Cancer-stromal cell interactions in breast cancer brain metastases induce glycocalyx-mediated resistance to HER2-targeting therapies

Brain metastatic breast cancer is particularly lethal largely due to therapeutic resistance. Almost half of the patients with metastatic HER2-positive breast cancer develop brain metastases, representing a major clinical challenge. We previously described that cancer-associated fibroblasts are an important source of resistance in primary tumors. Here, we report that breast cancer brain metastasis stromal cell interactions in 3D cocultures induce therapeutic resistance to HER2-targeting agents, particularly to the small molecule inhibitor of HER2/EGFR neratinib. We investigated the underlying mechanisms using a synthetic Notch reporter system enabling the sorting of cancer cells that directly interact with stromal cells. We identified mucins and bulky glycoprotein synthesis as top-up-regulated genes and pathways by comparing the gene expression and chromatin profiles of stroma-contact and no-contact cancer cells before and after neratinib treatment. Glycoprotein gene signatures were also enriched in human brain metastases compared to primary tumors. We confirmed increased glycocalyx surrounding cocultures by immunofluorescence and showed that mucinase treatment increased sensitivity to neratinib by enabling a more efficient inhibition of EGFR/HER2 signaling in cancer cells. Overexpression of truncated MUC1 lacking the intracellular domain as a model of increased glycocalyx-induced resistance to neratinib both in cell culture and in experimental brain metastases in immunodeficient mice. Our results highlight the importance of glycoproteins as a resistance mechanism to HER2-targeting therapies in breast cancer brain metastases.

Imaging the extracellular matrix in live tissues and organisms with a glycan-binding fluorophore

All multicellular systems produce and dynamically regulate extracellular matrices (ECM) that play important roles in both biochemical and mechanical signaling. Though the spatial arrangement of these extracellular assemblies is critical to their biological functions, visualization of ECM structure is challenging, in part because the biomolecules that compose the ECM are difficult to fluorescently label individually and collectively. Here, we present a cell-impermeable small molecule fluorophore, termed Rhobo6, that turns on and red shifts upon reversible binding to glycans. Given that most ECM components are densely glycosylated, the dye enables wash-free visualization of ECM, in systems ranging from in vitro substrates to in vivo mouse mammary tumors. Relative to existing techniques, Rhobo6 provides a broad substrate profile, superior tissue penetration, nonperturbative labeling, and negligible photobleaching. This work establishes a straightforward method for imaging the distribution of ECM in live tissues and organisms, lowering barriers for investigation of extracellular biology.

Design of a mucin-selective protease for targeted degradation of cancer-associated mucins

Targeted protein degradation is an emerging strategy for the elimination of classically undruggable proteins. Here, to expand the landscape of targetable substrates, we designed degraders that achieve substrate selectivity via recognition of a discrete peptide and glycan motif and achieve cell-type selectivity via antigen-driven cell-surface binding. We applied this approach to mucins, O-glycosylated proteins that drive cancer progression through biophysical and immunological mechanisms. Engineering of a bacterial mucin-selective protease yielded a variant for fusion to a cancer antigen-binding nanobody. The resulting conjugate selectively degraded mucins on cancer cells, promoted cell death in culture models of mucin-driven growth and survival, and reduced tumor growth in mouse models of breast cancer progression. This work establishes a blueprint for the development of biologics that degrade specific protein glycoforms on target cells.

Mechanosensitive hormone signaling promotes mammary progenitor expansion and breast cancer risk

Tissue stem-progenitor cell frequency has been implicated in tumor risk and progression, but tissue-specific factors linking these associations remain ill-defined. We observed that stiff breast tissue from women with high mammographic density, who exhibit increased lifetime risk for breast cancer, associates with abundant stem-progenitor epithelial cells. Using genetically engineered mouse models of elevated integrin mechanosignaling and collagen density, syngeneic manipulations, and spheroid models, we determined that a stiff matrix and high mechanosignaling increase mammary epithelial stem-progenitor cell frequency and enhance tumor initiation in vivo. Augmented tissue mechanics expand stemness by potentiating extracellular signal-related kinase (ERK) activity to foster progesterone receptor-dependent RANK signaling. Consistently, we detected elevated phosphorylated ERK and progesterone receptors and increased levels of RANK signaling in stiff breast tissue from women with high mammographic density. The findings link fibrosis and mechanosignaling to stem-progenitor cell frequency and breast cancer risk and causally implicate epidermal growth factor receptor-ERK-dependent hormone signaling in this phenotype.

A convolutional neural network STIFMap reveals associations between stromal stiffness and EMT in breast cancer

Intratumor heterogeneity associates with poor patient outcome. Stromal stiffening also accompanies cancer. Whether cancers demonstrate stiffness heterogeneity, and if this is linked to tumor cell heterogeneity remains unclear. We developed a method to measure the stiffness heterogeneity in human breast tumors that quantifies the stromal stiffness each cell experiences and permits visual registration with biomarkers of tumor progression. We present Spatially Transformed Inferential Force Map (STIFMap) which exploits computer vision to precisely automate atomic force microscopy (AFM) indentation combined with a trained convolutional neural network to predict stromal elasticity with micron-resolution using collagen morphological features and ground truth AFM data. We registered high-elasticity regions within human breast tumors colocalizing with markers of mechanical activation and an epithelial-to-mesenchymal transition (EMT). The findings highlight the utility of STIFMap to assess mechanical heterogeneity of human tumors across length scales from single cells to whole tissues and implicates stromal stiffness in tumor cell heterogeneity.

Extracellular Matrix Glycation and Crosslinking in Mammary Tumor Progression

Breast cancer progression is accompanied by profound extracellular matrix (ECM) remodeling. A greater abundance of aligned fibrillar collagen is characteristic of invasive and aggressive breast cancers and has been associated with elevated activity of collagen crosslinking enzymes, such as lysyl oxidase (LOX) and lysyl hydroxylases (LH) and the formation of more mature collagen matrix crosslinks. Aligned collagen fibers can facilitate metastatic dissemination of tumor cells, and LOX inhibitors have been used to inhibit tumor progression and metastasis in experimental models. Thus, a better understanding of how matrix crosslinking alters tumor cell phenotypes, and behaviors would improve our ability to effectively treat aggressive metastatic breast cancer. Herein described is an experimental approach to glycate and crosslink a collagen-I/basement membrane extract ECM to study the impact of ECM crosslinking on mammary tumor progression in vivo. Moreover, glycation of collagen by sugars to form advanced glycation end products naturally occurs during aging, extending the potential relevance of this approach to research on mechanisms of aging involved in disease progression.

ECM dimensionality tunes actin tension to modulate endoplasmic reticulum function and spheroid phenotypes of mammary epithelial cells

Patient-derived organoids and cellular spheroids recapitulate tissue physiology with remarkable fidelity. We investigated how engagement with a reconstituted basement membrane in three dimensions (3D) supports the polarized, stress resilient tissue phenotype of mammary epithelial spheroids. Cells interacting with reconstituted basement membrane in 3D had reduced levels of total and actin-associated filamin and decreased cortical actin tension that increased plasma membrane protrusions to promote negative plasma membrane curvature and plasma membrane protein associations linked to protein secretion. By contrast, cells engaging a reconstituted basement membrane in 2D had high cortical actin tension that forced filamin unfolding and endoplasmic reticulum (ER) associations. Enhanced filamin-ER interactions increased levels of PKR-like ER kinase effectors and ER-plasma membrane contact sites that compromised calcium homeostasis and diminished cell viability. Consequently, cells with decreased cortical actin tension had reduced ER stress and survived better. Consistently, cortical actin tension in cellular spheroids regulated polarized basement membrane membrane deposition and sensitivity to exogenous stress. The findings implicate cortical actin tension-mediated filamin unfolding in ER function and underscore the importance of tissue mechanics in organoid homeostasis.

Mechanosensitive Steroid Hormone Signaling and Cell Fate

Mechanical forces collaborate across length scales to coordinate cell fate during development and the dynamic homeostasis of adult tissues. Similarly, steroid hormones interact with their nuclear and nonnuclear receptors to regulate diverse physiological processes necessary for the appropriate development and function of complex multicellular tissues. Aberrant steroid hormone action is associated with tumors originating in hormone-sensitive tissues and its disruption forms the basis of several therapeutic interventions. Prolonged perturbations to mechanical forces may further foster tumor initiation and the evolution of aggressive metastatic disease. Recent evidence suggests that steroid hormone and mechanical signaling intersect to direct cell fate during development and tumor progression. Potential mechanosensitive steroid hormone signaling pathways along with their molecular effectors will be discussed in this context.

Abstract LB021: Mechanosensitive hormone signaling promotes mammary progenitor expansion and breast cancer progression

Tissue stem-progenitor cell frequency has been implicated in tumor risk and progression. Tissue-specific factors linking stem-progenitor cell frequency to cancer risk and progression remain ill defined. Using a genetically engineered mouse model that promotes integrin mechanosignaling with syngeneic manipulations, spheroid models, and patient-derived xenografts we determined that a stiff extracellular matrix and high integrin mechanosignaling increase stem-progenitor cell frequency to enhance breast tumor risk and progression. Studies revealed that high integrin-mechanosignaling expands breast epithelial stem-progenitor cell number by potentiating progesterone receptor-dependent RANK signaling. Consistently, we observed that the stiff breast tissue from women with high mammographic density, who exhibit an increased lifetime risk for breast cancer, also have elevated RANK signaling and a high frequency of stem-progenitor epithelial cells. The findings link tissue fibrosis and integrin mechanosignaling to stem-progenitor cell frequency and causally implicate hormone signaling in this phenotype. Accordingly, inhibiting RANK signaling could temper the tumor promoting impact of fibrosis on breast cancer and reduce the elevated breast cancer risk exhibited by women with high mammographic density.

Citation Format: Jason J. Northey, Yoshihiro Yui, Mary-Kate Hayward, Connor Stashko, FuiBoon Kai, Janna Mouw, Dhruv Thakar, Jonathon Lakins, Alastair Ironside, Susan Samson, Rita Mukhtar, E. Shelley Hwang, Valerie Weaver. Mechanosensitive hormone signaling promotes mammary progenitor expansion and breast cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB021.

Screening of organoids derived from patients with breast cancer implicates the repressor NCOR2 in cytotoxic stress response and antitumor immunity

Resistance to antitumor treatment contributes to patient mortality. Functional proteomic screening of organoids derived from chemotherapy-treated patients with breast cancer identified nuclear receptor corepressor 2 (NCOR2) histone deacetylase as an inhibitor of cytotoxic stress response and antitumor immunity. High NCOR2 in the tumors of patients with breast cancer predicted chemotherapy refractoriness, tumor recurrence and poor prognosis. Molecular studies revealed that NCOR2 inhibits antitumor treatment by regulating histone deacetylase 3 (HDAC3) to repress interferon regulatory factor 1 (IRF-1)-dependent gene expression and interferon (IFN) signaling. Reducing NCOR2 or impeding its epigenetic activity by modifying its interaction with HDAC3 enhanced chemotherapy responsiveness and restored antitumor immunity. An adeno-associated viral NCOR2-HDAC3 competitor potentiated chemotherapy and immune checkpoint therapy in culture and in vivo by permitting transcription of IRF-1-regulated proapoptosis and inflammatory genes to increase IFN-γ signaling. The findings illustrate the utility of patient-derived organoids for drug discovery and suggest that targeting stress and inflammatory-repressor complexes such as NCOR2-HDAC3 could overcome treatment resistance and improve the outcome of patients with cancer.

NCI's publication affiliation conundrum: Reframing innovation to incentivize an equitable path for advocate representation

Advocacy engagement has been at the forefront of National Cancer Institute (NCI) efforts to advance scientific discoveries and transform medical interventions. Nonetheless, the journey for advocates has been uneven. Case in Point: NCI publication affiliation rules of engagement pose unique equity challenges while raising questions about structural representation in biomedical research. Abiding by the core rationale that publication affiliation should be tailored to employment status, the NCI has systematically denied research advocate volunteers the opportunity to specifically list NCI as an institutional affiliation on academic publications. Unpacking advocate NCI publication affiliation restrictions and its links with advocacy heritage preservation and convergent science goals poses unique diversity, equity, and inclusion challenges and opportunities. Improving the quality of structural representation in biomedical research requires new theories of action and flexible planning to advance, promote and build capacity for strategic advocacy inclusion and equity within publication affiliation initiatives. Here we highlight several opportunities for how leadership might formulate a radically different vision for NCI's approach. This perspective interrogates the best way forward for ensuring that biomedical employee and volunteer advocate workforce publication affiliation intersections are characterized by increased creativity and representation parity. Imbuing the scientist and clinical researcher archetype with social dimensions, we join NCI critical thinkers in urging employees, funded academics, and volunteer citizen scientists to collectively assume the role as paladins of science and integrity who view the triumphs of making a difference in science alongside the social responsibility of promoting transdisciplinary professionalism and the democratization of science.

Mechanical Pressure Driving Proteoglycan Expression in Mammographic Density: a Self-perpetuating Cycle?

Regions of high mammographic density (MD) in the breast are characterised by a proteoglycan (PG)-rich fibrous stroma, where PGs mediate aligned collagen fibrils to control tissue stiffness and hence the response to mechanical forces. Literature is accumulating to support the notion that mechanical stiffness may drive PG synthesis in the breast contributing to MD. We review emerging patterns in MD and other biological settings, of a positive feedback cycle of force promoting PG synthesis, such as in articular cartilage, due to increased pressure on weight bearing joints. Furthermore, we present evidence to suggest a pro-tumorigenic effect of increased mechanical force on epithelial cells in contexts where PG-mediated, aligned collagen fibrous tissue abounds, with implications for breast cancer development attributable to high MD. Finally, we summarise means through which this positive feedback mechanism of PG synthesis may be intercepted to reduce mechanical force within tissues and thus reduce disease burden.

RASSF1A Suppression as a Potential Regulator of Mechano-Pathobiology Associated with Mammographic Density in BRCA Mutation Carriers

High mammographic density (MD) increases breast cancer (BC) risk and creates a stiff tissue environment. BC risk is also increased in BRCA1/2 gene mutation carriers, which may be in part due to genetic disruption of the tumour suppressor gene Ras association domain family member 1 (RASSF1A), a gene that is also directly regulated by tissue stiffness. High MD combined with BRCA1/2 mutations further increase breast cancer risk, yet BRCA1/2 mutations alone or in combination do not increase MD. The molecular basis for this additive effect therefore remains unclear. We studied the interplay between MD, stiffness, and BRCA1/2 mutation status in human mammary tissue obtained after prophylactic mastectomy from women at risk of developing BC. Our results demonstrate that RASSF1A expression increased in MCF10DCIS.com cell cultures with matrix stiffness up until ranges corresponding with BiRADs 4 stiffnesses (~16 kPa), but decreased in higher stiffnesses approaching malignancy levels (>50 kPa). Similarly, higher RASSF1A protein was seen in these cells when co-cultivated with high MD tissue in murine biochambers. Conversely, local stiffness, as measured by collagen I versus III abundance, repressed RASSF1A protein expression in BRCA1, but not BRCA2 gene mutated tissues; regional density as measured radiographically repressed RASSF1A in both BRCA1/2 mutated tissues. The combinatory effect of high MD and BRCA mutations on breast cancer risk may be due to RASSF1A gene repression in regions of increased tissue stiffness.

Matrix compliance permits NF-κB activation to drive therapy resistance in breast cancer

Triple-negative breast cancers (TNBCs) are associated with poor survival mediated by treatment resistance. TNBCs are fibrotic, yet little is known regarding how the extracellular matrix (ECM) evolves following therapy and whether it impacts treatment response. Analysis revealed that while primary untreated TNBCs are surrounded by a rigid stromal microenvironment, chemotherapy-resistant residual tumors inhabit a softer niche. TNBC organoid cultures and xenograft studies showed that organoids interacting with soft ECM exhibit striking resistance to chemotherapy, ionizing radiation, and death receptor ligand TRAIL. A stiff ECM enhanced proapoptotic JNK activity to sensitize cells to treatment, whereas a soft ECM promoted treatment resistance by elevating NF-κB activity and compromising JNK activity. Treatment-resistant residual TNBCs residing within soft stroma had elevated activated NF-κB levels, and disengaging NF-κB activity sensitized tumors in a soft matrix to therapy. Thus, the biophysical properties of the ECM modify treatment response, and agents that modulate stiffness-dependent NF-κB or JNK activity could enhance therapeutic efficacy in patients with TNBC.

Stiff stroma increases breast cancer risk by inducing the oncogene ZNF217

Women with dense breasts have an increased lifetime risk of malignancy that has been attributed to a higher epithelial density. Quantitative proteomics, collagen analysis, and mechanical measurements in normal tissue revealed that stroma in the high-density breast contains more oriented, fibrillar collagen that is stiffer and correlates with higher epithelial cell density. microRNA (miR) profiling of breast tissue identified miR-203 as a matrix stiffness-repressed transcript that is downregulated by collagen density and reduced in the breast epithelium of women with high mammographic density. Culture studies demonstrated that ZNF217 mediates a matrix stiffness- and collagen density-induced increase in Akt activity and mammary epithelial cell proliferation. Manipulation of the epithelium in a mouse model of mammographic density supported a causal relationship between stromal stiffness, reduced miR-203, higher levels of the murine homolog Zfp217, and increased Akt activity and mammary epithelial proliferation. ZNF217 was also increased in the normal breast epithelium of women with high mammographic density, correlated positively with epithelial proliferation and density, and inversely with miR-203. The findings identify ZNF217 as a potential target toward which preexisting therapies, such as the Akt inhibitor triciribine, could be used as a chemopreventive agent to reduce cancer risk in women with high mammographic density.

Abstract P5-07-13: Conceptual model of transdisciplinary science - Advocacy collaboration for the physical sciences and oncology: A case study focusing on breast density, biomarker discovery, and emerging therapeutics

BACKGROUND: What happens when you mix the foundations of tissue mechanics with advocacy? In a shared quest for exciting scientific frontiers, Bay Area physical scientists, clinical researchers, and advocates work in dynamic symbiotic relationships to integrate concepts drawn from their respective fields. Focusing on the mechanobiology of tumor progression in breast cancer, researchers and advocates are co-creating system change interventions for revamping convergent research processes.

METHODS:As vital catalysts of transdisciplinary innovation, advocates affiliated with the National Cancer Institute (NCI) Physical Sciences and Oncology Network (PS-ON) applied core principles that synergize with the evolving disciplines of Implementation Science (IS) and the Science of Team Science (STS). Diverse methodologies to describe the intersections of physical sciences, breast density, biomarker discovery, emerging therapeutics and advocacy are presented. Additionally, we introduce a theoretical framework and conceptual puzzle illustrating multimethod science advocacy engagement strategies, a typology of contextual factors influencing collaboration, as well as the antecedents, processes, strategic priorities, and overall potential impacts of collaborative transdisciplinary science advocacy exchanges.

RESULTS:Through proactive participation in four areas: 1) research and programmatic support, 2) education and outreach, 3) policy and strategy, and 4) representation and advisory, advocates, representing patient/consumer perspectives, worked toward a common set of goals with researchers and clinicians in determining how tumor microenvironments regulate cancer initiation and behavior through interactions among cell types (e.g., initiated cells, activated stromal cells, and components of the extracellular matrix). Applying NCI Office of Advocacy Relations (OAR) and NCI PS-ON Advocacy Working Group goals for strategic innovation, collaborative execution, and ethical codes of conduct, researchers and advocates codeveloped guiding conceptual frameworks based on organizational foundations, systems readiness, leadership commitment to change, and transdisciplinary levers to promote shared governance, bidirectional collaboration, advocacy inclusion, and the prioritization of research addressing questions of importance to patients.

DISCUSSION: Embedding advocate patient/consumer evidentiary and experiential insights/perspectives regarding mechanics-directed research priorities and clinical interventions in the early phase of convergent research efforts contributes to our understanding of the important role of the physical organization in cell-to-cell contacts, tissue architecture, tumor microenviroments, and mechanical properties in response to therapy. Notably, catalyzing and leveraging advocate engagement across the research continuum provides novel opportunities for advancing institutional changes, spurring unique training/mentoring exchanges, and fostering innovative research and translational opportunities.

Citation Format: Samson S, Northey JJ, Baas C, Weaver VM. Conceptual model of transdisciplinary science - Advocacy collaboration for the physical sciences and oncology: A case study focusing on breast density, biomarker discovery, and emerging therapeutics [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-07-13.

Abstract 4767: Regional strategies for expanding the evolving continuum of Physical Sciences-Oncology Network (PS-ON) research advocacy experiences

Background: The National Cancer Institute (NCI) Physical Sciences-Oncology Network (PS-ON), initiated in 2009, is an interdisciplinary hub currently consisting of eighteen regions across the nation to support the emergence of new scientific frontiers, principles, and opportunities within physical sciences and oncology. Based on the belief that the increasing momentum for cross-disciplinary connectivity between biologists, physicists, mathematicians, chemists, biomedical engineers, and oncologists would be enriched and enhanced by vigorous and diverse public and/or advocacy support, the PS-ON leadership, at program inception, incorporated the advocate voice in setting a national research agenda.

Methods: While the regional advocacy programs operate independently and utilize multilevel, multimethod strategies to expand the evolving umbrella of research advocacy experiences, they are connected through an administrative structure that communicates NCI program priorities to enhance capacity in the approaches utilized across the eighteen PS-ON regions.

Impact: As integral team members, advocates bring real-time diverse patient experiences, diverse professional expertise, and concerns into pioneering, innovative research practices. PS-ON regional engagement/communication strategies include: 1) integrating advocate perspectives to shape basic science research agendas, 2) developing conceptual models/roadmaps to holistic engagement focusing on organizational foundations and best practice strategies, 3) applying guiding frameworks and toolkits for setting the terms of principled engagement/shared governance/bidirectional collaboration, 4) implementing education, outreach, and professional development programs for early-stage investigators, students, and patient communities, and 5) translating, communicating and disseminating laboratory innovations into society.

Discussion: To better understand and fully address the complexities of intersecting physical sciences and oncology advocacy engagement, we explore the unique culture and guidelines set by selected participating institutions. Meeting key challenges regarding programmatic scope and policy impact requires a shift to a new, rapidly evolving paradigm. In parallel to incentives and policy measures created through federal and professional organizations, we offer recommendations for strengthening regional programs and encouraging equitable partnerships for advocates at earlier stages of research to help propel convergent science innovation.

Citation Format: Susan Samson, Nastaran Zahir, Sheila M. Judge, Stuart Cornew, Bob Riter, Jeri Francoeur, Anne Meyn, Laurie Cynkin, Jason J. Northey, Valerie M. Weaver, Carole Baas. Regional strategies for expanding the evolving continuum of Physical Sciences-Oncology Network (PS-ON) research advocacy experiences [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4767.

New Horizons in Advocacy Engaged Physical Sciences and Oncology Research

To address cancer as a multifaceted adaptive system, the increasing momentum for cross-disciplinary connectivity between cancer biologists, physical scientists, mathematicians, chemists, biomedical engineers, computer scientists, clinicians, and advocates is fueling the emergence of new scientific frontiers, principles, and opportunities within physical sciences and oncology. In parallel to highlighting the advances, challenges, and acceptance of advocates as credible contributors, we offer recommendations for addressing real world hurdles in advancing equitable partnerships among advocacy stakeholders.

PGC-1α Promotes Breast Cancer Metastasis and Confers Bioenergetic Flexibility against Metabolic Drugs

Metabolic adaptations play a key role in fueling tumor growth. However, less is known regarding the metabolic changes that promote cancer progression to metastatic disease. Herein, we reveal that breast cancer cells that preferentially metastasize to the lung or bone display relatively high expression of PGC-1α compared with those that metastasize to the liver. PGC-1α promotes breast cancer cell migration and invasion in vitro and augments lung metastasis in vivo. Pro-metastatic capabilities of PGC-1α are linked to enhanced global bioenergetic capacity, facilitating the ability to cope with bioenergetic disruptors like biguanides. Indeed, biguanides fail to mitigate the PGC-1α-dependent lung metastatic phenotype and PGC-1α confers resistance to stepwise increases in metformin concentration. Overall, our results reveal that PGC-1α stimulates bioenergetic potential, which promotes breast cancer metastasis and facilitates adaptation to metabolic drugs.

Tissue Force Programs Cell Fate and Tumor Aggression

Biomechanical and biochemical cues within a tissue collaborate across length scales to direct cell fate during development and are critical for the maintenance of tissue homeostasis. Loss of tensional homeostasis in a tissue not only accompanies malignancy but may also contribute to oncogenic transformation. High mechanical stress in solid tumors can impede drug delivery and may additionally drive tumor progression and promote metastasis. Mechanistically, biomechanical forces can drive tumor aggression by inducing a mesenchymal-like switch in transformed cells so that they attain tumor-initiating or stem-like cell properties. Given that cancer stem cells have been linked to metastasis and treatment resistance, this raises the intriguing possibility that the elevated tissue mechanics in tumors could promote their aggression by programming their phenotype toward that exhibited by a stem-like cell.Significance: Recent findings argue that mechanical stress and elevated mechanosignaling foster malignant transformation and metastasis. Prolonged corruption of tissue tension may drive tumor aggression by altering cell fate specification. Thus, strategies that could reduce tumor mechanics might comprise effective approaches to prevent the emergence of treatment-resilient metastatic cancers. Cancer Discov; 7(11); 1224-37. ©2017 AACR.

Tissue Force Programs Cell Fate and Tumor Aggression

Biomechanical and biochemical cues within a tissue collaborate across length scales to direct cell fate during development and are critical for the maintenance of tissue homeostasis. Loss of tensional homeostasis in a tissue not only accompanies malignancy but may also contribute to oncogenic transformation. High mechanical stress in solid tumors can impede drug delivery and may additionally drive tumor progression and promote metastasis. Mechanistically, biomechanical forces can drive tumor aggression by inducing a mesenchymal-like switch in transformed cells so that they attain tumor-initiating or stem-like cell properties. Given that cancer stem cells have been linked to metastasis and treatment resistance, this raises the intriguing possibility that the elevated tissue mechanics in tumors could promote their aggression by programming their phenotype toward that exhibited by a stem-like cell.Significance: Recent findings argue that mechanical stress and elevated mechanosignaling foster malignant transformation and metastasis. Prolonged corruption of tissue tension may drive tumor aggression by altering cell fate specification. Thus, strategies that could reduce tumor mechanics might comprise effective approaches to prevent the emergence of treatment-resilient metastatic cancers. Cancer Discov; 7(11); 1224-37. ©2017 AACR.

The Cdc42/Rac1 regulator CdGAP is a novel E-cadherin transcriptional co-repressor with Zeb2 in breast cancer

The loss of E-cadherin causes dysfunction of the cell-cell junction machinery, which is an initial step in epithelial-to-mesenchymal transition (EMT), facilitating cancer cell invasion and the formation of metastases. A set of transcriptional repressors of E-cadherin (CDH1) gene expression, including Snail1, Snail2 and Zeb2 mediate E-cadherin downregulation in breast cancer. However, the molecular mechanisms underlying the control of E-cadherin expression in breast cancer progression remain largely unknown. Here, by using global gene expression approaches, we uncover a novel function for Cdc42 GTPase-activating protein (CdGAP) in the regulation of expression of genes involved in EMT. We found that CdGAP used its proline-rich domain to form a functional complex with Zeb2 to mediate the repression of E-cadherin expression in ErbB2-transformed breast cancer cells. Conversely, knockdown of CdGAP expression led to a decrease of the transcriptional repressors Snail1 and Zeb2, and this correlated with an increase in E-cadherin levels, restoration of cell-cell junctions, and epithelial-like morphological changes. In vivo, loss of CdGAP in ErbB2-transformed breast cancer cells impaired tumor growth and suppressed metastasis to lungs. Finally, CdGAP was highly expressed in basal-type breast cancer cells, and its strong expression correlated with poor prognosis in breast cancer patients. Together, these data support a previously unknown nuclear function for CdGAP where it cooperates in a GAP-independent manner with transcriptional repressors to function as a critical modulator of breast cancer through repression of E-cadherin transcription. Targeting Zeb2-CdGAP interactions may represent novel therapeutic opportunities for breast cancer treatment.

Abstract 911: BRM loss promotes tumor progression through extracellular matrix remodeling and elevated mammary epithelial stem/progenitor activity

BRM expression is progressively lost in breast cancer and low levels are predictive of poor patient prognosis. We have previously shown that oncogenic downregulation of BRM promotes malignancy of mammary epithelial cells (MECs) through the CEBP/â-mediated induction of á5-integrin. BRM and BRG1 are necessary but mutually exclusive subunits of the SWI/SNF ATP-dependent chromatin remodeling complex that disrupts DNA-histone interactions to alter accessibility of specific genomic regions. To explore the physiological role of BRM in the normal mammary gland and in breast cancer, we studied BRM germline knockout mice (BRM KO). We first backcrossed BRM KO mice onto a clean genetic background and observed a 40% increase in animal size compared to wild type littermates. Histological examination of developing BRM KO mammary glands revealed enhanced ductal branching and a 60% increase in numbers of terminal end buds. Concordantly, immunohistochemistry for phospho-histone H3 exhibited significantly elevated proliferation of BRM KO MECs. Picrosirius red staining of mammary glands further demonstrated an accumulation of collagen around epithelial ducts in BRM KO mice that correlated with an upregulation of genes encoding the extracellular matrix (ECM) proteins Collagen-I and Fibronectin as well as the collagen remodeling enzymes Loxl1 and Loxl2 as assessed by quantitative PCR (qPCR). Subsequent flow cytometry analysis of mammary glands to sort luminal versus basal MEC populations demonstrated a preference for expansion of the basal lineage in BRM KO mice compared to controls. Basal MECs are in direct contact with the ECM and mammary stem cells are proposed to exist within this population. To investigate the possibility that BRM KO augments mammary stemness, we performed colony formation and limiting dilution transplantation assays, which served to confirm that the expanded basal population was indeed associated with elevated MEC stem/progenitor activity and also to verify the MEC dependence of these effects. To gain more mechanistic insight, we sorted luminal/basal MEC populations for qPCR analysis and found that MECs from BRM KO mice produce more abundant transcripts of genes associated with stemness. Our preliminary data now suggests a compensatory upregulation of BRG1 in BRM KO MECs and elevated expression of several known YAP/TAZ target genes involved in the control of cell proliferation. Finally, to describe a role for BRM in tumor progression, we examined the outcome of BRM KO in MMTV-NEU mice and observed more rapid tumor growth with a trend to higher tumor incidence and metastasis in mice lacking BRM. Taken together, our data indicate that SWI/SNF chromatin remodeling regulates YAP/TAZ control over MEC growth and a loss of BRM expression leads to BRG1-directed ECM remodeling, MEC proliferation and elevated mammary stemness, resulting in heightened mammary tumor aggression.

Citation Format: Jason J. Northey, Laura Damiano, Valerie M. Weaver. BRM loss promotes tumor progression through extracellular matrix remodeling and elevated mammary epithelial stem/progenitor activity. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 911.

Abstract PR04: Tissue tension promotes mammary stemness and breast cancer aggression

Breast cancers frequently develop treatment resistance that leads to recurrence, dissemination and patient mortality. Among the mechanisms that foster treatment resistance is the ability of tumor cells to undergo an epithelial-to-mesenchymal transition (EMT) and exhibit stem-like behavior. Accumulating evidence now supports the concept that the mechanical properties of the extracellular matrix microenvironment can critically influence developmental cell fate and modify several features of tumor progression. Data from our laboratory using preclinical models and clinical samples suggest that tissue tension and elevated mechanosignaling increase prior to and accompany malignant transformation. Therefore, we hypothesize that enhanced tissue mechanical tension and high mechanosignaling foster mammary stemness, EMT and breast cancer aggression. We tested this prediction by generating transgenic mice conditionally expressing a β1-Integrin clustering mutant (V737N) in the mammary epithelium. V737N expression stimulated integrin-mediated mechanosignaling in mammary epithelial cells (MECs), as determined by elevated phosphorylation of FAK and p130Cas, and this heightened mechanosignaling promoted precocious epithelial ductal branching, end bud formation and increased MEC proliferation in the mammary gland. These mammary phenotypes were accompanied by an increase in the ratio of basal/myoepithelial to luminal MECs in V737N mammary glands. Isolated V737N-expressing MECs possessed higher levels of genes associated with EMT and stemness, and Matrigel colony formation and transplantation assays revealed a functional increase in progenitor/stem cell frequency in the V737N-expressing basal/myoepithelial MECs compared to their corresponding controls. To examine the effect of tissue tension on breast cancer progression, we combined the V737N-β1-Integrin together with a mouse model of HER2-positive breast cancer (MMTV-NEU). While V737N expression had no observable effect on primary tumor outgrowth, overall tumor incidence and lung metastasis were significantly augmented. Further histological examination of tumors and gene expression analysis uncovered a phenotypic shift, such that V737N tumors displayed expression patterns resembling an EMT-like basal tumor when compared to control tumors. Thus, tissue tension by way of enhanced mechanosignaling promotes mammary stemness, higher mammary tumor incidence and a more basal-like aggressive tumor character. Potential V737N mechanistic actions currently under investigation involve altered orientation of cell divisions resulting from disrupted MEC polarity, as well as a heightened sensitivity to hormone-induced expansion of stem/progenitor cells. (Supp by: USMRAA Department of Defense-BCRP BC122990 and NIH NCI R01CA192914 to VW and AACR 15-40-01-NORT to JN).

Citation Format: Jason J. Northey, Yoshihiro Yui, Janna K. Mouw, Johnathan N. Lakins, Valerie M. Weaver. Tissue tension promotes mammary stemness and breast cancer aggression. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr PR04.

Fighting the force: Potential of homeobox genes for tumor microenvironment regulation

Tumor cells exist in a constantly evolving stromal microenvironment composed of vasculature, immune cells and cancer-associated fibroblasts, all residing within a dynamic extracellular matrix. In this review, we examine the biochemical and biophysical interactions between these various stromal cells and their matrix microenvironment. While the stroma can alter tumor progression via multiple mechanisms, we emphasize the role of homeobox genes in detecting and modulating the mechanical changes in the microenvironment during tumor progression.

A complex containing LPP and α-actinin mediates TGFβ-induced migration and invasion of ErbB2-expressing breast cancer cells

Transforming growth factor β (TGFβ) is a potent modifier of the malignant phenotype in ErbB2-expressing breast cancers. We demonstrate that epithelial-derived breast cancer cells, which undergo a TGFβ-induced epithelial-to-mesenchymal transition (EMT), engage signaling molecules that normally facilitate cellular migration and invasion of mesenchymal cells. We identify lipoma preferred partner (LPP) as an indispensable regulator of TGFβ-induced migration and invasion of ErbB2-expressing breast cancer cells. We show that LPP re-localizes to focal adhesion complexes upon TGFβ stimulation and is a critical determinant in TGFβ-mediated focal adhesion turnover. Finally, we have determined that the interaction between LPP and α-actinin, an actin cross-linking protein, is necessary for TGFβ-induced migration and invasion of ErbB2-expressing breast cancer cells. Thus, our data reveal that LPP, which is normally operative in cells of mesenchymal origin, can be co-opted by breast cancer cells during an EMT to promote their migration and invasion.

Abstract A65: ShcA is required for the TGFβ-induced repression of Chordin-like-1 in ErbB2-expressing breast cancer cells

Clinical data and transgenic mouse models have provided clear evidence of a critical role for the adaptor protein ShcA in mammary tumor formation and metastasis downstream of several oncogenes. Indeed, we have demonstrated that stable silencing of ShcA expression in ErbB2-expressing breast cancer cells impairs tumor outgrowth and metastasis in vivo. In addition, we have identified a requirement for an intact PTB domain and the three tyrosine residues in ShcA for mediating TGFβ-induced migration and invasion of ErbB2-expressing breast cancer cells. Together, these observations position the ShcA adaptor as an important signaling node that facilitates cooperation between the ErbB2 and TGFβ signaling pathways in breast cancer progression. To understand how ShcA signaling contributes to TGFβ-induced gene expression changes, we generated a doxycycline-inducible system to deplete ShcA levels from ErbB2-expressing breast cancer cells. The inducible silencing of ShcA in pre-established ErbB2-positive tumors resulted in impaired tumor cell proliferation and survival in vivo. Gene expressing profiling was then performed on cells with an inducible loss of ShcA expression to identify ShcA-dependent transcriptional responses downstream of active TGFβ and ErbB2 signaling in breast cancer cells. ShcA was found to mediate the suppression of Chordin-like 1, a BMP antagonist. Conditioned media taken from TGFβ-stimulated ErbB2-expressing cells treated with doxycycline to achieve reduced ShcA levels was confirmed to contain increased levels of Chordin-like-1 compared with unstimulated controls. This same conditioned media was efficient at inhibiting the BMP-stimulated phosphorylation of Smad proteins 1/5/8 in ErbB2-expressing cells. Furthermore, this TGFβ upregulation of Chordin-like 1 production resulting from ShcA loss correlated with decreased activation of Smad1/5/8 in ShcA-deficient tumor cells in vivo, and may represent a transcriptional mechanism through which ShcA coordinates ErbB2 and TGFβ initiated tumor growth and invasion.

Citation Format: Jason J. Northey, Zhifeng Dong, Chanele Cyr-Depauw, Sean Cory, Peter M. Siegel. ShcA is required for the TGFβ-induced repression of Chordin-like-1 in ErbB2-expressing breast cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr A65.

Distinct phosphotyrosine-dependent functions of the ShcA adaptor protein are required for transforming growth factor β (TGFβ)-induced breast cancer cell migration, invasion, and metastasis

The ErbB2 and TGFβ signaling pathways cooperate to promote the migratory, invasive, and metastatic behavior of breast cancer cells. We previously demonstrated that ShcA is necessary for these synergistic interactions. Through a structure/function approach, we now show that the phosphotyrosine-binding, but not the Src homology 2, domain of ShcA is required for TGFβ-induced migration and invasion of ErbB2-expressing breast cancer cells. We further demonstrate that the tyrosine phosphorylation sites within ShcA (Tyr(239)/Tyr(240) and Tyr(313)) transduce distinct and non-redundant signals that promote these TGFβ-mediated effects. We demonstrate that Grb2 is required specifically downstream of Tyr(313), whereas the Tyr(239)/Tyr(240) phosphorylation sites require the Crk adaptor proteins to augment TGFβ-induced migration and invasion. Furthermore, ShcA Tyr(313) phosphorylation enhances tumor cell survival, and ShcA Tyr(239)/Tyr(240) signaling promotes endothelial cell recruitment into ErbB2-expressing breast tumors in vivo, whereas all three ShcA tyrosine residues are required for efficient breast cancer metastasis to the lungs. Our data uncover a novel ShcA-dependent signaling axis downstream of TGFβ and ErbB2 that requires both the Grb2 and Crk adaptor proteins to increase the migratory and invasive properties of breast cancer cells. In addition, signaling downstream of specific ShcA tyrosine residues facilitates the survival, vascularization, and metastatic spread of breast tumors.

Abstract P1-05-22: Breast cancer cells that undergo an Epithelial-to-Mesenchymal transition co-opt LPP, a regulator of mesenchymal cell migration and invasion

Transforming Growth Factor β (TGFβ) promotes breast cancer cell metastasis to multiple sites, including the bone and lungs. TGFβ is a strong inducer of Epithelial-to-Mesenchymal transitions (EMT) and breast cancers that exhibit features of an EMT acquire stem cell-like characteristics, are highly aggressive, are resistant to therapy and are refractory to tumor suppressive processes. While TGFβ itself is non-oncogenic, it is a potent modifier of the malignant phenotype in breast cancer and is capable of enhancing the migration, invasion and metastasis of ErbB2 expressing breast cancer cells.

We have identified Lipoma Preferred Partner (LPP) as an indispensable regulator of TGFβ-induced migration and invasion of ErbB2 expressing breast cancer cells. LPP is ubiquitously expressed in smooth muscle cells where it mediates cell adhesion, migration and the formation of lamellipodial extensions. We hypothesize that breast cancer cells capable of undergoing an EMT can utilize novel mediators that are engaged in promoting the migration and invasion of mesenchymal cells. We propose that LPP is one such example, which promotes the migration and invasion of ErbB2 expressing breast cancer cells that have undergone a TGFβ-induced EMT.

We demonstrate that ErbB2 expressing breast cancer cells display significant increases in cell migration and invasion upon TGFβ stimulation, and such responses are dependent on LPP expression. We show that LPP re-localizes to focal adhesion complexes following TGFβ-induced EMT and it is a critical determinant in focal adhesion turnover. Furthermore, we determined that LPP targeting to focal adhesions through its LIM1 domain requires the cooperation of ErbB2 and TGFβ signaling pathways. Finally, we demonstrate that LPP promotes TGFβ-induced migration and invasion of ErbB2 expressing breast cancer cells through recruitment of α-Actinin, an actin cross-linking protein.

Overall, we have identified LPP as a novel mediator that integrates TGFβ and ErbB2 signaling to promote the migration and invasion of breast cancer cells that undergo an EMT. Our data reveal that breast cancer cells, which can transition from an epithelial to mesenchymal phenotype, can engage a regulator of mesenchymal cell migration and invasion.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-05-22.

The Ste20-like kinase SLK is required for ErbB2-driven breast cancer cell motility

The Ste20-like kinase, SLK, is involved in the control of cell motility through its effects on actin reorganization and focal adhesion turnover. Here we investigated the role of SLK in chemotaxis downstream of the tyrosine kinase receptor, HER2/ErbB2/Neu, which is frequently overexpressed in human breast cancers. Our results show that SLK is required for the efficient cell migration of human and mouse mammary epithelial cell lines in the presence of the Neu activator, heregulin, as a chemoattractant. SLK activity is stimulated by heregulin treatment or by overexpression of activated Neu. Phosphorylation of tyrosine 1201 or tyrosines 1226/7 on Neu is a key event for SLK activation and cell migration, and cancer cell invasion mediated by these tyrosines is inhibited by kinase-inactive SLK. Signaling pathway inhibitors show that Neu-mediated SLK activation is dependent on MEK, PI3K, PLCgamma and Shc signaling. Furthermore, heregulin-stimulated SLK activity requires signals from the focal adhesion proteins, FAK and src. Finally, phospho-FAK analysis shows that SLK is required for Neu-dependent focal adhesion turnover. Together, these studies define an interaction between Neu and SLK signaling in the regulation of cancer cell motility.