Molecular Mechanism Of Osteosarcoma Chemoresistance Mediated By Hippo/TAZ Signaling Pathway

Background:Osteosarcoma is the most frequent primary malignanncy of bone and neoadjuvant chemotherapy combined with surgery is the most common treatment. However, a certain percentage of patients are either intrinsically resistant or late-developed resistance to primary chemotherapy, leading to the poor survival rate compared with the patients who are sensitive to chemotherapy. Hippo signaling pathway involves a series of kinases and transcriptional co-activators, plays a key role in both physiological and pathological processes, such as proliferation, differentiation and apoptosis. Research in the past decade has revealed that dysregulated Hippo signaling pathway was involved in tumorigenesis, and played an important role in chemotherapeutic drug resistance as well. Our research aims to study the levels of Hippo/TAZ signaling pathway in osteosarcoma with chemotherapy, which may help us to illustrate the role of Hippo/TAZ signaling pathway in osteosarcoma chemoresistance.Methods:We successfully established MG63 stable cell line with TAZ knockdown, and we determined the proliferation by automated cell counter and chemosensitivity by flow cytometric analysis. MG63 cell line were treated with chemotherapeutic agents Methotrexate and Doxorubicin, followed by the analysis of TAZ expression levels by Western blotting and the levels of CTGF?Cyr61 by RT-PCR. Results:Knock-down of TAZ inhibited proliferation and increased chemosensitivity of MG63 cells. TAZ was found to be down-regulated in MG63 cells by chemotherapy. We also fround that doxorubicin decreased the transcriptional activation of TAZ and methotrexate promoted cytoplasmic retention and degradation of TAZ. Consistently chemotherapy could down-regulate CTGF and Cyr61, which are putative downstream target genes of TAZ.Conclusions:Knock-down of TAZ in osteosarcoma cells sensitizes cells to chemotherapeutic agents. Methotrexate and Doxorubicin down-regulate the levels of TAZ and decrease the expression of CTGF and Cyr61. These studies suggest that Hippo/TAZ signaling pathway may contribute to chemotherapeutic drug resistance in osteosarcoma with implication of a novel therapeutic way for osteosarcoma treatment.