Subcellular regulation of cancer cell mechanics

Tension directs cancer cell migration over fiber alignment through energy minimization

Cell migration during many fundamental biological processes including metastasis requires cells to traverse tissue with heterogeneous mechanical cues that direct migration as well as determine force and energy requirements for motility. However, the influence of discrete structural and mechanical cues on migration remains challenging to determine as they are often coupled. Here, we decouple the pro-invasive cues of collagen fiber alignment and tension to study their individual impact on migration. When presented with both cues, cells preferentially travel in the axis of tension against fiber alignment. Computational and experimental data show applying tension perpendicular to alignment increases potential energy stored within collagen fibers, lowering requirements for cell-induced matrix deformation and energy usage during migration compared to motility in the direction of fiber alignment. Energy minimization directs migration trajectory, and tension can facilitate migration against fiber alignment. These findings provide a conceptual understanding of bioenergetics during migration through a fibrous matrix.

Acousto-holographic reconstruction of whole-cell stiffness maps

Accurate assessment of cell stiffness distribution is essential due to the critical role of cell mechanobiology in regulation of vital cellular processes like proliferation, adhesion, migration, and motility. Stiffness provides critical information in understanding onset and progress of various diseases, including metastasis and differentiation of cancer. Atomic force microscopy and optical trapping set the gold standard in stiffness measurements. However, their widespread use has been hampered with long processing times, unreliable contact point determination, physical damage to cells, and unsuitability for multiple cell analysis. Here, we demonstrate a simple, fast, label-free, and high-resolution technique using acoustic stimulation and holographic imaging to reconstruct stiffness maps of single cells. We used this acousto-holographic method to determine stiffness maps of HCT116 and CTC-mimicking HCT116 cells and differentiate between them. Our system would enable widespread use of whole-cell stiffness measurements in clinical and research settings for cancer studies, disease modeling, drug testing, and diagnostics.

Gold Nano-Bio-Interaction to Modulate Mechanobiological Responses for Cancer Therapy Applications

In the present study, we investigate the mechanobiological responses of human lung cancer that may occur through their interactions with two different types of gold nanoparticles: nanostars and nanospheres. Hyperspectral images of nanoparticle-treated cells revealed different spatial distributions of nanoparticles in cells depending on their morphology, with nanospheres being more uniformly distributed in cells than nanostars. Gold nanospheres were also found to be more effective in mechanobiological modulations. They significantly suppressed the migratory ability of cells under different incubation times while lowering the bulk stiffness and adhesion of cells. This in vitro study suggests the potential applications of gold nanoparticles to manage cell migration. Nano-bio-interactions appeared to impact the cytoskeletal organization of cells and consequently alter the mechanical properties of cells, which could influence the cellular functions of cells. According to the results and migratory index model, it is thought that nanoparticle-treated cells experience mechanical changes in their body, which largely reduces their migratory potentials. These findings provide a better understanding of nano-bio-interaction in terms of cell mechanics and highlight the importance of mechanobiological responses in designing gold nanoparticles for cancer therapy.

Mechanoresponsive metabolism in cancer cell migration and metastasis

Altered tissue mechanics and metabolism are defining characteristics of cancer that impact not only proliferation but also migration. While migrating through a mechanically and spatially heterogeneous microenvironment, changes in metabolism allow cells to dynamically tune energy generation and bioenergetics in response to fluctuating energy needs. Physical cues from the extracellular matrix influence mechanosignaling pathways, cell mechanics, and cytoskeletal architecture to alter presentation and function of metabolic enzymes. In cancer, altered mechanosensing and metabolic reprogramming supports metabolic plasticity and high energy production while cells migrate and metastasize. Here, we discuss the role of mechanoresponsive metabolism in regulating cell migration and supporting metastasis as well as the potential of therapeutically targeting cancer metabolism to block motility and potentially metastasis.

Cell Cytoskeleton and Stiffness Are Mechanical Indicators of Organotropism in Breast Cancer

Simple Summary

Cancer cell dissemination exhibits organ preference or organotropism. Although the influence of intrinsic biochemical factors on organotropism has been intensely studied, little is known about the roles of mechanical properties of metastatic cancer cells. Our study suggests that there may be a correlation between cell cytoskeleton/stiffness and organotropism. We find that the cytoskeleton and stiffness of breast cancer cell subpopulations with different metastatic preference match the mechanics of the metastasized organs. The modification of cell cytoskeleton significantly influences the organotropism-related gene expression pattern and mechanoresponses on soft substrates which mimic brain tissue stiffness. These findings highlight the key role of cell cytoskeleton in specific organ metastasis, which may not only reflect but also impact the metastatic organ preference.

Abstract

Tumor metastasis involves the dissemination of tumor cells from the primary lesion to other organs and the subsequent formation of secondary tumors, which leads to the majority of cancer-related deaths. Clinical findings show that cancer cell dissemination is not random but exhibits organ preference or organotropism. While intrinsic biochemical factors of cancer cells have been extensively studied in organotropism, much less is known about the role of cell cytoskeleton and mechanics. Herein, we demonstrate that cell cytoskeleton and mechanics are correlated with organotropism. The result of cell stiffness measurements shows that breast cancer cells with bone tropism are much stiffer with enhanced F-actin, while tumor cells with brain tropism are softer with lower F-actin than their parental cells. The difference in cellular stiffness matches the difference in the rigidity of their metastasized organs. Further, disrupting the cytoskeleton of breast cancer cells with bone tropism not only elevates the expressions of brain metastasis-related genes but also increases cell spreading and proliferation on soft substrates mimicking the stiffness of brain tissue. Stabilizing the cytoskeleton of cancer cells with brain tropism upregulates bone metastasis-related genes while reduces the mechanoadaptation ability on soft substrates. Taken together, these findings demonstrate that cell cytoskeleton and biophysical properties of breast cancer subpopulations correlate with their metastatic preference in terms of gene expression pattern and mechanoadaptation ability, implying the potential role of cell cytoskeleton in organotropism.

Adenoviral protein E4orf4 interacts with the polarity protein Par3 to induce nuclear rupture and tumor cell death

The tumor cell–selective killing activity of the adenovirus type 2 early region 4 ORF4 (E4orf4) protein is poorly defined at the molecular level. Here, we show that the tumoricidal effect of E4orf4 is typified by changes in nuclear dynamics that depend on its interaction with the polarity protein Par3 and actomyosin contractility. Mechanistically, E4orf4 induced a high incidence of nuclear bleb formation and repetitive nuclear ruptures, which promoted nuclear efflux of E4orf4 and loss of nuclear integrity. This process was regulated by nucleocytoskeletal connections, Par3 clustering proximal to nuclear lamina folds, and retrograde movement of actin bundles that correlated with nuclear ruptures. Significantly, Par3 also regulated the incidence of spontaneous nuclear ruptures facilitated by the downmodulation of lamins. This work uncovered a novel role for Par3 in controlling the actin-dependent forces acting on the nuclear envelope to remodel nuclear shape, which might be a defining feature of tumor cells that is harnessed by E4orf4.

The Physical Microenvironment of Tumors: Characterization and Clinical Impact

The tumor microenvironment plays a critical role in tumorigenesis and metastasis. As tightly controlled extracellular matrix homeostasis is lost during tumor progression, a dysregulated extracellular matrix can significantly alter cellular phenotype and drive malignancy. Altered physical properties of the tumor microenvironment alter cancer cell behavior, limit delivery and efficacy of therapies, and correlate with tumorigenesis and patient prognosis. The physical features of the extracellular matrix during tumor progression have been characterized; however, a wide range of methods have been used between studies and cancer types resulting in a large range of reported values. Here, we discuss the significant mechanical and structural properties of the tumor microenvironment, summarizing their reported values and clinical impact across cancer type and grade. We attempt to integrate the values in the literature to identify sources of reported differences and commonalities to better understand how aberrant extracellular matrix dynamics contribute to cancer progression. An intimate understanding of altered matrix properties during malignant transformation will be crucial in effectively detecting, monitoring, and treating cancer.

Energetic costs regulated by cell mechanics and confinement are predictive of migration path during decision-making

Cell migration during the invasion-metastasis cascade requires cancer cells to navigate a spatially complex microenvironment that presents directional choices to migrating cells. Here, we investigate cellular energetics during migration decision-making in confined spaces. Theoretical and experimental data show that energetic costs for migration through confined spaces are mediated by a balance between cell and matrix compliance as well as the degree of spatial confinement to direct decision-making. Energetic costs, driven by the cellular work needed to generate force for matrix displacement, increase with increasing cell stiffness, matrix stiffness, and degree of spatial confinement, limiting migration. By assessing energetic costs between possible migration paths, we can predict the probability of migration choice. Our findings indicate that motility in confined spaces imposes high energetic demands on migrating cells, and cells migrate in the direction of least confinement to minimize energetic costs. Therefore, therapeutically targeting metabolism may limit cancer cell migration and metastasis.

Mechanical Forces in Tumor Angiogenesis

A defining hallmark of cancer and cancer development is upregulated angiogenesis. The vasculature formed in tumors is structurally abnormal, not organized in the conventional hierarchical arrangement, and more permeable than normal vasculature. These features contribute to leaky, tortuous, and dilated blood vessels, which act to create heterogeneous blood flow, compression of vessels, and elevated interstitial fluid pressure. As such, abnormalities in the tumor vasculature not only affect the delivery of nutrients and oxygen to the tumor, but also contribute to creating an abnormal tumor microenvironment that further promotes tumorigenesis. The role of chemical signaling events in mediating tumor angiogenesis has been well researched; however, the relative contribution of physical cues and mechanical regulation of tumor angiogenesis is less understood. Growing research indicates that the physical microenvironment plays a significant role in tumor progression and promoting abnormal tumor vasculature. Here, we review how mechanical cues found in the tumor microenvironment promote aberrant tumor angiogenesis. Specifically, we discuss the influence of matrix stiffness and mechanical stresses in tumor tissue on tumor vasculature, as well as the mechanosensory pathways utilized by endothelial cells to respond to the physical cues found in the tumor microenvironment. We also discuss the impact of the resulting aberrant tumor vasculature on tumor progression and therapeutic treatment.