PPAR? Promotes Survival Of Breast Cancer Cells In Harsh Metabolic Condition

Background and Objective: A hallmark of lethal breast cancers is their ability to live in metabolic conditions that would otherwise kill normal cells.This property is associated with resistance to chemo-and immune-therapy and is ultimately responsible for the incurable nature of most cancers.A better understanding of the mechanisms that allow breast cancer cells to survive in harsh conditions might lead to the identification of new targets to improve therapeutic outcomes.The nuclear receptor peroxisome proliferator activated receptor-delta(PPAR?)may be a central regulator of the ability of cancer cells to thrive in harsh conditions.PPAR? is a member of the PPAR family of nuclear receptors.It is activated by high concentrations of free fatty acids,bioactive lipids,and synthetic agonists such as GW50516 and GW0742.Following ligand-binding,PPAR? undergoes a conformational change and mediates transcription of genes such as PPARD itself,ANGPTL4,and antioxidant genes such as CAT(catalase)that serve as "signatures" for PPAR?-activity.PPAR? increases the endurance capacity of muscle cells and prevents exhaustion of hematopoietic stem cells by lowering oxidative stress and preventing symmetric cell divisions.For success in these situations,cells are required to function effectively over relatively long periods of time in the presence of increasingly unfavorable metabolic conditions.If PPAR? had similar activity in cancer cells as in muscle and stem cells,it might also sustain their growth in metabolically stressful conditions,which is a hallmark of aggressive cancers.We have shown that PPAR? m RNA and protein expression is up-regulated when glycolysis is inhibited in leukemia cells.The experiments in this manuscript were designed to investigate the effect of PPAR? in breast cancer cells in harsh conditions such as found in solid-tumor microenvironments.Methods: In order to define the function of PPAR? in breast cancer,we use retroviral and lentiviral infection,establish PPAR? overexpression and knockout breast cancer cell model,and give the corresponding agonist and antagonist intervention,observation of breast cancer cells in low glucose,hypoxia and other unfavorable conditions of cell survival proliferation.The expressions of PPAR? related proteins and genes were determined by Westernblot and real-time quantitative PCR.7AAD and DCFH staining were used to detect the apoptosis and ROS levels.The migration ability of Transwell cells was observed in vitro.Finally,the growth and metastasis of breast cancer cells were observed by establishing the model of breast cancer in mice.Results: We got theinformation that the expression of PPAR? was associated with the survival rate of breast cancer patientsfrom analyzing a public database.Then we established a rat model with breast adenocarcinomas,and found that the rapid growth of cancer cells(in vitro and in vivo)was also related with the high expression of PPAR?.Transgenic expression of PPAR? in human MCF-7 and SKB-R3 breast cancer cell-lines resulted in increased migration in vitro and lung metastases in mice along with the ability to grow in exhausted tissue culture media.Then we putthe cell lines into low glucose or other endoplasmic reticulum stress conditions(such as hypoxia),and flow cytometry analysis by 7AAD staining was found that breast cancer cells transfected with PPARD gene couldbe survival better.Up-regulation of PPAR? by glucocorticoids or synthetic agonists also protected MCF-7 cells from low-glucose.Flow cytometry analysis by DCFH staining indicated that high expression of PPAR? was related to increased anti-oxidant defenses mediated in part by catalase,which promoted the survival rate of the cancer cells.Western blot showed that the high expression of PPAR? was also related to higher expression of late AKT-phosphorylation,which is associated with the prolonged glucose-deprivation response and survival time.While given insulin or interferon ? to increase AKT levels in control cells also made the cell survival better.And with the AKT inhibitor IV in high PPARD expression cells we got the opposite results.Finally,the synthetic antagonists could reverse survival benefits conferred by PPAR? in vitro,which could be reduced by its agonists.Conclusion: 1.PPAR? can regulate the survival rate of breast cancer cells by reducing oxidativestress in the harsh metabolic microenvironmental conditions;2.PPAR? can enhance the survival rate(p-AKT)of breast cancer cells inharsh microenvironment;3.Small molecule inhibitors can reverse the protective effect of PPAR?in breast cancer;4.PPAR? can be used as a new therapeutic target,which may have a role and provide a new method in the treatment of breast cancer.