Extracellular Matrix Cues Regulate Mechanosensing and Mechanotransduction of Cancer Cells

Abstract

Extracellular biophysical properties have particular implications for a wide spectrum of cellular behaviors and functions, including growth, motility, differentiation, apoptosis, gene expression, cell-matrix and cell-cell adhesion, and signal transduction including mechanotransduction. Cells not only react to unambiguously mechanical cues from the extracellular matrix (ECM), but can occasionally manipulate the mechanical features of the matrix in parallel with biological characteristics, thus interfering with downstream matrix-based cues in both physiological and pathological processes. Bidirectional interactions between cells and (bio)materials in vitro can alter cell phenotype and mechanotransduction, as well as ECM structure, intentionally or unintentionally. Interactions between cell and matrix mechanics in vivo are of particular importance in a variety of diseases, including primarily cancer. Stiffness values between normal and cancerous tissue can range between 500 Pa (soft) and 48 kPa (stiff), respectively. Even the shear flow can increase from 0.1-1 dyn/cm² (normal tissue) to 1-10 dyn/cm² (cancerous tissue). There are currently many new areas of activity in tumor research on various biological length scales, which are highlighted in this review. Moreover, the complexity of interactions between ECM and cancer cells is reduced to common features of different tumors and the characteristics are highlighted to identify the main pathways of interaction. This all contributes to the standardization of mechanotransduction models and approaches, which, ultimately, increases the understanding of the complex interaction. Finally, both the in vitro and in vivo effects of this mechanics-biology pairing have key insights and implications for clinical practice in tumor treatment and, consequently, clinical translation.

Keywords: EMT; cancer cells; cancer-associated fibroblasts (CAFs); cell mechanics; extracellular matrix (ECM) remodeling; fibronectin; immune cells; mechanosensing; plasticity.

Figure 1

The TME represents various cellular and acellular elements for effective targeting of cancer. Tumor-surrounding cellular targets of therapeutic strategies (1–3) can be tumor endothelial cells (TECs), cancer-associated fibroblasts (CAFs), and tumor-associated macrophages (TAMs) that can be M2 TAMs or reprogrammed M1 TAMs. Besides tumor-surrounding cellular targets, there can be cancer-cell-derived non-cellular targets (6–8), such as exosomes, cell-free DNA (cfDNA) and apoptotic bodies, and circulating tumor cells (CTCs).

Figure 2

Tension-based invasion mode of cancer cells. The invasion of CT26 colon carcinoma cells out of the spheroid after cutting the collagen gel nearby the spheroid (dashed line). The black arrows show the direction of collagen contraction, as the CT26 cells pull on the ECM fibers (see also text). Left image is shortly after the cut; the grey arrow points to the right image of the spheroid several hours thereafter. The blue arrows illustrate that the expanding spheroid pushes the collagen fibers away. The invading CT26 cells (red) align along the radial fibers and move away from the spheroid. Cells from the underlying layers join in and exert further traction (yellow arrows), which leads to an increase in tension that finally causes the collagen to stiffen and the contraction to subside. When collagen fibers are cut (dotted line) and a free square area is created, the cells in the direction of the cut are unable to generate sufficient tension in the ECM to disengage from the spheroid.

Figure 3

The mechanism of descent plasticity’s contribution to carcinogenesis. Typically, solid tumors are categorized based on the organ in which they originate and their histologic, molecular, and/or transcriptomic profiles. For instance, primary hepatic cancers can be histologically categorized as hepatocellular carcinoma (HCC) or cholangiocarcinoma (CC). Since the cellular origins of the various kinds of tumors continue to be uncertain, there are two universally prevailing hypotheses. The first hypothesis is that the various kinds of cancers originate from differing cells of origin. For liver cancer, this would imply that HCC originates from hepatocytes, but CC originates from cholangiocytes. The second hypothesis states that various kinds of cancers develop in a solitary organ through lineage plasticity, wherein distinct genetic or epigenetic contingencies may predispose a common-origin cell to evolve diverse malignant phenotypes. There exists evidence of lineage plasticity in cancer types, encompassing esophagus (referred to as intestinal metaplasia), liver (referred to as biliary transdifferentiation), lung and cervix (referred to as squamous metaplasia), and pancreas (referred to as acinar-to-ductal metaplasia).

Figure 4

Biophysical properties of biomaterials are increasingly becoming the focus of physical cancer research because of their important role in providing cancer cell function in the context of cancer cell plasticity. EMT = epithelial-to-mesenchymal transition, CSCs = cancer stem cells, ECM = extracellular matrix.

Figure 5

Mechanisms of the mechanotransduction process. (A) Cells are subject to diverse mechanical forces and can themselves apply forces to their surrounding environment, which exhibit various mechanical characteristics. (B) The kinds of mechanisms of mechanotransduction and possible ones (dotted lines) for mechanosensory proteins and aggregates of proteins within cells are sketched. FAs and AJs that both comprise numerous mechanosensory proteins exhibiting specific mechanotransduction mechanisms (see insets). Even though solely AJs are sketched, it is assumed that other cell–cell adhesions, such as desmosomes and tight junctions, can transfer the forces in a similar way. The envelope of the nucleus comprises distinct proteins and protein assemblies that react to the tension of the nuclear membrane, such as the nuclear pore complex, or they are phosphorylated due to forces, for instance, emerin and lamin. It is still not yet clear whether these proteins are mechanosensors. Even though the gating role of force-sensitive ion channels is driven by force-based alteration in the tension of the membrane, multiple ion channels are directly controlled through forces that are transferred by the linked actin cytoskeleton of the cell. (C) Various mechanisms of mechanotransduction over specific mechanosensors, such as catch bonds (1), cryptic binding sites (2), cryptic proteolytic sites (3), cryptic phosphorylation motifs (4), disruption bonding motifs (5), membrane tension (6), and stabilization of conformation (7). The black arrows indicate the direction of the force (F) acting on the molecules or structure. Examples for each of the seven types are shown in red.

Figure 6

Selected drug (chemotherapy) resistance mechanisms. The ECM-related factors, such as collagen, elastin, hyaluronic acid, tenascin-C, cancer-associated fibroblasts (CAFs), fibronectin, and laminin, can lead to abnormal vascularization/high fibrosis (altered physical barriers) and altered signal transduction due to changed ECM proteins (adhesion-related issues), and altered interplay between the ECM and PCSCs can hinder the effectiveness of chemotherapy. Chemotherapy causes fibrosis and altered vascularization in PDACs that change the pH, and induce hypoxia and stiffness, which affect drug movement. Most ECM proteins promote chemoresistance through activation of EMT and oncogenic signal transduction pathways, like MAPK, PI3K, and YAP. PCSC and their interaction with the ECM are also key drivers of resistance to chemotherapy.

Figure 7

The Hedgehog (Hh) signaling pathway. When Hh ligand binding is not present, the PTCH1 receptor is a negative regulator of the Hh pathway, as it impairs SMO. Upon tethering of Hh to PTCH1, it liberates the SMO. Subsequently, the SMO induces the downstream signal transduction pathway that causes the activation of the transcription factor GLI. As a consequence, the GLI translocates in the nucleus and initiates the Hh-pathway-driven gene expression. Activated GLI (aGLI); inactivated GLI (iGLI).

Figure 8

Static ECM cues can be applied to mechanically regulate cancer cells. Models for elasticity and stiffness of microenvironments are hydrogels (soft/stiff) or bending models based on pillars or lipid bilayer membranes (beige arrows). Models for topography can be of different length scales, such as nano-/submicroscale (Lithography/pattern), intermediate scale (roughness of the surface), and microscale (material manipulation) models. The models for geometry denote Lithography/pattern designs. The models for ligand presentation (low and high force) involve Lithography/pattern/chemical engineering. The red arrows indicate what can be modulated and explored.

Figure 9

Dormancy of cancer stem cells (CSCs). CSCs possess the unique characteristics to switch into a dormant state, which renders them unavailable for external attack and keeps them as pool of highly proliferative cells, which can regrow and alter the whole tumor, when it is needed.

Figure 10

Mechanotransduction routes and the structure of chromatin. Environmental forces are perceived via mechanoreceptors (1–4) on the cell membrane. They transduce forces to the actin cytoskeleton (5) and trigger calcium ion influx (6). The contraction of the actin cytoskeleton transfers forces to LINC complex (7), which is positioned on the nuclear envelope. Thereby, the nuclear envelope deforms and strains the mechanosensitive ion channels, such as Piezzo on the ER nuclear membrane (7). Calcium influx in the cytoplasm and nucleus is induced. Nuclear pore complex becomes dilated (8) that elevates the nuclear import of YAP/TAZ and mechanosensitive transcription factors. Globular (G)-actin and HDAC3 can enter and leave the nucleus. LINC complex (6) transfers forces to nuclear lamina (9), which exerts forces on the chromatin via lamina-associate domains (10, yellow). Chromatin structure comprises chromatin states (11), compartments of chromatin (12), chromatin domains/topologically associated domains (TADs) (13) (lilac ring structures generated by CTCF and cohesion) and chromatin loops generated by CTCF and cohesion (14) or through local transcription mechanisms, chromatin fiber (15), individual nucleosomes (16), and DNA (17).

Figure 11

Inside-out mechanobiology through molecular cues impacting the chromatin-structure-based mechanical and structural cues. Principles of molecular cues resulting in changes of the chromatin structure (top, blue) and their mechanical transduction to the ECM (bottom, red). Top left dark blue denotes the restructuring of chromatin and top right light blue stands for the chromatin in crisis. Bottom left dark red illustrates mechanical alterations of cells and bottom right light red denotes the alterations of the microenvironment.

Figure 12

The concept of matricellular proteins. The blue and yellow arrows denote upregulation and downregulation, respectively.