Abstract
BACKGROUND: The pro-oncogenic anterior gradient 2 (AGR2) is involved in tumor growth and drug resistance of breast cancer. Mechanisms that regulate expression of AGR2 still need to be elucidated. METHODS: In this study, expression levels of AGR2 and miR-135b-5p were analyzed in different breast cancer cell lines as well as in clinical breast cancer tissues. The in vitro and in vivo functional effect of AGR2 and miR-135b-5p were also investigated. A luciferase reporter assay was applied to confirm the interaction between miR-135b-5p and AGR2 mRNA. RESULTS: We identified AGR2 as a target of miR-135b-5p. Expression of AGR2 was up-regulated in doxorubicin-resistant breast cancer cells. AGR2 mediated doxorubicin-sensitivity of breast cancer cells both in vitro and in vivo. miR-135b-5p negatively regulated AGR2-expression of breast cancer cells increasing doxorubicin-sensitivity. However, miR-135b-5p was down-regulated in doxorubicin-resistant breast cancer cells as well as during treatment with doxorubicin, which might be a probable reason for over-expression of AGR2. Up-regulation of miR-135b-5p increased doxorubicin-sensitivity of breast cancer cells in vivo. In addition, levels of AGR2 negatively correlated with levels of miR-135b-5p in clinical breast cancer tissue samples. CONCLUSION: Our results highlight the potential of miR-135b-5p as a target for treating AGR2-expressing breast cancer with doxorubicin-resistance.