Mathematical modelling of cancer cell invasion of tissue: local and non-local models and the effect of adhesion

The ability to invade tissue is one of the hallmarks of cancer. Cancer cells achieve this through the secretion of matrix degrading enzymes, cell proliferation, loss of cell–cell adhesion, enhanced cell–matrix adhesion and active migration. Invasion of tissue by the cancer cells is one of the key components in the metastatic cascade, whereby cancer cells spread to distant parts of the host and initiate the growth of secondary tumours (metastases). A better understanding of the complex processes involved in cancer invasion may ultimately lead to treatments being developed which can localise cancer and prevent metastasis. In this paper we formulate a novel continuum model of cancer cell invasion of tissue which explicitly incorporates the important biological processes of cell–cell and cell–matrix adhesion. This is achieved using non-local (integral) terms in a system of partial differential equations where the cells use a so-called “sensing radius” R to detect their environment. We show that in the limit as R→0 the non-local model converges to a related system of reaction–diffusion–taxis equations. A numerical exploration of this model using computational simulations shows that it can form the basis for future models incorporating more details of the invasion process.     

Cyclin D1 regulates lung cancer invasion and metastasis

Cyclin D1, as a regulatory factor in cell cycle, is highly expressed in many tumors, such as lung cancer, breast cancer and thyroid cancer. The aim of the present study was to study the role of Cyclin D1 in invasion and metastasis of lung cancer cells. Lung adenocarcinoma cell line A549 and squamous cell line SK-MES-1 were selected as the objects, because A549 expresses Cyclin D1 highly, and SK-MES-1 expresses lowly. Nude mice were injected with A549 or SK-MES-1 via tail vein, and were sacrificed after 4 weeks for cancer tissue isolation. The harvested cancer cells were reinjected into another nude mouse. After one more time of such seeding, highly metastatic lung cancer model was established. After A549 and SK-MES-1 were transfected with Cyclin D1 RNAi and expression vector respectively, transwell migration assay was used to analyze transferring capacity of lung cancer cells. Western blot was used to detect Cyclin D1 and WNT/TCF pathway proteins expressions in parental cell lines and cancer tissue from metastasis model animals. The results showed that, along with the increase of seeding times, lung cancer cells from model animals, no matter A549 or SK-MES-1, exhibited augmented metastasis activity and up-regulated Cyclin D1 expression. The transferring capacity was weakened significantly in A549 cells where the Cyclin D1 was interfered by RNAi, and it was enhanced significantly in SK-MES-1 cells which were transfected with the expression vector of Cyclin D1. The expressions of WNT/TCF pathway proteins, including β-catenin, lymphoid enhancer-binding factor (LEF) and T cell factor (TCF), increased significantly in highly metastatic model animals. The parental cell lines showed lower expressions of WNT/TCF pathway proteins compared with cancer tissue from metastasis model animals. These results suggest that Cyclin D1 is closely related with the invasion and metastasis of lung cancer cells, and the WNT/TCF signal pathway may promote the expression of Cyclin D1.     

Distinct roles for paxillin and Hic-5 in regulating breast cancer cell morphology, invasion, and metastasis

Individual metastatic tumor cells exhibit two interconvertible modes of cell motility during tissue invasion that are classified as either mesenchymal or amoeboid. The molecular mechanisms by which invasive breast cancer cells regulate this migratory plasticity have yet to be fully elucidated. Herein we show that the focal adhesion adaptor protein, paxillin , and the closely related Hic-5 have distinct and unique roles in the regulation of breast cancer cell lung metastasis by modulating cell morphology and cell invasion through three-dimensional extracellular matrices (3D ECMs). Cells depleted of paxillin by RNA interference displayed a highly elongated mesenchymal morphology, whereas Hic-5 knockdown induced an amoeboid phenotype with both cell populations exhibiting reduced plasticity, migration persistence, and velocity through 3D ECM environments. In evaluating associated signaling pathways, we determined that Rac1 activity was increased in cells devoid of paxillin whereas Hic-5 silencing resulted in elevated RhoA activity and associated Rho kinase–induced nonmuscle myosin II activity. Hic-5 was essential for adhesion formation in 3D ECMs, and analysis of adhesion dynamics and lifetime identified paxillin as a key regulator of 3D adhesion assembly, stabilization, and disassembly.     

Enterolobium contortisiliquum trypsin inhibitor (EcTI), a plant proteinase inhibitor, decreases in vitro cell adhesion and invasion by inhibition of Src protein-focal adhesion kinase (FAK) signaling pathways

Tumor cell invasion is vital for cancer progression and metastasis. Adhesion, migration, and degradation of the extracellular matrix are important events involved in the establishment of cancer cells at a new site, and therefore molecular targets are sought to inhibit such processes. The effect of a plant proteinase inhibitor, Enterolobium contortisiliquum trypsin inhibitor (EcTI), on the adhesion, migration, and invasion of gastric cancer cells was the focus of this study. EcTI showed no effect on the proliferation of gastric cancer cells or fibroblasts but inhibited the adhesion, migration, and cell invasion of gastric cancer cells; however, EcTI had no effect upon the adhesion of fibroblasts. EcTI was shown to decrease the expression and disrupt the cellular organization of molecules involved in the formation and maturation of invadopodia, such as integrin β1, cortactin, neuronal Wiskott-Aldrich syndrome protein, membrane type 1 metalloprotease, and metalloproteinase-2. Moreover, gastric cancer cells treated with EcTI presented a significant decrease in intracellular phosphorylated Src and focal adhesion kinase, integrin-dependent cell signaling components. Together, these results indicate that EcTI inhibits the invasion of gastric cancer cells through alterations in integrin-dependent cell signaling pathways.     

A Novel Zebrafish Xenotransplantation Model for Study of Glioma Stem Cell Invasion

Invasion and metastasis of solid tumors are the major causes of death in cancer patients. Cancer stem cells (CSCs) constitute a small fraction of tumor cell population, but play a critical role in tumor invasion and metastasis. The xenograft of tumor cells in immunodeficient mice is one of commonly used in vivo models to study the invasion and metastasis of cancer cells. However, this model is time-consuming and labor intensive. Zebrafish (Danio rerio) and their transparent embryos are emerging as a promising xenograft tumor model system for studies of tumor invasion. In this study, we established a tumor invasion model by using zebrafish embryo xenografted with human glioblastoma cell line U87 and its derived cancer stem cells (CSCs). We found that CSCs-enriched from U87 cells spreaded via the vessels within zebrafish embryos and such cells displayed an extremely high level of invasiveness which was associated with the up-regulated MMP-9 by CSCs. The invasion of glioma CSCs (GSCs) in zebrafish embryos was markedly inhibited by an MMP-9 inhibitor. Thus, our zebrafish embryo model is considered a cost-effective approach tostudies of the mechanisms underlying the invasion of CSCs and suitable for high-throughput screening of novel anti-tumor invasion/metastasis agents.     

Hypoxia-induced metastasis model in embryonic zebrafish

Hypoxia facilitates tumor invasion and metastasis by promoting neovascularization and co-option of tumor cells in the peritumoral vasculature, leading to dissemination of tumor cells into the circulation. However, until recently, animal models and imaging technology did not enable monitoring of the early events of tumor cell invasion and dissemination in living animals. We recently developed a zebrafish metastasis model to dissect the detailed events of hypoxia-induced tumor cell invasion and metastasis in association with angiogenesis at the single-cell level. In this model, fluorescent DiI-labeled human or mouse tumor cells are implanted into the perivitelline cavity of 48-h-old zebrafish embryos, which are subsequently placed in hypoxic water for 3 d. Tumor cell invasion, metastasis and pathological angiogenesis are detected under fluorescent microscopy in the living fish. The average experimental time for this model is 7 d. Our protocol offers a remarkable opportunity to study molecular mechanisms of hypoxia-induced cancer metastasis.     

TGF-beta induces formation of F-actin cores and matrix degradation in human breast cancer cells via distinct signaling pathways

Transforming growth factor beta regulates many biological processes including cell motility and invasion. Podosomes are specialized F-actin rich structures found in normal cells, such as osteoclasts and macrophages. Tumor cells often form related structures called invadopodia that are thought to promote invasion and metastasis. Here we show that human breast cancer cells organize F-actin rich structures in response to transforming growth factor beta that colocalize with areas of extracellular matrix degradation. We further show that organizing the complex of proteins needed to form these structures requires signaling through phosphatidylinositide 3-kinase and Src kinase, while activating the proteases involved in degradation of extracellular matrix requires extracellular signal-regulated kinase signaling, and that each of these pathways is activated by transforming growth factor beta in CA1D human breast cancer cells.     

Suppression of urokinase expression and tumor metastasis by bikunin overexpression [mini-review].

Bikunin (bik, also known as urinary trypsin inhibitor [UTI]), a Kunitz-type protease inhibitor, interacts with cells as a negative modulator of the invasive cells. Human ovarian cancer cell line, HRA, was treated with phorbol ester (PMA) in order to evaluate the effect on expression of urokinase-type plasminogen activator (uPA). Preincubation of the cells with bik reduced the ability of PMA to trigger the uPA expression at the gene level and at the protein level. We next asked whether the mechanism of inhibition of uPA expression by bik is due to interference with MAP kinase, since PMA could also activate a signaling pathway involving MEK/ERK/c-Jun-dependent uPA expression. When cells were preincubated with bik, we could detect suppression of phosphorylation of these proteins, demonstrating that bik markedly suppresses the cell motility possibly through negative regulation of MEK/ERK/c-Jun-dependent mechanisms, and that these changes in behavior are correlated with a coordinated down-regulation of uPA which is likely to contribute to the cell invasion processes. To clarify the role of bik on tumor metastasis, HRA cells were transfected with an expression vector harboring a cDNA encoding for human bik. Transfection of HRA with the bik cDNA resulted in five variants stably expressing functional bik and significantly reduced invasion, but not proliferation, adhesion, or migration relative to the parental cells. Animals with bik* transfectants induced reduced peritoneal dissemination and long term survival. These results suggest that transfection with the bik gene induces the suppression of tumor cell invasion and peritoneal dissemination, and can prolong survival. This pre-clinical animal model offers the possibility to explore gene therapy as a new treatment modality for ovarian cancer.     

Occupy tissue: The movement in cancer metastasis

The critical role of migration and invasion in cancer metastasis warrants new therapeutic approaches targeting the machinery regulating cell migration and invasion. While 2-dimensional (2D) models have helped identify a range of adhesion molecules, cytoskeletal components and regulators that are potentially important for cell migration, the use of models that better mimic the 3-dimensional (3D) environment has yielded new insights into the physiology of cell movement. For example, studying cells in 3D models has revealed that invading cancer cells may switch between heterogeneous invasion modes and thus evade pharmacological inhibition of invasion. Here we summarize published data in which the role of cell adhesion molecules in 2D vs. 3D migration have been directly compared and discuss mechanisms that regulate migration speed and persistence in 2D and 3D. Finally we discuss limits of 3D culture models to recapitulate the in vivo �situation.     

Enhanced expression of Rab27A gene by breast cancer cells promoting invasiveness and the metastasis potential by secretion of insulin-like growth factor-II

In addition to the functions of transporting melanosome in melanocytes and releasing contents of lytic granules in CTLs, Rab27A was recently shown to be involved in exocytosis of insulin and chromaffin granules in endocrine cells; it was also reported to be expressed in an exceptionally broad range of specialized secretory cells. As autocrine and paracrine cytokines are essential for invasion and metastasis in some solid tumors, blocking them may be an effective strategy to prevent tumor dissemination. In the present study, we show that Rab27A is associated with invasive and metastatic potentials of human breast cancer cells. The overexpression of Rab27A protein redistributed the cell cycle and increased the invasive and metastatic abilities in breast cancer cells both in vitro and in vivo. We also certified that Rab27A conferred the invasive and metastatic phenotypes on breast cancer cells by promoting the secretion of insulin-like growth factor-II (IGF-II), which regulates the expression of p16, vascular endothelial growth factor, matrix metalloproteinase-9, cathepsin D, cyclin D1, and urokinase-type plasminogen activator. These data provide functional evidence that Rab27A acts as a novel mediator of invasion and metastasis promotion in human breast cancer cells, at least in part, through regulating the secretion of IGF-II, suggesting that synergistic suppression of Rab27A and IGF-II activities holds a promise for preventing breast cancer invasion and metastasis.     

Cyclin B1 Suppresses Colorectal Cancer Invasion and Metastasis by Regulating E-Cadherin

Cyclin B1, a mitotic cyclin, has been implicated in malignances. However, its contribution to colorectal cancer invasion and metastasis are still not well understood. Here, we demonstrated that the invasion and metastasis of colorectal cancer is regulated by Cyclin B1. Overexpression of Cyclin B1 was observed in colorectal cancer tissues, but this elevated expression was negatively associated with lymph node metastasis, distant metastasis stage, and TNM stage. The Kaplan-Meier survival analysis proved that low Cyclin B1 expression was associated with poor overall survival of patients with colorectal cancer. Inhibition of Cyclin B1 in colorectal cancer cells enhanced the cell migration and invasion of three different colorectal cancer cell lines. In studying the possible mechanism by which Cyclin B1 suppresses colorectal cancer invasion and metastasis, we observed that suppression of Cyclin B1 decreased the expression of E-cadherin protein level. Our findings suggest that Cyclin B1 could suppress the invasion and metastasis of colorectal cancer cells through regulating E-cadherin expression, which enables the development of potential intervention strategies for colorectal cancer.     

AEG‐1 induces gastric cancer metastasis by upregulation of eIF4E expression

Gastric cancer is the third leading cause of cancer‐related deaths worldwide, and patients with lymph node, peritoneal and distant metastasis have a poor prognosis. Overexpression of Astrocyte‐elevated gene‐1 (AEG‐1) has been reported to be correlated with the progression and metastasis of gastric cancer. However, its mechanisms are quite unclear. In this study, we found that elevated expression of AEG‐1 was correlated with metastasis in human gastric cancer tissues. Moreover, gain‐ or loss‐of‐function of AEG‐1, respectively, promoted or suppressed epithelial–mesenchymal transition (EMT), migration and invasion of gastric cancer cells. AEG‐1 positively regulated eIF4E, MMP‐9 and Twist expression. Manipulating eIF4E expression by transfection of overexpression constructs or siRNAs partially eliminated AEG‐1‐regulated EMT, cell migration and invasion. In addition, overexpression or knockdown of eIF4E promoted or suppressed EMT, cell migration and invasion in parallel with upregulation of MMP‐9 and Twist expression, while manipulating eIF4E expression partially abrogated AEG‐1‐induced MMP‐9 and Twist. Finally, silencing of AEG‐1 expression not only inhibited tumour growth in parallel with downregulation of eIF4E, MMP‐9 and Twist expression in a xenograft nude mouse model, but also suppressed lymph node and peritoneal metastasis of gastric cancer in an orthotopic nude mouse model. These findings suggest that AEG‐1 promotes gastric cancer metastasis through upregulation of eIF4E‐mediated MMP‐9 and Twist, which provides new diagnostic markers and therapeutic targets for cancer metastasis.     

S-Allylcysteine reduces breast tumor cell adhesion and invasion

Previous studies show that aqueous garlic extract and its derivatives (e.g. S-allylcysteine [SAC]) prevent carcinogen-induced breast tumorigenesis. However, investigations testing the effect of SAC on later stages of breast tumorigenesis and/or metastasis have produced mixed results. Here we show that SAC significantly reduced anchorage-dependent and -independent growth of MDA-MB-231 breast tumor cells in a dose- and time-dependent fashion, and sub-lethal SAC-treatment altered mammary tumor cell adhesion and invasion through components of the extracellular matrix. We provide evidence to suggest increased expression of E-cadherin and reduced MMP-2 expression and activity are partially responsible for inhibition of mammary tumor cell invasion by SAC. Because E-cadherin and MMP-2 are important in cancer metastasis, these results suggest a link between SAC induction of E-cadherin and reduction of MMP2 activity with the inhibition of cell motility and invasion; thus providing evidence that events leading to breast cancer metastasis are repressed by sub-lethal SAC-treatment.     

Long noncoding RNA H19 participates in metformin-mediated inhibition of gastric cancer cell invasion

Recent research suggests that the first-line oral antidiabetes drug metformin may prevent gastric cancer progression and improve prognosis. Many studies have also shown that long noncoding RNAs (lncRNAs) play important roles in many biological processes. Therefore, we aimed to explore whether lncRNAs participate in the mechanisms by which metformin affects gastric cancer cells. In the current study, we found that metformin significantly inhibited the cellular functions of gastric cancer cells through Cell Counting Kit-8 and invasion assays. We found that lncRNA H19 was greatly downregulated in gastric cancer cells treated with metformin using lncRNA microassays. Based on bioinformatics analyses of the Oncomine and The Cancer Genome Atlas databases, H19 is shown to be overexpressed in gastric cancer tissues, with increased expression of H19 relating to advanced pathological tumor stage and pathological tumor node metastasis stage, indicating that H19 may be associated with the invasive ability of gastric cancer. We knocked down H19 in AGS and SGC7901 cell lines and found that knocked-down H19 could decrease gastric cancer cell invasion and that metformin could not further decrease invasion after the knock down. Moreover, H19 depletion increased AMPK activation and decreased MMP9 expression, and metformin could not further activate AMPK or decrease MMP9 in H19 knocked-down gastric cancer cells. In summary, metformin has a profound antitumor effect on gastric cancer cells, and H19 is a key component in the process of metformin suppressing gastric cancer cell invasion.     

Three-dimensional Co-culture Model for Tumor-stromal Interaction

Cancer progression (initiation, growth, invasion and metastasis) occurs through interactions between malignant cells and the surrounding tumor stromal cells. The tumor microenvironment is comprised of a variety of cell types, such as fibroblasts, immune cells, vascular endothelial cells, pericytes and bone-marrow-derived cells, embedded in the extracellular matrix (ECM). Cancer-associated fibroblasts (CAFs) have a pro-tumorigenic role through the secretion of soluble factors, angiogenesis and ECM remodeling. The experimental models for cancer cell survival, proliferation, migration, and invasion have mostly relied on two-dimensional monocellular and monolayer tissue cultures or Boyden chamber assays. However, these experiments do not precisely reflect the physiological or pathological conditions in a diseased organ. To gain a better understanding of tumor stromal or tumor matrix interactions, multicellular and three-dimensional cultures provide more powerful tools for investigating intercellular communication and ECM-dependent modulation of cancer cell behavior. As a platform for this type of study, we present an experimental model in which cancer cells are cultured on collagen gels embedded with primary cultures of CAFs.     

Tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone induces phosphorylation of mu- and m-calpain in association with increased secretion, cell migration, and invasion

Mounting evidence indicates that cigarette smoking not only promotes tumorigenesis but also may increase the spread of cancer cells in the body. However, the intracellular mechanism(s) by which cigarette smoking promotes metastasis of human lung cancer remains enigmatic. Nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is an important component in cigarette smoke and is formed by nitrosation of nicotine. mu- and m-calpain (calpain I and calpain II) are major members of the calpain family, which are ubiquitously expressed in both small cell lung cancer and non-small cell lung cancer cells. Our findings indicated that NNK potently induces phosphorylation of both mu- and m-calpain in association with their activation and increased migration as well as invasion of lung cancer cells. Treatment of cells with PD98059 blocked phosphorylation of m- and mu-calpain and resulted in suppression of NNK-induced cell migration and invasion. p44 MAPK/extracellular signal-regulated kinase 1 (ERK1) and p42 MAPK/ERK2 were activated by NNK, co-localized with mu- and m-calpain in cytoplasm, and directly phosphorylated mu- and m-calpain in vitro. These findings suggest a role for the ERK1/2 kinases as NNK-activated physiological calpain kinases. Specific knock-down of mu- and/or m-calpain expression by RNA interference blocked NNK-stimulated migration and invasion, suggesting that mu- and m-calpain may act as required targets in a NNK-induced metastatic signaling pathway. Furthermore, NNK promotes secretion of active mu- and m-calpain from lung cancer cells through vesicles, which may have the potential to cleave substrates in the extracellular matrix. Thus, NNK-induced cell migration and invasion may occur, at least in part, through a novel mechanism involving phosphorylation of calpains that leads to their activation and secretion, which may contribute to metastasis and/or progression of lung cancer.     

BMP2 accelerates the motility and invasiveness of gastric cancer cells via activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway

Up-regulation of bone morphogenetic proteins (BMPs) and their receptors by tumor is an important hallmark in cancer progression, as it contributes through autocrine and paracrine mechanisms to tumor development, invasion, and metastasis. Generally, increased motility and invasion are positively correlated with the epithelial-mesenchymal transition (EMT). The purpose of the present study was to determine whether BMP-2 signaling to induce gastric cancer cells to undergo EMT-mediated invasion might pass through the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. Herein we showed that gastric cancer cell lines express all the components of BMP-2 signaling, albeit to different extents. Moreover, an increased concentration of BMP-2 strongly enhanced motility and invasiveness in gastric cancer cells, whereas no increase was observed in cells treated with either Noggin (a BMP-2 inhibitor) or BMP-2 blocking antibodies. The stimulation of BMP-2 in gastric cancer cells induces a full EMT characterized by Snail induction, E-cadherin delocalization and down-regulation, and up-regulation of mesenchymal and invasiveness markers. Furthermore, blockade of BMP-2 signaling by Noggin or BMP-2 blocking antibodies also restored these changes in EMT markers. In addition, phosphorylation of Akt was also enhanced by treatment with BMP-2, but not Noggin or BMP-2 blocking antibodies. Pretreatment of gastric cancer cells with PI-3 kinase/Akt kinase inhibitor (kinase-dead Akt [DN-Akt], Akt siRNA, or LY294002) significantly inhibited BMP-2-induced EMT and invasiveness. Overall, our studies suggest that BMP-2 promotes motility and invasion of gastric cancer cells by activating PI-3 kinase/Akt and that targeting of this signaling pathway may provide therapeutic opportunities in preventing metastasis mediated by BMP-2.     

SB-431542抑制乳腺癌细胞BT-549的增殖和侵袭及其机理研究

肿瘤转移是导致肿瘤患者死亡的最主要原因,TGF-β超家族成员Nodal分子被证实参与肿瘤细胞的增殖和转移,因而基于Nodal信号为靶标开展抗肿瘤研究成为可能。该研究应用Western blot检测乳腺癌细胞株BT-549、T-47D、MCF-7、SK-BR-3和MDA—MB-231中的Nodal和基质金属蛋白酶-2（matrix metalloproteinase-2,MMP-2）的表达水平,发现它们在BT-549细胞中表达量最高。然后采用不同浓度_Nodal信号抑制剂SB．431542（1-50μmol／L）处理BT-549细胞48h,利用MTT法揭示20～50gmol／L的SB-431542抑制该细胞增殖。进一步利用细胞划痕和Transwell实验证明,10μmol／L的SB-431542可抑制乳腺癌细胞的迁移和侵袭。最后,通过明胶酶谱和Westernblot显示,10～30gmol／L的sB．431542可剂量依赖性地抑制MMP-2的表达和活性。上述结果说明,SB-431542通过阻断Nodal信号通路可效抑制乳腺癌细胞BT-549的增殖、迁移和侵袭,其作用机制可能与降低MMP-2的表达和活性有关。     

Hypoxia promotes HO-8910PM ovarian cancer cell invasion via Snail-mediated MT1-MMP upregulation

The molecular mechanisms of ovarian cancer cell invasion under hypoxia remain unclear. Here we employed a 3D collagen model and chick chorioallantoic membrane (CAM) invasion assay to explore the influence of hypoxia on ovarian cancer cell invasion. Hypoxia (both 1% O₂ and CoCl₂ 150 and 250 µM) induced HO-8910PM ovarian cancer cell invasion in 3D collagen and collagenolysis determined by hydroxyproline. Pretreatment with a hypoxia inducible factor-1α inhibitor, YC-1, or MMP inhibitor, GM6001, significantly inhibited 3D collagen invasion and degradation and cell proliferation. Hypoxia stimulated both mRNA and protein expressions of membrane-type 1 matrix metalloproteinase (MT1-MMP) and promoted MT1-MMP translocation to the cell surface in an YC-1 sensitive manner. MT1-siRNA transfection inhibited hypoxia-induced invasion, proliferation, and collagen degradation of cells in 3D collagen. Hypoxia stimulated Snail mRNA and protein expression as well as translocation to nucleus in an YC-1 sensitive manner. Overexpression of Snail with a recombinant plasmid in HO-8910PM cells resulted in an enhanced invasion in 3D collagen. Transfection with Snail-specific siRNA significantly decreased MT1-MMP expression and 3D collagen invasion. Hypoxia-treated cells significantly broke the upper CAM surface of 11-day-old chick embryos and infiltrated interstitial tissue, completely blocked in the presence of YC-1 or GM6001, or after MT1-MMP siRNA or Snail siRNA transfection. Together, these data suggest that hypoxia promotes HO-8910PM ovarian cancer cell traffic through 3D matrix via Snail-mediated MT1-MMP upregulation, a possible molecular mechanism of ovarian cancer cell invasion under hypoxia.     

3D Traction Stresses Activate Protease-Dependent Invasion of Cancer Cells

Cell invasion and migration that occurs, for example, in cancer metastasis is rooted in the ability of cells to navigate through varying levels of physical constraint exerted by the extracellular matrix. Cancer cells can invade matrices in either a protease-independent or a protease-dependent manner. An emerging critical component that influences the mode of cell invasion is the traction stresses generated by the cells in response to the physicostructural properties of the extracellular matrix. In this study, we have developed a reference-free quantitative assay for measuring three-dimensional (3D) traction stresses generated by cells during the initial stages of invasion into matrices exerting varying levels of mechanical resistance. Our results show that as cells encounter higher mechanical resistance, a larger fraction of them shift to protease-mediated invasion, and this process begins at lower values of cell invasion depth. On the other hand, the compressive stress generated by the cells at the onset of protease-mediated invasion is found to be independent of matrix stiffness, suggesting that 3D traction stress is a key factor in triggering protease-mediated cancer cell invasion. At low 3D compressive traction stresses, cells utilize bleb formation to indent the matrix in a protease independent manner. However, at higher stress values, cells utilize invadopodia-like structures to mediate protease-dependent invasion into the 3D matrix. The critical value of compressive traction stress at the transition from a protease-independent to a protease-dependent mode of invasion is found to be ∼165 Pa.