Objective      To determine the expression of miR-335 in breast cancer cells (BT474

T47D

MCF-7

SK-BR-3

and MDA-MB-231) and normal breast cells (MCF-10A) and in primary breast cancer and lymph node metastatic breast cancer

and investigate the effect of miR-335 on the proliferation

apoptosis

and migration of MDA-MB-231 cells.       Methods      MDA-MB-231 cells were divided into 3 groups: a miR-335 group (transfected with miR-335 mimics)

a control group (transfected with negative control) and a blank group (non-transfected). The expression of miR-335 in normal breast cells and breast cancer cells was detected by real-time PCR. MTT assay was performed to observe the proliferation ability. The effect of over-expression of miR-335 on cell apoptosis was determined by flow cytometry. Transwell chamber assay was carried out to investigate the effect of miR-335 on migration of MDA-MB-231 cells. The expression of MMP-2 and MMP-9 was detected by Western blotting.       Results      The level of miR-335 in the breast cancer cells

especially

MDA-MB-231 cells

was lower than that in the normal breast cells (P0.01). In the tissues of randomly paired primary breast cancer (10 cases) and lymph node metastatic breast cancer (10 cases)

the expression of miR-335 in 7 cases of lymph node metastatic breast cancer was lower than that in the corresponding primary breast cancer (P0.05). Over-expression of miR-335 had no significant effect on the proliferation and apoptosis of MDA-MB-231 cells (P0.05)

but could significantly inhibit the cell migration (P0.05). Western blot results showed that the protein levels of MMP-2 and MMP-9 in the miR-335 group were lower than those in the control group and the blank group.       Conclusion      The expression of miR-335 is particularly reduced in the MDA-MB-231 cells and in the lymph node metastatic breast cancer tissues. The over-expression of miR-335 markedly inhibits the migration of MDA-MB-231 cells

but has no effect on the cell proliferation and apoptosis. MiR-335 inhibits the migration of MDA-MB-231 cells through down-regulating the levels of MMP-2 and MMP-9.