Objective: To investigate the effect of miR-503 on migration and invasion in human melanoma cells A375 and its mechanism. Methods: The real-time quantitative PCR (qRT-PCR) was used to detect the expression level of miR-503 in melanoma tissues and cell lines; miR-503 mimics or miR-503 inhibitors were used to perform transient transfection to A375 cells

and Transwell assay was used to test cell migration and invasion abilities. The potential binding site of miR-503 on the CXCL9 was predicted by using online bioinformative databases

and the result was verified by double luciferase assay. The migration and invasive ability of A375 cells were detected after transfected with CXCL9 alone or in combination with miR-503. Results: Expression of miR-503 was significantly downregulated in melanoma tissues when compared with adjacent normal tissues (t=6.602

P=0.000). In addition

expression of miR-503 in the three melanoma cell lines (A375

SK-MEL-1 and SK-MEL-5) was significantly lower than that in the HEM cells (F=19.445

P=0.000). Migration and invasion abilities in A375 cells after transfection of miR-503 mimics were significantly inhibited (P=0.017

P=0.049)

while in A375 cells after transfection of miR-503 inhibitors were promoted (P=0.004

P=0.000). CXCL9 was the direct target gene of miR-503 and promoted the migration and invasion of A375 cells (P=0.000

P=0.009)

of which effectiveness was able to be reversed by miR-503. Conclusion: The miR-503 suppresses migration and invasion of melanoma cells by targeted-regulating CXCL9.