Introduction Osteosarcoma OS is the most common type of bone

Introduction Osteosarcoma (OS) is the most common type of bone tumor occurred in adolescents and children [1]. OS is highly malignant and accounts for about half of bone sarcomas with high potential of metastasis [2]. Treatment for OS is mainly depended on surgical operation, assisted with chemotherapy [3]. However, even with multiple chemotherapies, it is still less optimistic due to the poor 5-year survival rates of OS, regardless of increasing kinds or dosages of chemotherapeutic drugs [4]. Recently, drug resistance in OS has draw more attention in understanding the molecular mechanism in OS treatement [5]. However, it is still an ongoing progress in discovering and developing novel therapeutic target. microRNAs (miRNAs) are non-coding RNAs with 17–25 nucleotides [6,7]. As is known, miRNAs have diverse functions in multiple physiological progression [8–10]. Since the initiation, more than 1000 miRNAs have been found to regulate the development and progression in human diseases and tumorigenesis [11–14]. miRNAs regulate the target genes at the post-transcriptional level by binding with 3′ untranslated region. Recently, growing evidence showed that the dysfunction and dysregulation of miRNAs resulted in the occurrence and development of tumor [15–17]. In OS, multiple miRNAs had showed differential nor-Binaltorphimine dihydrochloride between tumor tissues and normal counterparts, and some had been verified to be involved with drug resistance [18,19]. miR-367 has been recognized to be a tumor suppressor gene in gastric cancer by inhibiting invasion and metastasis via regulating Rab23 [20]. On other hand, miR-367 also functioned as an oncogene in pancreatic ductal adenocarcinoma by promoting epithelial-to-mesenchymal transition through the Smad7-TGF-beta signaling pathway [21]. Thus studies showed the diverse functions of miR-367 in different tumorigenesis. However, little is known about the functions of miR-367 in OS and in drug resistance.
Materials and methods
Results
Discussion Discovery and developing novel therapeutic target and strategy against osteosarcoma remains less optimistic. Recently, miRNAs have been investigated to regulate diverse physiological and pathological progression, even the tumorigenesis [13,25]. Though accumulating evidences show that miRNAs participate in tumor initiation and progression by regulating their target genes, however, their functions have not been fully understood. Previous studies showed that miR-367 acted multiple functions in different kinds of cancer by targeting different genes through inhibiting or promoting cellular invasion and metastasis [20,21,26]. However, the expression of miR-367 and its function in OS is little known. In our study, we confirmed that miR-367 increased in osteosarcoma and OS cell lines, indicating that miR-367 could be an oncogene in OS. Our data also demonstrated that miR-367 was involved in ADR-induced apoptosis in OS cells. ADR is a kind of chemotherapeutic drug applied in kinds of malignant cancers [27,28]. ADR induced OS cells apoptosis, meanwhile, decreased the expression of miR-367. To further investigate the role of miR-367 on regulating of the apoptosis, we found KLF4, a tumor suppressor gene which could facilitate apoptosis [29,30], could be a direct target of miR-367 in OS cells. Luciferase reporter system was constructed to verify the interaction of miR-367 and the 3\'UTR of KLF4. The results showed that miR-367 binded to the 3\'UTR of KLF4, indicating that KLF4 was regulated at the translational level by miR-367. We also found that overexpression of miR-367 suppressed the expression of KLF4 at mRNA and protein level. Definitive evidences in Fig. 4 showed transfection of anti-miR367 induced apoptosis, increased KLF4 expression, and also enhanced the sensitivity to ADR in OS cells, all which were reversed by overexpression of miR-367. Thus strongly demonstrated miR-367 acted as an oncogene in OS, and could be involved with the chemotherapy resistance of OS. These findings also suggested KLF4 might play the key role in miR-367-involved cellular proliferation and anti-apoptosis in OS.