Visualizing dynamic microvillar search and stabilization during ligand detection by T cells

During immune surveillance, T cells survey the surface of antigen-presenting cells. In searching for peptide-loaded major histocompatibility complexes (pMHCs), they must solve a classic trade-off between speed and sensitivity. It has long been supposed that microvilli on T cells act as sensory organs to enable search, but their strategy has been unknown. We used lattice light-sheet and quantum dot-enabled synaptic contact mapping microscopy to show that anomalous diffusion and fractal organization of microvilli survey the majority of opposing surfaces within 1 minute. Individual dwell times were long enough to discriminate pMHC half-lives and T cell receptor (TCR) accumulation selectively stabilized microvilli. Stabilization was independent of tyrosine kinase signaling and the actin cytoskeleton, suggesting selection for avid TCR microclusters. This work defines the efficient cellular search process against which ligand detection takes place.

Excess area dependent scaling behavior of nano-sized membrane tethers

Thermal fluctuations in cell membranes manifest as an excess area ([Formula: see text]) which governs a multitude of physical process at the sub-micron scale. We present a theoretical framework, based on an in silico tether pulling method, which may be used to reliably estimate [Formula: see text] in live cells. We perform our simulations in two different thermodynamic ensembles: (i) the constant projected area and (ii) the constant frame tension ensembles and show the equivalence of our results in the two. The tether forces estimated from our simulations compare well with our experimental measurements for tethers extracted from ruptured GUVs and HeLa cells. We demonstrate the significance and validity of our method by showing that all our calculations performed in the initial tether formation regime (i.e. when the length of the tether is comparable to its radius) along with experiments of tether extraction in 15 different cell types collapse onto two unified scaling relationships mapping tether force, tether radius, bending stiffness κ, and membrane tension σ. We show that [Formula: see text] is an important determinant of the radius of the extracted tether, which is equal to the characteristic length [Formula: see text] for [Formula: see text], and is equal to [Formula: see text] for [Formula: see text]. We also find that the estimated excess area follows a linear scaling behavior that only depends on the true value of [Formula: see text] for the membrane, based on which we propose a self-consistent technique to estimate the range of excess membrane areas in a cell.

A bulky glycocalyx fosters metastasis formation by promoting G1 cell cycle progression

Metastasis depends upon cancer cell growth and survival within the metastatic niche. Tumors which remodel their glycocalyces, by overexpressing bulky glycoproteins like mucins, exhibit a higher predisposition to metastasize, but the role of mucins in oncogenesis remains poorly understood. Here we report that a bulky glycocalyx promotes the expansion of disseminated tumor cells in vivo by fostering integrin adhesion assembly to permit G1 cell cycle progression. We engineered tumor cells to display glycocalyces of various thicknesses by coating them with synthetic mucin-mimetic glycopolymers. Cells adorned with longer glycopolymers showed increased metastatic potential, enhanced cell cycle progression, and greater levels of integrin-FAK mechanosignaling and Akt signaling in a syngeneic mouse model of metastasis. These effects were mirrored by expression of the ectodomain of cancer-associated mucin MUC1. These findings functionally link mucinous proteins with tumor aggression, and offer a new view of the cancer glycocalyx as a major driver of disease progression.

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.

Lysyl Oxidase-like Protein LOXL2 Promotes Lung Metastasis of Breast Cancer

The lysyl oxidase-like protein LOXL2 has been suggested to contribute to tumor progression and metastasis, but in vivo evidence has been lacking. Here we provide functional evidence that LOXL2 is a key driver of breast cancer metastasis in two conditional transgenic mouse models of PyMT-induced breast cancer. LOXL2 ablation in mammary tumor cells dramatically decreased lung metastasis, whereas LOXL2 overexpression promoted metastatic tumor growth. LOXL2 depletion or overexpression in tumor cells does not affect extracellular matrix stiffness or organization in primary and metastatic tumors, implying a function for LOXL2 independent of its conventional role in extracellular matrix remodeling. In support of this likelihood, cellular and molecular analyses revealed an association of LOXL2 action with elevated levels of the EMT regulatory transcription factor Snail1 and expression of several cytokines that promote premetastatic niche formation. Taken together, our findings established a pathophysiologic role and new function for LOXL2 in breast cancer metastasis. Cancer Res; 77(21); 5846-59. ©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.

α5β1-Integrin promotes tension-dependent mammary epithelial cell invasion by engaging the fibronectin synergy site

Fibronectin-ligated α5β1 integrin promotes malignancy by inducing tissue tension.

Tumors are fibrotic and characterized by abundant, remodeled, and cross-linked collagen that stiffens the extracellular matrix stroma. The stiffened collagenous stroma fosters malignant transformation of the tissue by increasing tumor cell tension to promote focal adhesion formation and potentiate growth factor receptor signaling through kinase. Importantly, collagen cross-linking requires fibronectin (FN). Fibrotic tumors contain abundant FN, and tumor cells frequently up-regulate the FN receptor α5β1 integrin. Using transgenic and xenograft models and tunable two- and three-dimensional substrates, we show that FN-bound α5β1 integrin promotes tension-dependent malignant transformation through engagement of the synergy site that enhances integrin adhesion force. We determined that ligation of the synergy site of FN permits tumor cells to engage a zyxin-stabilized, vinculin-linked scaffold that facilitates nucleation of phosphatidylinositol (3,4,5)-triphosphate at the plasma membrane to enhance phosphoinositide 3-kinase (PI3K)-dependent tumor cell invasion. The data explain why rigid collagen fibrils potentiate PI3K activation to promote malignancy and offer a perspective regarding the consistent up-regulation of α5β1 integrin and FN in many tumors and their correlation with cancer aggression.

Tissue mechanics regulate brain development, homeostasis and disease

All cells sense and integrate mechanical and biochemical cues from their environment to orchestrate organismal development and maintain tissue homeostasis. Mechanotransduction is the evolutionarily conserved process whereby mechanical force is translated into biochemical signals that can influence cell differentiation, survival, proliferation and migration to change tissue behavior. Not surprisingly, disease develops if these mechanical cues are abnormal or are misinterpreted by the cells - for example, when interstitial pressure or compression force aberrantly increases, or the extracellular matrix (ECM) abnormally stiffens. Disease might also develop if the ability of cells to regulate their contractility becomes corrupted. Consistently, disease states, such as cardiovascular disease, fibrosis and cancer, are characterized by dramatic changes in cell and tissue mechanics, and dysregulation of forces at the cell and tissue level can activate mechanosignaling to compromise tissue integrity and function, and promote disease progression. In this Commentary, we discuss the impact of cell and tissue mechanics on tissue homeostasis and disease, focusing on their role in brain development, homeostasis and neural degeneration, as well as in brain cancer.

Development of Aggressive Pancreatic Ductal Adenocarcinomas Depends on Granulocyte Colony Stimulating Factor Secretion in Carcinoma Cells

The survival rate for pancreatic ductal adenocarcinoma (PDAC) remains low. More therapeutic options to treat this disease are needed, for the current standard of care is ineffective. Using an animal model of aggressive PDAC (Kras/p48^TGFβRIIKO), we discovered an effect of TGFβ signaling in regulation of G-CSF secretion in pancreatic epithelium. Elevated concentrations of G-CSF in PDAC promoted differentiation of Ly6G⁺ cells from progenitors, stimulated IL10 secretion from myeloid cells, and decreased T-cell proliferation via upregulation of Arg, iNOS, VEGF, IL6, and IL1b from CD11b⁺ cells. Deletion of csf3 in PDAC cells or use of a G-CSF-blocking antibody decreased tumor growth. Anti-G-CSF treatment in combination with the DNA synthesis inhibitor gemcitabine reduced tumor size, increased the number of infiltrating T cells, and decreased the number of Ly6G⁺ cells more effectively than gemcitabine alone. Human analysis of human datasets from The Cancer Genome Atlas and tissue microarrays correlated with observations from our mouse model experiments, especially in patients with grade 1, stage II disease. We propose that in aggressive PDAC, elevated G-CSF contributes to tumor progression through promoting increases in infiltration of neutrophil-like cells with high immunosuppressive activity. Such a mechanism provides an avenue for a neoadjuvant therapeutic approach for this devastating disease. Cancer Immunol Res; 5(9); 718-29. ©2017 AACR.

Abstract 5912: Tumor micoenvironment modulates RTK signaling

Receptor tyrosine kinases (RTKs) and their associated signaling molecules are mutated or dysregulated in many aggressive cancers such as non-small cell lung carcinoma (NSCLC), breast cancer, and colorectal cancer. Despite therapeutic interventions such as tyrosine kinase inhibitors (TKI) that target RTKs, majority of patients develop resistance even after initial tumor regression. Although clinical studies suggest sequential treatments with TKI, chemotherapy, and radiation can eliminate most cancer cells, resistance inevitably emerges (Sequist, et al., Sci Trans Med, 2011). We demonstrated that alterations in the extracellular matrix (ECM) correlate with cancer progression and that RTK signaling is subject to spatiotemporal regulation (Paszek, et al., Cancer Cell, 2005.; Salaita, et al., Science, 2010). Thus, geometric and mechanical properties of the ECM may directly modulate RTK signaling. Here, we use silicone gel substrates that exhibit tunable stiffness in the physiological range (100s Pa - 100s kPa) to measure RTK-adaptor protein interactions in mammary epithelial cells (MECs; MCF10A) (Ou, et al. Integ. Biol., 2016). These gels are compatible with total internal reflection fluorescence (TIRF) imaging and enable single molecule detection of activated RTK phosphotyrosine residues via recruitment of Grb2 tagged with the fluorescent protein mEos3.2. We demonstrate a spectrum of Grb2 behaviors that are determined by the stiffness of the substrate. This indicates that the same receptor is capable of different signaling activities that are dictated by material properties. These new insights create opportunities to target the tumor microenvironment to address RTK inhibitor resistance and metastasis in cancer patients and to develop effective therapeutic strategies for better prognosis and prolonged patient survival.

Citation Format: Dhruv Thakar, Shalini T. Low-Nam, Jay T. Groves, Valerie M. Weaver. Tumor micoenvironment modulates RTK signaling [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 5912. doi:10.1158/1538-7445.AM2017-5912

Abstract 3985: NCoR2 regulates glioblastoma progression and treatment resistance

Glioblastoma Multiforme (GBM, WHO Grade IV glioma) is one of the deadliest adult CNS tumors with a median survival of less than two years. It is largely resistant to aggressive therapeutic regimes, which combine radiation, chemotherapy and surgery. Thus, it is imperative to identify the molecular players and pathways that facilitate GBM resistance and recurrence. Nuclear co-repressor protein NCoR2 is upregulated in GBM and its increased expression correlates with poor prognosis in GBM patients (Alrfaei. Plos one. 2013). NCoR2, through its binding to the histone deacetylase protein HDAC3, mediates transcriptional repression (Zhu et al. Brain Res. 2013). NCoR2 is also involved in maintenance of neural stem cells (Jepson et al. Nature. 2007), which contribute to treatment resistance. Our study employs two distinct lineages of glioma - the less aggressive proneural and the highly aggressive mesenchymal subtypes. We show that NCoR2 is differentially expressed across these subtypes, suggesting a role for NCoR2-mediated transcriptional reprogramming in GBM progression. Moreover, knockdown of NCoR2 leads to phenotypic changes both in vitro and in vivo - including effects on neurosphere formation and proliferation, differential expression of stem-like markers as well as regulation of tumor growth and progression in mice. We also demonstrate that NCoR2 expression is increased upon treatment with temozolomide (used for GBM therapy), indicating a protective pro-tumor role for NCoR2. Finally, we explore the contribution of the GBM microenvironment to GBM progression by varying the three-dimensional properties as well as the rigidity of the extracellular matrix and investigating changes in NCoR2 expression and its regulation of tumor progression. We conclude that NCoR2 regulates GBM progression and resistance to therapy potentially via inducing a stem-like phenotype as well as responding to the tumor-promoting mechanical cues within the GBM microenvironment.

Citation Format: Shelly Kaushik, Joanna J. Phillips, Valerie M. Weaver. NCoR2 regulates glioblastoma progression and treatment resistance [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 3985. doi:10.1158/1538-7445.AM2017-3985

Physical and Chemical Gradients in the Tumor Microenvironment Regulate Tumor Cell Invasion, Migration, and Metastasis

Cancer metastasis requires the invasion of tumor cells into the stroma and the directed migration of tumor cells through the stroma toward the vasculature and lymphatics where they can disseminate and colonize secondary organs. Physical and biochemical gradients that form within the primary tumor tissue promote tumor cell invasion and drive persistent migration toward blood vessels and the lymphatics to facilitate tumor cell dissemination. These microenvironment cues include hypoxia and pH gradients, gradients of soluble cues that induce chemotaxis, and ions that facilitate galvanotaxis, as well as modifications to the concentration, organization, and stiffness of the extracellular matrix that produce haptotactic, alignotactic, and durotactic gradients. These gradients form through dynamic interactions between the tumor cells and the resident fibroblasts, adipocytes, nerves, endothelial cells, infiltrating immune cells, and mesenchymal stem cells. Malignant progression results from the integrated response of the tumor to these extrinsic physical and chemical cues. Here, we first describe how these physical and chemical gradients develop, and we discuss their role in tumor progression. We then review assays to study these gradients. We conclude with a discussion of clinical strategies used to detect and inhibit these gradients in tumors and of new intervention opportunities. Clarifying the role of these gradients in tumor evolution offers a unique approach to target metastasis.

Comprehensive characterization of DNA methylation changes in Fuchs endothelial corneal dystrophy

Transparency of the human cornea is necessary for vision. Fuchs Endothelial Corneal Dystrophy (FECD) is a bilateral, heritable degeneration of the corneal endothelium, and a leading indication for corneal transplantation in developed countries. While the early onset, and rarer, form of FECD has been linked to COL8A2 mutations, the more common, late onset form of FECD has genetic mutations linked to only a minority of cases. Epigenetic modifications that occur in FECD are unknown. Here, we report on and compare the DNA methylation landscape of normal human corneal endothelial (CE) tissue and CE from FECD patients using the Illumina Infinium HumanMethylation450 (HM450) DNA methylation array. We show that DNA methylation profiles are distinct between control and FECD samples. Differentially methylated probes (10,961) were identified in the FECD samples compared with the control samples, with the majority of probes being hypermethylated in the FECD samples. Genes containing differentially methylated sites were disproportionately annotated to ontological categories involving cytoskeletal organization, ion transport, hematopoetic cell differentiation, and cellular metabolism. Our results suggest that altered DNA methylation patterns may contribute to loss of corneal transparency in FECD through a global accumulation of sporadic DNA methylation changes in genes critical to basic CE biological processes.

Integrin-mediated traction force enhances paxillin molecular associations and adhesion dynamics that increase the invasiveness of tumor cells into a three-dimensional extracellular matrix

Mammary tumor cells adopt a basal-like phenotype when invading through a dense, stiffened, 3D matrix. These cells exert higher integrin-mediated traction forces, consistent with a physical motor-clutch model, display an altered molecular organization at the nanoscale, and recruit a suite of paxillin-associated proteins implicated in metastasis.

Metastasis requires tumor cells to navigate through a stiff stroma and squeeze through confined microenvironments. Whether tumors exploit unique biophysical properties to metastasize remains unclear. Data show that invading mammary tumor cells, when cultured in a stiffened three-dimensional extracellular matrix that recapitulates the primary tumor stroma, adopt a basal-like phenotype. Metastatic tumor cells and basal-like tumor cells exert higher integrin-mediated traction forces at the bulk and molecular levels, consistent with a motor-clutch model in which motors and clutches are both increased. Basal-like nonmalignant mammary epithelial cells also display an altered integrin adhesion molecular organization at the nanoscale and recruit a suite of paxillin-associated proteins implicated in invasion and metastasis. Phosphorylation of paxillin by Src family kinases, which regulates adhesion turnover, is similarly enhanced in the metastatic and basal-like tumor cells, fostered by a stiff matrix, and critical for tumor cell invasion in our assays. Bioinformatics reveals an unappreciated relationship between Src kinases, paxillin, and survival of breast cancer patients. Thus adoption of the basal-like adhesion phenotype may favor the recruitment of molecules that facilitate tumor metastasis to integrin-based adhesions. Analysis of the physical properties of tumor cells and integrin adhesion composition in biopsies may be predictive of patient outcome.

Abstract PR05: Glycoprotein-mediated tissue mechanics regulate glioblastoma aggression

Glioblastoma multiforme (GBM) is a malignant glioma whose progression is associated with rampant extracellular matrix (ECM) remodeling. We recently found that GBM ECM stiffness predicts reduced survival in human patients. Instead of collagen fibrosis, which is common in many solid tumors, we showed that GBM stiffening involves increased production of extracellular glycoproteins, glycosaminoglycans, and sugar-binding proteins. Using bioinformatics, we revealed that genes of the glycocalyx (transmembrane glycoproteins and their interacting partners) are disproportionately upregulated in GBM relative to lower grade gliomas. Further, these genes are overexpressed within GBM in the mesenchymal (MES) relative to the proneural (PRO) subtype, the former of which is associated with treatment resistance and relapse. Using mouse models of human GBM, we showed that MES tumors are more lethal than PRO, and present with elevated ECM stiffness and mechanical signaling. To test our hypothesis that mechanical signaling can drive the MES phenotype, we engineered PRO GBM cells with constitutively-elevated integrin signaling. Compared to control PRO cells, these undergo a robust MES-like transition, upregulate bulky glycoprotein expression, and result in stiffer and more lethal tumors. This phenotype was reversed by the inhibition of focal adhesion kinase in MES cells. To test whether an enhanced glycocalyx can directly elevate mechanical signaling, we decorated GBM cells with synthetic glycoprotein polymers. Indeed, this resulted in enhanced integrin-focal adhesion signaling and more aggressive tumor progression. The invasive properties and therapy resistance observed in mesenchymal tumor cells are often associated with elevated stem cell-like features. To investigate a link between the glycocalyx, tissue mechanics, and the mesenchymal-stem cell phenotype, we interfered with components of the gylcocalyx or mechanical signaling machinery and found a reduction in stem cell genes and surface proteins, as well as increased sensitivity to chemotherapy. These data support a model in which glycoprotein-mediated tissue stiffening drives GBM aggression through promotion of a mesenchymal phenotype.

This abstract is also being presented as Poster A39.

Citation Format: J. Matthew Barnes, Elliot C. Woods, Russell O. Bainer, Yekaterina A. Miroshnikova, Kan Lu, Gabriele Bergers, Carolyn Bertozzi, Valerie M. Weaver. Glycoprotein-mediated tissue mechanics regulate glioblastoma aggression. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr PR05.

Force-dependent breaching of the basement membrane

Clinically, non-invasive carcinomas are confined to the epithelial side of the basement membrane and are classified as benign, whereas invasive cancers invade through the basement membrane and thereby acquire the potential to metastasize. Recent findings suggest that, in addition to protease-mediated degradation and chemotaxis-stimulated migration, basement membrane invasion by malignant cells is significantly influenced by the stiffness of the associated interstitial extracellular matrix and the contractility of the tumor cells that is dictated in part by their oncogenic genotype. In this review, we highlight recent findings that illustrate unifying molecular mechanisms whereby these physical cues contribute to tissue fibrosis and malignancy in three epithelial organs: breast, pancreas, and liver. We also discuss the clinical implications of these findings and the biological properties and clinical challenges linked to the unique biology of each of these organs.

From transformation to metastasis: deconstructing the extracellular matrix in breast cancer

The extracellular matrix (ECM) is a guiding force that regulates various developmental stages of the breast. In addition to providing structural support for the cells, it mediates epithelial-stromal communication and provides cues for cell survival, proliferation, and differentiation. Perturbations in ECM architecture profoundly influence breast tumor progression and metastasis. Understanding how a dysregulated ECM can facilitate malignant transformation is crucial to designing treatments to effectively target the tumor microenvironment. Here, we address the contribution of ECM mechanics to breast cancer progression, metastasis, and treatment resistance and discuss potential therapeutic strategies targeting the ECM.

Tissue mechanics promote IDH1-dependent HIF1α-tenascin C feedback to regulate glioblastoma aggression

Increased overall survival for patients with glioma brain tumours is associated with mutations in the metabolic regulator isocitrate dehydrogenase 1 (IDH1). Gliomas develop within a mechanically challenged microenvironment that is characterized by a dense extracellular matrix (ECM) that compromises vascular integrity to induce hypoxia and activate HIF1α. We found that glioma aggression and patient prognosis correlate with HIF1α levels and the stiffness of a tenascin C (TNC)-enriched ECM. Gain- and loss-of-function xenograft manipulations demonstrated that a mutant IDH1 restricts glioma aggression by reducing HIF1α-dependent TNC expression to decrease ECM stiffness and mechanosignalling. Recurrent IDH1-mutant patient gliomas had a stiffer TNC-enriched ECM that our studies attributed to reduced miR-203 suppression of HIF1α and TNC mediated via a tension-dependent positive feedback loop. Thus, our work suggests that elevated ECM stiffness can independently foster glioblastoma aggression and contribute to glioblastoma recurrence via bypassing the protective activity of IDH1 mutational status.

Metronomic chemotherapy prevents therapy-induced stromal activation and induction of tumor-initiating cells

Chan et al. report that treatment of tumor-bearing mice with low-dose metronomic chemotherapy prevents stromal secretion of ELR⁺ chemokines and induction of tumor-initiating cells usually observed with administration of drugs at maximum tolerated dose.

Although traditional chemotherapy kills a fraction of tumor cells, it also activates the stroma and can promote the growth and survival of residual cancer cells to foster tumor recurrence and metastasis. Accordingly, overcoming the host response induced by chemotherapy could substantially improve therapeutic outcome and patient survival. In this study, resistance to treatment and metastasis has been attributed to expansion of stem-like tumor-initiating cells (TICs). Molecular analysis of the tumor stroma in neoadjuvant chemotherapy–treated human desmoplastic cancers and orthotopic tumor xenografts revealed that traditional maximum-tolerated dose chemotherapy, regardless of the agents used, induces persistent STAT-1 and NF-κB activity in carcinoma-associated fibroblasts. This induction results in the expression and secretion of ELR motif–positive (ELR⁺) chemokines, which signal through CXCR-2 on carcinoma cells to trigger their phenotypic conversion into TICs and promote their invasive behaviors, leading to paradoxical tumor aggression after therapy. In contrast, the same overall dose administered as a low-dose metronomic chemotherapy regimen largely prevented therapy-induced stromal ELR⁺ chemokine paracrine signaling, thus enhancing treatment response and extending survival of mice carrying desmoplastic cancers. These experiments illustrate the importance of stroma in cancer therapy and how its impact on treatment resistance could be tempered by altering the dosing schedule of systemic chemotherapy.

Cellular adaptation to biomechanical stress across length scales in tissue homeostasis and disease

Human tissues are remarkably adaptable and robust, harboring the collective ability to detect and respond to external stresses while maintaining tissue integrity. Following injury, many tissues have the capacity to repair the damage - and restore form and function - by deploying cellular and molecular mechanisms reminiscent of developmental programs. Indeed, it is increasingly clear that cancer and chronic conditions that develop with age arise as a result of cells and tissues re-implementing and deregulating a selection of developmental programs. Therefore, understanding the fundamental molecular mechanisms that drive cell and tissue responses is a necessity when designing therapies to treat human conditions. Extracellular matrix stiffness synergizes with chemical cues to drive single cell and collective cell behavior in culture and acts to establish and maintain tissue homeostasis in the body. This review will highlight recent advances that elucidate the impact of matrix mechanics on cell behavior and fate across these length scales during times of homeostasis and in disease states.

Abstract PR10: A glycoprotein-mediated mechanical switch promotes glioma aggression

Glioblastoma multiforme (GBM) is a malignant brain tumor whose progression is associated with rampant extracellular matrix (ECM) remodeling. We recently found that ECM stiffness correlates with poor survival in human GBM specimens. Glycoproteins are the major constituent of normal brain ECM and many are overexpressed in brain tumors, yet the interplay between glycoproteins and mechanical signaling in GBM pathogenesis remains poorly understood. Here, we show that bulky glycoproteins and sugar-binding proteins are broadly upregulated in GBM relative to lower grade gliomas. Further, these genes are overexpressed in the mesenchymal (Mes) relative to the proneural (Pro) GBM subclass, the former of which is associated with treatment resistance and relapse. We took a specific interest in the hyaluronic acid (HA)-producing enzyme, HAS2, and the galactoside-binding lectin galectin-1 (Gal1) due to their ability to modulate tissue structure and rheology. Using mouse models of human GBM we showed that Mes tumors are enriched in HA and fibronectin, coincident with elevated ECM stiffness and mechanical signaling. These data suggest the possibility that aberrant glycoprotein expression drives GBM aggression through enhanced mechanical signaling resulting from tissue stiffening. Consistent with this hypothesis, by elevating mechanical signaling in Pro GBMs we induce a robust Mes-like transition and we see the opposite when reducing Gal1 expression or HA content in Mes tumors. Our data provides evidence of a feed-forward mechanism whereby mechanical signaling drives Gal1 and HA production which reinforce ECM stiffness, thus sustaining pro-tumorigenic mechanical signaling.

This abstract is also presented as Poster A21.

Citation Format: J Matthew Barnes, Yekaterina A. Miroshnikova, Jason C. Tung, Russel O. Bainer, Valerie M. Weaver. A glycoprotein-mediated mechanical switch promotes glioma aggression. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr PR10.