α-actinin-4 drives invasiveness by regulating myosin IIB expression and myosin IIA localization

Faster Amylin Aggregation on Fibrillar Collagen I Hastens Diabetic Progression through β-Cell Death and Loss of Function

Amyloid deposition of the neuroendocrine peptide amylin in islet tissues is a hallmark of type 2 diabetes (T2DM), leading to β-cell toxicity through nutrient deprivation, membrane rupture, and apoptosis. Though accumulation of toxic amylin aggregates in islet matrices is well documented, the role of the islet extracellular matrix in mediating amylin aggregation and its pathological consequences remains elusive. Here, we address this question by probing amylin interaction with collagen I (Col)─whose expression in the islet tissue increases during diabetes progression. By combining multiple biophysical techniques, we show that hydrophobic, hydrophilic, and cation-π interactions regulate amylin binding to Col, with fibrillar Col driving faster amylin aggregation. Amylin-entangled Col matrices containing high amounts of amylin induce death and loss of function in INS1E β-cells. Together, our results illustrate how amylin incorporation in islet matrices through amylin-Col interactions drives T2DM progression by impacting β-cell viability and insulin secretion.

Reassessing the Role of Tissue Factor Pathway Inhibitor 2 in Neoplastic and Non-Neoplastic Lesions

OBJECTIVES

Tissue factor pathway inhibitor 2 (TFPI2) is a serine protease inhibitor that suppresses tumors by preventing extracellular matrix degradation and invasion. In many malignancies, the TFPI2 promoter hypermethylation silences its transcription, increasing tumor aggressiveness. However, TFPI2 paradoxically facilitates tumor progression in certain malignancies. Elevated circulating TFPI2 levels correlate with increased cancer aggressiveness and poor prognosis in ovarian, endometrial, and renal cell carcinoma, though the mechanisms underlying its tumor-promoting effects remain unclear. This review consolidates recent findings on TFPI2 regulation, its downstream targets in cellular homeostasis, and its prognostic significance. Additionally, we reassess TFPI2's role in tumorigenesis, particularly in clear cell carcinoma, as well as in chronic inflammation.

METHODS

A comprehensive literature search was performed in PubMed and Google Scholar without time restriction.

RESULTS

TFPI2 expression is tightly regulated by transcription factors, signaling molecules, growth factors, cytokines, and epigenetic modification. TFPI2 regulates cell proliferation, inflammation, and extracellular matrix (ECM) remodeling, preserving tissue homeostasis. TFPI2 also regulates vascular endothelial and smooth muscle cell proliferation, key elements of the tumor microenvironment (TME). In the nucleus, it may modulate transcription factors to influence tumor-associated macrophage (TAM) polarization, facilitating cancer invasion. Its expression may be shaped by interactions between cancer cells and TAM activation. Beyond tumorigenesis, TFPI2 contributes to both inflammatory progression and resolution in diabetes, atherosclerosis, and preeclampsia.

CONCLUSIONS

TFPI2 may interact with TAMs and inflammatory cells to regulate cell proliferation and inflammation, maintaining tissue homeostasis.

Cell crowding activates pro-invasive mechanotransduction pathway in high-grade DCIS via TRPV4 inhibition and cell volume reduction

Cell crowding is a common microenvironmental factor influencing various disease processes, but its role in promoting cell invasiveness remains unclear. This study investigates the biomechanical changes induced by cell crowding, focusing on pro-invasive cell volume reduction in ductal carcinoma in situ (DCIS). Crowding specifically enhanced invasiveness in high-grade DCIS cells through significant volume reduction compared to hyperplasia-mimicking or normal cells. Mass spectrometry revealed that crowding selectively relocated ion channels, including TRPV4, to the plasma membrane in high-grade DCIS cells. TRPV4 inhibition triggered by crowding decreased intracellular calcium levels, reduced cell volume, and increased invasion and motility. During this process, TRPV4 membrane relocation primed the channel for later activation, compensating for calcium loss. Analyses of patient-derived breast cancer tissues confirmed that plasma membrane-associated TRPV4 is specific to high-grade DCIS and indicates the presence of a pro-invasive cell volume reduction mechanotransduction pathway. Hyperosmotic conditions and pharmacologic TRPV4 inhibition mimicked crowding-induced effects, while TRPV4 activation reversed them. Silencing TRPV4 diminished mechanotransduction in high-grade DCIS cells, reducing calcium depletion, volume reduction, and motility. This study uncovers a novel pro-invasive mechanotransduction pathway driven by cell crowding and identifies TRPV4 as a potential biomarker for predicting invasion risk in DCIS patients.

Nuclear α-actinin-4 regulates breast cancer invasiveness and EMT

Epithelial-to-mesenchymal transition (EMT) is a key process where cells lose their adhesion properties and augment their invasive properties. α-Actinin4 (ACTN4) is an actin crosslinking protein that responds to mechanical stimuli and is found to be elevated in breast cancer patients. While ACTN4 has been implicated in regulating cancer invasiveness by modulating cytoskeletal organization, its nuclear functions remain much less explored. Here we address this question by first establishing a correlation between nuclear localization and invasiveness in breast cancer cells. Using cancer databases, we then establish a correlation between ACTN4 expression and EMT in breast cancer. Interestingly, TGFβ-induced EMT induction in MCF10A normal mammary epithelial cells leads to increased ACTN4 expression and nuclear enrichment. We then show that ACTN4 knockdown in MDA-MB-231 breast cancer cells, which harbor sizeable fraction of nuclear ACTN4, leads to reduced invasiveness and loss of mesenchymal traits. Similar behavior was observed in knockdown cells expressing K255E ACTN4, which is primarily localized to the cytosol. Together, our findings establish a role for nuclear ACTN4 in regulating invasiveness via modulation of EMT.

CD44/Integrin β1 Association Drives Fast Motility on Hyaluronic Acid Substrates

In addition to proteins such as collagen (Col) and fibronectin, the extracellular matrix (ECM) is enriched with bulky proteoglycan molecules such as hyaluronic acid (HA). However, how ECM proteins and proteoglycans collectively regulate cellular processes has not been adequately explored. Here, we address this question by studying cytoskeletal and focal adhesion organization and dynamics on cells cultured on polyacrylamide hydrogels functionalized with Col, HA and a combination of Col and HA (Col/HA). We show that fastest migration on HA substrates is attributed to the presence of smaller and weaker focal adhesions. Integrinβ $\beta $ 1 co-localization and its association with CD44-which is the receptor for HA, and insensitivity of cell spreading to RGD on HA substrates suggests that focal adhesions on HA substrates are formed via integrin association with HA bound CD44. Consistent with this, adhesion formation and cell motility were inhibited when CD44 was knocked out. Collectively, our results suggest that association of integrinβ $\beta $ 1 with CD44 drives fast motility on HA substrates.

Live-cell imaging and CLEM reveal the existence of ACTN4-dependent ruffle-edge lamellipodia acting as a novel mode of cell migration

α-Actinin-4 (ACTN4) expression levels are correlated with the invasive and metastatic potential of cancer cells; however, the underlying mechanism remains unclear. Here, we identified ACTN4-localized ruffle-edge lamellipodia using live-cell imaging and correlative light and electron microscopy (CLEM). BSC-1 cells expressing EGFP-ACTN4 showed that ACTN4 was most abundant in the leading edges of lamellipodia, although it was also present in stress fibers and focal adhesions. ACTN4 localization in lamellipodia was markedly diminished by phosphoinositide 3-kinase inhibition, whereas its localization in stress fibers and focal adhesions remained. Furthermore, overexpression of ACTN4, but not ACTN1, promoted lamellipodial formation. Live-cell analysis demonstrated that ACTN4-enriched lamellipodia are highly dynamic and associated with cell migration. CLEM revealed that ACTN4-enriched lamellipodia exhibit a characteristic morphology of multilayered ruffle-edges that differs from canonical flat lamellipodia. Similar ruffle-edge lamellipodia were observed in A549 and MDA-MB-231 invasive cancer cells. ACTN4 knockdown suppressed the formation of ruffle-edge lamellipodia and cell migration during wound healing in A549 monolayer cultures. Additionally, membrane-type 1 matrix metalloproteinase was observed in the membrane ruffles, suggesting that ruffle-edge lamellipodia have the ability to degrade the extracellular matrix and may contribute to active cell migration/invasion in certain cancer cell types.

Unveiling the enigmatic role of MYH9 in tumor biology: a comprehensive review

Non-muscle myosin heavy chain IIA (MYH9), a member of the non-muscle myosin II (NM II) family, is widely expressed in cells. The interaction of MYH9 with actin in the cytoplasm can hydrolyze ATP, completing the conversion of chemical energy to mechanical motion. MYH9 participates in various cellular processes, such as cell adhesion, migration, movement, and even signal transduction. Mutations in MYH9 are often associated with autosomal dominant platelet disorders and kidney diseases. Over the past decade, tumor-related research has gradually revealed a close relationship between MYH9 and the occurrence and development of tumors. This article provides a review of the research progress on the role of MYH9 in cancer regulation. We also discussed the anti-cancer effects of MYH9 under special circumstances, as well as its regulation of T cell function. In addition, given the importance of MYH9 as a key hub in oncogenic signal transduction, we summarize the current therapeutic strategies targeting MYH9 as well as the ongoing challenges.

Bulky glycocalyx drives cancer invasiveness by modulating substrate-specific adhesion

The majority of the eukaryotic cell surface is decorated with a layer of membrane-attached polysaccharides and glycoproteins collectively referred to as the glycocalyx. While the formation of a bulky glycocalyx has been associated with the cancer progression, the mechanisms by which the glycocalyx regulates cancer invasiveness are incompletely understood. We address this question by first documenting subtype-specific expression of the major glycocalyx glycoprotein Mucin-1 (MUC1) in breast cancer patient samples and breast cancer cell lines. Strikingly, glycocalyx disruption led to inhibition of 2D motility, loss of 3D invasion, and reduction of clonal scattering in breast cancer cells at the population level. Tracking of 2D cell motility and 3D invasiveness of MUC1-based sorted subpopulations revealed the fastest motility and invasiveness in intermediate MUC1-expressing cells, with glycocalyx disruption abolishing these effects. While differential sensitivity in 2D motility is attributed to a nonmonotonic dependence of focal adhesion size on MUC1 levels, higher MUC1 levels enhance 3D invasiveness via increased traction generation. In contrast to inducing cell rounding on collagen-coated substrates, high MUC1 level promotes cell adhesion and confers resistance to shear flow on substrates coated with the endothelial surface protein E-selectin. Collectively, our findings illustrate how MUC1 drives cancer invasiveness by differentially regulating cell-substrate adhesion in a substrate-dependent manner.

Bulky glycocalyx shields cancer cells from invasion-associated stresses

The glycocalyx-that forms a protective barrier around cells-has been implicated in cancer cell proliferation, survival, and metastasis. However, its role in maintaining the integrity of DNA/nucleus during migration through dense matrices remains unexplored. In this study, we address this question by first documenting heterogeneity in glycocalyx expression in highly invasive MDA-MB-231 breast cancer cells, and establishing a negative correlation between cell size and glycocalyx levels. Next, we set-up transwell migration through 3 µm pores, to isolate two distinct sub-populations and to show that the early migrating cell sub-population possesses a bulkier glycocalyx and undergoes less DNA damage and nuclear rupture, assessed using γH2AX foci formation and nuclear/cytoplasmic distribution of Ku70/80. Interestingly, enzymatic removal of glycocalyx led to disintegration of the nuclear membrane indicated by increased cytoplasmic localisation of Ku70/80, increased nuclear blebbing and reduction in nuclear area. Together, these results illustrate an inverse association between bulkiness of the glycocalyx and nuclear stresses, and highlights the mechanical role of the glycocalyx in shielding migration associated stresses.

Particle-based model of mechanosensory contractility kit assembly

Cell shape change processes, such as proliferation, polarization, migration, and cancer metastasis, rely on a dynamic network of macromolecules. The proper function of this network enables mechanosensation, the ability of cells to sense and respond to mechanical cues. Myosin II and cortexillin I, critical elements of the cellular mechanosensory machinery, preassemble in the cytoplasm of Dictyostelium cells into complexes that we have termed contractility kits (CKs). Two IQGAP proteins then differentially regulate the mechanoresponsiveness of the cortexillin I-myosin II elements within CKs. To investigate the mechanism of CK self-assembly and gain insight into possible molecular means for IQGAP regulation, we developed a coarse-grained excluded volume molecular model in which all protein polymers are represented by nm-sized spheres connected by spring-like links. The model is parameterized using experimentally measured parameters acquired through fluorescence cross-correlation spectroscopy and fluorescence correlation spectroscopy, which describe the interaction affinities and diffusion coefficients for individual molecular components, and which have also been validated via several orthogonal methods. Simulations of wild-type and null-mutant conditions implied that the temporal order of assembly of these kits is dominated by myosin II dimer formation and that IQGAP proteins mediate cluster growth. In addition, our simulations predicted the existence of "ambiguous" CKs that incorporate both classes of IQGAPs, and we confirmed this experimentally using fluorescence cross-correlation spectroscopy. The model serves to describe the formation of the CKs and how their assembly enables and regulates mechanosensation at the molecular level.

The lectin Discoidin I acts in the cytoplasm to help assemble the contractile machinery

Cellular functions, such as division and migration, require cells to undergo robust shape changes. Through their contractility machinery, cells also sense, respond, and adapt to their physical surroundings. In the cytoplasm, the contractility machinery organizes into higher order assemblies termed contractility kits (CKs). Using Dictyostelium discoideum, we previously identified Discoidin I (DscI), a classic secreted lectin, as a CK component through its physical interactions with the actin crosslinker Cortexillin I (CortI) and the scaffolding protein IQGAP2. Here, we find that DscI ensures robust cytokinesis through regulating intracellular components of the contractile machinery. Specifically, DscI is necessary for normal cytokinesis, cortical tension, membrane-cortex connections, and cortical distribution and mechanoresponsiveness of CortI. The dscI deletion mutants also have complex genetic epistatic relationships with CK components, acting as a genetic suppressor of cortI and iqgap1, but as an enhancer of iqgap2. This work underscores the fact that proteins like DiscI contribute in diverse ways to the activities necessary for optimal cell function.

Cancer as a biophysical disease: Targeting the mechanical-adaptability program

With the number of cancer cases projected to significantly increase over time, researchers are currently exploring "nontraditional" research fields in the pursuit of novel therapeutics. One emerging area that is steadily gathering interest revolves around cellular mechanical machinery. When looking broadly at the physical properties of cancer, it has been debated whether a cancer could be defined as either stiffer or softer across cancer types. With numerous articles supporting both sides, the evidence instead suggests that cancer is not particularly regimented. Instead, cancer is highly adaptable, allowing it to endure the constantly changing microenvironments cancer cells encounter, such as tumor compression and the shear forces in the vascular system and body. What allows cancer cells to achieve this adaptability are the particular proteins that make up the mechanical network, leading to a particular mechanical program of the cancer cell. Coincidentally, some of these proteins, such as myosin II, α-actinins, filamins, and actin, have either altered expression in cancer and/or some type of direct involvement in cancer progression. For this reason, targeting the mechanical system as a therapeutic strategy may lead to more efficacious treatments in the future. However, targeting the mechanical program is far from trivial. As involved as the mechanical program is in cancer development and metastasis, it also helps drive many other key cellular processes, such as cell division, cell adhesion, metabolism, and motility. Therefore, anti-cancer treatments targeting the mechanical program must take great care to avoid potential side effects. Here, we introduce the potential of targeting the mechanical program while also providing its challenges and shortcomings as a strategy for cancer treatment.

First person – Amlan Barai

First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Amlan Barai is first author on ‘ α-Actinin-4 drives invasiveness by regulating myosin IIB expression and myosin IIA localization’, published in JCS. Amlan is an Institute Postdoctoral Fellow in the lab of Prof. Shamik Sen at Indian Institute of Technology Bombay, where he uses multidisciplinary approaches to understand cell behavior and cellular dynamic processes including cancer development, metastasis and tumor heterogeneity.