mTOR Directs Breast Morphogenesis through the PKC-alpha-Rac1 Signaling Axis

Morrison, Meghan M.; Young, Christian D.; Wang, Shan; Sobolik, Tammy; Sánchez, Violeta; Hicks, Donna J.; Cook, Rebecca S.; Brantley-Sieders, Dana M.

doi:10.1371/journal.pgen.1005291

Cited by 40 publications

(41 citation statements)

References 62 publications

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“…These findings suggest that mTORC2 controls epidermal stratification through PKCα activation. In line with our hypothesis for a role of mTORC2-PKCα activation in epidermal cell differentiation are recent reports demonstrating that mTORC2-mediated PKCα-pS657 activation regulates tissue differentiation during neuron and mammary morphogenesis535455. These studies revealed that mTORC2 controls actin cytoskeleton rearrangement in neurons and regulates neuron morphology through PKC signalling and the Tiam1-Rac1-PAK-cofilin pathway5354.…”

Section: Discussionsupporting

confidence: 85%

mTORC1 and mTORC2 regulate skin morphogenesis and epidermal barrier formation

et al. 2016

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Mammalian target of rapamycin (mTOR), a regulator of growth in many tissues, mediates its activity through two multiprotein complexes, mTORC1 or mTORC2. The role of mTOR signalling in skin morphogenesis and epidermal development is unknown. Here we identify mTOR as an essential regulator in skin morphogenesis by epidermis-specific deletion of Mtor in mice (mTOREKO). mTOREKO mutants are viable, but die shortly after birth due to deficits primarily during the early epidermal differentiation programme and lack of a protective barrier development. Epidermis-specific loss of Raptor, which encodes an essential component of mTORC1, confers the same skin phenotype as seen in mTOREKO mutants. In contrast, newborns with an epidermal deficiency of Rictor, an essential component of mTORC2, survive despite a hypoplastic epidermis and disruption in late stage terminal differentiation. These findings highlight a fundamental role for mTOR in epidermal morphogenesis that is regulated by distinct functions for mTORC1 and mTORC2.

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Section: Discussionsupporting

confidence: 85%

mTORC1 and mTORC2 regulate skin morphogenesis and epidermal barrier formation

et al. 2016

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“…These previous reports, taken together with data shown here, highlight the numerous signaling pathways that can converge on Rac1 to promote dissemination of cancer cells [9]. We show evidence that the endogenous Rac inhibitor RhoGDI2 is an important molecular brake for restraining Rac activity.…”

Section: Discussionsupporting

confidence: 83%

“…The small GTPase Rac1 potently activates cell motility in breast tumor cells, and is required in normal mammary epithelial cells downstream of mTORC2 [9]. Active, GTP-loaded Rac1 was measured using a PAK1 binding domain (PBD)-glutathione S transferase (GST) in situ binding assay [21] in Rictor +/+ NIC and Rictor FL/FL NIC tumors, revealing abundant PBD-GST binding in Rictor +/+ samples (Fig.…”

Section: Resultsmentioning

confidence: 99%

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

et al. 2017

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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.

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“…Given that mTORC1 and mTORC2 utilize distinct co-factors and substrates, mTORC1 and mTORC2 may have distinct physiological roles, and their dysregulation may produce distinct pathological consequences. This notion is supported by recent findings that Rictor/mTORC2, but not Raptor/mTORC1 is required during mammary gland development for ductal branching, mammary epithelial cell (MEC) motility, and MEC survival (8). …”

Section: Introductionmentioning

confidence: 67%

“…However, our studies suggest that HER2+ human breast cancer cells and mouse mammary tumors specifically require Rictor/mTORC2 for Akt S473 phosphorylation, as Rictor ablation eliminated Akt phosphorylation and decreased cell survival. Interestingly, this is distinct from what is seen in untransformed MECs, which rely on an Akt-independent, Rictor-PKCa-Rac1 signaling axis for cell survival, invasion, and morphogenesis (8). …”

Section: Discussionmentioning

confidence: 93%

Rictor/mTORC2 Drives Progression and Therapeutic Resistance of HER2-Amplified Breast Cancers

et al. 2016

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HER2 overexpression drives Akt signaling and cell survival and HER2-enriched breast tumors have a poor outcome when Akt is upregulated. Akt is activated by phosphorylation at T308 via PI3K and S473 via mTORC2. The importance of PI3K activated Akt signaling is well documented in HER2-amplified breast cancer models, but the significance of mTORC2 activated Akt signaling in this setting remains uncertain. We report here that the mTORC2 obligate cofactor Rictor is enriched in HER2-amplified samples, correlating with increased phosphorylation at S473 on Akt. In invasive breast cancer specimens, Rictor expression was upregulated significantly compared to non-malignant tissues. In a HER2/Neu mouse model of breast cancer, genetic ablation of Rictor decreased cell survival and phosphorylation at S473 on Akt, delaying tumor latency, penetrance and burden. In HER2-amplified cells, exposure to an mTORC1/2 dual kinase inhibitor decreased Akt-dependent cell survival, including in cells resistant to lapatinib where cytotoxicity could be restored. We replicated these findings by silencing Rictor in breast cancer cell lines, but not silencing the mTORC1 cofactor Raptor (RPTOR). Taken together, our findings establish that Rictor/mTORC2 signaling drives Akt-dependent tumor progression in HER2-amplified breast cancers, rationalizing clinical investigation of dual mTORC1/2 kinase inhibitors and development of mTORC2-specific inhibitors for use in this setting.

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mTOR Directs Breast Morphogenesis through the PKC-alpha-Rac1 Signaling Axis

Cited by 40 publications

References 62 publications

mTORC1 and mTORC2 regulate skin morphogenesis and epidermal barrier formation

mTORC1 and mTORC2 regulate skin morphogenesis and epidermal barrier formation

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

Rictor/mTORC2 Drives Progression and Therapeutic Resistance of HER2-Amplified Breast Cancers

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