Data Availability StatementThe authors declare that the data supporting the findings of this study are available within the article. pathway plays a key role in the development and progression of cancer , which include cell proliferation, senescence, differentiation, migration, apoptosis and many more [13C15]. There are three major MAPK cascades in humans: c-Jun em N /em -terminal kinase (JNK), extracellular signal-regulated kinase (ERK1/2) and p38 MAPK. JNK can function as a pro-apoptotic kinase in response to a variety of extracellular stimuli, including chemotherapeutic drugs, tumor necrosis factor (TNF), UV irradiation and cytokines. Some studies had proved that the JNK pathway activates caspases and regulates apoptosis-related proteins, including Bcl-2 and Bax . The sAJM589 ERK activation is associated with the pathogenesis, progression, and oncogenic behavior of human breast cancer and colorectal cancer [17, 18]. The effect of p38 MAPK signaling is diverse, and p38 MAPK has been shown to promote cell death or enhance cell growth and survival [19, 20]. Thus, the MAPK pathway is one important signaling pathway associated with breast cancer progression [21, 22]. In our study, we investigated the role of sAJM589 C-phycocyanin as an anti-breast cancer agent on triple-negative breast cancer MDA-MB-231 cells in vitro and uncovered the molecular mechanism of anti-cancer activity. sAJM589 We found that C-phycocyanin effectively inhibited MDA-MB-231 cell proliferation, induced cell apoptotic and triggered G0/G1 cell cycle arrest. Furthermore, the molecular mechanism of cell cycle arrest caused by C-phycocyanin might be attributed to down-regulate the expression of Cyclin D1 and CDK2, and at the same time up-regulate the protein expression levels of p21 and p27 in MDA-MB-231 cells. Moreover, we uncovered that C-phycocyanin-mediated apoptosis was regulated by the inhibition of the ERK pathway and the sAJM589 activation of the JNK pathway and p38 MAPK pathway. Methods Materials C-Phycocyanin was extracted and purified in our lab, and dissolved in PBS as a stock solution and conserved at ??20?C . The cell cycle and apoptosis analysis kit and annexin V-FITC/PI apoptosis detection kit were purchased from Shanghai YEASEN Biotechnology Co., Ltd., Shanghai, China. The TUNEL detection kit was obtained from Beyotime Biotechnology, Shanghai, China. CCK8 and all other chemicals were of analytic grade and were also purchased from Beijing Solarbio Science & Technology, Beijing, China. Mouse anti-human COX-2, Cyclin D1, Cyclin E, CDK2, CDK4, p21, p27, Fas, cleaved-caspase 3, pro-caspase 3, ERK1/2, p-ERK1/2, JNK, p-JNK, p38 MAPK, p-p38 MAPK, AKT, and p-AKT monoclonal antibodies were obtained from Santa Cruz Biotechnology (Santa Cruz, CA, USA). Antibodies against -actin and all the second antibodies were purchased from Sigma-Aldrich. Cell culture Human breast cancer cell line MDA-MB-231 was obtained from the Cell Bank of Chinese Academy of Sciences (Shanghai). MDA-MB-231 was cultured in high glucose DMEM supplemented with 10% (v/v) FBS, 100?mg/ml streptomycin and 100?units/ml penicillin in a humidified incubator with 5% CO2/95% air atmosphere at 37?C. Cell viability assay The effect of C-phycocyanin on MDA-MB-231 cell was detected using CCK8 assays. MDA-MB-231 cells (1??104 cells per well) were plated into 96-well cell culture plates for 24?h. Then the medium was replaced with fresh medium with various concentrations of C-phycocyanin (0, 50, 100, 150, 200, 250, 300?g/ml) for 24 or 48?h. After treatment, CCK8 was added into the medium according to manufacturers instructions for 2?h. Finally, the absorbance value was measured at 490?nm and the absorbance value was positively correlated with cell viability. Clonogenic assay MDA-MB-231 was incubated in a six-well plate at about 1000 cells per well for 24?h, and then treated with different concentrations of C-phycocyanin (0, 50, 100, 150, 200, 250?g/ml) for another 24?h. After incubation for 10?days, cells were washed with PBS twice, fixed with methanol for 15?min, stained with 0.5% crystal violet for 15?min at room temperature, and then observed under light microscope. Analysis of cell cycle and apoptosis by flow cytometry The synchronized cells treated with different concentrations of C-phycocyanin (0, 100, 200?g/ml) were collected using 0.25% trypsin, centrifuged (800?rpm), and washed with cold PBS twice. The synchronized cells were resuspended in pre-cooling 70% ethanol at 4?C for 4?h. The synchronized cells were incubated with propidium iodide solution (20?g/ml PI, 0.1% Triton X-100 staining solution, 0.1?mg/ml RNase A) for 30?min. The DNA contents distribution GDF2 was determined by the BD Biosciences FACSCanto II Analyzer. The number of cells per sample was at least 2??104. The analysis of apoptosis was detected using Annexin V-FITC apoptosis recognition kit based on the producers suggestions, the MDA-MB-231 cells with or without C-phycocyanin treatment was gathered using 0.25% Trypsin, centrifuged (800?rpm), and washed with chilly PBS twice. After that cells had been resuspended in 1 binding buffer at a denseness of just one 1??106?cells/ml..