Signaling events at TMEM doorways provide potential targets for inhibiting breast cancer dissemination

Tumor cell intravasation is essential for metastatic dissemination, but its exact mechanism is incompletely understood. We have previously shown that in breast cancer, the direct and stable association of a tumor cell expressing Mena, a Tie2hi/VEGFhi macrophage, and a vascular endothelial cell, creates an intravasation portal, called a "tumor microenvironment of metastasis" (TMEM) doorway, for tumor cell intravasation, leading to dissemination to distant sites. The density of TMEM doorways, also called TMEM doorway score, is a clinically validated prognostic marker of distant metastasis in breast cancer patients. Although we know that tumor cells utilize TMEM doorway-associated transient vascular openings to intravasate, the precise signaling mechanisms involved in TMEM doorway function are only partially understood. Using two mouse models of breast cancer and an in vitro assay of intravasation, we report that CSF-1 secreted by the TMEM doorway tumor cell stimulates local secretion of VEGF-A from the Tie2hi TMEM doorway macrophage, leading to the dissociation of endothelial junctions between TMEM doorway associated endothelial cells, supporting tumor cell intravasation. Acute blockade of CSF-1R signaling decreases macrophage VEGF-A secretion as well as TMEM doorway-associated vascular opening, tumor cell trans-endothelial migration, and dissemination. These new insights into signaling events regulating TMEM doorway function should be explored further as treatment strategies for metastatic disease.

Live tumor imaging shows macrophage induction and TMEM-mediated enrichment of cancer stem cells during metastatic dissemination

Cancer stem cells (CSCs) play an important role during metastasis, but the dynamic behavior and induction mechanisms of CSCs are not well understood. Here, we employ high-resolution intravital microscopy using a CSC biosensor to directly observe CSCs in live mice with mammary tumors. CSCs display the slow-migratory, invadopod-rich phenotype that is the hallmark of disseminating tumor cells. CSCs are enriched near macrophages, particularly near macrophage-containing intravasation sites called Tumor Microenvironment of Metastasis (TMEM) doorways. Substantial enrichment of CSCs occurs on association with TMEM doorways, contributing to the finding that CSCs represent >60% of circulating tumor cells. Mechanistically, stemness is induced in non-stem cancer cells upon their direct contact with macrophages via Notch-Jagged signaling. In breast cancers from patients, the density of TMEM doorways correlates with the proportion of cancer cells expressing stem cell markers, indicating that in human breast cancer TMEM doorways are not only cancer cell intravasation portals but also CSC programming sites.

Abstract 372: Macrophage contact-dependent stemness induction and progressive CSC enrichment during metastatic dissemination in breast cancer

Background: Cancer stem cells (CSCs) play an important role during metastatic progression of breast cancer. However, little is known, at the single cell level, about the process of stemness induction in non-stem cells or the dynamic behavior of CSCs during hematogenous dissemination.

Methods: Here, we employed high-resolution intravital multiphoton microscopy with a SOX2/OCT4 responsive fluorescent biosensor for stemness to directly observe the induction of stemness in single non-stem cells and their evolution through the metastatic cascade in living animals using orthotopic breast cancer xenograft model. We confirmed our findings in vitro using tumor cell-macrophage co-culture assays.

Results: We report that, both in vitro and in vivo, direct physical contact with macrophages induces stemness in non-stem cancer cells via juxtacrine Notch-Jagged1 signaling. In vivo, macrophage depletion with clodronate treatment showed a significant decrease in stem cells. In vitro, using either the fate mapping of non-stem cells with or without macrophage contact, or the origin-mapping of stem cells to find whether they originated from non-stem cells or pre-existing stem cells, we found that there was four-fold increase in new CSC induction after direct macrophage contact. In contrast, we did not see any role of macrophages in the expansion of pre-existing CSCs, both in vivo and in vitro, indicating that macrophage contact-dependent stem induction is the primary mechanism of CSC generation.

Using immunohistochemical staining in fixed tissue and live imaging of primary tumors and lungs in mice using optical windows, we found that during the course of dissemination of tumor cells from the primary site, CSCs become progressively enriched in the tumor cell population as they approach dissemination doorways (known as TMEM, Tumor MicroEnvironment of Metastasis), intravasate, circulate and arrive at the lung. Association with and passage through TMEM doorways is the step that generates the greatest enrichment in CSCs (~ 60-fold). On arrival in the lung, CSCs represent more than 75% of the disseminated tumor cell population, greatly enriched compared with their representation in the bulk primary tumor of ~ 1%.

Conclusion: Overall, these data indicate, for the first time, that macrophages associated with TMEM induce CSCs and promote TMEM-mediated CSC intravasation and early metastatic seeding. Our results are consistent with the dramatic enrichment of cancer stem cell markers in association with TMEM in breast cancer patients (Kim et al 2020 AACR abstract) and support a strategy for anti-metastatic therapy.

Citation Format: Ved P. Sharma, Yarong Wang, Binwu Tang, George S. Karagiannis, Emily A. Xue, David Entenberg, Lucia Borriello, Anouchka Coste, Joan G. Jones, Chinmay R. Surve, Dominic Esposito, Maja H. Oktay, Lalage M. Wakefield, John S. Condeelis. Macrophage contact-dependent stemness induction and progressive CSC enrichment during metastatic dissemination in breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 372.

Abstract 976: Regulation of breast tumor metastasis by the dynamic interaction between the TMEM macrophage, tumor, and endothelial cells

Tumor cell intravasation is an essential step in the metastatic cascade, but its exact mechanism is not completely understood. We have previously shown that the direct physical association of a tumor cell over-expressing Mena, a perivascular Tie2hi/Vegfhi macrophage and an endothelial cell, forming a cell triad termed “tumor microenvironment of metastasis” (TMEM), increases vascular permeability, facilitating intravasation of tumor cells. It is only at the TMEM site that intravasation occurs leading to breast tumor metastasis. TMEM density is a clinically validated prognostic marker of distant metastasis in breast cancer patients. The precise molecular mechanisms relating TMEM function had not been elucidated. Here we describe the molecular mechanism. We show here that TMEM function involves the three cells in TMEM: firstly endothelial cell-secreted Ang2 stimulates VEGF build up in the TMEM macrophage, secondly a tumor cell secretes CSF1 which, third, stimulates the TMEM macrophage VEGF secretion, leading to vascular opening and metastasis. In addition, we show that acute blockage of CSF1R and Tie2-Ang2 signaling by inhibitors and blocking antibodies both in vitro and in mammary tumors leads to decreased macrophage VEGF production and secretion, decreased trans-endothelial migration of tumor cells, and decreased TMEM-dependent vascular permeability, circulating tumor cells and lung metastases. We conclude that dynamic interaction between the cells associated with TMEM leads to Ang2 and CSF1-mediated stimulation of macrophage VEGF expression and secretion leading to vascular opening, resulting in tumor cell intravasation. This is the first description of the molecular mechanism behind the predictive power of the clinically used prognostic marker TMEM and represents a major step in defining new biomarkers and targets for the treatment of metastatic tumors.

Citation Format: Chinmay R. Surve, Allison Harney, Yarong Wang, Xiaoming Chen, Ved Sharma, Richard Stanley, Maja Oktay, John Condeelis. Regulation of breast tumor metastasis by the dynamic interaction between the TMEM macrophage, tumor, and endothelial cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 976.

Abstract 972: Direct observation in living tumors shows macrophage-dependent induction and dissemination of cancer stem cells in breast cancer

Cancer stem cells (CSCs) play an important role during metastatic progression of breast cancer. However, the in vivo properties and dynamic behavior of CSCs are not well understood. Here, we employed high-resolution intravital multiphoton microscopy using a SOX2/OCT4 responsive fluorescent stem cell biosensor to directly observe CSC dynamics in the living animal using an orthotopic breast cancer xenograft model. We report that CSCs constitute a minority population (1-3%) in the primary tumors, and display the slow-migratory, invasive phenotype that is specifically associated with disseminating tumor cell population. We also report, for the first time, that CSCs are preferentially localized in direct contact with macrophages near and in tumor microenvironment of metastasis (TMEM) sites, the macrophage-containing intravasation doorway for tumor cells and that CSCs metastasize to lung and are strikingly enriched in early lung metastatic colonies. This is explained by our observation that, in vitro and in vivo, direct physical contact with macrophages induces stemness in non-stem cancer cells via juxtacrine Notch-Jagged1 signaling. These data indicate for the first time that macrophages play an actively inductive role in the CSC niche and promote TMEM-mediated CSC intravasation and early metastatic seeding.

Citation Format: Ved P. Sharma, Yarong Wang, Binwu Tang, George S. Karagiannis, Emily A. Xue, David Entenberg, Lucia Borriello, Anouchka Coste, Chinmay R. Surve, Dominic Esposito, Maja H. Oktay, Lalage M. Wakefield, John S. Condeelis. Direct observation in living tumors shows macrophage-dependent induction and dissemination of cancer stem cells in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 972.

A novel neuregulin - jagged1 paracrine loop in breast cancer transendothelial migration

Background

The interaction of breast cancer cells with other cells in the tumor microenvironment plays an important role in metastasis. Invasion and intravasation, two critical steps in the metastatic process, are influenced by these interactions. Macrophages are of particular interest when it comes to studying tumor cell invasiveness. Previous studies have shown that there is paracrine loop signaling between breast cancer cells and macrophages involving colony stimulating factor 1 (CSF-1) produced by tumor cells and epidermal growth factor (EGF) production by macrophages. In this paper, we identify a novel paracrine loop between tumor cells and macrophages involving neuregulin (NRG1) and notch signaling.

Methods

The aim of this study was to determine the role of NRG1, a ligand of the ErbB3 receptor, in macrophage stimulation of tumor cell transendothelial migration and intravasation. We used fluorescence-activated cell sorting (FACS) and western blot to determine ErbB3 and NRG1 expression, respectively. An in vitro transendothelial migration (iTEM) assay was used to examine the effects of short hairpin (sh)RNA targeting NRG1 in tumor cells and clustered regularly interspaced short palindromic repeats (CRISPR) knockout of jagged 1 (JAG1) in macrophages. Orthotopic xenograft injections in mice were used to confirm results in vivo.

Results

In our system, macrophages were the primary cells showing expression of ErbB3, and a blocking antibody against ErbB3 resulted in a significant decrease in macrophage-induced transendothelial migration of breast cancer cells. Stimulation of macrophages with NRG1 upregulated mRNA and protein expression of JAG1, a ligand of the Notch receptor, and JAG1 production by macrophages was important for transendothelial migration of tumor cells.

Conclusions

This study demonstrates that stimulation of macrophages by tumor cell NRG1 can enhance transendothelial migration and intravasation. We also demonstrate that this effect is due to induction of macrophage JAG1, an important ligand of the Notch signaling pathway.

Abstract 898: Elucidation of the molecular mechanism of MenaINV expression, invadopodium maturation and tumor cell intravasation during breast cancer dissemination by TMEM

Numerous clinical studies have identified Tumor MicroEnvironment of Metastasis (TMEM) and MenaCalc as distinct but functionally interrelated prognostic indicators of distant metastasis in breast cancer patients. TMEM sites are the only sites where tumor cells intravasate in mammary tumors. TMEM score is calculated histologically as the density of tripartite microanatomical structures involving a perivascular macrophage, a Mena-expressing tumor cell and an endothelial cell, all three in direct physical contact. On the other hand, MenaCalc represents the pattern of Mena splice-isoforms present in a tumor sample. MenaINV is the key metastasis-promoting Mena splice-isoform driving tumor cell migration toward blood vessels, intravasation and dissemination. However, the precise molecular mechanisms relating TMEM formation and function and MenaINV expression in these critical steps of the metastatic cascade have not been elucidated.

Here we show that MenaINV promotes invadopodium-based proteolysis, which is required for tumor cell invasion and transendothelial migration, by preventing the localization of the phosphatase PTP1B to invadopodia. Interestingly, PTP1B regulates invadopodium maturation by limiting cortactin phosphorylation at a key residue (Y421) that is necessary for actin polymerization during invadopodium maturation. Additionally, we demonstrate that MenaINV expression, invadopodium activity, and subsequent transendothelial migration are induced in tumor cells via Notch1-mediated signaling induced by contact of tumor cells with macrophages. Knock-down of MenaINV expression in tumor cells leads to a proportional decrease in mature invadopodium formation. Complete knock-out of Mena in mouse mammary tumors (PyMT-MMTV) abolishes TMEM assembly and TMEM functions, including TMEM-dependent vascular permeability, circulating tumor cells and lung metastases.

In summary, our work shows that macrophage contact of TMEM-associated tumor cells during TMEM assembly stimulates Notch1 to drive expression of MenaINV in tumor cells. MenaINV expression then inhibits PTP1B at invadopodia to promote cortactin phosphorylation at invadopodium precursors, driving invadopodium maturation and promoting transendothelial migration. These findings provide, for the first time, an integrative molecular mechanism for two clinically validated prognostic indicators of metastatic risk, TMEM and MenaCalc, and identify new drug targets for limiting the metastatic spread of breast cancer.

Citation Format: Maxwell D. Weidmann, Chinmay R. Surve, Jeanine Pignatelli, Javier J. Bravo-Cordero, George S. Karagiannis, Maja H. Oktay, John S. Condeelis. Elucidation of the molecular mechanism of MenaINV expression, invadopodium maturation and tumor cell intravasation during breast cancer dissemination by TMEM [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 898. doi:10.1158/1538-7445.AM2017-898

Dynamic regulation of neutrophil polarity and migration by the heterotrimeric G protein subunits Gαi-GTP and Gβγ

Activation of the Gi family of heterotrimeric guanine nucleotide-binding proteins (G proteins) releases βγ subunits, which are the major transducers of chemotactic G protein-coupled receptor (GPCR)-dependent cell migration. The small molecule 12155 binds directly to Gβγ and activates Gβγ signaling without activating the Gαi subunit in the Gi heterotrimer. We used 12155 to examine the relative roles of Gαi and Gβγ activation in the migration of neutrophils on surfaces coated with the integrin ligand intercellular adhesion molecule-1 (ICAM-1). We found that 12155 suppressed basal migration by inhibiting the polarization of neutrophils and increasing their adhesion to ICAM-1-coated surfaces. GPCR-independent activation of endogenous Gαi and Gβγ with the mastoparan analog Mas7 resulted in normal migration. Furthermore, 12155-treated cells expressing a constitutively active form of Gαi1 became polarized and migrated. The extent and duration of signaling by the second messenger cyclic adenosine monophosphate (cAMP) were enhanced by 12155. Inhibiting the activity of cAMP-dependent protein kinase (PKA) restored the polarity of 12155-treated cells but did not decrease their adhesion to ICAM-1 and failed to restore migration. Together, these data provide evidence for a direct role of activated Gαi in promoting cell polarization through a cAMP-dependent mechanism and in inhibiting adhesion through a cAMP-independent mechanism.

A chemical biology approach demonstrates G protein βγ subunits are sufficient to mediate directional neutrophil chemotaxis

Our laboratory has identified a number of small molecules that bind to G protein βγ subunits (Gβγ) by competing for peptide binding to the Gβγ "hot spot." M119/Gallein were identified as inhibitors of Gβγ subunit signaling. Here we examine the activity of another molecule identified in this screen, 12155, which we show that in contrast to M119/Gallein had no effect on Gβγ-mediated phospholipase C or phosphoinositide 3-kinase (PI3K) γ activation in vitro. Also in direct contrast to M119/Gallein, 12155 caused receptor-independent Ca(2+) release, and activated other downstream targets of Gβγ including extracellular signal regulated kinase (ERK), protein kinase B (Akt) in HL60 cells differentiated to neutrophils. We show that 12155 releases Gβγ in vitro from Gαi1β1γ2 heterotrimers by causing its dissociation from GαGDP without inducing nucleotide exchange in the Gα subunit. We used this novel probe to examine the hypothesis that Gβγ release is sufficient to direct chemotaxis of neutrophils in the absence of receptor or G protein α subunit activation. 12155 directed chemotaxis of HL60 cells and primary neutrophils in a transwell migration assay with responses similar to those seen for the natural chemotactic peptide n-formyl-Met-Leu-Phe. These data indicate that release of free Gβγ is sufficient to drive directional chemotaxis in a G protein-coupled receptor signaling-independent manner.