Preliminary studies showed that miR-21 is overexpressed in some human
cancers. However, the role of miR-21 in
cancer is still unclear and even controversial. Our purpose was to investigate the
biological effects of miR-21 on A549
non-small cell lung cancer (NSCLC) cells and the underlying mechanisms of those effects. The expression of miR-21 was quantified in serum samples from patients with NSCLC. A549 cells were transfected with miR-NC-sponge or miR-21-sponge only, or with miR-21-sponge plus PDCD4
small-interfering RNA (
siRNA). The expression of miR-21 and PDCD4
mRNA in transfected cells was quantified by real-time polymerase chain reaction and the expression of PDCD4
protein by Western blot. Cell proliferation, apoptosis, migration, and invasion assays were performed to determine the
biological effects of miR-21 expression and PDCD4 inhibition. miR-21 was overexpressed in serum from patients with NSCLC. Reduced miR-21 expression was observed following transfection with miR-21-sponge in A549 NSCLC cells. Co-transfection of miR-21-sponge with PDCD4
siRNA upregulated miR-21 expression in these cells. PDCD4
mRNA and
protein levels were increased 2.14-fold and 2.16-fold, respectively, following inhibition of miR-21 expression. Inhibition of miR-21 expression following transfection of miR-21-sponge reduced cell proliferation, migration, and invasion of A549 cells. Depletion of PDCD4 by
siRNA transfection reversed the reduction of cell proliferation, migration, and invasion induced by inhibition of miR-21 in A549 cells. It indicates that miR-21 is highly expressed in patients with NSCLC and inhibition of miR-21 expression reduces proliferation, migration, and invasion of A549 cells by upregulating PDCD4 expression. Modulation of miR-21 or PDCD4 expression may provide a potentially novel therapeutic approach for NSCLC.