PLoS ONE (Jan 2014)

The MyD88+ phenotype is an adverse prognostic factor in epithelial ovarian cancer.

  • Charles J d'Adhemar,
  • Cathy D Spillane,
  • Michael F Gallagher,
  • Mark Bates,
  • Katie M Costello,
  • Jacqui Barry-O'Crowley,
  • Kathryn Haley,
  • Niamh Kernan,
  • Ciara Murphy,
  • Paul C Smyth,
  • Ken O'Byrne,
  • Stephen Pennington,
  • Aoife A Cooke,
  • Brendan Ffrench,
  • Cara M Martin,
  • Dearbhaile O'Donnell,
  • Bryan Hennessy,
  • Britta Stordal,
  • Stephen Finn,
  • Amanda McCann,
  • Noreen Gleeson,
  • Tom D'Arcy,
  • Brian Flood,
  • Luke A J O'Neill,
  • Orla Sheils,
  • Sharon O'Toole,
  • John J O'Leary

DOI
https://doi.org/10.1371/journal.pone.0100816
Journal volume & issue
Vol. 9, no. 6
p. e100816

Abstract

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The prognosis of epithelial ovarian cancer is poor in part due to the high frequency of chemoresistance. Recent evidence points to the Toll-like receptor-4 (TLR4), and particularly its adaptor protein MyD88, as one potential mediator of this resistance. This study aims to provide further evidence that MyD88 positive cancer cells are clinically significant, stem-like and reproducibly detectable for the purposes of prognostic stratification. Expression of TLR4 and MyD88 was assessed immunohistochemically in 198 paraffin-embedded ovarian tissues and in an embryonal carcinoma model of cancer stemness. In parallel, expression of TLR4 and MyD88 mRNA and regulatory microRNAs (miR-21 and miR-146a) was assessed, as well as in a series of chemosensitive and resistant cancer cells lines. Functional analysis of the pathway was assessed in chemoresistant SKOV-3 ovarian cancer cells. TLR4 and MyD88 expression can be reproducibly assessed via immunohistochemistry using a semi-quantitative scoring system. TLR4 expression was present in all ovarian epithelium (normal and neoplastic), whereas MyD88 was restricted to neoplastic cells, independent of tumour grade and associated with reduced progression-free and overall survival, in an immunohistological specific subset of serous carcinomas, p<0.05. MiR-21 and miR-146a expression was significantly increased in MyD88 negative cancers (p<0.05), indicating their participation in regulation. Significant alterations in MyD88 mRNA expression were observed between chemosensitive and chemoresistant cells and tissue. Knockdown of TLR4 in SKOV-3 ovarian cells recovered chemosensitivity. Knockdown of MyD88 alone did not. MyD88 expression was down-regulated in differentiated embryonal carcinoma (NTera2) cells, supporting the MyD88+ cancer stem cell hypothesis. Our findings demonstrate that expression of MyD88 is associated with significantly reduced patient survival and altered microRNA levels and suggest an intact/functioning TLR4/MyD88 pathway is required for acquisition of the chemoresistant phenotype. Ex vivo manipulation of ovarian cancer stem cell (CSC) differentiation can decrease MyD88 expression, providing a potentially valuable CSC model for ovarian cancer.