Abstract: Objective   To explore the relationship between MALAT1 and miR-205 and to reveal the molecular mechanism of MALAT1 to promote the occurrence and development of osteosarcoma. Methods   Real time fluorescence quantitative PCR （QPCR） was used to detect the expression of MALAT1 and miR-205 in osteosarcoma tissue， paracancerous normal tissue， human osteoblasts （hFOB）， and MG63 and Sao-2 osteosarcoma cells. Bioinformatics and fluoro enzyme experimental was used to observe the targeting regulation of miR-205 by MALAT1. After transfection of miR-205 mimics to Sao-2 and MG63 cells， the expression of MALAT1 was detected by QPCR. After transfection of si-MALAT1 to Sao-2 and MG63 cells， the expression of miR-205 was detected by QPCR. MG63 cells were transfected by miR-205 mimics and si-MALAT1 respectively. The ability of invasion and metastasis was detected by Transwell compartment， and the expression of MMP-2 and MMP-9 was detected by Western blotting assay. Results  The expression level of MALATI and miR-205 in osteosarcoma tissue， paracancerous normal tissue were 4.7±0.6，2.6±0.08 and 2.2±0.09，3.7±0.3（P＜0.05）. The expression of MALAT1 and miR-205 in hFOB, MG63 cell line and Sao-2 cell line were 0.9±0.01, 2.4±0.7, 2.1±0.05 and 0.82±0.04, 0.53±0.04, 0.47±0.02（P＜0.05）. Bioinformatics and luciferase detection showed that there were three complementary sequences of miR-205 in the MALAT1 sequence， and both of them had a targeting regulation. The expression of miR-205 in Sao-2 and MG63 cells transfected with si-MALAT1 were 3.4±0.7 and 3.8±0.6， while that in the control group was 1.4±0.5 and 1±0.1. The difference was statistically significant （P＜0.05）. The expression of MALAT1 in Sao-2 and MG63 cells transfected with miR-205 mimics was 0.51 ± 0.05， 0.42 ± 0.03， while the control group was 1.5 ± 0.7， 1.28 ± 0.4. The difference was statistically significant （P＜0.05）. The number of MG63 cells invasion in miR-205 mimics group was 28.52 ± 3.68， which was lower than that in miR-205 and pMALAT1 co-transfection group （42.63 ± 5.67）， the difference was statistically significant （P＜0.05）. The expression levels of MMP-2 and MMP-9 in miR-205 mimics group were 0.41 ± 0.02， 0.49 ± 0.04， which were significantly lower than those in miR-205 and pMALAT1 co-transfection group， the difference was statistically significant （P＜0.05）. Conclusion  There is a bi-directional inhibition relationship between MALAT1 and miR-205， and MALAT1 promotes the invasion and metastasis of osteosarcoma cells by inhibiting the expression of miR-205.

Key words: Osteosarcoma, Metastasis-associated lung adenocarcinoma transcript 1（MALAT1）, miR-205, Invasion