Abstract
IntroductionToll-like receptors (TLRs) are a family of pattern recognition receptors that are expressed on cells of the innate immune system. The ligands can be pathogen derived (pathogen associated molecular patterns; PAMPs) or endogenous (damage associated molecular patters; DAMPs) that when bound induces activation of nuclear factor kappa B (NF-κB) and transcription of pro-inflammatory genes. TLRs have also been discovered in various malignant cell types, but with unknown function.MethodsIn this study we performed a detailed analysis of TLR and co-receptor expression pattern and function in breast cancer. Expression patterns were examined using real-time quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry (IHC) on three estrogen receptor-positive (ER+) and four estrogen receptor/progesterone receptor-negative (ER−/PR−; ER/PR-negative) breast cancer cell lines, and a breast cancer cohort consisting of 144 primary breast cancer samples. The function was investigated using in vitro assays comprising PAMP/DAMP-stimulation, downstream signaling and TLR-silencing experiments.ResultsWe found that TLR4 was expressed in a biologically active form and responded to both PAMPs and DAMPs primarily in ER/PR-negative breast cancers. Stimulation of TLR2/4 in vitro induced expression of pro-inflammatory genes and a gene expression analysis of primary breast cancers showed a strong correlation between TLR4 expression and expression of pro-inflammatory mediators. In line with this, TLR4 protein expression correlated with a decreased survival.ConclusionsThese findings suggest that TLR4 is expressed in a functional form in ER/PR-negative breast cancers. Studies regarding TLR4-antagonist therapies should be focusing on ER/PR-negative breast cancer particularly.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-015-0640-x) contains supplementary material, which is available to authorized users.
Highlights
Toll-like receptors (TLRs) are a family of pattern recognition receptors that are expressed on cells of the innate immune system
Using three cell lines of estrogen receptor (ER)+ phenotype and four cell lines of the TN phenotype, we further showed that the expressed TLR4 was biologically active and responding to both pathogen associated molecular pattern (PAMP) and damage-associated molecular pattern (DAMP), primarily in the TN breast cancer cell lines
Cell culture The human breast cancer cell lines MCF-7, T47D, MDAMB-231 and MDA-MB-468 were purchased from ATCC and were cultured in RPMI 1640 medium supplemented with 10 % fetal bovine serum (FBS) (Biosera, Boussens, France), 1 % sodium pyruvate, 1 % HEPES and penicillin/ streptomycin (100 U/ml and 100 μg/ml respectively); CAMA-1 was cultured in MEM/EBSS supplemented with 10 % FBS and penicillin/ streptomycin, and SUM-149 and SUM-159 were cultured in F-12 HAM’S medium supplemented with 5 % FBS, 1 mM L-Glutamine, 1 μg/ml hydrocortisone (BD BioScience, San Diego, CA, USA) and 5 μg/ml insulin (Novo Nordisk A/S, Måløv, Denmark)
Summary
Toll-like receptors (TLRs) are a family of pattern recognition receptors that are expressed on cells of the innate immune system. The ligands can be pathogen derived (pathogen associated molecular patterns; PAMPs) or endogenous (damage associated molecular patters; DAMPs) that when bound induces activation of nuclear factor kappa B (NF-κB) and transcription of pro-inflammatory genes. One of the worst prognosis subtypes is the triple-negative (TN) breast cancer subtype, where the malignant cells lack expression of the hormone receptors, estrogen receptor (ER) and progesterone receptor (PR), and human epidermal growth factor receptor 2 (Her2) (ER−PR−Her2−). Toll-like receptors (TLRs) are a family of receptors that are expressed on innate immune cells [5] They are part of the pattern recognition receptor (PRR) family and recognize molecular patterns from pathogens (pathogen-associated molecular patterns; PAMPs) or from endogenous stress-induced proteins (damage-associated molecular patterns; DAMPs) [6,7,8,9]. There are 10 different TLRs (TLR1-10) in humans, and these are divided into two subgroups depending on cellular localization; on the surface of the cell (TLR1, TLR2, TLR4, TLR5 and TLR6), or in vesicles such as endoplasmic reticulum, endosomes or lysosomes (TLR3, TLR7, Mehmeti et al Breast Cancer Research (2015) 17:130
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