Abstract
Toll-like receptor (TLR)4-mediated signaling has been implicated in tumor cell invasion, survival, and metastasis in a variety of cancers. This study investigated the expression and biological role of TLR4 in human breast cancer metastasis. MCF-7 and MDA-MB-231 are human breast cancer cell lines with low and high metastatic potential, respectively. Using lipopolysaccharide (LPS) to stimulate MCF-7 and MDA-MB-231 cells, expression of TLR4 mRNA and protein increased compared with that in control cells. TLR4 activation notably up-regulated expression of matrix metalloproteinase (MMP)-2, MMP-9 and vascular endothelial growth factor(VEGF) mRNA and their secretion in the supernatants of both cell lines. LPS enhanced invasion of MDA-MB-231 cells by transwell assay and MCF-7 cells by wound healing assay. LPS triggered increased expression of TLR4 downstream signaling pathway protein myeloid differentiation factor 88(MyD88) and resulted in interleukin (IL)-6 and IL-10 higher production by human breast cancer cells. Stimulation of TLR4 with LPS promoted tumorigenesis and formed metastatic lesions in liver of nude mice. Moreover, expression of TLR4 and MyD88 as well as invasiveness and migration of the cells could be blocked by TLR4 antagonist. Combined with clinicopathological parameters, TLR4 was overexpressed in human breast cancer tissue and correlated with lymph node metastasis. These findings indicated that TLR4 may participate in the progression and metastasis of human breast cancer and provide a new therapeutic target.
Highlights
Despite advances in treatment of breast cancer, the effective control of metastasis remains a complex problem
Both of the breast cancer cell lines expressed TLR4 mRNA detected by Reverse transcriptase polymerase chain reaction (RT-PCR) (Fig. 1A) and protein was detected by western blotting (Fig. 1D), and after LPS stimulation, the increased expression of TLR4 was clearly observed
matrix metalloproteinase (MMP)-2, MMP-9 and VEGF expression was obviously increased in both MCF-7 and MDA-MB-231 cells treated with LPS at the mRNA level, as detected by RT-PCR (Fig. 2A)
Summary
Despite advances in treatment of breast cancer, the effective control of metastasis remains a complex problem. It was reported that over 90% of the deaths of cancer patients is caused by metastasis, which is formed by the spread of disseminated primary tumor cells to distant anatomic sites [1]. Finding new modalities that treat the local and systemic components of the disease, in particular for patients who do not respond to conventional treatments, has become increasingly important. Evidence suggests that several PAMPs can stimulate TLR4. These molecules include LPS from Gram-negative bacteria, fusion protein from respiratory syncytial virus, and envelope protein from mouse mammary tumor virus [7,8]. These include the heat-shock 60-kDa protein (HSP60) and HSP70, oligosaccharides of hyaluronan [9], and high-mobility group box 1 (HMGB1) [10]
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