Abstract 1468: MiR-200b targets ARHGAP18 and suppresses triple negative breast cancer metastasis

Triple negative breast cancer (TNBC) refers to a group of highly heterogeneous malignant tumors that lack estrogen receptor and progesterone receptor expression, and human epidermal growth factor receptor 2 amplification, accounting for 10-20% of newly diagnosed breast cancer cases. Compared to other subtypes of breast cancer, TNBCs usually show worse clinical features such as rapid tumor growth, earlier recurrence, and more aggressive metastasis. Unfortunately, the mechanism of TNBC metastatic behavior has not been well understood. Moreover, no efficient targeted therapies for TNBCs are currently available, representing a real unmet need for effective new therapies. MiR-200 family members are among the first miRNAs reported to function as potent inhibitors of cancer metastasis. However, the mechanism of miR-200 family on cancer metastasis has not been well understood. In this study, we investigated the effect of miR-200b, one member of the miR-200 family, on TNBC metastasis using cell culture and mouse orthotopic mammary xenograft tumor models. We found that the expression level of miR-200b is significantly lower in TNBC cells and tissues than that in other types of breast cancer. Stably expressing miR-200b significantly reduced TNBC cell migration and invasion and suppressed TNBC metastasis in a mouse orthotopic mammary xenograft tumor model. Mechanistic studies revealed that miR-200b overexpression in TNBC cells caused drastic changes in cellular actin cytoskeleton organization patterns as evidenced by reduced lamellipodia formation but increased stress fiber formation. In consistent with these findings, Rho GTPase pulldown assays demonstrated that stably expressing miR-200b significantly increased the Rho GTPase Rho A activation, but reduced the Rho GTPase Rac1 activation. Moreover, inhibition of Rho A signaling impaired the inhibitory effect of miR-200b on TNBC cell migration. Bioinformatics analysis indicated that ARHGAP18, a specific Rho A GTPase activating protein (GAP), is a predicate target of miR-200b. Further Q-PCR, Western blot and 3’UTR reporter analysis confirmed that ARHGAP18 is a target of miR-200b. Knocking down ARHGAP18 in TNBC cells using siRNAs significantly increased Rho A activation but reduced Rac1 activation. To further determine the role of ARHGAP18 in TNBC, ARHGAP knockout TNBC cells were generated using the CRISPR technology. It was found that knockout ARHGAP18 phenocopied the effect of miR-200b overexpression. Moreover, overexpressing ARHGAP18 in miR-200b stable expression cells overcome the inhibitory effect of miR-200b on TNBC metastasis. Together, these findings suggest that miR-200b suppresses triple negative breast cancer metastasis by targeting ARHGAP18 and enhancing Rho A activation. Note: This abstract was not presented at the meeting. Citation Format: Chengfeng Yang, Brock Humphries, Yunfei Li, Zhishan Wang. MiR-200b targets ARHGAP18 and suppresses triple negative breast cancer metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1468. doi:10.1158/1538-7445.AM2017-1468