MALAT1 Promotes the Proliferation and Metastasis of Osteosarcoma Cells By Activating the Rac1/JNK Pathway Via Targeting MiR-509

Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) is a long noncoding RNA (lncRNA) that contributes to the initiation and development of many solid tumors, including osteosarcoma (OS). In this study, we showed that MALAT1 was increased in human OS tissues and cell lines. MALAT1 knockdown suppressed OS cell growth and metastasis, induced OS cell apoptosis and delayed tumor growth in an OS xenograft model. We also detected downregulation of microRNA-509 (miR-509), a suppressor of OS growth, in OS tissues and cell lines. Then, we identified that miR-509 is a direct target of MALAT1 and Ras-related C3 botulinum toxin substrate 1 (Rac1) is a direct target of miR-509. MALAT1 may promote OS cell growth through inhibition of miR-509, leading to the activation of Rac1/JNK pathway. Our results suggest a MALAT1/miR-509/Rac1 axis that mediates OS cell proliferation and tumor progression.