MyD88 Is Central to the Process of Differentiation in Cancer Stem Cells Which May Explain Its Role in Chemoresistance of Ovarian Cancer
Charles D'Adhemar, Cathy Spillane, Michael Gallagher, Sharon O'Toole, Cara Martin, Britta Stordal, Aoife Cooke, Brendan Ffrench, Stephen Finn, Richard Flavin, Orla Sheils, John O'Leary. Trinity College Dublin, Dublin, Ireland
Background: The prognosis of ovarian cancer is poor in part due to the high frequency of chemoresistance. Toll-like receptor-4 (TLR-4), its adaptor protein MyD88 and two MyD88-targeting microRNAs (miRs-21 and -146a) have been linked to ovarian cancer and cancer stem cells (CSCs), and the TLR-4/MyD88 pathway is believed to mediate some of this resistance and aggressive behaviour. The aim of this study was two-fold; to investigate the functional role of TLR-4/MyD88 in ovarian cancer and chemoresistance and to determine the role of TLR-4/MyD88 in a cancer stem cell model.
Design: Archival tissue samples, from 129 patients with EON and 50 with normal ovaries, were evaluated for TLR-4 and MyD88 by immunohistochemistry. Expression of microRNAs miR-21 and -146a was assessed in a subset of cancers in parallel with TLR-4/MyD88 gene expression, as well as in a series of chemosensitive and resistant ovarian cancer cell lines (n=9) using RT-PCR. Knockdown of TLR-4/MyD88 was carried out in SKOV-3 ovarian cancer cells. 2102Ep [nullipotent] and NTERA-2 [pluripotent] embryonal carcinoma cells were used as a model system to examine the influence of MyD88 on differentiation capacities in embryonal CSCs. In addition, differentiation capacity assays using retinoic acid [RA] were performed using the embryonal CSC model.
Results: TLR-4 expression was ubiquitous, whereas MyD88 was restricted to neoplastic cells, independent of tumour grade, associated with reduced patient survival, chemoresistance, and inversely linked to miR-21 and miR-146a. Knockdown of TLR-4 in SKOV-3 ovarian cells recovered chemosensitivity. Knockdown of MyD88 alone did not suggesting an intact/functioning TLR-4/MyD88 pathway is required for the acquisition of the chemoresistant phenotype. RA differentiation of pluripotent NTERA-2 cells demonstrated significant down-regulation of MyD88 protein expression. Forced RA differentiation in nullipotent 2012Ep cells did not show MyD88 down-regulation. Knockdown of MyD88 renders 2102Ep open to RA differentiation. Over-expression of MyD88 renders NTERA-2 cells nullipotent suggesting that MyD88 is centrally involved in differentiation mechanisms in embryonal CSCs. Thus MyD88 is necessary and sufficient for embryonal carcinoma nullipotency.
Conclusions: These findings demonstrate that expression of MyD88 is linked to ovarian malignancy and associated with significantly reduced patient survival, chemoresistance and altered microRNA levels. In addition, MyD88 is central to differentiation in a cancer stem cell model which may explain its role in chemoresistance in ovarian cancer.
Category: Gynecologic & Obstetrics
Wednesday, March 6, 2013 9:30 AM
Poster Session V # 191, Wednesday Morning