Objective To investigate the effects of downregulating microRNA (miR)-550a-5p on the proliferation, migration and invasion of non-small cell lung cancer (NSCLC) and to explore its molecular mechanisms.

Methods The miR-550a-5p inhibitor and its negative control (inhibitor NC), as well as small interfering RNA targeting scavenger receptor class A member 3 (si-SCARA3) and its negative control (si-NC) were individually or co-transfected into A549 cells. These cells were designated as inhibitor NC group, miR-550a-5p inhibitor group, miR-550a-5p inhibitor + si-NC (co-transfection) group and miR-550a-5p inhibitor + si-SCARA3 (co-transfection) group. Cell proliferation was assessed by CCK-8 assay; colony formation ability was evaluated using a plate cloning method; cell migration and invasion were detected by scratch assay and Transwell chamber assay, respectively; levels of matrix metalloproteinase (MMP)-2 and MMP-9 in the supernatant of A549 cells were measured by enzyme-linked immunosorbent assay (ELISA); apoptosis levels were determined by Annexin V/PI double staining.

Results Compared with adjacent normal tissues, the expression level of miR-550a-5p was increased, while SCARA3 mRNA expression was decreased in NSCLC tissues (P < 0.05). Dual-luciferase reporter assays confirmed that miR-550a-5p directly targeted SCARA3. Compared with the inhibitor NC group, cell proliferation rate, colony formation number, migration and invasion ability of the miR-550a-5p inhibitor group decreased, apoptosis rate increased (P < 0.05). Compared with the inhibitor NC group, the expression levels of MMP-2 and MMP-9 in cell supernatant of the miR-550a-5p inhibitor group were decreased, and the expression levels of SCARA3 protein were increased (P < 0.05). Compared with the miR-550a-5p inhibitor group or the miR-550a-5p inhibitor+si-NC group, cell proliferation rate, clonal colony formation number, migration and invasion ability of the miR-550a-5p inhibitor+si-SCARA3 group were increased, and apoptosis rate was decreased (P < 0.05). Compared with the miR-550a-5p inhibitor group or the miR-550a-5p inhibitor+si-NC group, the miR-550a-5p inhibitor+si-SCARA3 group showed increased expression levels of MMP-2 and MMP-9 in the cell supernatant and decreased SCARA3 protein expression levels (P < 0.05).

Conclusion Downregulation of miR-550a-5p inhibits the proliferation, migration and invasion of NSCLC cells, and promotes apoptosis, possibly through upregulating SCARA3 expression.