Structural centrosome aberrations promote non-cell-autonomous invasiveness.

Centrosomes are the main microtubule-organizing centers of animal cells. Although centrosome aberrations are common in tumors, their consequences remain subject to debate. Here, we studied the impact of structural centrosome aberrations, induced by deregulated expression of ninein-like protein (NLP), on epithelial spheres grown in Matrigel matrices. We demonstrate that NLP-induced structural centrosome aberrations trigger the escape ("budding") of living cells from epithelia. Remarkably, all cells disseminating into the matrix were undergoing mitosis. This invasive behavior reflects a novel mechanism that depends on the acquisition of two distinct properties. First, NLP-induced centrosome aberrations trigger a re-organization of the cytoskeleton, which stabilizes microtubules and weakens E-cadherin junctions during mitosis. Second, atomic force microscopy reveals that cells harboring these centrosome aberrations display increased stiffness. As a consequence, mitotic cells are pushed out of mosaic epithelia, particularly if they lack centrosome aberrations. We conclude that centrosome aberrations can trigger cell dissemination through a novel, non-cell-autonomous mechanism, raising the prospect that centrosome aberrations contribute to the dissemination of metastatic cells harboring normal centrosomes.

Dedifferentiation-mediated stem cell niche maintenance in early-stage ductal carcinoma in situ progression: insights from a multiscale modeling study.

We present a multiscale agent-based model of ductal carcinoma in situ (DCIS) to study how key phenotypic and signaling pathways are involved in the early stages of disease progression. The model includes a phenotypic hierarchy, and key endocrine and paracrine signaling pathways, and simulates cancer ductal growth in a 3D lattice-free domain. In particular, by considering stochastic cell dedifferentiation plasticity, the model allows for study of how dedifferentiation to a more stem-like phenotype plays key roles in the maintenance of cancer stem cell populations and disease progression. Through extensive parameter perturbation studies, we have quantified and ranked how DCIS is sensitive to perturbations in several key mechanisms that are instrumental to early disease development. Our studies reveal that long-term maintenance of multipotent stem-like cell niches within the tumor are dependent on cell dedifferentiation plasticity, and that disease progression will become arrested due to dilution of the multipotent stem-like population in the absence of dedifferentiation. We have identified dedifferentiation rates necessary to maintain biologically relevant multipotent cell populations, and also explored quantitative relationships between dedifferentiation rates and disease progression rates, which may potentially help to optimize the efficacy of emerging anti-cancer stem cell therapeutics.

The nanomechanical properties of rat fibroblasts are modulated by interfering with the vimentin intermediate filament system.

The contribution of the intermediate filament (IF) network to the mechanical response of cells has so far received little attention, possibly because the assembly and regulation of IFs are not as well understood as that of the actin cytoskeleton or of microtubules. The mechanical role of IFs has been mostly inferred from measurements performed on individual filaments or gels in vitro. In this study we employ atomic force microscopy (AFM) to examine the contribution of vimentin IFs to the nanomechanical properties of living cells under native conditions. To specifically target and modulate the vimentin network, Rat-2 fibroblasts were transfected with GFP-desmin variants. Cells expressing desmin variants were identified by the fluorescence microscopy extension of the AFM instrument. This allowed us to directly compare the nanomechanical response of transfected and untransfected cells at high spatial resolution by means of AFM. Depending on the variant desmin, transfectants were either softer or stiffer than untransfected fibroblasts. Expression of the non-filament forming GFP-DesL345P mutant led to a collapse of the endogenous vimentin network in the perinuclear region that was accompanied by localized stiffening. Correlative confocal microscopy indicates that the expression of desmin variants specifically targets the endogenous vimentin IF network without major rearrangements of other cytoskeletal components. By measuring functional changes caused by IF rearrangements in intact cells, we show that IFs play a crucial role in mechanical behavior not only at large deformations but also in the nanomechanical response of individual cells.

A mathematical model for the quantification of a patient's sensitivity to checkpoint inhibitors and long-term tumour burden.

A large proportion of patients with cancer are unresponsive to treatment with immune checkpoint blockade and other immunotherapies. Here, we report a mathematical model of the time course of tumour responses to immune checkpoint inhibitors. The model takes into account intrinsic tumour growth rates, the rates of immune activation and of tumour-immune cell interactions, and the efficacy of immune-mediated tumour killing. For 124 patients, four cancer types and two immunotherapy agents, the model reliably described the immune responses and final tumour burden across all different cancers and drug combinations examined. In validation cohorts from four clinical trials of checkpoint inhibitors (with a total of 177 patients), the model accurately stratified the patients according to reduced or increased long-term tumour burden. We also provide model-derived quantitative measures of treatment sensitivity for specific drug-cancer combinations. The model can be used to predict responses to therapy and to quantify specific drug-cancer sensitivities in individual patients.

A Mathematical Model to Estimate Chemotherapy Concentration at the Tumor-Site and Predict Therapy Response in Colorectal Cancer Patients with Liver Metastases.

Chemotherapy remains a primary treatment for metastatic cancer, with tumor response being the benchmark outcome marker. However, therapeutic response in cancer is unpredictable due to heterogeneity in drug delivery from systemic circulation to solid tumors. In this proof-of-concept study, we evaluated chemotherapy concentration at the tumor-site and its association with therapy response by applying a mathematical model. By using pre-treatment imaging, clinical and biologic variables, and chemotherapy regimen to inform the model, we estimated tumor-site chemotherapy concentration in patients with colorectal cancer liver metastases, who received treatment prior to surgical hepatic resection with curative-intent. The differential response to therapy in resected specimens, measured with the gold-standard Tumor Regression Grade (TRG; from 1, complete response to 5, no response) was examined, relative to the model predicted systemic and tumor-site chemotherapy concentrations. We found that the average calculated plasma concentration of the cytotoxic drug was essentially equivalent across patients exhibiting different TRGs, while the estimated tumor-site chemotherapeutic concentration (eTSCC) showed a quadratic decline from TRG = 1 to TRG = 5 (p < 0.001). The eTSCC was significantly lower than the observed plasma concentration and dropped by a factor of ~5 between patients with complete response (TRG = 1) and those with no response (TRG = 5), while the plasma concentration remained stable across TRG groups. TRG variations were driven and predicted by differences in tumor perfusion and eTSCC. If confirmed in carefully planned prospective studies, these findings will form the basis of a paradigm shift in the care of patients with potentially curable colorectal cancer and liver metastases.

Spatial organization acts on cell signaling: how physical force contributes to the development of cancer.

Cells constantly encounter physical forces and respond to neighbors and circulating factors by triggering intracellular signaling cascades that in turn affect their behavior. The mechanisms by which cells transduce mechanical signals to downstream biochemical changes are not well understood. In their work, Salaita and coworkers show that the spatial organization of cell surface receptors is crucial for mechanotransduction. Consequently, force modulation that disrupts the mechanochemical coupling may represent a critical step in cancerogenesis.

GPER Activation Inhibits Cancer Cell Mechanotransduction and Basement Membrane Invasion via RhoA.

The invasive properties of cancer cells are intimately linked to their mechanical phenotype, which can be regulated by intracellular biochemical signalling. Cell contractility, induced by mechanotransduction of a stiff fibrotic matrix, and the epithelial-mesenchymal transition (EMT) promote invasion. Metastasis involves cells pushing through the basement membrane into the stroma-both of which are altered in composition with cancer progression. Agonists of the G protein-coupled oestrogen receptor (GPER), such as tamoxifen, have been largely used in the clinic, and interest in GPER, which is abundantly expressed in tissues, has greatly increased despite a lack of understanding regarding the mechanisms which promote its multiple effects. Here, we show that specific activation of GPER inhibits EMT, mechanotransduction and cell contractility in cancer cells via the GTPase Ras homolog family member A (RhoA). We further show that GPER activation inhibits invasion through an in vitro basement membrane mimic, similar in structure to the pancreatic basement membrane that we reveal as an asymmetric bilayer, which differs in composition between healthy and cancer patients.

Length Scale Matters: Real-Time Elastography versus Nanomechanical Profiling by Atomic Force Microscopy for the Diagnosis of Breast Lesions.

Real-time elastography (RTE) is a noninvasive imaging modality where tumor-associated changes in tissue architecture are recognized as increased stiffness of the lesion compared to surrounding normal tissue. In contrast to this macroscopic appraisal, quantifying stiffness properties at the subcellular level by atomic force microscopy (AFM) reveals aggressive cancer cells to be soft. We compared RTE and AFM profiling of the same breast lesion to explore the diagnostic potential of tissue elasticity at different length scales. Patients were recruited from women who were scheduled for a biopsy in the outpatient breast clinic of the University Hospital Basel, Switzerland. RTE was performed as part of a standard breast work-up. Individual elastograms were characterized based on the Tsukuba elasticity score. Additionally, lesion elasticity was semiquantitatively assessed by the strain ratio. Core biopsies were obtained for histologic diagnosis and nanomechanical profiling by AFM under near-physiological conditions. Bulk stiffness evaluation by RTE does not always allow for a clear distinction between benign and malignant lesions and may result in the false assessment of breast lesions. AFM on the other hand enables quantitative stiffness measurements at higher spatial, i.e., subcellular, and force resolution. Consequently, lesions that were false positive or false negative by RTE were correctly identified by their nanomechanical AFM profiles as confirmed by histological diagnosis. Nanomechanical measurements can be used as unique markers of benign and cancerous breast lesions by providing relevant information at the molecular level. This is of particular significance considering the heterogeneity of tumors and may improve diagnostic accuracy compared to RTE.

Correction: Diabetes-related changes in the protein composition and the biomechanical properties of human retinal vascular basement membranes.

[This corrects the article DOI: 10.1371/journal.pone.0189857.].

A three-dimensional in vitro dynamic micro-tissue model of cardiac scar formation.

In vitro cardiac models able to mimic the fibrotic process are paramount to develop an effective anti-fibrosis therapy that can regulate fibroblast behaviour upon myocardial injury. In previously developed in vitro models, typical fibrosis features were induced by using scar-like stiffness substrates and/or potent morphogen supplementation in monolayer cultures. In our model, we aimed to mimic in vitro a fibrosis-like environment by applying cyclic stretching of cardiac fibroblasts embedded in three-dimensional fibrin-hydrogels alone. Using a microfluidic device capable of delivering controlled cyclic mechanical stretching (10% strain at 1 Hz), some of the main fibrosis hallmarks were successfully reproduced in 7 days. Cyclic strain indeed increased cell proliferation, extracellular matrix (ECM) deposition (e.g. type-I-collagen, fibronectin) and its stiffness, forming a scar-like tissue with superior quality compared to the supplementation of TGFß1 alone. Taken together, the observed findings resemble some of the key steps in the formation of a scar: (i) early fibroblast proliferation, (ii) later phenotype switch into myofibroblasts, (iii) ECM deposition and (iv) stiffening. This in vitro scar-on-a-chip model represents a big step forward to investigate the early mechanisms possibly leading later to fibrosis without any possible confounding supplementation of exogenous potent morphogens.

Author Correction: Cancer-associated fibroblasts induce metalloprotease-independent cancer cell invasion of the basement membrane.

In the original version of this Article, financial support and contributions in manuscript preparation were not fully acknowledged. The PDF and HTML versions of the Article have now been corrected to include the following:'M.P. and P.O. would like to thank Prof. Roderick Y.H. Lim for advice during manuscript preparation and for providing the laboratory and microscopy infrastructure.… [We also thank] the NanoteraProject, awarded to the PATLiSciII Consortium (M.P and P.O)…'.

HtrA1 Mediated Intracellular Effects on Tubulin Using a Polarized RPE Disease Model.

Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss. The protein HtrA1 is enriched in retinal pigment epithelial (RPE) cells isolated from AMD patients and in drusen deposits. However, it is poorly understood how increased levels of HtrA1 affect the physiological function of the RPE at the intracellular level. Here, we developed hfRPE (human fetal retinal pigment epithelial) cell culture model where cells fully differentiated into a polarized functional monolayer. In this model, we fine-tuned the cellular levels of HtrA1 by targeted overexpression. Our data show that HtrA1 enzymatic activity leads to intracellular degradation of tubulin with a corresponding reduction in the number of microtubules, and consequently to an altered mechanical cell phenotype. HtrA1 overexpression further leads to impaired apical processes and decreased phagocytosis, an essential function for photoreceptor survival. These cellular alterations correlate with the AMD phenotype and thus highlight HtrA1 as an intracellular target for therapeutic interventions towards AMD treatment.

Diabetes-related changes in the protein composition and the biomechanical properties of human retinal vascular basement membranes.

Basement membranes (BMs) are specialized sheets of extracellular matrix that outline epithelial cell layers, muscle fibers, blood vessels, and peripheral nerves. A well-documented histological hallmark of progressing diabetes is a major increase in vascular BM thickness. In order to investigate whether this structural change is accompanied by a change in the protein composition, we compared the proteomes of retinal vascular BMs from diabetic and non-diabetic donors by using LC-MS/MS. Data analysis showed that seventeen extracellular matrix (ECM)-associated proteins were more abundant in diabetic than non-diabetic vascular BMs. Four ECM proteins were more abundant in non-diabetic than in diabetic BMs. Most of the over-expressed proteins implicate a complement-mediated chronic inflammatory process in the diabetic retinal vasculature. We also found an up-regulation of norrin, a protein that is known to promote vascular proliferation, possibly contributing to the vascular remodeling during diabetes. Many of the over-expressed proteins were localized to microvascular aneurisms. Further, the overall stoichiometry of proteins was changed, such that the relative abundance of collagens in BMs from diabetic patients was higher than normal. Biomechanical measurements of vascular BM flat mounts using AFM showed that their outer surface was softer than normal.

Cancer-associated fibroblasts induce metalloprotease-independent cancer cell invasion of the basement membrane.

At the stage of carcinoma in situ, the basement membrane (BM) segregates tumor cells from the stroma. This barrier must be breached to allow dissemination of the tumor cells to adjacent tissues. Cancer cells can perforate the BM using proteolysis; however, whether stromal cells play a role in this process remains unknown. Here we show that an abundant stromal cell population, cancer-associated fibroblasts (CAFs), promote cancer cell invasion through the BM. CAFs facilitate the breaching of the BM in a matrix metalloproteinase-independent manner. Instead, CAFs pull, stretch, and soften the BM leading to the formation of gaps through which cancer cells can migrate. By exerting contractile forces, CAFs alter the organization and the physical properties of the BM, making it permissive for cancer cell invasion. Blocking the ability of stromal cells to exert mechanical forces on the BM could therefore represent a new therapeutic strategy against aggressive tumors.Stromal cells play various roles in tumor establishment and metastasis. Here the authors, using an ex-vivo model, show that cancer-associated fibroblasts facilitate colon cancer cells invasion in a matrix metalloproteinase-independent manner, likely by pulling and stretching the basement membrane to form gaps.

Nanomechanical characterization of living mammary tissues by atomic force microscopy.

The mechanical properties of living cells and tissues are important for a variety of functional processes in vivo, including cell adhesion, migration, proliferation and differentiation. Changes in mechano-cellular phenotype, for instance, are associated with cancer progression. Atomic force microscopy (AFM) is an enabling technique that topographically maps and quantifies the mechanical properties of complex biological matter in physiological aqueous environments at the nanometer length scale. Recently we applied AFM to spatially resolve the distribution of nanomechanical stiffness across human breast cancer biopsies in comparison to healthy tissue and benign tumors. This led to the finding that AFM provides quantitative mechano-markers that may have translational significance for the clinical diagnosis of cancer. Here, we provide a comprehensive description of sample preparation methodology, instrumentation, data acquisition and analysis that allows for the quantitative nanomechanical profiling of unadulterated tissue at submicron spatial resolution and nano-Newton (nN) force sensitivity in physiological conditions.

New concepts in basement membrane biology.

Basement membranes (BMs) are thin sheets of extracellular matrix that outline epithelia, muscle fibers, blood vessels and peripheral nerves. The current view of BM structure and functions is based mainly on transmission electron microscopy imaging, in vitro protein binding assays, and phenotype analysis of human patients, mutant mice and invertebrata. Recently, MS-based protein analysis, biomechanical testing and cell adhesion assays with in vivo derived BMs have led to new and unexpected insights. Proteomic analysis combined with ultrastructural studies showed that many BMs undergo compositional and structural changes with advancing age. Atomic force microscopy measurements in combination with phenotype analysis have revealed an altered mechanical stiffness that correlates with specific BM pathologies in mutant mice and human patients. Atomic force microscopy-based height measurements strongly suggest that BMs are more than two-fold thicker than previously estimated, providing greater freedom for modelling the large protein polymers within BMs. In addition, data gathered using BMs extracted from mutant mice showed that laminin has a crucial role in BM stability. Finally, recent evidence demonstrate that BMs are bi-functionally organized, leading to the proposition that BM-sidedness contributes to the alternating epithelial and stromal tissue arrangements that are found in all metazoan species. We propose that BMs are ancient structures with tissue-organizing functions and were essential in the evolution of metazoan species.

A tumorigenic actin mutant alters fibroblast morphology and multicellular assembly properties.

Tumor initiation and progression are accompanied by complex changes in the cytoarchitecture that at the cellular level involve remodeling of the cytoskeleton. We report on the impact of a mutant ß-actin (G245D-actin) on cell structure and multicellular assembly properties. To appreciate the effects of the Gly245Asp substitution on the organization of the actin cytoskeleton, we examined the polymerization properties of G245D-actin in vitro by pyrene polymerization assays and total internal reflection fluorescence microscopy (TIRF). The mutant actin on its own has a significantly reduced polymerization efficiency compared to native actin but also modifies the polymerization of actin in copolymerization experiments. Comparison of the structure of Rat-2 fibroblasts and a stably transfected derivate called Rat-2-sm9 revealed the effects of G245D-actin in a cellular environment. The overall actin levels in Rat-2-sm9 show a 1.6-fold increase with similar amounts of mutant and wild-type actin. G245D-actin expression renders Rat-2-sm9 cells highly tumorigenic in nude mice. In Rat-2-sm9 monolayers, G245D-actin triggers the formation of extensive membrane ruffles, which is a characteristic feature of many transformed cells. To approximate complex cell-cell and cell-matrix interactions that occur in tumors and might modulate the effects of G245D-actin, we extended our studies to scaffold-free 3D spheroid cultures. Bright field and scanning electron microscopy (SEM) show that Rat-2-sm9 and Rat-2 cells share essential features of spheroid formation and compaction. However, the resulting spheroids exhibit distinct phenotypes that differ mainly in surface structure and size. The systematic comparison of transformed and normal spheroids by SEM provides new insights into scaffold-free fibroblast spheroid formation.

The nanomechanical signature of breast cancer.

Cancer initiation and progression follow complex molecular and structural changes in the extracellular matrix and cellular architecture of living tissue. However, it remains poorly understood how the transformation from health to malignancy alters the mechanical properties of cells within the tumour microenvironment. Here, we show using an indentation-type atomic force microscope (IT-AFM) that unadulterated human breast biopsies display distinct stiffness profiles. Correlative stiffness maps obtained on normal and benign tissues show uniform stiffness profiles that are characterized by a single distinct peak. In contrast, malignant tissues have a broad distribution resulting from tissue heterogeneity, with a prominent low-stiffness peak representative of cancer cells. Similar findings are seen in specific stages of breast cancer in MMTV-PyMT transgenic mice. Further evidence obtained from the lungs of mice with late-stage tumours shows that migration and metastatic spreading is correlated to the low stiffness of hypoxia-associated cancer cells. Overall, nanomechanical profiling by IT-AFM provides quantitative indicators in the clinical diagnostics of breast cancer with translational significance.

Imaging articular cartilage tissue using atomic force microscopy (AFM).

Cartilage is a complex avascular tissue composed of cells ("chondrocytes") embedded in an extracellular matrix (ECM) consisting of 70%-80% water. The primary components of the ECM are negatively charged aggrecans and collagen II fibrils, which possess a characteristic, ordered three-dimensional structure. The components interact to ensure that the cartilage is able to absorb shock and can function to protect the bone ends. Atomic force microscopy (AFM) can be used to examine structure-function relationships of cartilage at both micrometer and nanometer scales. When imaged at the micrometer scale with microspheres, only the ECM and chondrocytes can be distinguished. Correspondingly, mechanical testing of cartilage at the micrometer scale results in unimodal distribution of the stiffness because the bulk elastic property of the ECM is probed. In contrast, bare AFM tips are able to reveal the molecular components of the ECM at the nanometer scale. Mechanical testing at the nanometer scale reveals a bimodal distribution of the stiffness and reflects the distinct stiffness of the collagen network and the proteoglycan moiety. In this protocol, the corresponding AFM image and force map are used to reveal the distinct morphology of the collagen fibers and proteoglycan gel. Although, in principle, these experiments can be performed using any AFM, an AFM with tube scanners that have manual screws for tilting the sample is preferable because cartilage has macroscopically rough surface features. By manually tilting the probe over the sample, an optimal angle for tip approach can be achieved.

Imaging fibroblast cells using atomic force microscopy (AFM).

Atomic force microscopy (AFM) can be used to visualize the three major cytoskeletal components that contribute to the mechanical properties of the cell. These are actin microfilaments, intermediate filaments, and microtubules. In this protocol, rat embryonic fibroblasts expressing actin tagged with green fluorescent protein (GFP) are used to demonstrate this procedure.