Two distinct mTORC2-dependent pathways converge on Rac1 to drive breast cancer metastasis

Abstract

BackgroundThe importance of the mTOR complex 2 (mTORC2) signaling complex in tumor progression is becoming increasingly recognized. HER2-amplified breast cancers use Rictor/mTORC2 signaling to drive tumor formation, tumor cell survival and resistance to human epidermal growth factor receptor 2 (HER2)-targeted therapy. Cell motility, a key step in the metastatic process, can be activated by mTORC2 in luminal and triple negative breast cancer cell lines, but its role in promoting metastases from HER2-amplified breast cancers is not yet clear.MethodsBecause Rictor is an obligate cofactor of mTORC2, we genetically engineered Rictor ablation or overexpression in mouse and human HER2-amplified breast cancer models for modulation of mTORC2 activity. Signaling through mTORC2-dependent pathways was also manipulated using pharmacological inhibitors of mTOR, Akt, and Rac. Signaling was assessed by western analysis and biochemical pull-down assays specific for Rac-GTP and for active Rac guanine nucleotide exchange factors (GEFs). Metastases were assessed from spontaneous tumors and from intravenously delivered tumor cells. Motility and invasion of cells was assessed using Matrigel-coated transwell assays.ResultsWe found that Rictor ablation potently impaired, while Rictor overexpression increased, metastasis in spontaneous and intravenously seeded models of HER2-overexpressing breast cancers. Additionally, migration and invasion of HER2-amplified human breast cancer cells was diminished in the absence of Rictor, or upon pharmacological mTOR kinase inhibition. Active Rac1 was required for Rictor-dependent invasion and motility, which rescued invasion/motility in Rictor depleted cells. Rictor/mTORC2-dependent dampening of the endogenous Rac1 inhibitor RhoGDI2, a factor that correlated directly with increased overall survival in HER2-amplified breast cancer patients, promoted Rac1 activity and tumor cell invasion/migration. The mTORC2 substrate Akt did not affect RhoGDI2 dampening, but partially increased Rac1 activity through the Rac-GEF Tiam1, thus partially rescuing cell invasion/motility. The mTORC2 effector protein kinase C (PKC)α did rescue Rictor-mediated RhoGDI2 downregulation, partially rescuing Rac-guanosine triphosphate (GTP) and migration/motility.ConclusionThese findings suggest that mTORC2 uses two coordinated pathways to activate cell invasion/motility, both of which converge on Rac1. Akt signaling activates Rac1 through the Rac-GEF Tiam1, while PKC signaling dampens expression of the endogenous Rac1 inhibitor, RhoGDI2.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-017-0868-8) contains supplementary material, which is available to authorized users.

Analysis of Copy-Number Variations and Feline Mammary Carcinoma Survival

“…MYL10, ACTB, RAC1, and MYLPF) involved in cell movement, actin cytoskeleton remodelling, and cellular proliferation and motion such as SBDS, ITGAM, PDGFA, and RAC1. Among them, RAC1 actively promotes cell motility in breast cancer cells 64,65 and PDGFA has been reported as highly expressed in FMCs and derived cell lines 66 . Furthermore, E3 1.1-34.5 Mb harboured SERPINE1; a gene encoding a cell adhesion protein involved in invasion and metastasis promotion in different human malignancies including HBCs [67][68][69] Analysis of common CNLs significantly correlated with reduced survival intervals.…”

Targeting Rac and Cdc42 GEFs in Metastatic Cancer

“…Numerous studies have implicated Rac/PAK activities with the maintenance of mesenchymal stem cell-like populations in epithelial cancers; and thus, therapy resistance (Zhao et al, 2011;Ong et al, 2013;Zhu et al, 2015;Goel et al, 2016;Huynh et al, 2016;Aboukameel et al, 2017;Lai et al, 2017;Morrison Joly et al, 2017;Cardama et al, 2018;Goka et al, 2019). Specifically in breast cancer, Rac/Cdc42/PAK signaling is implicated with therapy resistance of HER2-type (Wang et al, 2006;Ebi et al, 2013;Laurin et al, 2013;Dokmanovic et al, 2014;Desai et al, 2016;Hampsch et al, 2017), triple negative (De et al, 2017), and ER(+) cancers (Cai et al, 2003;Gonzalez et al, 2017).…”

RhoB is regulated by hypoxia and modulates metastasis in breast cancer

“…Further, induction of RhoC and TNF‐α expression by downregulation of miR‐509 significantly enhanced brain metastasis of breast cancer cells in mice . Rac1 was shown to be required for two different mTORC2 signaling pathways in HER2+ breast cancer to drive metastasis . Transcriptional inhibition of miR‐124 resulted in the activation of Rac1, which further activated the JNK pathway to drive pancreatic cancer cell proliferation, invasion, and metastasis .…”

“…53 Rac1 was shown to be required for two different mTORC2 signaling pathways in HER2+ breast cancer to drive metastasis. 54 Transcriptional inhibition of miR-124 resulted in the activation of Rac1, which further activated the JNK pathway to drive pancreatic cancer cell proliferation, invasion, and metastasis. 55 In contrast, it has been proposed that RhoB can either act as a tumor suppressor or tumor promoter based on the circumstance.…”