MicroRNA-618 Directly Targets Metadherin mRNA To Suppress The Malignant Phenotype Of Osteosarcoma Cells By Reducing PTEN-AKT Pathway Output

Bohan Li,1 Jie Zhao,2 Qian Zhao,3 Dongjin Wu,2 Cheng Zhang,2 Kun Zhao,2 Yang Song,2 Chunzheng Gao2 1Health Management Center, The Second Hospital of Shandong University, Shandong 250033, People’s Republic of China; 2Department of Spine Surgery, The Second Hospital of Shandong University, Shandong 250033, People’s Republic of China; 3Jinan Central Hospital, The Affiliated Hospital of Shandong University, Shandong 250013, People’s Republic of ChinaCorrespondence: Dongjin WuDepartment of Spine Surgery, The Second Hospital of Shandong University, Shandong 250033, People’s Republic of ChinaEmail wuwudj2143@163.comPurpose: Dysregulation of microRNA-618 (miR-618) has been observed in multiple types of human cancer. However, whether miR-618 is implicated in osteosarcoma (OS) initiation and progression is still unclear. Hence, we measured the expression of miR-618 in OS tissues and cell lines. In addition, the roles of miR-618 and the mechanisms underlying its activities in OS cells were examined.Methods: The expression status of miR-618 in OS was analyzed by reverse-transcription quantitative PCR. The regulatory roles of miR-618 overexpression in OS were explored by the Cell Counting Kit-8 assay, flow-cytometric analysis, Transwell cell migration and invasion assays, and a tumor xenograft experiment.Results: The results revealed that the expression of miR-618 was notably lower in OS tissues and cell lines, and that the low miR-618 expression significantly correlated with the clinical stage and distant metastasis among patients with OS. Exogenous miR-618 expression significantly suppressed OS cell proliferation, migration, and invasion and induced apoptosis in vitro as well as slowed tumor growth in vivo. Mechanism investigation indicated that metadherin (MTDH) is a direct target gene of miR-618 in OS cells. A knockdown of MTDH mimicked the tumor-suppressive effects of miR-618 upregulation on OS cells. Notably, resumption of MTDH expression attenuated the miR-618–mediated reduction in OS cell growth and metastasis in vitro. In addition, miR-618 overexpression reduced the PTEN–AKT pathway output in OS cells both in vitro and in vivo through downregulation of MTDH.Conclusion: To the best of our knowledge, this is the first study to show that miR-618 exerts crucial tumor-suppressive actions in OS pathogenesis by directly targeting MTDH mRNA and reducing PTEN–AKT pathway output. These results will help to elucidate the functions of miR-618 in OS and suggest that this miRNA may be investigated as a therapeutic target in this disease.Keywords: microRNA-618, osteosarcoma, metadherin, proliferation, invasion