The N-terminal polypeptide derived from viral macrophage inflammatory protein II reverses breast cancer epithelial-to-mesenchymal transition via a PDGFRα-dependent mechanism

NT21MP, a 21-residue peptide derived from the viral macrophage inflammatory protein II, competed effectively with the natural ligand of CXC chemokine receptor 4 (CXCR4), stromal cell-derived factor 1-alpha, to induce apoptosis and inhibit growth in breast cancer. Its role in tumor epithelial-to-mesenchymal transition (EMT) regulation remains unknown. In this study, we evaluated the reversal of EMT upon NT21MP treatment and examined its role in the inhibition of EMT in breast cancer. The parental cells of breast cancer (SKBR-3 and MCF-7) and paclitaxel-resistant (SKBR-3 PR and MCF-7 PR) cells were studied in vitro and in combined immunodeficient mice. The mice injected with SKBR-3 PR cells were treated with NT21MP through the tail vein or intraperitoneally with paclitaxel or saline. Sections from tumors were evaluated for tumor weight and EMT markers based on Western blot. In vitro, the effects of NT21MP, CXCR4 and PDGFRα on tumor EMT were assessed by relative quantitative real-time reverse transcription–polymerase chain reaction, western blot and biological activity in breast cancer cell lines expressing high or low levels of CXCR4. Our results illustrated that NT21MP could reverse the phenotype of EMT in paclitaxel-resistant cells. Furthermore, we found that NT21MP governed PR-mediated EMT partly due to controlling platelet-derived growth factors A and B (PDGFA and PDGFB) and their receptor (PDGFRα). More importantly, NT21MP down-regulated AKT and ERK1/2 activity, which were activated by PDGFRα, and eventually reversed the EMT. Together, these results indicated that CXCR4 overexpression drives acquired paclitaxel resistance, partly by activating the PDGFA and PDGFB/PDGFRα autocrine signaling loops that activate AKT and ERK1/2. Inhibition of the oncogenic EMT process by targeting CXCR4/PDGFRα-mediated pathways using NT21MP may provide a novel therapeutic approach towards breast cancer.


INTRODUCTION
In China, more than 1.6 million people are newly diagnosed with breast cancer and 1.2 million breast cancer deaths are expected to occur among women each year [1]. The American Cancer Society released the 2013 national cancer statistics report that ranked breast cancer as the highest incidence in women (29%) and the second highest death rate [2].
Paclitaxel (Taxol) is a powerful chemotherapeutic that has been used to treat ovarian, breast, lung, pancreatic, chemoresistance. Paclitaxel resistance is associated with the acquisition of the epithelial-to-mesenchymal transition (EMT) [5]. Classical EMT-related signaling pathways, breast carcinoma [6,7].
protein-coupled receptor CXCR4 pathways in liver tumors CXCL12, also known as stromal cell-derived factor-1 in breast cancer and has been correlated with poor has been shown to play a key role in tumor growth, invasion, and angiogenesis [11][12][13][14]. The results of these tumor microenvironment may alter invasive capacity as well as the tumor-associated immune cells that are linked to increased metastasis and poor prognosis [15]. also been studied in breast cancer treatment [16,17]. High CXCR4 overexpression from breast cancer patients receiving neoadjuvant chemotherapy was predictive of pathway caused chemoresistance, while CXCR2 blockers tumors, particularly against metastasis [19]. An oncolytic virus armed with a CXCR4 antagonist effectively inhibited the development of spontaneous metastasis and increased overall tumor-free survival [20].
In a previous study, we reported that and invasion in breast cancer cells by reducing the signaling pathway and the subsequent activation of cancer has not been investigated. In the current study, we discussed whether platelet-derived growth factor reversing CXCR4-induced EMT to provide insight chemotherapy for breast cancer.

The overexpression of PDGF and PDGFR were found in PR cells
Here, we established paclitaxel-resistant breast cancer cells (PR cells) that exhibited resistance to paclitaxel and acquired an EMT feature as described cancer oncogenesis, and chemoresistance was associated with EMT in PR cells.

DISCUSSION
The EMT is associated with tumorigenesis and metastasis as well as chemoresistance of cancer. Therefore, elucidating the mechanisms that govern the acquisition of EMT would likely be useful for devising targeted therapeutic approaches to overcome or prevent resistance to conventional cancer therapeutics. Paclitaxel promotes the polymerization of tubulin, thereby causing cell death by disrupting the normal microtubule dynamics Recent studies have shown that links between paclitaxel resistance and EMT lead breast cancer patients to develop chemoresistance [29,30]. In our previous studies, we acquired EMT feature, as described previously [25,26], cells.
CXCR4 expression is higher in dedifferentiated cells than in normal cells and independently predicted poor survival in tumors [31]. The activation of molecular progression and is associated with CXCR4 expression.
which is a selective synthetic polypeptide derived from vMIP-II, from interacting with its natural ligand, our previous study achieved the inhibition of primary tumor growth and metastasis [22,23]. www.impactjournals.com/oncotarget  Diego, CA). Resulting cells were subjected to C6 Accuri PR cells (5 × 10 3 ) were seeded in each well of the 96well plates overnight. The cells were then treated with 1 performed as described previously [27].
The cells were seeded into six-well plates. After the a 10 µL pipette tip, and the detached cells were removed 20 h. Images were collected at 0 and 20 h.