The N-terminal Polypeptide Derived From Viral Macrophage Inflammatory Protein ? Reverses Breast Cancer Epithelial-to-mesenchymal Transition Via A PDGFR?-dependent

Tumor metastasis is not only a sign of disease severity but also a major factor that causes treatment failure and cancer-related death.Therefore,studies on the molecular mechanisms of tumor metastasis are critical for the development of treatments and for the improvement of survival.The epithelial-mesenchymal transition(EMT)is an orderly,polygenic biological process that plays an important role in tumor cell invasion,metastasis and chemoresistance.It's crucially important to explore the intrinsic mechanism of EMT.Paclitaxel(Taxol)is a feasible first-line choice as either single or combination chemotherapy for the treatment of recurrent or metastatic breast cancer.However,drug resistance is a big obstacle that causes breast cancer chemotherapy failure.It is necessary to explore the molecular mechanism of chemoresistance and subsequently find a novel strategy to overcome such limitations for achieving better therapeutic effects in breast cancer patients.CXCR4 whose ligand stromal cell-derived factor-1(SDF-1?)can promote the proliferation,survival,and invasion of cancer cells.They have been shown to play an important role in regulating metastasis of breast cancer to specific organs such as lymph nodes,lung and bone.There is cross-talking between CXCR4 signal pathway and paclitaxel-induced EMT.So,CXCR4 might be a target of clinical adjuvant chemotherapy.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 EMT regulation remains unknown.The platelet-derived growth factor(PDGF)signaling pathway has been found to play important roles in the development and progression of human cancers by regulating the processes of cell proliferation,apoptosis,migration,invasion,metastasis,and the acquisition of the epithelial-mesenchymal transition(EMT)phenotype.PDGFRa(platelet-derived growth factor receptor-a),which show frequent aberrant activation in breast cancer,are associated with a process of EMT that confers a more invasive and drug-resistant phenotype.In this study,we first analyzed the key residues of NT21MP binding to CXCR4 and the chemicophysical properties by bioinformatics technology.Second,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(MCF-7,SKBR-3 and MDA-MB-231)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 PDGFRa on tumor EMT were assessed by relative quantitative real-time reverse transcription polymerase chain reaction,western blot and biological activity assays in breast cancer cell lines that express high or low levels of CXCR4.Our results illustrated that Lysl and Ser4 at the N-terminus of SDF-1? interacted with Asp262 and Arg 188,which were activated amino acids in CXCR4,by hydrophobic contacts and hydrogen bonds.And this combination could play the key role to block CXCR4 signal pathway.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(PDGFRa).More importantly,NT21MP down-regulated AKT and ERK1/2 activity,which were activated by PDGFR?,and eventually reversed the EMT.