A Functional Role of S100A4/Non-Muscle Myosin IIA Axis for Pro-Tumorigenic Vascular Functions in Glioblastoma

Background Glioblastoma (GBM) is the most aggressive form of brain tumor and has vascular-rich features. The S100A4/non-muscle myosin IIA (NMIIA) axis contributes to aggressive phenotypes in a variety of human malignancies, but little is known about its involvement in GBM tumorigenesis. Herein, we examined the role of the S100A4/NMIIA axis during tumor progression and vasculogenesis in GBM Methods We performed immunohistochemistry for S100A4, NMIIA, and two hypoxic markers including hypoxia-inducible factor-1α (HIF-1α) and carbonic anhydrase 9 (CA9) in samples from 94 GBM cases. The functional impact of S100A4 knockdown and hypoxia were also assessed using a GBM cell line. Results In clinical GBM samples, overexpression of S100A4 and NMIIA was observed in both non-pseudopalisading (Ps) and Ps (-associated) perinecrotic lesions, consistent with stabilization of HIF-1α and CA9. CD34(+) microvascular densities (MVDs) and the interaction of S100A4 and NMIIA were significantly higher in non-Ps perinecrotic lesions compared to those in Ps perinecrotic areas. In non-Ps perinecrotic lesions, S100A4(+)/HIF-1α(-) GBM cells were recruited to the surface of host preexisting vessels in the vascular-rich areas. Elevated vascular endothelial growth factor A (VEGFA) mRNA expression was found in S100A4(+)/HIF-1α(+) GBM cells adjacent to the vascular-rich areas. In addition, GBM patients with high S100A4 protein expression had significantly worse OS and PFS than did patients with low S100A4 expression. Knockdown of S100A4 in the GBM cell line KS-1 decreased migration capability, concomitant with decreased Slug expression; the opposite effects were elicited by blebbistatin-dependent inhibition of NMIIA. Conclusion S100A4(+)/HIF-1α(-) GBM cells are recruited to (and migrate along) preexisting vessels through inhibition of NMIIA activity. This is likely stimulated by extracellular VEGF that is released by S100A4(+)/HIF-1α(+) tumor cells in non-Ps perinecrotic lesions. In turn, these events engender tumor progression via acceleration of pro-tumorigenic vascular functions.

Myosin phosphatase target subunit 1 governs integrity of the embryonic gut epithelium to circumvent atresia development in medaka, Oryzias latipes

BackgroundIntestinal atresia (IA) is a congenital gut obstruction caused by the absence of gut opening. Genetic factors are assumed to be critical for the development of IA, in addition to accidental vascular insufficiency or mechanical strangulation. However, the molecular mechanism underlying IA remains poorly understood.ResultsIn this study, to better understand such a mechanism, we isolated a mutant of Oryzias latipes (the Japanese rice fish known as medaka) generated by N-ethyl-N-nitrosourea mutagenesis, in which IA develops during embryogenesis. Positional cloning identified a nonsense mutation in the myosin phosphatase target subunit 1 (mypt1) gene. Consistent with known Mypt1 function, the active form of myosin regulatory light chain (MRLC), which is essential for actomyosin contraction, and F-actin were ectopically accumulated in the intestinal epithelium of mutant embryos, whereas cell motility, proliferation and cell death were not substantially affected. Corresponding to the accumulation site of F-actin/active MRLC, the intestinal epithelium architecture was disordered. Importantly, blebbistatin, a non-muscle myosin inhibitor, attenuated the development of IA in the mutant.ConclusionsCytoskeletal contraction governed by mypt1 regulates the integrity of the embryonic intestinal epithelium. This study provides new insight into our understanding of the mechanism of IA development in humans.Bullet PointsMedaka mypt1 mutants display intestinal atresia.The level of phosphorylated myosin regulatory light chain was higher in mypt1 mutant embryos than in wild-type embryos.The levels of F-actin appeared elevated in the intestinal epithelium of mypt1 mutants.Blebbistatin, an inhibitor of non-muscle myosin II, rescued intestinal atresia in mypt1 mutant embryos.

MYH10 governs adipocyte function and adipogenesis through its interaction with GLUT4

Adipocyte differentiation is dependent on cytoskeletal remodeling processes that determine and maintain cellular shape and function. In turn, cytoskeletal proteins contribute to the filament-based network responsible for controlling adipocyte’s shape and promoting the intracellular trafficking of key cellular components. Currently, our understanding of these mechanisms remains incomplete. In this study, we identified the non-muscle myosin 10 (MYH10) as an important regulator of adipogenesis and adipocyte function through its interaction with the insulin dependent, Glucose transporter 4 (GLUT4). MYH10 depletion in preadipocytes resulted in impaired adipogenesis, with knockdown cells exhibiting disrupted morphology and reduced molecular adipogenic signals. MYH10 was shown to be in complex with GLUT4 in adipocytes, an interaction regulated by insulin induction. The missing adipogenic capacity of MYH10-KD cells was restored when they uptook GLUT4 vesicles up from neighbor wild-type cells in a co-culture system. Our results provide the first demonstration that MYH10 interacts with GLUT4 in cells and adipose tissue through the insulin pathway. The signaling cascade is regulated by the protein kinase C ζ (PKCζ), which interacts with MYH10 to modify the localization and interaction of both GLUT4 and MYH10 in adipocytes as PKCζ inhibition resulted in reduced GLUT4 and MYH10 translocation and interactions. Overall, our study establishes MYH10 as an essential regulator of GLUT4 translocation, affecting both adipogenesis and adipocyte function, highlighting its importance in future cytoskeleton-based studies in adipocytes.

Patterned mechanical feedback establishes a global myosin gradient

Morphogenesis, the coordinated execution of developmental programs that shape embryos, raises many fundamental questions at the interface between physics and biology. In particular, how the dynamics of active cytoskeletal processes are coordinated across the surface of entire embryos to generate global cell flows is poorly understood. Two distinct regulatory principles have been identified: genetic programs and dynamic response to mechanical stimuli. Despite progress, disentangling these two contributions remains challenging. Here, we combine in toto light sheet microscopy with genetic and optogenetic perturbations of tissue mechanics to examine theoretically predicted dynamic recruitment of non-muscle myosin II to cell junctions during Drosophila embryogenesis. We find dynamic recruitment has a long-range impact on global myosin configuration, and the rate of junction deformation sets the rate of myosin recruitment. Mathematical modeling and high frequency analysis reveal myosin fluctuations on junctions around a mean value set by mechanical feedback. Our model accounts for the early establishment of the global myosin pattern at 80% fidelity. Taken together our results indicate spatially modulated mechanical feedback as a key regulatory input in the establishment of long-range gradients of cytoskeletal configurations and global tissue flow patterns.

Gonococcal invasion into epithelial cells depends on both cell polarity and ezrin

Neisseria gonorrhoeae (GC) establishes infection in women from the cervix, lined with heterogeneous epithelial cells from non-polarized stratified at the ectocervix to polarized columnar at the endocervix. We have previously shown that GC differentially colonize and transmigrate across the ecto and endocervical epithelia. However, whether and how GC invade into heterogeneous cervical epithelial cells is unknown. This study examined GC entry of epithelial cells with various properties, using human cervical tissue explant and non-polarized/polarized epithelial cell line models. While adhering to non-polarized and polarized epithelial cells at similar levels, GC invaded into non-polarized more efficiently than polarized epithelial cells. The enhanced GC invasion in non-polarized epithelial cells was associated with increased ezrin phosphorylation, F-actin and ezrin recruitment to GC adherent sites, and the elongation of GC-associated microvilli. Inhibition of ezrin phosphorylation inhibited F-actin and ezrin recruitment and microvilli elongation, leading to a reduction in GC invasion. The reduced GC invasion in polarized epithelial cells was associated with non-muscle myosin II-mediated F-actin disassembly and microvilli denudation at GC adherence sites. Surprisingly, intraepithelial GC were only detected inside epithelial cells shedding from the cervix by immunofluorescence microscopy, but not significantly in the ectocervical and the endocervical regions. We observed similar ezrin and F-actin recruitment in exfoliated cervical epithelial cells but not in those that remained in the ectocervical epithelium, as the luminal layer of ectocervical epithelial cells expressed ten-fold lower levels of ezrin than those beneath. However, GC inoculation induced F-actin reduction and myosin recruitment in the endocervix, similar to what was seen in polarized epithelial cells. Collectively, our results suggest that while GC invade non-polarized epithelial cells through ezrin-driven microvilli elongation, the apical polarization of ezrin and F-actin inhibits GC entry into polarized epithelial cells.

The Central Role of the F-Actin Surface in Myosin Force Generation

Actin is one of the most abundant and versatile proteins in eukaryotic cells. As discussed in many contributions to this Special Issue, its transition from a monomeric G-actin to a filamentous F-actin form plays a critical role in a variety of cellular processes, including control of cell shape and cell motility. Once polymerized from G-actin, F-actin forms the central core of muscle-thin filaments and acts as molecular tracks for myosin-based motor activity. The ATP-dependent cross-bridge cycle of myosin attachment and detachment drives the sliding of myosin thick filaments past thin filaments in muscle and the translocation of cargo in somatic cells. The variation in actin function is dependent on the variation in muscle and non-muscle myosin isoform behavior as well as interactions with a plethora of additional actin-binding proteins. Extensive work has been devoted to defining the kinetics of actin-based force generation powered by the ATPase activity of myosin. In addition, over the past decade, cryo-electron microscopy has revealed the atomic-evel details of the binding of myosin isoforms on the F-actin surface. Most accounts of the structural interactions between myosin and actin are described from the perspective of the myosin molecule. Here, we discuss myosin-binding to actin as viewed from the actin surface. We then describe conserved structural features of actin required for the binding of all or most myosin isoforms while also noting specific interactions unique to myosin isoforms.

Reduced platelet forces underlie impaired hemostasis in mouse models of MYH9-related disease

MYH9-related disease patients with mutations in the contractile protein non-muscle myosin heavy chain IIA display, among others, macrothrombocytopenia and a mild to moderate bleeding tendency. In this study, we used three mouse lines, each with one point mutation in the Myh9 gene at positions 702, 1424, or 1841, to investigate mechanisms underlying the increased bleeding risk. Agonist-induced activation of Myh9 mutant platelets was comparable to controls. However, myosin light chain phosphorylation after activation was reduced in mutant platelets, which displayed altered biophysical characteristics and generated lower adhesion, interaction, and traction forces. Treatment with tranexamic acid restored clot retraction and reduced bleeding. We verified our findings from the mutant mice with platelets from patients with the respective mutation. These data suggest that reduced platelet forces lead to an increased bleeding tendency in MYH9-related disease patients, and treatment with tranexamic acid can improve the hemostatic function.

Skeletal Muscle Myosin Is Procoagulant By Binding Factor XI Via Its A3 Domain and Enhancing Factor XI Activation By Thrombin

Blood coagulation mechanisms play key roles in health and disease. Pilot studies using selected human plasmas showed the potential associations of plasma skeletal muscle myosin (SkM) isoforms and phenotypes with pulmonary embolism and thrombin generation, suggesting SkM may contribute to blood coagulation reactions in plasma. Here we report that ex vivo studies of the coagulability of fresh flowing human blood over SkM-coated surfaces showed that an anti-factor XI (FXI) mAb, but not an anti-tissue factor mAb, inhibited clot formation, indicating that FXI is an essential contributor for the normal observed procoagulant response of blood during its exposure to immobilized SkM. This raised the question of whether procoagulant SkM's requirement for FXI involves direct or indirect effects on FXI. To assess direct interactions between SkM and FXI, Bio-Layer Interferometry (BLI) (Octet Red system) was used to record kinetics for binding of soluble FXI to immobilized SkM. BLI data showed that FXI bound to SkM with a Kd of 0.2 nM (k on= 2.92x10 6 M -1s -1 and k off=9.25x10 -3 s -1) (Fig. 1A). In contrast, prekallikrein (PK) did not bind to the SkM (Fig.1A), indicating the specificity of SkM for binding FXI. The anti-FXI mAb1A6, which recognizes the Apple (A)3 domain of FXI, potently inhibited binding of FXI to immobilized SkM, implying SkM binds the FXI A3 domain. Studies using purified clotting factors were made to identify which FXI-related activities might be affected by SkM. When FXI activation by thrombin was evaluated under conditions where polyphosphate (PolyP) 100-mer and 700-mer enhance FXI activation, SkM concentration-dependently enhanced FXI activation by thrombin (Fig. 1B). Whereas alkaline phosphatase destroyed PolyP's ability to stimulate FXI activation by thrombin, it did not cause a reduction of SkM's ability to enhance FXI activation, indicating SkM's activity is independent of PolyP-like sequences in SkM. Small unilamellar phospholipid vesicles (20% phosphatidylserine (PS) / 80% phosphatidylcholine) did not affect FXI activation by thrombin; furthermore, reagents that neutralize procoagulant PS, i.e., lactadherin, annexin V, and phospholipase A2, did not affect SkM's enhancement of FXI activation by thrombin, indicating that this activity is not due to anionic phospholipids linked to SkM. The effects of SkM on FXI autoactivation and FXI activation by FXIIa were evaluated. As is well known, PolyP and some other anionic reagents, e.g., nucleic acid polymers, enhance not only FXI activation by thrombin but also FXI autoactivation and FXI activation by FXIIa. However, SkM did not significantly affect FXI autoactivation or FXI activation by factor XIIa, further emphasizing that SkM's enhancement of FXI activation by thrombin is not due to any PolyP-like compounds and that it is a unique property of procoagulant SkM. This also suggests that SkM has a unique mechanism for its procoagulant activity on FXI activation which is limited to the thrombin positive feedback loop. To evaluate further the basis for interactions between FXI and SkM, we employed FXI- PK chimeras because BLI binding studies showed that, in contrast to FXI, PK did not bind to SkM. Recombinant FXI proteins in which each of the four A domains of the heavy chain (designated A1 through A4) were individually replaced with the corresponding A domain from PK and were used to identify the site of factor XI to interact with SkM for FXI activation by thrombin. The FXI chimera with the substitution of the PKA1 domain was not activated by thrombin, which is consistent with the fact that the FXI A1 domain is an interactive site for thrombin. Thrombin activation of the two FXI chimeras (FXI/PKA3 and FXI/PKA4) with substitutions of either the A3 or A4 domains was not enhanced by SkM, whereas substitution of the A2 domain (FXI/PKA2) did not reduce the enhancement of activation by thrombin compared to wild type FXI. Furthermore, mAb1A6, which recognizes the A3 domain and which inhibited the prothrombotic activity of fresh blood flowing over a SkM-coated surface, potently inhibited FXI binding to SkM in BLI studies. These data strongly suggest that functional interaction sites on FXI for SkM involve the A3 and A4 domains of FXI. In summary, we found that SkM's ex vivo procoagulant activity requires FXI, that SkM enhances FXI activation by thrombin and this requires FXI's A3 and A4 domains, and that SkM's high affinity binding of FXI requires the FXI A3 domain (Fig. 1C). Figure 1 Figure 1. Disclosures Gruber: Aronora Inc.: Current Employment, Current equity holder in publicly-traded company; Oregon Health and Science University: Current Employment. Gailani: Anthos Therapeutics: Consultancy; Aronora: Membership on an entity's Board of Directors or advisory committees; Bayer Pharma: Consultancy; Bristol Myer Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees; Ionis: Consultancy; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Dia- and Rok-dependent enrichment of capping proteins in a cortical region

Rho signaling with its major targets the formin Dia, Rho kinase (Rok) and non-muscle myosin II control turnover, amount and contractility of actomyosin. Much less investigated has been a potential function for the distribution of F-actin plus and minus ends. In syncytial Drosophila embryos Rho1 signaling is high between actin caps, i. e. the cortical intercap region. Capping protein binds to free plus ends of F-actin to prevent elongation of the filament. Capping protein has served as a marker to visualize the distribution of F-actin plus ends in cells and in vitro. Here, we probed the distribution of plus ends with capping protein in syncytial Drosophila embryos. We found that Capping proteins are specifically enriched in the intercap region similar to Dia and MyoII but distinct from overall F-actin. The intercap enrichment of Capping protein was impaired in dia mutants and embryos, in which Rok and MyoII activation was inhibited. Our observations reveal that Dia and Rok/MyoII control Capping protein enrichment and support a model that Dia and Rok/MyoII control the organization of cortical actin cytoskeleton downstream of Rho1 signaling.