Cytoskeleton (Hoboken, N.J.)最新文献

A key characteristic of cancer cells is their ability to induce changes in their microenvironment that render it permissive to tumor growth, invasion and metastasis. Indeed, these changes are required for tumor progression. Consequently, the tumor microenvironment is emerging as a key source of new targets against cancer, with novel therapies aimed at reversing tumor-promoting changes, reinstating a tumor-hostile microenvironment and suppressing disease progression. RHO-ROCK signaling, and consequent tension within the cellular actomyosin cytoskeleton, regulates a paracrine signaling cascade that establishes a tumor-promoting microenvironment. Here, we show that consistent with our observations in breast cancer, enhanced ROCK activity and consequent production of CRELD2 is associated with the recruitment and tumor-promoting polarization of cancer-associated fibroblasts in cutaneous squamous cell carcinoma. Our observations provide support for the notion that the role of RHO-ROCK signaling in establishing a tumor-promoting microenvironment may be conserved across patients and potentially also different cancer types.

Introduction: Actin has been implicated in lens opacification; however, the specific actin-related pathways involved in cataracts remain unelucidated. In this study, actin-related proteome changes and signaling pathways involved in the development of cataracts were evaluated.

Methods: The anterior capsule and phacoemulsification (phaco) cassette contents were collected during cataract surgery from 11 patients with diabetic cataract (DC), 12 patients with age-related cataract (ARC), and seven patients with post-vitrectomy cataract (PVC). Untargeted, global identification and quantification of proteins was performed through liquid chromatography-mass spectrometry with the data-independent acquisition (DIA).

Results: In phaco cassette samples, proteins with significantly lower expression in ARC than in DC and PVC were involved in various pathways, including actin binding, actin cytoskeleton reorganization, actin filament capping, cortical actin cytoskeleton organization, and small GTPase-mediated signal transduction pathways. In anterior capsules, proteins with significantly lower expression in ARC than in DC and PVC were involved in actin binding and actin cytoskeleton reorganization pathways.

Conclusion: Actin cytoskeleton and actin-binding proteins are involved in lens fiber elongation and differentiation. Rho GTPases contribute to actin cytoskeletal reorganization, and their inactivation is linked to abnormal lens fiber migration. These findings link actin binding to lens fiber integrity, lens opacification, and cataracts.

Wolbachia are obligate intracellular alphaproteobacteria that enhance their spreading by altering the reproductive mechanisms of several invertebrates. Among the reproductive alterations, Wolbachia also causes cytoplasmic incompatibility that leads to embryo death when infected males are crossed with uninfected females, thus selecting infected females. However, the presence of Wolbachia has important fitness costs and infected Drosophila simulans males produce less sperm than their uninfected counterparts. Such sperm suffer, indeed, of some structural alterations that hinder their proper function. We took advantage of the fact that several sperm have abnormal distal regions of the tail, in which the plasma membrane is broken and the axonemal components splayed, making the ultrastructural aspects clearly observable. We found that axoneme reduction in the distal region of the sperm does not follow a unique pattern as observed in other insects, but occurs by losing accessory tubules or peripheral doublets. The axonemal tubules contain distinct coaxial ring-like structures that are still observed after axoneme fragmentation and form large clusters of several units.

The actin cytoskeleton is composed of both branched and unbranched actin filaments. In mammals, the unbranched actin filaments are primarily copolymers of actin and tropomyosin. Biochemical and imaging studies indicate that different tropomyosin isoforms are segregated to different actin filament populations in cells and tissues, providing isoform-specific functionality to the actin filament. Intrinsic to this model is the prediction that single-molecule imaging of tropomyosin isoforms would confirm homopolymer formation along the length of single actin filaments, a knowledge gap that remains unaddressed in the cellular environment. We combined chemical labeling of genetically engineered tropomyosin isoforms with electron tomography to locate individual tropomyosin molecules in fibroblasts. We find that the organization of two non-muscle tropomyosins, Tpm3.1 with Tpm4.2, can be distinguished from each other using light and electron microscopy. Visualization of single tropomyosin molecules associated with actin filaments supports the hypothesis that tropomyosins form continuous homopolymers, instead of heteropolymers, in the presence of all physiologically native actin-binding proteins. This is true for both isoforms tested. Furthermore, the data suggest that the tropomyosin molecules on one side of an actin filament may not be in register with those on the opposite side, indicating that each tropomyosin polymer may assembly independently.

The Ras-induced ERK pathway (Raf-MEK-ERK signaling cascade) regulates a variety of cellular responses including cell proliferation, survival, and migration. Activating mutations in RAS genes, particularly in the KRAS gene, constitutively activate the ERK pathway, resulting in tumorigenesis, cancer cell invasion, and metastasis. DA-Raf1 (DA-Raf) is a splicing isoform of A-Raf and contains the Ras-binding domain but lacks the kinase domain. Consequently, DA-Raf antagonizes the Ras-ERK pathway in a dominant-negative manner and can serve as a tumor suppressor that targets mutant Ras protein-induced tumorigenesis. We show here that MEK inhibitors and DA-Raf interfere with the in vitro collective cell migration and invasion of human KRAS-mutant carcinoma cell lines, the lung adenocarcinoma A549, colorectal carcinoma HCT116, and pancreatic carcinoma MIA PaCa-2 cells. DA-Raf expression was silenced in these cancer cell lines. All these cell lines had high collective migration abilities and invasion properties in Matrigel, compared with nontumor cells. Their migration and invasion abilities were impaired by suppressing the ERK pathway with the MEK inhibitors U0126 and trametinib, an approved anticancer drug. Expression of DA-Raf in MIA PaCa-2 cells reduced the ERK activity and hindered the migration and invasion abilities. Therefore, DA-Raf may function as an invasion suppressor protein in the KRAS-mutant cancer cells by blocking the Ras-ERK pathway when DA-Raf expression is induced in invasive cancer cells.

Focal adhesions serve as structural and signaling hubs, facilitating bidirectional communication at the cell-extracellular matrix interface. Paxillin and the related Hic-5 (TGFβ1i1) are adaptor/scaffold proteins that recruit numerous structural and regulatory proteins to focal adhesions, where they perform both overlapping and discrete functions. In this study, paxillin and Hic-5 were expressed in U2OS osteosarcoma cells as biotin ligase (BioID2) fusion proteins and used as bait proteins for proximity-dependent biotinylation in order to directly compare their respective interactomes. The fusion proteins localized to both focal adhesions and the centrosome, resulting in biotinylation of components of each of these structures. Biotinylated proteins were purified and analyzed by mass spectrometry. The list of proximity interactors for paxillin and Hic-5 comprised numerous shared core focal adhesion proteins that likely contribute to their similar functions in cell adhesion and migration, as well as proteins unique to paxillin and Hic-5 that have been previously localized to focal adhesions, the centrosome, or the nucleus. Western blotting confirmed biotinylation and enrichment of FAK and vinculin, known interactors of Hic-5 and paxillin, as well as several potentially unique proximity interactors of Hic-5 and paxillin, including septin 7 and ponsin, respectively. Further investigation into the functional relationship between the unique interactors and Hic-5 or paxillin may yield novel insights into their distinct roles in cell migration.

The tissue invasive capacity of cancer cells is determined by their phenotypic plasticity. For instance, mesenchymal to amoeboid transition has been found to facilitate the passage of cancer cells through confined environments. This phenotypic transition is also heavily regulated by the architecture of the actin cytoskeleton, which may increase myosin contractility and the intracellular pressure that is known to drive bleb formation. In this review, we highlight several Diaphanous related formins (DRFs) that have been found to promote or suppress bleb formation in cancer cells, which is a hallmark of amoeboid migration. Based on the work discussed here, the role of the DRFs in cancer(s) is worthy of further scrutiny in animal models, as they may prove to be therapeutic targets.

Protozoan parasites cause life-threatening infections in both humans and animals, including agriculturally significant livestock. Available treatments are typically narrow spectrum and are complicated by drug toxicity and the development of resistant parasites. Protozoan tubulin is an attractive target for the development of broad-spectrum antimitotic agents. The Medicines for Malaria Pathogen Box compound MMV676477 was previously shown to inhibit replication of kinetoplastid parasites, such as Leishmania amazonensis and Trypanosoma brucei, and the apicomplexan parasite Plasmodium falciparum by selectively stabilizing protozoan microtubules. In this report, we show that MMV676477 inhibits intracellular growth of the human apicomplexan pathogen Toxoplasma gondii with an EC₅₀ value of ~50 nM. MMV676477 does not stabilize vertebrate microtubules or cause other toxic effects in human fibroblasts. The availability of tools for genetic studies makes Toxoplasma a useful model for studies of the cytoskeleton. We conducted a forward genetics screen for MMV676477 resistance, anticipating that missense mutations would delineate the binding site on protozoan tubulin. Unfortunately, we were unable to use genetics to dissect target interactions because no resistant parasites emerged. This outcome suggests that future drugs based on the MMV676477 scaffold would be less likely to be undermined by the emergence of drug resistance.