The Role Of Hippo/YAP Signaling Pathway In Osteosarcoma Chemoresistance

Background:Osteosarcoma is the most prevalent bone malignancy and mainly occurs in adolescents. Because of the high degree malignancy of osteosarcoma, patients often develop metastasis and suffer from a relative high mortality, which leads to a devastating impact on our social harmony and prosperity. Since the introduction of adjuvant chemotherapy in the 80s, the survival rate of osteosarcoma patients significantly increased. Currently, neoadjuvant chemotherapy plus surgery has become a standard treatment regime for osteosarcoma, and the 5 year survival rate of osteosarcoma patients increased up to 60-70%. However, in the past 2 decade, the survival rate of osteosarcoma patients remained unchanged. The advance of immune and targeted therapy could barely promote the survival of osteosarcoma patients. Osteosarcoma chemoresistance has been revealed in many researches, which was believed to be one of the important factors leading to poor prognosis. Thus, many surgeons started to pay more attention to the research of the mechanism of osteosarcoma chemoresistance. Hippo/YAP signaling pathway is a highly conserved signaling cascade that regulates cell proliferation. It has been extensively reported that Hippo/YAP signaling pathway inhibits cell proliferation, induces cell apoptosis and modulates organ size. Recently, Hippo/YAP signaling pathway has been shown to regulate chemoresistance in hepatic cancer cells and ovarian tumor cells. In our work, we aim to illustrate the role of Hippo/YAP signaling pathway in osteosarcoma chemoresistance and to explore a potential target for treating osteosarcoma chemoresistance.Method:YAP overexpression or knockdown stable MG63 cell lines were constructed and the proliferation and chemoresistance were measured by Cell Titer-Glo Luminescent assay kit and flow cytometric analysis. YAP, phosphorylation of YAP,MST1, LATS 1/2 protein levels were determined by western blotting and MST1 mRNA expression was analyzed by quantitative PCR (Polymerase Chain Reaction) in methotrexate or doxorubicin treated MG63/U2OS osteosarcoma cells. Nuclear localization of YAP in methotrexate/doxorubicin treated osteosarcoma cells was detected by immunofluorescence. MST1 degradation rate was also investigated in methotrexate/doxorubicin treated U2OS cells to better understand the mechanism of Hippo/YAP signaling pathway in osteosarcoma chemoresistance.Results:YAP regulated the proliferation and chemoresistance of MG63 osteosarcoma cells. MST1 was destabilized and LATS1/2 total protein level was decreased in methotrexate/doxorubicin treated osteosarcoma cells, leading to increased YAP activity and nuclear translocation.Conclusion:Hippo/YAP signaling pathway is involved in osteosarcoma chemoresistance and YAP might be a potential target for overcoming this chemoresistance.