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Myosins on the Move: A Special Issue on Myosins and Myosin‐Dependent Cell Processes

2024; Wiley; Linguagem: Inglês

10.1002/cm.21953

1949-3584

Joanna Moraczewska, Julian A. Guttman,

Cellular Mechanics and Interactions

The cellular functions that depend on the interactions of myosin motors and actin filaments are astonishingly diverse and range from muscle contraction, non-muscle cell migration, intracellular transport, cytokinesis, cell adhesion, plasma membrane organization, morphogenesis, and mechanotransduction to DNA organization and repair (Busselman et al. 2024; Herzog and Schappacher-Tilp 2023; Krendel and Mooseker 2005; Quintanilla, Hammer, and Beach 2023; Shahid-Fuente and Toseland 2023). To perform this broad spectrum of functions, mammalian cells use only six actin paralogs—four α-actin variants expressed in striated and smooth muscle and cytoskeletal β- and γ-actin (Khaitlina 2001; Simiczyjew et al. 2017; Vedula and Kashina 2018). In contrast, myosins constitute a large superfamily of molecular motors that have evolved into 79 classes across different taxa (Kollmar and Mühlhausen 2017). It therefore appears that the diverse and complex myosin repertoire contributes greatly to the complexity of actomyosin functions. The backbone of myosin is formed by the myosin heavy chain that folds into three distinct domains. The motor domain, referred to as the myosin head, converts energy of ATP hydrolysis into mechanical interactions with actin filaments. The neck domain binds one or more regulatory light chains and connects the motor domain to the C-terminal tail, which is the most diverse part of the molecule that interacts with various intracellular cargoes. The structure of the tail domain determines whether a given myosin is a single-headed monomer, a double-headed dimer, or a multimer. Heavy chains of the conventional myosin II consist of long α-helical tails that allow dimerization by folding into rod-like coiled coil that further assemble into thick filaments. The bipolar arrangement of molecules in thick filaments is perfectly suited to generate contractile forces by pulling parallel actin filaments (Billington et al. 2013; Ojima 2019). In contrast, unconventional myosins contain one or two motor domains and a large variety of neck and tail domains, but are not capable of forming filaments (Fili and Toseland 2019). Given the complexity of myosin-dependent cellular processes, it is rather expected that even small deviations from the native myosin and actin structures may have severe consequences on the overall state of humans and other animals. Indeed, mutations in both myosin and actin genes have been implicated in human diseases ranging from cardiomyopathies and myopathies of skeletal muscle to breast or skin cancer and deafness (Coluccio 2020). The issue begins with the memories of Dr. Edward D. Korn and Dr. Robert S. Adelstein, outstanding scientists who passed away in 2024. For decades, Dr. Korn and Dr. Adelstein led studies on the cytoskeleton and myosin motors at the National Heart, Lung and Blood Institute at the National Institutes of Health in Bethesda, MD. They participated in scientific activities until the very end, sharing their passion, knowledge, and experience with the community. The organization of highly ordered thick filaments in striated muscle sarcomeres is crucial for the precision of actin−myosin interactions and force development. In Caenorhabditis elegans, thick filaments contain two myosin II heavy chains: myosin A and myosin B present in the middle and outer arms of the thick filament, respectively (Miller et al. 1983). It is well established that assembly and maintenance of the thick filaments require extensive interactions within M-line proteins; however, exact mechanisms are not fully defined. The results presented in two papers by Pamela Hoppe's group shed light on the molecular interactions within the M-line that are necessary for the formation of fully functional thick filaments. In a series of carefully designed experiments, the authors revealed unknown interactions between myosin A and M-line proteins. By using myosin A and B chimeric constructs, the authors localized regions in the myosin A rod domain responsible for binding the giant scaffolding protein UNC-89/obscurin and the zinc finger protein UNC-98/ZnF. These results led to the modification of a thick filament assembly model (Almuhanna et al. 2024). The second paper by this group (Schiller, Almuhanna, and Hoppe 2023) reports the discovery of a direct and specific interaction between myosin A and the UNC-82 kinase, the orthologue of the NUAK1/2 kinase in vertebrates. UNC-82 activity was found to be important for myosin A thick filament elongation, though the exact phosphorylation site remains unknown. Three isoforms of non-muscle myosin II drive movement and maintain tension of various cells, which is essential for tissue development. In an elegant study, Fowler and colleagues have progressed our understanding of the role of non-muscle myosin IIA (NMIIA) contractility in maturation and differentiation of ocular lens epithelial cells into hexagonally shaped fiber cells. Experiments with genetic knock-in mice heterozygous for disease-linked missense mutations demonstrated that the specific structure of the NMIIA rod domain is indispensable for the parallel alignment of these fine, specialized cells (Islam et al. 2024). The involvement of single-headed myosin 1e (Myo1e) in glomerular filtration and nephron pathology has been described in a paper from Mira Krendel's group. This comprehensive review summarizes the current knowledge and presents hypotheses regarding the function of Myo1e in the physiology and pathology of the kidney. The functions of epithelial and endothelial cells present in nephrons are largely dependent on the actin cytoskeleton, with Myo1e playing an important role, as judged from effects of mutations in the MYO1E causing familial nephrotic syndrome (Liu et al. 2024). Two papers address the molecular mechanisms that underlie hypertrophic cardiomyopathy (HCM), the congenital heart disease associated with missense mutations in at least 11 genes, including the genes encoding the myosin heavy chain, myosin light chains, and actin (Maron and Maron 2013). The work performed in Danuta Szczesna-Cordary's lab is focused on HCM-linked mutation in the MYL2 gene encoding the human ventricular myosin regulatory light chain (RLC). Using transgenic mice, the authors showed that a phosphomimetic mutation in RLC can rescue the phenotype by establishing a balance between the Super-relaxed and Disordered Relaxed states of the myosin heads (Liang et al. 2024). Dietmar Manstein's group compared the functional consequences of two cardiomyopathy-related missense mutations in the ACTC1 gene encoding cardiac α-actin on cardiac β-myosin enzymatic and motor activities. Their biochemical in vitro analyzes are in line with the view that the interface between the myosin motor domain and the actin filament forms the structural basis for cardiac myosin enzymatic and motor performance (Greve et al. 2024). Disorders of striated muscle can also be related to dysregulation of posttranslational modifications of the myosin heavy chain (MyHC). Advances of this quite new research area were reviewed by Pinto and his collaborators. The authors described the types of MyHC modifications, their localizations, and their significance in the modulation of the physiological performance of different myosin isoforms (Morales et al. 2024). Tumor growth and metastasis triggered by alterations in cell signaling cause changes in cell shape, motility, and modifications of extracellular environment. The work performed in Mira Krendel's laboratory revealed that Myo1e is responsible for certain dynamics of focal adhesions, a process required for the invasiveness of 4T1 breast cancer cells (Garone et al. 2023). A study by Samuel and colleagues demonstrated that actomyosin contractility can shape the environment of cutaneous squamous cell carcinoma. The authors have established that increased tension in cancer cells plays a key role in the recruitment of tumor-promoting fibroblasts via cysteine-rich with EGF-like domains 2 (CREDL2) paracrine stimulation. This appears to be a consequence of the phosphorylation of myosin phosphatase targeting subunit 1 (MYPT1), the regulatory subunit of myosin phosphatase (MP), which is downstream of the Rho-ROCK signaling pathway. Such a mechanism seems to affect the cell environment in different types of tumors, including those from breast cancer (Pittar et al. 2024). An interesting paper authored by Fumio Matsumura and colleagues extends our understanding of the variety of MYPT1-dependent signaling pathways. A well-known feature of MYPT1 is that it targets not only myosin, but also other cellular substrates (Kiss, Erdodi, and Lontay 2019). The authors present evidence that MYPT1 forms a complex with the dynein intermediate chain (DIC) facilitating DIC dephosphorylation by MP. This in turn activates transportation of Rab7-containing vesicles by dynein. As suggested by the authors, reduced expression of MYPT1 in various cancer cells may contribute to the development of pathological features by compromising turnover of some receptors (e.g., EGFR) by Rab7-containing vesicles (Matsumura et al. 2024). Various types of in vitro methods using reconstituted actomyosin and assemblies of molecular machinery of the actin cytoskeleton are being developed to study actomyosin contractility and to decipher molecules that collaborate to drive cell division, adhesion, or migration. Papers describing progress in the development of different methods and in understanding the factors affecting the results are an important part of this special issue. In vitro motility assays are widely used methods that allow for studying motility of actin filaments propelled by myosin motors attached to a glass surface (Spudich 2024). Computational modeling work done by Taeyoon Kim's group advanced our knowledge on the experimental parameters that lead to the formation homogeneous networks, flocks, bands, and rings observed in motility assay under certain conditions (Slater, Jung, and Kim 2023). The development of a method enabling the study of actin-activated ATP turnover by myosin S1 at the single-molecule level was described by Månsson and colleagues. Expression of human myosin in mammalian cells allows for obtaining a fully folded, native protein, but in quantities that limit their further applications. As documented by the authors, cross-linking of recombinant myosin S1 to actin filaments with EDC makes it possible to follow the kinetics of fluorescent ATP turnover using TIRF microscopy. This approach opens the way to high-throughput screening of disease-related myosin mutants that are available in small quantities (Berg et al. 2024). In their review paper, Robinson and colleagues discuss benefits and challenges of recently developed membrane-based reconstitution methods that were applied to study essential molecular components of the actin cortex, the actin-based structure that is built underneath the plasma membrane (Waechtler et al. 2024). A description of methods applied in the studies of the post-translational modifications of proteins, in particular in the research on myosin modifications, is included in the review paper by Pinto and colleagues (Morales et al. 2024). In summary, the Special Issue on "Myosins and Myosin-Dependent Cell Processes" is a collection of 13 research and review papers that address various aspects of conventional and unconventional myosin structure, their functions, molecular interactions, and regulation in physiological and pathological states. Along with experimental results, the papers report advances in research methodology pertinent to myosin and actin. Authors from 11 laboratories working on myosin, actin, and myosin regulatory proteins accepted our invitation to create this collection of papers reporting the most recent, exciting results. In addition, authors of two memoirs, John Hammer and James Sellers, portrait lives and groundbreaking scientific discoveries of Edward Korn and Robert Adelstein, great scientists who recently passed away. The authors declare no conflicts of interest.