Actomyosin contractility and collective migration: may the force be with you

Mechanical Strain Promotes Proliferation of Adipose-Derived Stem Cells Through the Integrin β1-Mediated RhoA/Myosin Light Chain Pathway

External volume expansion (EVE) promotes proliferation of adipose-derived stem cells (ADSCs) during adipose tissue regeneration. However, the mechanism by which EVE is translated into biochemical signals and subsequently induces proliferation of ADSCs is poorly understood. Here, we investigated the strain in adipose tissue and mechanochemical signaling upon EVE in rats. In addition, the effect of mechanical strain on proliferation of ADSCs was assessed using a custom-built Flexcell device. The level of strain in adipose tissue upon EVE peaked at week 1 and then decreased over time, and the cell proliferation rate was similarly affected. Mechanical strain-dependent activation of integrin β1 and the RhoA/myosin light chain (MLC) pathway was involved in cell proliferation. The proliferation rate of ADSCs was higher under 12% mechanical strain than under 6% and 0% mechanical strain in vitro. Mechanical strain-dependent activation of integrin β1 promoted activation of the small GTPase RhoA and phosphorylation of MLC. Furthermore, knockdown of integrin β1 attenuated activation of the RhoA/MLC pathway and proliferation of ADSCs in response to mechanical strain. Taken together, this study provides the first evidence of mechanochemical signaling in response to EVE. These data may help elucidate the effects of different strain levels on adipose tissue regeneration. Impact statement External volume expansion (EVE) induces adipose tissue regeneration and has great therapeutic potential to correct soft tissue defects. This study showed that EVE promotes proliferation of adipose-derived stem cells by activating integrin β1 and its crucial downstream signaling molecules, namely the small GTPase RhoA and p-myosin light chain. The findings of this study may assist clinical tissue engineering applications and provide new insights into the regulation of adipose tissue regeneration in clinical practice.

PGC1α Suppresses Prostate Cancer Cell Invasion through ERRα Transcriptional Control

The PPARγ coactivator 1 alpha (PGC1α) is a prostate tumor suppressor that controls the balance between anabolism and catabolism. PGC1A downregulation in prostate cancer is causally associated with the development of metastasis. Here we show that the transcriptional complex formed by PGC1α and estrogen-related receptor 1 alpha (ERRα) controls the aggressive properties of prostate cancer cells. PGC1α expression significantly decreased migration and invasion of various prostate cancer cell lines. This phenotype was consistent with remarkable cytoskeletal remodeling and inhibition of integrin alpha 1 and beta 4 expression, both in vitro and in vivo. CRISPR/Cas9-based deletion of ERRα suppressed PGC1α regulation of cytoskeletal organization and invasiveness. Mechanistically, PGC1α expression decreased MYC levels and activity prior to inhibition of invasiveness. In addition, PGC1α and ERRα associated at the MYC promoter, supporting the inhibitory activity PGC1α. The inverse correlation between PGC1α-ERRα activity and MYC levels was corroborated in multiple prostate cancer datasets. Altogether, these results support that PGC1α-ERRα functions as a tumor-suppressive transcriptional complex through the regulation of metabolic and signaling events. SIGNIFICANCE: These findings describe how downregulation of the prostate tumor suppressor PGC1 drives invasiveness and migration of prostate cancer cells.

Genetic heterogeneity within collective invasion packs drives leader and follower cell phenotypes

Collective invasion, the coordinated movement of cohesive packs of cells, has become recognized as a major mode of metastasis for solid tumors. These packs are phenotypically heterogeneous and include specialized cells that lead the invasive pack and others that follow behind. To better understand how these unique cell types cooperate to facilitate collective invasion, we analyzed transcriptomic sequence variation between leader and follower populations isolated from the H1299 non-small cell lung cancer cell line using an image-guided selection technique. We now identify 14 expressed mutations that are selectively enriched in leader or follower cells, suggesting a novel link between genomic and phenotypic heterogeneity within a collectively invading tumor cell population. Functional characterization of two phenotype-specific candidate mutations showed that ARP3 enhances collective invasion by promoting the leader cell phenotype and that wild-type KDM5B suppresses chain-like cooperative behavior. These results demonstrate an important role for distinct genetic variants in establishing leader and follower phenotypes and highlight the necessity of maintaining a capacity for phenotypic plasticity during collective cancer invasion.

Unravelling tumour heterogeneity by single-cell profiling of circulating tumour cells

Single-cell technologies have contributed to unravelling tumour heterogeneity, now considered a hallmark of cancer and one of the main causes of tumour resistance to cancer therapies. Liquid biopsy (LB), defined as the detection and analysis of cells or cell products released by tumours into the blood, offers an appealing minimally invasive approach that allows the characterization and monitoring of tumour heterogeneity in individual patients. Here, we will review and discuss how circulating tumour cell (CTC) analysis at single-cell resolution provides unique insights into tumour heterogeneity that are not revealed by analysis of circulating tumour DNA (ctDNA) derived from LBs. The molecular analysis of CTCs provides complementary information to that of genomic aberrations determined using ctDNA to fully describe many different cellular components (for example, DNA, RNA, proteins and metabolites) that can influence tumour heterogeneity.

The transmembrane protein fibrocystin/polyductin regulates cell mechanics and cell motility

Polycystic kidney disease is a disorder that leads to fluid filled cysts that replace normal renal tubes. During the process of cellular development and in the progression of the diseases, fibrocystin can lead to impaired organ formation and even cause organ defects. Besides cellular polarity, mechanical properties play major roles in providing the optimal apical-basal or anterior-posterior symmetry within epithelial cells. A breakdown of the cell symmetry that is usually associated with mechanical property changes and it is known to be essential in many biological processes such as cell migration, polarity and pattern formation especially during development and diseases such as the autosomal recessive cystic kidney disease. Since the breakdown of the cell symmetry can be evoked by several proteins including fibrocystin, we hypothesized that cell mechanics are altered by fibrocystin. However, the effect of fibrocystin on cell migration and cellular mechanical properties is still unclear. In order to explore the function of fibrocystin on cell migration and mechanics, we analyzed fibrocystin knockdown epithelial cells in comparison to fibrocystin control cells. We found that invasiveness of fibrocystin knockdown cells into dense 3D matrices was increased and more efficient compared to control cells. Using optical cell stretching and atomic force microscopy, fibrocystin knockdown cells were more deformable and exhibited weaker cell-matrix as well as cell-cell adhesion forces, respectively. In summary, these findings show that fibrocystin knockdown cells displayed increased 3D matrix invasion through providing increased cellular deformability, decreased cell-matrix and reduced cell-cell adhesion forces.

Signaling pathways in cytoskeletal responses to plasma membrane depolarization in corneal endothelial cells

In previous work, we reported that plasma membrane potential depolarization (PMPD) provokes cortical F-actin remodeling in bovine corneal endothelial (BCE) cells in culture, which eventually leads to the appearance of intercellular gaps. In kidney epithelial cells it has been shown that PMPD determines an extracellular-signal-regulated kinase (ERK)/Rho-dependent increase in diphosphorylated myosin light chain (ppMLC). The present study investigated the signaling pathways involved in the response of BCE cells to PMPD. Differently to renal epithelial cells, we observed that PMPD leads to a decrease in monophosphorylated MLC (pMLC) without affecting diphosphorylated MLC. Also, that the pMLC reduction is a consequence of cyclic adenosine 3',5'-monophosphate (cAMP)/protein kinase A (PKA) activation. In addition, we found evidence that the cAMP increase mostly depends on soluble adenylyl cyclase activity. Inhibition of this enzyme reduces the effect of PMPD on the cAMP rise, F-actin remodeling, and pMLC decrease. No changes in phosho-ERK were observed, although we could determine that RhoA undergoes activation. Our results suggested that active RhoA is not involved in the intercellular gap formation. Overall, the findings of this study support the view that, differently to renal epithelial cells, in BCE cells PMPD determines cytoskeletal reorganization via activation of the cAMP/PKA pathway.

An emerging tumor invasion mechanism about the collective cell migration

Traditionally, the metastasis has been detected in the late stage of the cancer, which mostly leads to death. The classical opinion about tumor metastasis is that tumor cell migration begins with the single tumor cell and goes through a series of complicated procedures, and lastly arrives and survives at distant tissues and organs. However, emerging studies have found a new migration mechanism called collective cell migration in many cancers. The collective cell migration could move as clusters with the tight cell-cell junction in the tumor microenvironments, toward the traction established by the leader cells. In addition, the collective cell migration has been shown to have higher invasive capacity and higher resistance to the clinical treatments than the single tumor cell migration. Interestingly, the collective clusters of tumor cells have been detected in the early stage of the cancer patient, which has led to the understanding of the significance of early cancer screenings. Here, we reviewed the major principles and guidance of the collective cell migration mechanisms, and the specific manifestations in the different tumors such as breast cancer and lung cancer.

Adjustable viscoelasticity allows for efficient collective cell migration

Cell migration is essential for a wide range of biological processes such as embryo morphogenesis, wound healing, regeneration, and also in pathological conditions, such as cancer. In such contexts, cells are required to migrate as individual entities or as highly coordinated collectives, both of which requiring cells to respond to molecular and mechanical cues from their environment. However, whilst the function of chemical cues in cell migration is comparatively well understood, the role of tissue mechanics on cell migration is just starting to be studied. Recent studies suggest that the dynamic tuning of the viscoelasticity within a migratory cluster of cells, and the adequate elastic properties of its surrounding tissues, are essential to allow efficient collective cell migration in vivo. In this review we focus on the role of viscoelasticity in the control of collective cell migration in various cellular systems, mentioning briefly some aspects of single cell migration. We aim to provide details on how viscoelasticity of collectively migrating groups of cells and their surroundings is adjusted to ensure correct morphogenesis, wound healing, and metastasis. Finally, we attempt to show that environmental viscoelasticity triggers molecular changes within migrating clusters and that these new molecular setups modify clusters' viscoelasticity, ultimately allowing them to migrate across the challenging geometries of their microenvironment.

Therapeutic Targeting of Collective Invasion in Ovarian Cancer

Ovarian cancer is the seventh most commonly diagnosed cancer amongst women and has the highest mortality rate of all gynaecological malignancies. It is a heterogeneous disease attributed to one of three cell types found within the reproductive milieu: epithelial, stromal, and germ cell. Each histotype differs in etiology, pathogenesis, molecular biology, risk factors, and prognosis. Furthermore, the origin of ovarian cancer remains unclear, with ovarian involvement secondary to the contribution of other gynaecological tissues. Despite these complexities, the disease is often treated as a single entity, resulting in minimal improvement to survival rates since the introduction of platinum-based chemotherapy over 30 years ago. Despite concerted research efforts, ovarian cancer remains one of the most difficult cancers to detect and treat, which is in part due to the unique mode of its dissemination. Ovarian cancers tend to invade locally to neighbouring tissues by direct extension from the primary tumour, and passively to pelvic and distal organs within the peritoneal fluid or ascites as multicellular spheroids. Once at their target tissue, ovarian cancers, like most epithelial cancers including colorectal, melanoma, and breast, tend to invade as a cohesive unit in a process termed collective invasion, driven by specialized cells termed "leader cells". Emerging evidence implicates leader cells as essential drivers of collective invasion and metastasis, identifying collective invasion and leader cells as a viable target for the management of metastatic disease. However, the development of targeted therapies specifically against this process and this subset of cells is lacking. Here, we review our understanding of metastasis, collective invasion, and the role of leader cells in ovarian cancer. We will discuss emerging research into the development of novel therapies targeting collective invasion and the leader cell population.

Mechanical regulation of myofibroblast phenoconversion and collagen contraction

Activated fibroblasts promote physiological wound repair following tissue injury. However, dysregulation of fibroblast activation contributes to the development of fibrosis by enhanced production and contraction of collagen-rich extracellular matrix. At the peak of their activities, fibroblasts undergo phenotypic conversion into highly contractile myofibroblasts by developing muscle-like features, including formation of contractile actin-myosin bundles. The phenotype and function of fibroblasts and myofibroblasts are mechanically regulated by matrix stiffness using a feedback control system that is integrated with the progress of tissue remodelling. The actomyosin contraction machinery and cell-matrix adhesion receptors are critical elements that are needed for mechanosensing by fibroblasts and the translation of mechanical signals into biological responses. Here, we focus on mechanical and chemical regulation of collagen contraction by fibroblasts and the involvement of these factors in their phenotypic conversion to myofibroblasts.

Expression of the Alternative Oxidase Influences Jun N-Terminal Kinase Signaling and Cell Migration

Downregulation of Jun N-terminal kinase (JNK) signaling inhibits cell migration in diverse model systems. In Drosophila pupal development, attenuated JNK signaling in the thoracic dorsal epithelium leads to defective midline closure, resulting in cleft thorax. Here we report that concomitant expression of the Ciona intestinalis alternative oxidase (AOX) was able to compensate for JNK pathway downregulation, substantially correcting the cleft thorax phenotype. AOX expression also promoted wound-healing behavior and single-cell migration in immortalized mouse embryonic fibroblasts (iMEFs), counteracting the effect of JNK pathway inhibition. However, AOX was not able to rescue developmental phenotypes resulting from knockdown of the AP-1 transcription factor, the canonical target of JNK, nor its targets and had no effect on AP-1-dependent transcription. The migration of AOX-expressing iMEFs in the wound-healing assay was differentially stimulated by antimycin A, which redirects respiratory electron flow through AOX, altering the balance between mitochondrial ATP and heat production. Since other treatments affecting mitochondrial ATP did not stimulate wound healing, we propose increased mitochondrial heat production as the most likely primary mechanism of action of AOX in promoting cell migration in these various contexts.

Endothelial cell rearrangements during vascular patterning require PI3-kinase-mediated inhibition of actomyosin contractility

Angiogenesis is a dynamic process relying on endothelial cell rearrangements within vascular tubes, yet the underlying mechanisms and functional relevance are poorly understood. Here we show that PI3Kα regulates endothelial cell rearrangements using a combination of a PI3Kα-selective inhibitor and endothelial-specific genetic deletion to abrogate PI3Kα activity during vessel development. Quantitative phosphoproteomics together with detailed cell biology analyses in vivo and in vitro reveal that PI3K signalling prevents NUAK1-dependent phosphorylation of the myosin phosphatase targeting-1 (MYPT1) protein, thereby allowing myosin light chain phosphatase (MLCP) activity and ultimately downregulating actomyosin contractility. Decreased PI3K activity enhances actomyosin contractility and impairs junctional remodelling and stabilization. This leads to overstretched endothelial cells that fail to anastomose properly and form aberrant superimposed layers within the vasculature. Our findings define the PI3K/NUAK1/MYPT1/MLCP axis as a critical pathway to regulate actomyosin contractility in endothelial cells, supporting vascular patterning and expansion through the control of cell rearrangement.

Angiogenesis requires dynamic endothelial rearrangements and relative position changes within the vascular tubes. Here the authors show that a PI3K/NUAK1/MYPT1/MLCP pathway regulates actomyosin contractility in endothelial cells and cellular rearrangement during vascular patterning.

Myh10 deficiency leads to defective extracellular matrix remodeling and pulmonary disease

Impaired alveolar formation and maintenance are features of many pulmonary diseases that are associated with significant morbidity and mortality. In a forward genetic screen for modulators of mouse lung development, we identified the non-muscle myosin II heavy chain gene, Myh10. Myh10 mutant pups exhibit cyanosis and respiratory distress, and die shortly after birth from differentiation defects in alveolar epithelium and mesenchyme. From omics analyses and follow up studies, we find decreased Thrombospondin expression accompanied with increased matrix metalloproteinase activity in both mutant lungs and cultured mutant fibroblasts, as well as disrupted extracellular matrix (ECM) remodeling. Loss of Myh10 specifically in mesenchymal cells results in ECM deposition defects and alveolar simplification. Notably, MYH10 expression is downregulated in the lung of emphysema patients. Altogether, our findings reveal critical roles for Myh10 in alveologenesis at least in part via the regulation of ECM remodeling, which may contribute to the pathogenesis of emphysema.

Regulation of epithelial migration by epithelial cell adhesion molecule requires its Claudin-7 interaction domain

Epithelial cell adhesion molecule (EpCAM) is a glycoprotein on the surface of epithelial cells that is essential for intestinal epithelial integrity and expressed at high levels in many epithelial derived cancers and circulating tumor cells. Here we show the effect of EpCAM levels on migration of Madin-Darby-Canine Kidney (MDCK) epithelial cells. MDCK cells depleted of EpCAM show increased activation of extracellular signal-regulated kinase (ERK) and of myosin, and increased cell spreading and epithelial sheet migration into a gap. In contrast, over-expression of EpCAM inhibits ERK and myosin activation, and slows epithelial sheet migration. Loss of EpCAM is rescued by EpCAM-YFP mutated in the extracellular domain required for cis-dimerization whereas EpCAM-YFP with a mutation that inhibits Claudin-7 interaction cannot rescue increased ERK, myosin activation, and increased migration in EpCAM-depleted cells. In summary, these results indicate that interaction of EpCAM and Claudin-7 at the cell surface negatively regulates epithelial migration by inhibiting ERK and actomyosin contractility.

Gold Nanorod Photothermal Therapy Alters Cell Junctions and Actin Network in Inhibiting Cancer Cell Collective Migration

Most cancer-related deaths come from metastasis. It was recently discovered that nanoparticles could inhibit cancer cell migration. Whereas most researchers focus on single-cell migration, the effect of nanoparticle treatment on collective cell migration has not been explored. Collective migration occurs commonly in many types of cancer metastasis, where a group of cancer cells move together, which requires the contractility of the cytoskeleton filaments and the connection of neighboring cells by the cell junction proteins. Here, we demonstrate that gold nanorods (AuNRs) and the introduction of near-infrared light could inhibit the cancer cell collective migration by altering the actin filaments and cell junctions with significantly triggered phosphorylation changes of essential proteins, using mass spectrometry-based phosphoproteomics. Further observation using super-resolution stochastic optical reconstruction microscopy (STORM) showed the actin cytoskeleton filament bundles were disturbed, which is difficult to differentiate under a normal fluorescence microscope. The decreased expression level of N-cadherin junctions and morphological changes of tight junction protein zonula occludens 2 were also observed. All of these results indicate possible functions of the AuNR treatments in regulating and remodeling the actin filaments and cell junction proteins, which contribute to decreasing cancer cell collective migration.

Cadherins: cellular adhesive molecules serving as signalling mediators

The single pass, transmembrane proteins of the cadherin family have been appreciated as important proteins that regulate intercellular adhesion. In addition to this critical function, cadherins contribute to important signalling events that control cellular homeostasis. Many examples exist of classical, desmosomal and atypical cadherins participating in the regulation of signalling events that control homeostatic functions in cells. Much of the work on cadherin mediated signalling focuses on classical cadherins or on specific disease states such as pemphigus vulgaris. Cadherin mediated signalling has been shown to play critical roles during development, in proliferation, apoptosis, disease pathobiology and beyond. It is becoming increasingly clear that cadherins operate through a range of molecular mechanisms. The diversity of pathways and cellular functions regulated by cadherins suggests that we have only scratched the surface in terms of the roles that these versatile proteins play in signalling and cellular function.

Recent advances in understanding the complexities of metastasis

Tumour metastasis is a dynamic and systemic process. It is no longer seen as a tumour cell-autonomous program but as a multifaceted and complex series of events, which is influenced by the intrinsic cellular mutational burden of cancer cells and the numerous bidirectional interactions between malignant and non-malignant cells and fine-tuned by the various extrinsic cues of the extracellular matrix. In cancer biology, metastasis as a process is one of the most technically challenging aspects of cancer biology to study. As a result, new platforms and technologies are continually being developed to better understand this process. In this review, we discuss some of the recent advances in metastasis and how the information gleaned is re-shaping our understanding of metastatic dissemination.

Recent advances in understanding the complexities of metastasis

Tumour metastasis is a dynamic and systemic process. It is no longer seen as a tumour cell-autonomous program but as a multifaceted and complex series of events, which is influenced by the intrinsic cellular mutational burden of cancer cells and the numerous bidirectional interactions between malignant and non-malignant cells and fine-tuned by the various extrinsic cues of the extracellular matrix. In cancer biology, metastasis as a process is one of the most technically challenging aspects of cancer biology to study. As a result, new platforms and technologies are continually being developed to better understand this process. In this review, we discuss some of the recent advances in metastasis and how the information gleaned is re-shaping our understanding of metastatic dissemination.

The mechanical microenvironment regulates ovarian cancer cell morphology, migration, and spheroid disaggregation

There is growing appreciation of the importance of the mechanical properties of the tumor microenvironment on disease progression. However, the role of extracellular matrix (ECM) stiffness and cellular mechanotransduction in epithelial ovarian cancer (EOC) is largely unknown. Here, we investigated the effect of substrate rigidity on various aspects of SKOV3 human EOC cell morphology and migration. Young’s modulus values of normal mouse peritoneum, a principal target tissue for EOC metastasis, were determined by atomic force microscopy (AFM) and hydrogels were fabricated to mimic these values. We find that cell spreading, focal adhesion formation, myosin light chain phosphorylation, and cellular traction forces all increase on stiffer matrices. Substrate rigidity also positively regulates random cell migration and, importantly, directional increases in matrix tension promote SKOV3 cell durotaxis. Matrix rigidity also promotes nuclear translocation of YAP1, an oncogenic transcription factor associated with aggressive metastatic EOC. Furthermore, disaggregation of multicellular EOC spheroids, a behavior associated with dissemination and metastasis, is enhanced by matrix stiffness through a mechanotransduction pathway involving ROCK, actomyosin contractility, and FAK. Finally, this pattern of mechanosensitivity is maintained in highly metastatic SKOV3ip.1 cells. These results establish that the mechanical properties of the tumor microenvironment may play a role in EOC metastasis.

Feedback inhibition of actin on Rho mediates content release from large secretory vesicles

This work identified a cycle of actin assembly and disassembly in large secretory vesicles of Drosophila salivary glands. Actin disassembly is triggered by actin-dependent recruitment of a RhoGAP protein and is essential for the contractility of the vesicle, leading to content release to the lumen.

Secretion of adhesive glycoproteins to the lumen of Drosophila melanogaster larval salivary glands is performed by contraction of an actomyosin network assembled around large secretory vesicles, after their fusion to the apical membranes. We have identified a cycle of actin coat nucleation and disassembly that is independent of myosin. Recruitment of active Rho1 to the fused vesicle triggers activation of the formin Diaphanous and actin nucleation. This leads to actin-dependent localization of a RhoGAP protein that locally shuts off Rho1, promoting disassembly of the actin coat. When contraction of vesicles is blocked, the strict temporal order of the recruited elements generates repeated oscillations of actin coat formation and disassembly. Interestingly, different blocks to actin coat disassembly arrested vesicle contraction, indicating that actin turnover is an integral part of the actomyosin contraction cycle. The capacity of F-actin to trigger a negative feedback on its own production may be widely used to coordinate a succession of morphogenetic events or maintain homeostasis.

EphrinB1 promotes cancer cell migration and invasion through the interaction with RhoGDI1

Eph receptors and their corresponding ephrin ligands have been associated with regulating cell–cell adhesion and motility, and thus have a critical role in various biological processes including tissue morphogenesis and homeostasis, as well as pathogenesis of several diseases. Aberrant regulation of Eph/ephrin signaling pathways is implicated in tumor progression of various human cancers. Here, we show that a Rho family GTPase regulator, Rho guanine nucleotide dissociation inhibitor 1 (RhoGDI1), can interact with ephrinB1, and this interaction is enhanced upon binding the extracellular domain of the cognate EphB2 receptor. Deletion mutagenesis revealed that amino acids 327–334 of the ephrinB1 intracellular domain are critical for the interaction with RhoGDI1. Stimulation with an EphB2 extracellular domain-Fc fusion protein (EphB2-Fc) induces RhoA activation and enhances the motility as well as invasiveness of wild-type ephrinB1-expressing cells. These Eph-Fc-induced effects were markedly diminished in cells expressing the mutant ephrinB1 construct (Δ327–334) that is ineffective at interacting with RhoGDI1. Furthermore, ephrinB1 depletion by siRNA suppresses EphB2-Fc-induced RhoA activation, and reduces motility and invasiveness of the SW480 and Hs578T human cancer cell lines. Our study connects the interaction between RhoGDI1 and ephrinB1 to the promotion of cancer cell behavior associated with tumor progression. This interaction may represent a therapeutic target in cancers that express ephrinB1.