Membrane tension buffering by caveolae: a role in cancer?

The adaptable caveola coat generates a plasma membrane sensory system

Caveolae are atypical plasma membrane invaginations that take part in lipid sorting and regulation of oxidative and mechanical plasma membrane stress. Caveola formation requires caveolin, cavin, and specific lipid types. The recent advances in understanding the structure and assembly of caveolin and cavin complexes within the membrane context have clarified the fundamental processes underlying caveola biogenesis. In addition, the curvature of the caveola membrane is controlled by the regulatory proteins EHD2, pacsin2, and dynamin2, which also function to restrain the scission of caveolae from the plasma membrane (PM). Here, this is integrated with novel insights on caveolae as lipid and mechanosensing complexes that can dynamically flatten or disassemble to counteract mechanical, and oxidative stress.

EH domain-containing protein 2 (EHD2): Overview, biological function, and therapeutic potential

EH domain-containing protein 2 (EHD2) is a member of the EHD protein family and is mainly located in the plasma membrane, but can also be found in the cytoplasm and endosomes. EHD2 is also a nuclear-cytoplasmic shuttle protein. After entering the cell nuclear, EHD2 acts as a corepressor of transcription to inhibit gene transcription. EHD2 regulates a series of biological processes. As a key regulator of endocytic transport, EHD2 is involved in the formation and maintenance of endosomal tubules and vesicles, which are critical for the intracellular transport of proteins and other substances. The N-terminal of EHD2 is attached to the cell membrane, while its C-terminal binds to the actin-binding protein. After binding, EHD2 connects with the actin cytoskeleton, forming the curvature of the membrane and promoting cell endocytosis. EHD2 is also associated with membrane protein trafficking and receptor signaling, as well as in glucose metabolism and lipid metabolism. In this review, we highlight the recent advances in the function of EHD2 in various cellular processes and its potential implications in human diseases such as cancer and metabolic disease. We also discussed the prospects for the future of EHD2. EHD2 has a broad prospect as a therapeutic target for a variety of diseases. Further research is needed to explore its mechanism, which could pave the way for the development of targeted treatments.

A mechanosensitive caveolae-invadosome interplay drives matrix remodelling for cancer cell invasion

Invadosomes and caveolae are mechanosensitive structures that are implicated in metastasis. Here, we describe a unique juxtaposition of caveola clusters and matrix degradative invadosomes at contact sites between the plasma membrane of cancer cells and constricting fibrils both in 2D and 3D type I collagen matrix environments. Preferential association between caveolae and straight segments of the fibrils, and between invadosomes and bent segments of the fibrils, was observed along with matrix remodelling. Caveola recruitment precedes and is required for invadosome formation and activity. Reciprocally, invadosome disruption results in the accumulation of fibril-associated caveolae. Moreover, caveolae and the collagen receptor β1 integrin co-localize at contact sites with the fibrils, and integrins control caveola recruitment to fibrils. In turn, caveolae mediate the clearance of β1 integrin and collagen uptake in an invadosome-dependent and collagen-cleavage-dependent mechanism. Our data reveal a reciprocal interplay between caveolae and invadosomes that coordinates adhesion to and proteolytic remodelling of confining fibrils to support tumour cell dissemination.

Role of Caveolae family-related proteins in the development of breast cancer

Breast cancer has become the most significant malignant tumor threatening women's lives. Caveolae are concave pits formed by invagination of the plasma membrane that participate in many biological functions of the cell membrane, such as endocytosis, cell membrane assembly, and signal transduction. In recent years, Caveolae family-related proteins have been found to be closely related to the occurrence and development of breast cancer. The proteins associated with the Caveolae family-related include Caveolin (Cav) and Cavins. The Cav proteins include Cav-1, Cav-2 and Cav-3, among which Cav-1 has attracted the most attention as a tumor suppressor and promoting factor affecting the proliferation, apoptosis, migration, invasion and metastasis of breast cancer cells. Cav-2 also has dual functions of inhibiting and promoting cancer and can be expressed in combination with Cav-1 or play a regulatory role alone. Cav-3 has been less studied in breast cancer, and the loss of its expression can form an antitumor microenvironment. Cavins include Cavin-1, Cavin-2, Cavin-3 and Cavin-4. Cavin-1 inhibits Cav-1-induced cell membrane tubule formation, and its specific role in breast cancer remains controversial. Cavin-2 acts as a breast cancer suppressor, inhibiting breast cancer progression by blocking the transforming growth factor (TGF-β) signaling pathway. Cavin-3 plays an anticancer role in breast cancer, but its specific mechanism of action is still unclear. The relationship between Cavin-4 and breast cancer is unclear. In this paper, the role of Caveolae family-related proteins in the occurrence and development of breast cancer and their related mechanisms are discussed in detail to provide evidence supporting the further study of Caveolae family-related proteins as potential targets for the diagnosis and treatment of breast cancer.

Endocytosis in cancer and cancer therapy

Endocytosis is a complex process whereby cell surface proteins, lipids and fluid from the extracellular environment are packaged, sorted and internalized into cells. Endocytosis is also a mechanism of drug internalization into cells. There are multiple routes of endocytosis that determine the fate of molecules, from degradation in the lysosomes to recycling back to the plasma membrane. The overall rates of endocytosis and temporal regulation of molecules transiting through endocytic pathways are also intricately linked with signalling outcomes. This process relies on an array of factors, such as intrinsic amino acid motifs and post-translational modifications. Endocytosis is frequently disrupted in cancer. These disruptions lead to inappropriate retention of receptor tyrosine kinases on the tumour cell membrane, changes in the recycling of oncogenic molecules, defective signalling feedback loops and loss of cell polarity. In the past decade, endocytosis has emerged as a pivotal regulator of nutrient scavenging, response to and regulation of immune surveillance and tumour immune evasion, tumour metastasis and therapeutic drug delivery. This Review summarizes and integrates these advances into the understanding of endocytosis in cancer. The potential to regulate these pathways in the clinic to improve cancer therapy is also discussed.

The building blocks of caveolae revealed: caveolins finally take center stage

The ability of cells to divide, migrate, relay signals, sense mechanical stimuli, and respond to stress all rely on nanoscale invaginations of the plasma membrane known as caveolae. The caveolins, a family of monotopic membrane proteins, form the inner layer of the caveolar coat. Caveolins have long been implicated in the generation of membrane curvature, in addition to serving as scaffolds for signaling proteins. Until recently, however, the molecular architecture of caveolins was unknown, making it impossible to understand how they operate at a mechanistic level. Over the past year, two independent lines of evidence - experimental and computational - have now converged to provide the first-ever glimpse into the structure of the oligomeric caveolin complexes that function as the building blocks of caveolae. Here, we summarize how these discoveries are transforming our understanding of this long-enigmatic protein family and their role in caveolae assembly and function. We present new models inspired by the structure for how caveolins oligomerize, remodel membranes, interact with their binding partners, and reorganize when mutated. Finally, we discuss emerging insights into structural differences among caveolin family members that enable them to support the proper functions of diverse tissues and organisms.

Exploring cell and tissue mechanics with optical tweezers

Cellular and tissue biosystems emerge from the assembly of their constituent molecules and obtain a set of specific material properties. To measure these properties and understand how they influence cellular function is a central goal of mechanobiology. From a bottoms-up, physics or engineering point-of-view, such systems are a composition of basic mechanical elements. However, the sheer number and dynamic complexity of them, including active molecular machines and their emergent properties, makes it currently intractable to calculate how biosystems respond to forces. Because many diseases result from an aberrant mechanotransduction, it is thus essential to measure this response. Recent advances in the technology of optical tweezers have broadened their scope from single-molecule applications to measurements inside complex cellular environments, even within tissues and animals. Here, we summarize the basic optical trapping principles, implementations and calibration procedures that enable force measurements using optical tweezers directly inside cells of living animals, in combination with complementary techniques. We review their versatility to manipulate subcellular organelles and measure cellular frequency-dependent mechanics in the piconewton force range from microseconds to hours. As an outlook, we address future challenges to fully unlock the potential of optical tweezers for mechanobiology.

Interplay between mechanics and signalling in regulating cell fate

Mechanical signalling affects multiple biological processes during development and in adult organisms, including cell fate transitions, cell migration, morphogenesis and immune responses. Here, we review recent insights into the mechanisms and functions of two main routes of mechanical signalling: outside-in mechanical signalling, such as mechanosensing of substrate properties or shear stresses; and mechanical signalling regulated by the physical properties of the cell surface itself. We discuss examples of how these two classes of mechanical signalling regulate stem cell function, as well as developmental processes in vivo. We also discuss how cell surface mechanics affects intracellular signalling and, in turn, how intracellular signalling controls cell surface mechanics, generating feedback into the regulation of mechanosensing. The cooperation between mechanosensing, intracellular signalling and cell surface mechanics has a profound impact on biological processes. We discuss here our understanding of how these three elements interact to regulate stem cell fate and development.

Trafficking in blood vessel development

Blood vessels demonstrate a multitude of complex signaling programs that work in concert to produce functional vasculature networks during development. A known, but less widely studied, area of endothelial cell regulation is vesicular trafficking, also termed sorting. After moving through the Golgi apparatus, proteins are shuttled to organelles, plugged into membranes, recycled, or degraded depending on the internal and extrinsic cues. A snapshot of these protein-sorting systems can be viewed as a trafficking signature that is not only unique to endothelial tissue, but critically important for blood vessel form and function. In this review, we will cover how vesicular trafficking impacts various aspects of angiogenesis, such as sprouting, lumen formation, vessel stabilization, and secretion, emphasizing the role of Rab GTPase family members and their various effectors.

Monoclonal Antibody Discovery Based on Precise Selection of Single Transgenic Hybridomas with an On-Cell-Surface and Antigen-Specific Anchor

Hybridoma technology is widely used for monoclonal antibody (mAb) discovery, whereas the generation and identification of single hybridomas by the limiting dilution method (LDM) are tedious, inefficient, and time- and cost-consuming, especially for hapten molecules. Here, we describe a single transgenic hybridoma selection method (STHSM) that employs a transgenic Sp2/0 with an artificial and stable on-cell-surface anchor. The anchor was designed by combining the truncated variant transmembrane domain of EGFR with a biotin acceptor peptide AVI-tag, which was stably integrated into the genome of Sp2/0 via a piggyBac transposon. To ensure the subsequent precise selection of the hybridoma, the number of on-cell-surface anchors of the transfected Sp2/0 for fusion with immunized splenocytes was further normalized by flow cytometry at the single cell level. Then the single antigen-specific transgenic hybridomas were precisely identified and automatically selected using a CellenONE platform based on the fluorescence assay of the on-cell-surface anchor with the corresponding secreted antigen-specific mAb. The STHSM produced 579 single chloramphenicol (CAP)-specific transgenic hybridomas with a positive rate of 62.7% in 10 plates within 2 h by one-step selection, while only 12 single CAP-specific hybridomas with a positive rate of 6.3% in 40 plates required at least 32 days using the LDM with multiple subcloning steps. The best affinity of mAbs from the STHSM was more than 2-fold higher than that of those from the LDM, and this was mainly due to the preaffinity selection based on the on-cell-surface anchors and more interactions between the mAb and CAP. Then the mAbs from the STHSM and LDM were used to develop an immunoassay for CAP in spiked and natural biological samples. The method displayed satisfactory sensitivity, accuracy, and precision, demonstrating that the STHSM we developed is a versatile, practical, and efficient method for mAb discovery.

Caveolae promote successful abscission by controlling intercellular bridge tension during cytokinesis

During cytokinesis, the intercellular bridge (ICB) connecting the daughter cells experiences pulling forces, which delay abscission by preventing the assembly of the ESCRT scission machinery. Abscission is thus triggered by tension release, but how ICB tension is controlled is unknown. Here, we report that caveolae, which are known to regulate membrane tension upon mechanical stress in interphase cells, are located at the midbody, at the abscission site, and at the ICB/cell interface in dividing cells. Functionally, the loss of caveolae delays ESCRT-III recruitment during cytokinesis and impairs abscission. This is the consequence of a twofold increase of ICB tension measured by laser ablation, associated with a local increase in myosin II activity at the ICB/cell interface. We thus propose that caveolae buffer membrane tension and limit contractibility at the ICB to promote ESCRT-III assembly and cytokinetic abscission. Together, this work reveals an unexpected connection between caveolae and the ESCRT machinery and the first role of caveolae in cell division.

Substrate Stiffness-Driven Membrane Tension Modulates Vesicular Trafficking via Caveolin-1

Liver fibrosis, a condition characterized by extensive deposition and cross-linking of extracellular matrix (ECM) proteins, is idiosyncratic in cases of chronic liver injury. The dysregulation of ECM remodeling by hepatic stellate cells (HSCs), the main mediators of fibrosis, results in an elevated ECM stiffness that drives the development of chronic liver disease such as cirrhosis and hepatocellular carcinoma. Tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) is a key element in the regulation of ECM remodeling, which modulates the degradation and turnover of ECM components. We have previously reported that a rigid, fibrotic-like substrate can impact TIMP-1 expression at the protein level in HSCs without altering its mRNA expression. While HSCs are known to be highly susceptible to mechanical stimuli, the mechanisms through which mechanical cues regulate TIMP-1 at the post-translational level remain unclear. Here, we show a mechanism of regulation of plasma membrane tension by matrix stiffness. We found that this effect is orchestrated by the β1 integrin/RhoA axis and results in elevated exocytosis and secretion of TIMP-1 in a caveolin-1- and dynamin-2-dependent manner. We then show that TIMP-1 and caveolin-1 expression increases in cirrhosis and hepatocellular carcinoma. These conditions are associated with fibrosis, and this effect can be recapitulated in 3D fibrosis models consisting of hepatic stellate cells encapsulated in a self-assembling polypeptide hydrogel. This work positions stiffness-dependent membrane tension as a key regulator of enzyme secretion and function and a potential target for therapeutic strategies that aim at modulating ECM remodeling in chronic liver disease.

Shutting the gate: targeting endocytosis in acute leukemia

Endocytosis entails selective packaging of cell surface cargos in cytoplasmic vesicles, thereby controlling key intrinsic cellular processes as well as the response of normal and malignant cells to their microenvironment. The purpose of this review is to outline the latest advances in the development of endocytosis-targeting therapeutic strategies in hematological malignancies.

Caveolin1: its roles in normal and cancer stem cells

PURPOSE

Stem cells are characterized by the capability of self-renewal and multi-differentiation. Normal stem cells, which are important for tissue repair and tissue regeneration, can be divided into embryonic stem cells (ESCs) and somatic stem cells (SSCs) depending on their origin. As a subpopulation of cells within cancer, cancer stem cells (CSCs) are at the root of therapeutic resistance. Tumor-initiating cells (TICs) are necessary for tumor initiation. Caveolin1 (Cav1), a membrane protein located at the caveolae, participates in cell lipid transport, cell migration, cell proliferation, and cell signal transduction. The purpose of this review was to explore the relationship between Cav1 and stem cells.

RESULTS

In ESCs, Cav1 is beneficial for self-renewal, proliferation, and migration. In SSCs, Cav1 exhibits positive or/and negative effects on stem cell self-renewal, differentiation, proliferation, migration, and angiogenic capacity. Cav1 deficiency impairs normal stem cell-based tissue repair. In CSCs, Cav1 inhibits or/and promotes CSC self-renewal, differentiation, invasion, migration, tumorigenicity ability, and CSC formation. And suppressing Cav1 promotes chemo-sensitivity in CSCs and TICs.

CONCLUSION

Cav1 shows dual roles in stem cell biology. Targeting the Cav1-stem cell axis would be a new way for tissue repair and cancer drug resistance.

The role of extracellular matrix in tumour angiogenesis: the throne has NOx servants

The extracellular matrix (ECM) dynamics in tumour tissue are deregulated compared to the ECM in healthy tissue along with disorganized architecture and irregular behaviour of the residing cells. Nitric oxide (NO) as a pleiotropic molecule exerts different effects on the components of the ECM driving or inhibiting augmented angiogenesis and tumour progression and tumour cell proliferation and metastasis. These effects rely on the concentration of NO within the tumour tissue, the nature of the surrounding microenvironment and the sensitivity of resident cells to NO. In this review article, we summarize the recent findings on the correlation between the levels of NO and the ECM components towards the modulation of tumour angiogenesis in different types of cancers. These are discussed principally in the context of how NO modulates the expression of ECM proteins resulting in either the promotion or inhibition of tumour growth via tumour angiogenesis. Furthermore, the regulatory effects of individual ECM components on the expression of the NO synthase enzymes and NO production were reviewed. These findings support the current efforts for developing effective therapeutics for cancers.

Cav1/EREG/YAP Axis in the Treatment Resistance of Cav1-Expressing Head and Neck Squamous Cell Carcinoma

Simple Summary

The EGFR-targeting antibody cetuximab (CTX) combined with radiotherapy has been proven effective for the treatment of locally advanced head and neck squamous cell carcinoma (LA-HNSCC). Due to resistance to CTX, some patients do not benefit from the treatment and recurrence is observed. As caveolin-1 (Cav1) has been reported to affect the EGFR pathway, we aimed to elucidate how it might affect the response to CTX-radiotherapy. We showed that Cav1 expression conferred surviving, growing and motile capacities that protect cells against the combination of CTX-radiotherapy. The protecting effects of Cav1 are mediated by the Cav1/EREG/YAP axis. We also showed in a retrospective study that a high expression of Cav1 was predictive of locoregional relapse of LA-HNSCC. Cav1 should be taken into consideration in the future as a prognosis marker to identify the subgroup of advanced HNSCC at higher risk of recurrence, but also to help clinicians to choose the more appropriate therapeutic strategies.

Abstract

The EGFR-targeting antibody cetuximab (CTX) combined with radiotherapy is the only targeted therapy that has been proven effective for the treatment of locally advanced head and neck squamous cell carcinoma (LA-HNSCC). Recurrence arises in 50% of patients with HNSCC in the years following treatment. In clinicopathological practice, it is difficult to assign patients to classes of risk because no reliable biomarkers are available to predict the outcome of HPV-unrelated HNSCC. In the present study, we investigated the role of Caveolin-1 (Cav1) in the sensitivity of HNSCC cell lines to CTX-radiotherapy that might predict HNSCC relapse. Ctrl- and Cav-1-overexpressing HNSCC cell lines were exposed to solvent, CTX, or irradiation, or exposed to CTX before irradiation. Growth, clonogenicity, cell cycle progression, apoptosis, metabolism and signaling pathways were analyzed. Cav1 expression was analyzed in 173 tumor samples and correlated to locoregional recurrence and overall survival. We showed that Cav1-overexpressing cells demonstrate better survival capacities and remain proliferative and motile when exposed to CTX-radiotherapy. Resistance is mediated by the Cav1/EREG/YAP axis. Patients whose tumors overexpressed Cav1 experienced regional recurrence a few years after adjuvant radiotherapy ± chemotherapy. Together, our observations suggest that a high expression of Cav1 might be predictive of locoregional relapse of LA-HNSCC.

Lentinan Attenuated the PM2.5 Exposure-Induced Inflammatory Response, Epithelial-Mesenchymal Transition and Migration by Inhibiting the PVT1/miR-199a-5p/caveolin1 Pathway in Lung Cancer

PM2.5 plays an important role in the physiological and pathological progression of lung cancer. Lentinan exerts antitumor activity in many kinds of human cancers. Plasmacytoma variant translocation 1 (PVT1) exerts antitumor activity in many kinds of human cancers. However, the role and underlying molecular mechanism of PVT1 in the role of lentinan in PM2.5-exposed lung cancer are still largely unknown. Our study confirmed that PM2.5 exposure induced the production of inflammatory factors, epithelial-mesenchymal transition (EMT) and migration of lung cancer cells. Lentinan exerted antitumor effects by inhibiting the production of inflammatory factors, EMT, and migration of lung cancer cells. Lentinan suppressed PM2.5 exposure-induced cellular progression by inhibiting the PM2.5 exposure-induced elevation of PVT1 expression. PVT1 absorbed miR-199a, and miR-199a inhibited caveolin1 expression and thus formed the PVT1/miR-199a/caveolin1 signaling pathway in lung cancer cells. Our study revealed that silencing of the PVT1/miR-199a/caveolin1 signaling pathway affected the role of lentinan in PM2.5-exposed lung cancer cells. Thus, this study first investigated the role of lentinan in PM2.5-exposed lung cancer cells and further displayed the underlying molecular mechanism, providing a potential treatment for PM2.5-exposed lung cancer.

Caveolae: Mechanosensing and mechanotransduction devices linking membrane trafficking to mechanoadaptation

Mechanical forces (extracellular matrix stiffness, vascular shear stress, and muscle stretching) reaching the plasma membrane (PM) determine cell behavior. Caveolae are PM-invaginated nanodomains with specific lipid and protein composition. Being highly abundant in mechanically challenged tissues (muscles, lungs, vessels, and adipose tissues), they protect cells from mechanical stress damage. Caveolae flatten upon increased PM tension, enabling both force sensing and accommodation, critical for cell mechanoprotection and homeostasis. Thus, caveolae are highly plastic, ranging in complexity from flattened membranes to vacuolar invaginations surrounded by caveolae-rosettes-which also contribute to mechanoprotection. Caveolar components crosstalk with mechanotransduction pathways and recent studies show that they translocate from the PM to the nucleus to convey stress information. Furthermore, caveolae components can regulate membrane traffic from/to the PM to adapt to environmental mechanical forces. The interdependence between lipids and caveolae starts to be understood, and the relevance of caveolae-dependent membrane trafficking linked to mechanoadaption to different physiopathological processes is emerging.

Cisplatin-loaded albumin nanoparticle and study their internalization effect by using β-cyclodextrin

The present study with aim at enhancing the therapeutic and anti-cancer properties of cisplatin (CPT)-loaded bovine serum albumin (BSA) nanoparticles. The BSA nanoparticles containing CPT (CPT-BSANPs) were successfully prepared by the desolvation technique. The physicochemical characterization of the CPT-BSANPs were used by Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The particle size of CPT-BSANPs was found less than 200 nm with 75.02 ± 0.15% entrapment efficiency (EE), while zeta potential and PDI were -17.6 mV and 0.2, respectively. In vitro release behavior of the CPT from the carrier suggests that about 64% of the drug gets released after 48 hrs. The anti-cancer activities of the CPT-BSANPs were tested on MCF-7 cell lines. Our studies show that CPT-BSANPs nanoparticles showed specific targeting and enhanced cytotoxicity to MCF-7 cells when compared to the bare CPT. Thus results suggest that CPT-BSANPs fallowed caveolae-mediated endocytosis, it may become better option for intracellular delivery of anticancer drug.