. designed this research project. D.X. performed most of the experiments. S.-H.K. contributed to establish the DNMT1 and DNMT3B knockdown stable cell lines, and H.K. conducted the DNA methylation analysis for the human tissues samples. D.X. and D.W. conducted the data analyses. D.W. wrote the manuscript with help from D.X. R.N.D. supervised the project.

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The authors declare no competing financial interests.

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    Supplementary Figures 1–5, Supplementary Tables 1 and 2, Supplementary Discussion and Supplementary Methods

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