RASAL2 activates RAC1 to promote triple-negative breast cancer progression
Min Feng, … , Dave S.B. Hoon, Qiang Yu
Min Feng, … , Dave S.B. Hoon, Qiang Yu
Published November 10, 2014
Citation Information: J Clin Invest. 2014;124(12):5291-5304. https://doi.org/10.1172/JCI76711.
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Research Article Oncology

RASAL2 activates RAC1 to promote triple-negative breast cancer progression

Abstract

Patients with triple-negative breast cancer (TNBC) have a high incidence of early relapse and metastasis; however, the molecular basis for recurrence in these individuals remains poorly understood. Here, we demonstrate that RASAL2, which encodes a RAS-GTPase–activating protein (RAS-GAP), is a functional target of anti-invasive microRNA-203 and is overexpressed in a subset of triple-negative or estrogen receptor–negative (ER-negative) breast tumors. As opposed to luminal B ER-positive breast cancers, in which RASAL2 has been shown to act as a RAS-GAP tumor suppressor, we found that RASAL2 is oncogenic in TNBC and drives mesenchymal invasion and metastasis. Moreover, high RASAL2 expression was predictive of poor disease outcomes in patients with TNBC. RASAL2 acted independently of its RAS-GAP catalytic activity in TNBC; however, RASAL2 promoted small GTPase RAC1 signaling, which promotes mesenchymal invasion, through binding and antagonizing the RAC1-GAP protein ARHGAP24. Together, these results indicate that activation of a RASAL2/ARHGAP24/RAC1 module contributes to TNBC tumorigenesis and identify a context-dependent role of RASAL2 in breast cancer.

Authors

Min Feng, Yi Bao, Zhimei Li, Juntao Li, Min Gong, Stella Lam, Jinhua Wang, Diego M. Marzese, Nicholas Donovan, Ern Yu Tan, Dave S.B. Hoon, Qiang Yu

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Figure 1

miRNA and mRNA profiling identifies concurrent deregulations of miR-203 and RASAL2 in TNBC.

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miRNA and mRNA profiling identifies concurrent deregulations of miR-203 ...
(A) Heat map of miRNA profiling showing the 10 top-ranked downregulated miRNAs in indicated cell lines. (B) Venn diagram of putative miR-203 target genes predicted by TargetScan and miRDB algorithms and the 103 TNBC upregulated genes identified previously (24) in addition to the 4 genes that overlap, with number of putative miR-203 target sites. (C) The diagram shows the 2 regions containing miR-203–binding sites (a single miRNA recognition element [MRE] in P1 and 6 MREs [MRE2–MRE7] in P2) of the luciferase reporter construct of the 3’ UTR of RASAL2. Reporter activity was normalized to wild-type reporter activity in cells expressing a nontargeting control (NC) microRNA. (D) qPCR and Western blot analysis of RASAL2 levels in MDA-MB-231 and BT-549 cells treated with miR-203 mimics. (E) qPCR and Western blot analysis of RASAL2 levels in MCF-7 and T47D cells treated with miR-203 antagomir inhibitor. (F) qPCR analysis of miR-203 and RASAL2 in breast tumor specimens. ΔCq, quantification cycle. (G) Representative images and quantification of IHC staining for RASAL2 in luminal or TNBC tumors. (H) Correlation analysis of RASAL2 and miR-203 in luminal and TNBC tumors expressing high (upper quartile) and low (lower quartile) levels of miR-203. (I) IHC analysis of the TMA cohort, showing the percentages of staining of different tumor subtypes (strong [67%–100%], moderate [34%–66%], or absent/weak [0%–33%]) for RASAL2 protein. (J) Scatter plot showing RASAL2 protein expression in indicated breast tumors. The data shown represent mean ± SEM of 3 independent experiments. Scale bar: 100 μm (G); 300 μm (I). *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001.