mTORC1/rpS6 and mTORC2/PKC regulate spermatogenesis through Arp3-mediated actin microfilament organization in Eriocheir sinensis

Mammalian target of rapamycin (mTOR) is a crucial signaling protein regulating a range of cellular events. Numerous studies have reported that the mTOR pathway is related to spermatogenesis in mammals. However, its functions and underlying mechanisms in crustaceans remain largely unknown. mTOR exists as two multimeric functional complexes termed mTOR complex 1 (mTORC1) and mTORC2. Herein, we first cloned ribosomal protein S6 (rpS6, a downstream molecule of mTORC1) and protein kinase C (PKC, a downstream effector of mTORC2) from the testis of Eriocheir sinensis. The dynamic localization of rpS6 and PKC suggested that both proteins may be essential for spermatogenesis. rpS6/PKC knockdown and Torin1 treatment led to defects in spermatogenesis, including germ cell loss, retention of mature sperm and empty lumen formation. In addition, the integrity of the testis barrier (similar to the blood-testis barrier in mammals) was disrupted in the rpS6/PKC knockdown and Torin1 treatment groups, accompanied by changing in expression and distribution of junction proteins. Further study demonstrated that these findings may result from the disorganization of filamentous actin (F-actin) networks, which were mediated by the expression of actin-related protein 3 (Arp3) rather than epidermal growth factor receptor pathway substrate 8 (Eps8). In summary, our study illustrated that mTORC1/rpS6 and mTORC2/PKC regulated spermatogenesis via Arp3-mediated actin microfilament organization in E. sinensis.

Amorphous silica nanoparticles cause abnormal cytokinesis and multinucleation through dysfunction of the centralspindlin complex and microfilaments

BACKGROUND

With the large-scale production and application of amorphous silica nanoparticles (aSiNPs), its adverse health effects are more worthy of our attention. Our previous research has demonstrated for the first time that aSiNPs induced cytokinesis failure, which resulted in abnormally high incidences of multinucleation in vitro, but the underlying mechanisms remain unclear. Therefore, the purpose of this study was firstly to explore whether aSiNPs induced multinucleation in vivo, and secondly to investigate the underlying mechanism of how aSiNPs caused abnormal cytokinesis and multinucleation.

METHODS

Male ICR mice with intratracheal instillation of aSiNPs were used as an experimental model in vivo. Human hepatic cell line (L-02) was introduced for further mechanism study in vitro.

RESULTS

In vivo, histopathological results showed that the rate of multinucleation was significantly increased in the liver and lung tissue after aSiNPs treatment. In vitro, immunofluorescence results manifested that aSiNPs directly caused microfilaments aggregation. Following mechanism studies indicated that aSiNPs increased ROS levels. The accumulation of ROS further inhibited the PI3k 110β/Aurora B pathway, leading to a decrease in the expression of centralspindlin subunits MKLP1 and CYK4 as well as downstream cytokines regulation related proteins Ect2, Cep55, CHMP2A and RhoA. Meanwhile, the particles caused abnormal co-localization of the key mitotic regulatory kinase Aurora B and the centralspindlin complex by inhibiting the PI3k 110β/Aurora B pathway. PI3K activator IGF increased the phosphorylation level of Aurora B and improved the relative ratio of the centralspindlin cluster. And ROS inhibitors NAC reduced the ratio of multinucleation, alleviated the PI3k 110β/Aurora B pathway inhibition, and then increased the expression of MKLP1, CYK4 and cytokinesis-related proteins, whilst NAC restored the clustering of the centralspindlin.

CONCLUSION

This study demonstrated that aSiNPs led to multinucleation formation both in vivo and in vitro. ASiNPs exposure caused microfilaments aggregation and inhibited the PI3k 110β/Aurora B pathway through excessive ROS, which then hindered the centralspindlin cluster as well as restrained the expression of centralspindlin subunits and cytokinesis-related proteins, which ultimately resulted in cytokinesis failure and the formation of multinucleation.

es-Arp3 and es-Eps8 regulate spermatogenesis via microfilaments in the seminiferous tubule of Eriocheir sinensis

Spermatogenesis is a complicated process that includes spermatogonia differentiation, spermatocytes meiosis, spermatids spermiogenesis and final release of spermatozoa. Actin-related protein 3 (Arp3) and epidermal growth factor receptor pathway substrate 8 (Eps8) are two actin binding proteins that regulate cell adhesion in seminiferous tubules during mammalian spermatogenesis. However, the functions of these two proteins during spermatogenesis in nonmammalian species, especially Crustacea, are still unknown. Here, we cloned es-Arp3 and es-Eps8 from the testis of Chinese mitten crab Eriocheir sinensis. es-Arp3 and es-Eps8 were located in spermatocytes, spermatids and spermatozoa. Knockdown of es-Arp3 and es-Eps8 in vivo caused morphological changes to seminiferous tubules including delayed spermatozoa release, shedding of germ cells and vacuoles. Filamentous-actin (F-actin) filaments network was disorganized due to deficiency of es-Arp3 and es-Eps8. Accompanying this, four junctional proteins (α-catenin, β-catenin, pinin and ZO1) displayed abnormal expression levels as well as penetrating biotin signals in seminiferous tubules. We also used the Arp2/3 complex inhibitor CK666 to block es-Arp3 activity and supported es-Arp3 knockdown results. In summary, our study demonstrated for the first time that es-Arp3 and es-Eps8 are important for spermatogenesis via regulating microfilament-mediated cell adhesion in Eriocheir sinensis.

Total flavonoids of Oxytropis falcata Bunge have a positive effect on idiopathic pulmonary fibrosis by inhibiting the TGF-β1/Smad signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Idiopathic pulmonary fibrosis (IPF) is an interstitial lung disease with unknown etiology. Oxytropis falcata Bunge (O. falcata) is a 1-35 cm high perennial clustered herb, also known as edaxia, has viscosity and a special smell, and is mainly distributed in the western areas of China. The root of O. falcata has a diameter of 6 mm, is straight and deep, dark red and its stems are shortened, woody and multibranched. O. falcata has heat-clearing, detoxification, analgesic, anti-inflammatory, antibacterial, hemostatic and antitumor activities. Furthermore, O. falcata has excellent anti-inflammatory and analgesic effects, and it is one of the three major anti-inflammatory drugs in Tibetan medicine, known as "the king of herbs". Total flavonoids of Oxytropis falcata Bunge (FOFB) were previously extracted, and their pharmacological activities are consistent with those of the whole herb. In this study, FOFB was extracted from O. falcata by ethanol extraction, and the mechanism of FOFB on IPF was verified by in vivo and in vitro experiments.

AIM OF THE STUDY

In this study, we aimed to observe the effects of FOFB on idiopathic pulmonary fibrosis.

MATERIALS AND METHODS

In in vivo experiments, an IPF rat model was established by bleomycin induction. The rats were treated with FOFB (100, 200, 400 mg kg^-1·d^-1) for 4 weeks. Masson staining and the expression of TGF-β, p-Smad2, p-Smad3 and Smad7 in the lung tissue of rats were detected. In in vitro experiments, we perfused normal rats with FOFB (100, 200, 400 mg kg^-1·d^-1) and obtained the corresponding drug-containing serum. The HFL-1 cell model induced by TGF-β1 was used to detect the corresponding indices through intervention with drug-containing serum. The best intervention time for drug-containing serum was detected by the CCK-8 method. Changes in apoptosis, cytoskeleton and rough endoplasmic reticulum structure were detected. Finally, the expression of TGF-β, p-Smad2, p-Smad3 and Smad7 in cells was examined.

RESULTS

In vivo, Masson staining indicated that the degree of pulmonary fibrosis increased significantly, the expression of TGF-β, p-smad2 and p-Smad3 increased significantly, and the expression of Smad7 decreased in the model group. We found that the degree of pulmonary fibrosis gradually decreased and that the inhibition of the TGF-β/Smad signaling pathway became more obvious with increasing FOFB dose. FOFB (400 mg kg^-1·d^-1) significantly improved the degree of pulmonary fibrosis in rats. In in vitro experiments, the CCK-8 results showed that 120 h was the best intervention time for drug-containing serum. In the model group, there was no obvious apoptosis or changes in microfilaments and microtubules, the number of rough endoplasmic reticulum increased, and the expression of TGF-β, p-Smad2 and p-Smad3 increased significantly, while the expression of Smad7 decreased significantly. We found that with the increase in drug-containing serum concentration, the apoptosis, cytoskeleton and degree of destruction of the rough endoplasmic reticulum in the HFL-1 cell model also increased, and the inhibition of the TGF-β/Smad signaling pathway became more pronounced; the effect of the drug-containing serum administered with FOFB (400 mg kg^-1·d^-1) was the most significant.

CONCLUSIONS

The results suggest that FOFB can improve the occurrence and development of IPF. The effect of FOFB on IPF may be mediated by inhibition of the TGF-β1/Smad signaling pathway.

Proteomic dissection of rice cytoskeleton reveals the dominance of microtubule and microfilament proteins, and novel components in the cytoskeleton-bound polysome

The plant cytoskeleton persistently undergoes remodeling to achieve its roles in supporting cell division, differentiation, cell expansion and organelle transport. However, the links between cell metabolism and cytoskeletal networks, particularly how the proteinaceous components execute such processes remain poorly understood. We investigated the cytoskeletal proteome landscape of rice to gain better understanding of such events. Proteins were extracted from highly enriched cytoskeletal fraction of four-week-old rice seedlings, and the purity of the fraction was stringently monitored. A total of 2577 non-redundant proteins were identified using both gel-based and gel-free approaches, which constitutes the most comprehensive dataset, thus far, for plant cytoskeleton. The data set includes both microtubule and microfilament-associated proteins and their binding proteins comprising hypothetical as well as novel cytoskeletal proteins. Further, various in-silico analyses were performed, and the proteins were functionally classified on the basis of their gene ontology. The catalogued proteins were validated through their sequence analysis. Extensive comparative analysis of our dataset with the non-redundant set of cytoskeletal proteins across plant species affirms unique as well as overlapping candidates. Together, these findings unveil new insights of how cytoskeletons undergo dynamic remodeling in rice to drive seedling development processes in rapidly changing in planta environment.

Ca2+-dependent binding of S100A6 to cofilin-1 regulates actin filament polymerization-depolymerization dynamics

S100A6 is a Ca²⁺-binding protein belonging to the S100 family. Many reports indicate that S100A6 is involved in actin filament organization, however the mechanism of S100A6 action in this process is not fully understood. By screening S100A6 binding partners in NIH3T3 mouse fibroblasts, we have found that S100A6 binds cofilin-1, a protein required for the dynamics of actin polymerization and depolymerization. By applying various biochemical and cell biology assays, we have shown that S100A6 bound to cofilin-1 in a Ca²⁺-dependent manner and increased cofilin-1 affinity for F-actin. Microscopic analysis indicated that S100A6 significantly decreased severing of the actin filaments induced by cofilin-1. Moreover, in the presence of cofilin-1, S100A6 stabilized the filaments by inhibiting their depolymerization. When S100A6 was present at sub-stoichiometric concentrations in relation to actin, polymerization of G-actin accelerated by cofilin-1 was increased. At higher S100A6:actin ratios the polymerization rate was decreased. Altogether, these results show that S100A6 regulates actin filament dynamics by controlling activity of cofilin-1 and suggest that this regulation is Ca²⁺ -dependent.

Preparation and analysis of standards containing microfilaments/microplastic with fibre shape

Synthetic clothing represents a primary source of environmental pollution because of shedding of microfilaments during laundry washing or in textile processes. Although many approaches can be used for the evaluation of microplastic, there are no precise guideline to follow for the analysis labs. Here, an accurate method for the preparation of microfilaments standard suspensions to facilitate lab tests and the monitoring of microplastic in different matrices was developed. Different standard suspensions were prepared by using five different synthetic threads consisting of a different number of filaments cut with a predetermined length of 0.2 mm suspended in three different volumes of water. The suspensions were filtered and the microfilaments were counted. The number of microfilaments for each polymer solution were statistically elaborated with a logit model and the results showed that the probability of detecting them is higher than 95% when the concentration of microfilaments/L is lower than 200. Moreover, a relationship between the theoretical microfilaments contained in the samples and the detection probability of the single microfilament, for each suspension volume was highlighted.

The structural organization of Giardia intestinalis cytoskeleton

Giardia intestinalis, the causative agent of giardiasis, has complex cytoskeleton organization with structures involved in motility, adhesion, cell division, and cell differentiation. Microtubules are key components of the cytoskeleton and are the main elements of the ventral disc, median body, funis, in addition to four pairs of flagella. These cytoskeletal elements are basically stable microtubule arrangements. Although tubulins are the main proteins of these elements, molecular and biochemical analyses of Giardia trophozoites have revealed the presence of several new and not yet characterized proteins in these structures, which may contribute to their nanoarchitecture (mainly in the ventral disc). Despite these findings, morphological data are still required for understanding the organization and biogenesis of the cytoskeletal structures. In the study of this complex and specialized network of filaments in Giardia, two distinct and complementary approaches have been used in recent years: (a) transmission electron microscopy tomography of conventionally processed as well as cryo-fixed samples and (b) high-resolution scanning electron microscopy and helium ion microscopy in combination with new plasma membrane extraction protocols. In this review we include the most recent studies that have allowed better understanding of new Giardia components and their association with other filamentous structures of this parasite, thus providing new insights in the role of the cytoskeletal structures and their function in Giardia trophozoites.

Automatic directional analysis of cell fluorescence images and morphological modeling of microfilaments

Cytoskeleton and nucleus are two important anatomic components in eukaryotic cells. Cell fluorescence images are employed to study their realignment and deformation during cell extrusion. Quantitative analysis and modeling of cell orientation are investigated in this paper. For orientation measurement, alignment orientation of microfilaments is calculated using structure tensor method. Nuclei is segmented and fitted to ellipses in nuclei images. Based on the fitted ellipse, orientation and aspect ratio of each nucleus are computed. A morphological model is proposed to describe the movement of microfilaments quantitatively. The parameters of the model are determined by in-plane stresses obtained by numerical simulation. The proposed automatic orientation measurement algorithms can help to analyze the relationship between cell orientation and stress qualitatively. The proposed morphological model is the first model to quantitatively describe the relationship of microfilament movement with stress. Experimental results show that cell and nucleus tend to align along in-plane maximum shear stress and the proposed morphological model is a reasonable model for cell movement. The modeling of cell behavior under different stress can facilitate biomedical research such as tissue engineering and cancer analysis. Graphical abstract ᅟ.

Brief Overview of Prostate Cancer Statistics, Grading, Diagnosis and Treatment Strategies

This chapter provides a brief overview of prostate cancer statistics, grading, diagnosis and treatment strategies that are discussed in more detail in the subsequent chapters of this book and the companion book titled "Clinical Molecular and Diagnostic Imaging of Prostate Cancer and Treatment Strategies". It also points to websites that provide additional useful information for patients affected by prostate cancer and for students and teachers to obtain practical and updated information on research, new diagnostic modalities and new therapies including new updated clinical trials. Three sections are focused on overview of prostate cancer statistics; overview of detection, diagnosis, stages and grading of prostate cancer; and treatment possibilities and options.

Mammalian Diaphanous-related formin-1 restricts early phases of influenza A/NWS/33 virus (H1N1) infection in LLC-MK2 cells by affecting cytoskeleton dynamics

Viruses depend on cellular machinery to efficiently replicate. The host cytoskeleton is one of the first cellular systems hijacked by viruses in order to ensure their intracellular transport and promote the development of infection. Our previous results demonstrated that stable microfilaments and microtubules interfered with human influenza A/NWS/33 virus (H1N1) infection in semi-permissive LLC-MK2 cells. Although formins play a key role in cytoskeletal remodelling, few studies addressed a possible role of these proteins in development of viral infection. Here, we have demonstrated that mammalian Diaphanous-related formin-1 (mDia1) is involved in the control of cytoskeleton dynamics during human influenza A virus infection. First, by employing cytoskeleton-perturbing drugs, we evidenced a cross-talk occurring between microtubules and microfilaments that also has implications on the intracellular localization of mDia1. In influenza A/NWS/33 virus-infected LLC-MK2 cells, mDia1 showed a highly dynamic intracellular localization and partially co-localized with actin and tubulin. A depletion of mDia1 by RNA-mediated RNA interference was found to improve the outcome of influenza A/NWS/33 virus infection and to increase the dynamics of microfilament and microtubule networks in LLC-MK2 cells. Consistent with these findings, observations made in epithelial respiratory cells from paediatric patients with acute respiratory disease assessed that the expression of mDia1 is stimulated by influenza A virus but not by respiratory syncytial virus. Taken together, the obtained results suggest that mDia1 restricts the initiation of influenza A/NWS/33 virus infection in LLC-MK2 cells by counteracting cytoskeletal dynamics.

Host cytoskeleton in respiratory syncytial virus assembly and budding

Respiratory syncytial virus (RSV) is one of the major pathogens responsible for lower respiratory tract infections (LRTI) in young children, the elderly, and the immunosuppressed. Currently, there are no antiviral drugs or vaccines available that effectively target RSV infections, proving a significant challenge in regards to prevention and treatment. An in-depth understanding of the host-virus interactions that underlie assembly and budding would inform new targets for antiviral development.Current research suggests that the polymerised form of actin, the filamentous or F-actin, plays a role in RSV assembly and budding. Treatment with cytochalasin D, which disrupts F-actin, has been shown to inhibit virus release. In addition, the actin cytoskeleton has been shown to interact with the RSV matrix (M) protein, which plays a central role in RSV assembly. For this reason, the interaction between these two components is hypothesised to facilitate the movement of viral components in the cytoplasm and to the budding site. Despite increases in our knowledge of RSV assembly and budding, M-actin interactions are not well understood. In this review, we discuss the current literature on the role of actin cytoskeleton during assembly and budding of RSV with the aim to integrate disparate studies to build a hypothetical model of the various molecular interactions between actin and RSV M protein that facilitate RSV assembly and budding.

GPCRs and actin-cytoskeleton dynamics

A multitude of physiological processes regulated by G protein-coupled receptors (GPCRs) signaling are accomplished by the participation of active rearrangements of the cytoskeleton. In general, it is common that a cross talk occurs among networks of microfilaments, microtubules, and intermediate filaments in order to reach specific cell responses. In particular, actin-cytoskeleton dynamics regulate processes such as cell shape, cell division, cell motility, and cell polarization, among others. This chapter describes the current knowledge about the regulation of actin-cytoskeleton dynamic by diverse GPCR signaling pathways, and also includes some protocols combining immunofluorescence and confocal microscopy for the visualization of the different rearrangements of the actin-cytoskeleton. We report how both the S1P-GPCR/G12/13/Rho/ROCK and glucagon-GPCR/Gs/cAMP axes induce differential actin-cytoskeleton rearrangements in epithelial cells. We also show that specific actin-binding molecules, like phalloidin and LifeAct, are very useful to analyze F-actin reorganization by confocal microscopy, and also that both molecules show similar results in fixed cells, whereas the anti-actin antibody is useful to detect both the G- and F-actin, as well as their compartmentalization. Thus, it is highly recommended to utilize different approaches to investigate the regulation of actin dynamics by GPCR signaling, with the aim to get a better picture of the phenomenon under study.

Role of cytoskeleton network in anisosmotic volume changes of intact and permeabilized A549 cells

Recently we found that cytoplasm of permeabilized mammalian cells behaves as a hydrogel displaying intrinsic osmosensitivity. This study examined the role of microfilaments and microtubules in the regulation of hydrogel osmosensitivity, volume-sensitive ion transporters, and their contribution to volume modulation of intact cells. We found that intact and digitonin-permeabilized A549 cells displayed similar rate of shrinkage triggered by hyperosmotic medium. It was significantly slowed-down in both cell preparations after disruption of actin microfilaments by cytochalasin B, suggesting that rapid water release by intact cytoplasmic hydrogel contributes to hyperosmotic shrinkage. In hyposmotic swelling experiments, disruption of microtubules by vinblastine attenuated the maximal amplitude of swelling in intact cells and completely abolished it in permeabilized cells. The swelling of intact cells also triggered ~10-fold elevation of furosemide-resistant (86)Rb+ (K+) permeability and the regulatory volume decrease (RVD), both of which were abolished by Ba2+. Interestingly, RVD and K+ permeability remained unaffected in cytocholasin/vinblastine treated cells demonstrating that cytoskeleton disruption has no direct impact on Ba2+-sensitive K+-channels involved in RVD. Our results show, for the first time, that the cytoskeleton network contributes directly to passive cell volume adjustments in anisosmotic media via the modulation of the water retained by the cytoplasmic hydrogel.

Actin and Keratin are Binding Partners of the 1,25D3-MARRS Receptor/PDIA3/ERp57

We have shown that the 1,25D₃-MARRS receptor is necessary for the rapid, pre-genomic effects of 1,25(OH)₂D₃ on phosphate and/or calcium absorption in chick intestines. However, a clear understanding of the proteins involved in the signaling mechanisms by which the 1,25D₃-MARRS receptor facilitates 1,25(OH)₂D₃-mediated phosphate or calcium uptake, as well as other cellular effects, is still under investigation. We used co-immunoprecipitation studies and mass spectroscopy to identify actin and keratin as proteins that interact with the 1,25D₃-MARRS receptor. Using confocal microscopy, we visualized 1,25(OH)₂D₃- MARRS receptor localizations relative to actin and/or keratin distribution in chick enterocytes. Cells cultured in media containing phenol red had the 1,25D₃-MARRS receptor and actin localized largely in the nucleus, which was dispersed upon addition of (OH)₂ 1,25(OH)₂D₃. In the absence of phenol red, staining was cytoplasmic. Addition of steroid caused diminished staining at 10 s and 30 s, with a return of intensity between 1 and 5 min. Nuclear staining was observed after 1 min. We found that F-actin concentrations are maximal when 1,25D₃-MARRS receptor localizations within enterocytes are low suggesting that cyclical conversions of F-actin to G-actin are involved in the 1,25(OH)₂D₃-mediated redistribution of the 1,25D₃-MARRS receptor within the cell. We also found that keratin distribution remains constant with 1,25(OH)₂D₃ exposure when Factin depolymerizes into G-actin, which suggests that actin and keratin work in concert to facilitate hormonemediated redistribution of the 1,25D₃-MARRS receptor. We subsequently investigated whether the cyclical redistribution was related to either 1,25(OH)₂D₃-stimulated phosphate or calcium uptake, but no congruent pattern was found.

Transmissible gastroenteritis virus and porcine epidemic diarrhoea virus infection induces dramatic changes in the tight junctions and microfilaments of polarized IPEC-J2 cells

Viral infection converts the normal constitution of a cell to optimise viral entry, replication, and virion production. These conversions contain alterations or disruptions of the tight and adherens junctions between cells as part of their pathogenesis, and reorganise cellular microfilaments that initiate, sustain and spread the viral infections and so on. Using porcine epidemic diarrhoea virus (PEDV), transmissible gastroenteritis virus (TGEV) and a model of normal intestinal epithelial cells (IPEC-J2), we researched the interaction between tight and adherens junctions and microfilaments of IPEC-J2 cells with these viruses. In our work, the results showed that IPEC-J2 cells were susceptible to TGEV and PEDV infection. And TGEV could impair the barrier integrity of IPEC-J2 cells at early stages of infection through down-regulating some proteins of tight and adherens junctions, while PEDV cloud cause a slight of damage in the integrity of epithelial barrier. In addition, they also could affect the microfilaments remodelling of IPEC-J2 cells, and the drug-interfered microfilaments could inhibit viral replication and release. Furthermore, PEDV+TGEV co-infection was more aggravating to damage of tight junctions and remodelling of microfilaments than their single infection. Finally, the PEDV and TGEV infection affected the MAPK pathway, and inhibition of MAPK pathway regulated the changes of tight junctions and microfilaments of cells. These studies provide a new insight from the perspective of the epithelial barrier and microfilaments into the pathogenesis of PEDV and TGEV.

Collapsin response mediator protein 4 regulates growth cone dynamics through the actin and microtubule cytoskeleton

Coordinated control of the growth cone cytoskeleton underlies axon extension and guidance. Members of the collapsin response mediator protein (CRMP) family of cytosolic phosphoproteins regulate the microtubule and actin cytoskeleton, but their roles in regulating growth cone dynamics remain largely unexplored. Here, we examine how CRMP4 regulates the growth cone cytoskeleton. Hippocampal neurons from CRMP4-/- mice exhibited a selective decrease in axon extension and reduced growth cone area, whereas overexpression of CRMP4 enhanced the formation and length of growth cone filopodia. Biochemically, CRMP4 can impact both microtubule assembly and F-actin bundling in vitro. Through a structure function analysis of CRMP4, we found that the effects of CRMP4 on axon growth and growth cone morphology were dependent on microtubule assembly, whereas filopodial extension relied on actin bundling. Intriguingly, anterograde movement of EB3 comets, which track microtubule protrusion, slowed significantly in neurons derived from CRMP4-/- mice, and rescue of microtubule dynamics required CRMP4 activity toward both the actin and microtubule cytoskeleton. Together, this study identified a dual role for CRMP4 in regulating the actin and microtubule growth cone cytoskeleton.

Exploiting the cytoskeletal filaments of neoplastic cells to potentiate a novel therapeutic approach

Although cytoskeletal-directed agents have been a mainstay in chemotherapeutic protocols due to their ability to readily interfere with the rapid mitotic progression of neoplastic cells, they are all microtubule-based drugs, and there has yet to be any microfilament- or intermediate filament-directed agents approved for clinical use. There are many inherent differences between the cytoskeletal networks of malignant and normal cells, providing an ideal target to attain preferential damage. Further, numerous microfilament-directed agents, and an intermediate filament-directed agent of particular interest (withaferin A) have demonstrated in vitro and in vivo efficacy, suggesting that cytoskeletal filaments may be exploited to supplement chemotherapeutic approaches currently used in the clinical setting. Therefore, this review is intended to expose academics and clinicians to the tremendous variety of cytoskeletal filament-directed agents that are currently available for further chemotherapeutic evaluation. The mechanisms by which microfilament directed- and intermediate filament-directed agents damage malignant cells are discussed in detail in order to establish how the drugs can be used in combination with each other, or with currently approved chemotherapeutic agents to generate a substantial synergistic attack, potentially establishing a new paradigm of chemotherapeutic agents.

Transmissible gastroenteritis virus and porcine epidemic diarrhoea virus infection induces dramatic changes in the tight junctions and microfilaments of polarized IPEC-J2 cells. Virus Res. 2014;192:34-45. [PMID: 25173696 DOI: 10.1016/j.virusres.2014]

Viral infection converts the normal constitution of a cell to optimise viral entry, replication, and virion production. These conversions contain alterations or disruptions of the tight and adherens junctions between cells as part of their pathogenesis, and reorganise cellular microfilaments that initiate, sustain and spread the viral infections and so on. Using porcine epidemic diarrhoea virus (PEDV), transmissible gastroenteritis virus (TGEV) and a model of normal intestinal epithelial cells (IPEC-J2), we researched the interaction between tight and adherens junctions and microfilaments of IPEC-J2 cells with these viruses. In our work, the results showed that IPEC-J2 cells were susceptible to TGEV and PEDV infection. And TGEV could impair the barrier integrity of IPEC-J2 cells at early stages of infection through down-regulating some proteins of tight and adherens junctions, while PEDV cloud cause a slight of damage in the integrity of epithelial barrier. In addition, they also could affect the microfilaments remodelling of IPEC-J2 cells, and the drug-interfered microfilaments could inhibit viral replication and release. Furthermore, PEDV+TGEV co-infection was more aggravating to damage of tight junctions and remodelling of microfilaments than their single infection. Finally, the PEDV and TGEV infection affected the MAPK pathway, and inhibition of MAPK pathway regulated the changes of tight junctions and microfilaments of cells. These studies provide a new insight from the perspective of the epithelial barrier and microfilaments into the pathogenesis of PEDV and TGEV.

Cytoskeleton and CFTR

Cystic Fibrosis Transmembrane conductance Regulator, CFTR, is a membrane protein expressed in epithelia. A protein kinase A (PKA)-regulated Cl(-) channel, it is a rate-limiting factor in fluid transport. Mutations in CFTR are responsible for cystic fibrosis, CF, an autosomal recessive disease. The most frequent mutation is deletion of phenylalanine at position 508, ΔF508. The regulation of trafficking and degradation of CFTR/ΔF508CFTR as well as its function(s) is a complex process which involves a number of proteins including chaperones and adaptors. It is now known that cytoskeletal proteins, previously considered only as structural proteins, are also important factors in the regulation of cellular processes and functions. The aim of the present review is to focus on how microfilaments, microtubules and intermediary filaments form a dynamic interactome with CFTR to participate in the regulation of CFTR-dependent transepithelial ion transport, CFTR trafficking and degradation.

A novel structural unit in the N-terminal region of filamins

Immunoglobulin-like (Ig) domains are a widely expanded superfamily that act as interaction motifs or as structural spacers in multidomain proteins. Vertebrate filamins (FLNs), which are multifunctional actin-binding proteins, consist of 24 Ig domains. We have recently discovered that in the C-terminal rod 2 region of FLN, Ig domains interact with each other forming functional domain pairs, where the interaction with signaling and transmembrane proteins is mechanically regulated by weak actomyosin contraction forces. Here, we investigated if there are similar inter-domain interactions around domain 4 in the N-terminal rod 1 region of FLN. Protein crystal structures revealed a new type of domain organization between domains 3, 4, and 5. In this module, domains 4 and 5 interact rather tightly, whereas domain 3 has a partially flexible interface with domain 4. NMR peptide titration experiments showed that within the three-domain module, domain 4 is capable for interaction with a peptide derived from platelet glycoprotein Ib. Crystal structures of FLN domains 4 and 5 in complex with the peptide revealed a typical β sheet augmentation interaction observed for many FLN ligands. Domain 5 was found to stabilize domain 4, and this could provide a mechanism for the regulation of domain 4 interactions.

Structure of Clostridium difficile PilJ exhibits unprecedented divergence from known type IV pilins

Type IV pili are produced by many pathogenic Gram-negative bacteria and are important for processes as diverse as twitching motility, cellular adhesion, and colonization. Recently, there has been an increased appreciation of the ability of Gram-positive species, including Clostridium difficile, to produce Type IV pili. Here we report the first three-dimensional structure of a Gram-positive Type IV pilin, PilJ, demonstrate its incorporation into Type IV pili, and offer insights into how the Type IV pili of C. difficile may assemble and function. PilJ has several unique structural features, including a dual-pilin fold and the incorporation of a structural zinc ion. We show that PilJ is incorporated into Type IV pili in C. difficile and present a model in which the incorporation of PilJ into pili exposes the C-terminal domain of PilJ to create a novel interaction surface.

Protein kinase C, focal adhesions and the regulation of cell migration

Cell adhesion to extracellular matrix is a complex process involving protrusive activity driven by the actin cytoskeleton, engagement of specific receptors, followed by signaling and cytoskeletal organization. Thereafter, contractile and endocytic/recycling activities may facilitate migration and adhesion turnover. Focal adhesions, or focal contacts, are widespread organelles at the cell-matrix interface. They arise as a result of receptor interactions with matrix ligands, together with clustering. Recent analysis shows that focal adhesions contain a very large number of protein components in their intracellular compartment. Among these are tyrosine kinases, which have received a great deal of attention, whereas the serine/threonine kinase protein kinase C has received much less. Here the status of protein kinase C in focal adhesions and cell migration is reviewed, together with discussion of its roles and potential substrates.