PTBP1 plays an important role in the development of gastric cancer.

BACKGROUND: Polypyrimidine tract binding protein 1 (PTBP1) has been found to play an important role in the occurrence and development of various tumors. At present, the role of PTBP1 in gastric cancer (GC) is still unknown and worthy of further investigation. METHODS: We used bioinformatics to analyze the expression of PTBP1 in patients with GC. Cell proliferation related experiments were used to detect cell proliferation after PTBP1 knockdown. Skeleton staining, scanning electron microscopy and transmission electron microscopy were used to observe the changes of actin skeleton. Proliferation and actin skeleton remodeling signaling pathways were detected by Western Blots. The relationship between PTBP1 and proliferation of gastric cancer cells was further detected by subcutaneous tumor transplantation. Finally, tissue microarray data from clinical samples were used to further explore the expression of PTBP1 in patients with gastric cancer and its correlation with prognosis. RESULTS: Through bioinformatics studies, we found that PTBP1 was highly expressed in GC patients and correlated with poor prognosis. Cell proliferation and cycle analysis showed that PTBP1 down-regulation could significantly inhibit cell proliferation. The results of cell proliferation detection related experiments showed that PTBP1 down-regulation could inhibit the division and proliferation of GC cells. Furthermore, changes in the morphology of the actin skeleton of cells showed that PTBP1 down-regulation inhibited actin skeletal remodeling in GC cells. Western Blots showed that PTBP1 could regulate proliferation and actin skeleton remodeling signaling pathways. In addition, we constructed PTBP1 Cas9-KO mouse model and performed xenograft assays to further confirm that down-regulation of PTBP1 could inhibit the proliferation of GC cells. Finally, tissue microarray was used to further verify the close correlation between PTBP1 and poor prognosis in patients with GC. CONCLUSIONS: Our study demonstrates for the first time that PTBP1 may affect the proliferation of GC cells by regulating actin skeleton remodeling. In addition, PTBP1 is closely related to actin skeleton remodeling and proliferation signaling pathways. We suppose that PTBP1 might be a potential target for the treatment of GC.

Comprehensive analysis of cell-extracellular matrix protein Ras suppressor-1 in function and prognosis of gastrointestinal cancers.

BACKGROUND: Ras suppressor 1 (RSU1), a highly conserved protein, plays an important role in actin cytoskeleton remodeling and cell-extracellular matrix adhesion. Aberration of RSU1 activity can cause changes in cell adhesion and migration, thereby enhancing tumor proliferation and metastasis. However, the correlation between RSU1 and gastrointestinal cancers (GICs), as well as its prognostic role related to tumor-infiltrating immune cells (TIICs) remains unclear. AIM: To shows RSU1 plays a potential promoting role in facilitating tumor immune escape in GIC. METHODS: Differential expression of RSU1 in different tumors and their corresponding normal tissues was evaluated by exploring the Gene Expression Profiling Interactive Analysis (GEPIA) dataset. The correlation between RSU1 expression and prognosis of GIC cancer patients was evaluated by Kaplan-Meier plotter. Then, RSU1-correlated genes were screened and functionally characterized via enrichment analysis. The correlation between RSU1 and TIICs was further characterized using the Tumor Immune Estimation Resource (TIMER). In addition, the correlation between RSU1 and immune cell surface molecules was also analyzed by TIMER. RESULTS: High RSU1 expression was associated with poor overall survival of gastric cancer patients, exhibiting a hazard ratio (HR) = 1.36, first progression HR = 1.53, and post progression survival HR = 1.6. Specifically, high RSU1 Levels were associated with prognosis of gastric cancer in females, T4 and N3 stages, and Her-2-negative subtypes. Regarding immune-infiltrating cells, RSU1 expression level was positively correlated with infiltration of CD4+ T cells, macrophages, neutrophils, and dendritic cells (DCs) in colorectal adenocarcinoma and stomach adenocarcinoma. RSU1 expression was also predicted to be strongly correlated with immune marker sets in M2 macrophage, DCs and T cell exhaustion in GICs. CONCLUSION: In gastrointestinal cancers, RSU1 is increased in tumor tissues, and predicts poor survival of patients. Increased RSU1 may be involved in promoting macrophage polarization, DC infiltration, and T cell exhaustion, inducing tumor immune escape and the development of tumors in GICs. We suggest that RSU1 is a promising prognostic biomarker reflecting immune infiltration level of GICs, as well as a potential therapeutic target for precision treatment through improving the immune response.

Triptonodiol, a Diterpenoid Extracted from Tripterygium wilfordii, Inhibits the Migration and Invasion of Non-Small-Cell Lung Cancer.

Lung cancer is the most prevalent oncological disease worldwide, with non-small-cell lung cancer accounting for approximately 85% of lung cancer cases. Tripterygium wilfordii is a traditional Chinese herb that is widely used to treat rheumatism, pain, inflammation, tumors, and other diseases. In this study, we found that Triptonodiol extracted from Tripterygium wilfordii inhibited the migration and invasion of non-small-cell lung cancer and inhibited cytoskeletal remodeling, which has not been previously reported. Triptonodiol significantly inhibited the motility activity of NSCLC at low toxic concentrations and suppressed the migration and invasion of NSCLC. These results can be confirmed by wound healing, cell trajectory tracking, and Transwell assays. We found that cytoskeletal remodeling was inhibited in Triptonodiol-treated NSCLC, as evidenced by the reduced aggregation of actin and altered pseudopod morphology. Additionally, this study found that Triptonodiol induced an increase in complete autophagic flux in NSCLC. This study suggests that Triptonodiol reduces the aggressive phenotype of NSCLC by inhibiting cytoskeletal remodeling and is a promising anti-tumor compound.

Celastrus orbiculatus Thunb. extract inhibits EMT and metastasis of gastric cancer by regulating actin cytoskeleton remodeling.

ETHNOPHARMACOLOGICAL RELEVANCE: The traditional Chinese medicine herb Celastrus orbiculatus Thunb. is an important folk medicinal plant in China that has been used as an anti-inflammatory, antitumor, and analgesic in various diseases. Recent years, many studies have reported the significant effects of Celastrus orbiculatus Thunb. extract (COE) on gastric cancer. However, the specific mechanism by which COE regulates gastric cancer cytoskeleton remodeling and thus inhibits EMT has not yet been reported. AIM OF STUDY: To study the effect and mechanism of COE in inhibiting the epithelial-mesenchymal transition (EMT) and metastasis of gastric cancer cells, laying an experimental foundation for the clinical application and further development of COE. METHODS: The high-content cell dynamic tracking system was used to continuously track the trajectory of cell movement in real time. Through the high-content data, the average movement distance and movement speed of the cells are calculated. Additionally, the dynamic images of the cell movement in the high-content imaging system are derived to analyze the impact of COE on the movement of gastric cancer cells. Cytoskeleton staining experiment was performed to detect the effect of COE on the assembly of gastric cancer cell cytoskeleton proteins. Western blot was employed to detect the changes of EMT and metastasis-related proteins in the gastric cancer cells treated by COE. The effect of COE on the key regulatory protein Cofilin-1 (CFL1) of cell movement was examined by Western blot and protein degradation experiment. The effect of COE on EMT and metastasis of the gastric cancer cells lacking CFL1 was assessed by a transwell assay. The in vivo inhibitory effect of COE on EMT and metastasis of gastric cancer was determined by the animal living image system. IHC assays were used to detect the levels of EMT-related proteins in COE reversal in vivo. RESULT: The results showed that the movement distance and average movement speed of gastric cancer cells after COE treatment were significantly lower than those of the control group. Cytoskeleton staining experiments revealed that COE can significantly change the distribution of skeletal proteins in gastric cancer cells. Additionally, COE treatment significantly reduced the expression of Matrix metalloproteinases (MMP-2, MMP-9) and other proteins. Furthermore, COE can significantly accelerate the degradation of CFL1 protein, and both COE treatment and CFL1 deletion can significantly inhibit EMT and metastasis of gastric cancer cells. Lastly, the number of peritoneal metastases of gastric cancer cells was significantly reduced in animals after COE treatment. COE can reverse the levels of EMT-related proteins while reducing the expression levels of CFL1 protein in vivo. CONCLUSION: COE can significantly inhibit EMT and metastasis of gastric cancer cells in vivo and in vitro. This effect may be achieved by reducing the stability of CFL1 and inhibiting the assembly of actin in gastric cancer cells.

SEMA6A/RhoA/YAP axis mediates tumor-stroma interactions and prevents response to dual BRAF/MEK inhibition in BRAF-mutant melanoma.

BACKGROUND: Despite the promise of dual BRAF/MEK inhibition as a therapy for BRAF-mutant (BRAF-mut) melanoma, heterogeneous responses have been observed in patients, thus predictors of benefit from therapy are needed. We have previously identified semaphorin 6A (SEMA6A) as a BRAF-mut-associated protein involved in actin cytoskeleton remodeling. The purpose of the present study is to dissect the role of SEMA6A in the biology of BRAF-mut melanoma, and to explore its predictive potential towards dual BRAF/MEK inhibition. METHODS: SEMA6A expression was assessed by immunohistochemistry in melanoma cohort RECI1 (N = 112) and its prognostic potential was investigated in BRAF-mut melanoma patients from DFCI and TCGA datasets (N = 258). The molecular mechanisms regulated by SEMA6A to sustain tumor aggressiveness and targeted therapy resistance were investigated in vitro by using BRAF-mut and BRAF-wt melanoma cell lines, an inducible SEMA6A silencing cell model and a microenvironment-mimicking fibroblasts-coculturing model. Finally, SEMA6A prediction of benefit from dual BRAF/MEK inhibition was investigated in melanoma cohort RECI2 (N = 14). RESULTS: Our results indicate higher protein expression of SEMA6A in BRAF-mut compared with BRAF-wt melanoma patients and show that SEMA6A is a prognostic indicator in BRAF-mut melanoma from TCGA and DFCI patients cohorts. In BRAF-mut melanoma cells, SEMA6A coordinates actin cytoskeleton remodeling by the RhoA-dependent activation of YAP and dual BRAF/MEK inhibition by dabrafenib+trametinib induces SEMA6A/RhoA/YAP axis. In microenvironment-mimicking co-culture condition, fibroblasts confer to melanoma cells a proliferative stimulus and protect them from targeted therapies, whereas SEMA6A depletion rescues the efficacy of dual BRAF/MEK inhibition. Finally, in BRAF-mut melanoma patients treated with dabrafenib+trametinib, high SEMA6A predicts shorter recurrence-free interval. CONCLUSIONS: Overall, our results indicate that SEMA6A contributes to microenvironment-coordinated evasion of melanoma cells from dual BRAF/MEK inhibition and it might be a good candidate predictor of short-term benefit from dual BRAF/MEK inhibition.

Dysregulation of Cytoskeleton Remodeling Drives Invasive Leading Cells Detachment.

Detachment of cancer cells is the first step in tumor metastasis and malignancy. However, studies on the balance of initial tumor anchoring and detachment are limited. Herein, we revealed that the regulation of cytoskeleton proteins potentiates tumor detachment. The blockage of TGF-ß1 using neutralizing antibodies induced cancer cell detachment in the Boyden chamber and 3D in-gel spheroid models. Moreover, treatment with latrunculin B, an actin polymerization inhibitor, enhanced cell dissociation by abolishing actin fibers, indicating that TGF-ß1 mediates the formation of actin stress fibers, and is likely responsible for the dynamics of anchoring and detachment. Indeed, latrunculin B disrupted the formation of external TGF-ß1-induced actin fibers and translocation of intracellular vinculin, a focal adhesion protein, resulting in the suppression of cell adhesion. Moreover, the silencing of vimentin substantially reduced cell adhesion and enhanced cell detachment, revealing that cell adhesion and focal adhesion protein translocation stimulated by TGF-ß1 require vimentin. Using the 3D in-gel spheroid model, we found that latrunculin B suppressed the cell adhesion promoted by external TGF-ß1, increasing the number of cells that penetrated the Matrigel and detached from the tumor spheres. Thus, cytoskeleton remodeling maintained the balance of cell anchoring and detachment, and the TGF-ß1/vimentin/focal adhesion protein assembly axis was involved in the control dynamics of initial tumor detachment.

Actin Dynamics at the T Cell Synapse as Revealed by Immune-Related Actinopathies.

The actin cytoskeleton is composed of dynamic filament networks that build adaptable local architectures to sustain nearly all cellular activities in response to a myriad of stimuli. Although the function of numerous players that tune actin remodeling is known, the coordinated molecular orchestration of the actin cytoskeleton to guide cellular decisions is still ill defined. T lymphocytes provide a prototypical example of how a complex program of actin cytoskeleton remodeling sustains the spatio-temporal control of key cellular activities, namely antigen scanning and sensing, as well as polarized delivery of effector molecules, via the immunological synapse. We here review the unique knowledge on actin dynamics at the T lymphocyte synapse gained through the study of primary immunodeficiences caused by mutations in genes encoding actin regulatory proteins. Beyond the specific roles of individual actin remodelers, we further develop the view that these operate in a coordinated manner and are an integral part of multiple signaling pathways in T lymphocytes.

Confirming whether KLHL23 deficiency potentiates migration in urothelial carcinoma.

Epithelial-mesenchymal transition (EMT) is associated with malignant tumors. In a previous study, we found that KLHL23 is a tumor suppressor gene that inhibits EMT and cancer dissemination. However, the correlation between its expression and cancer progression in urothelial carcinoma (UC) remains unknown. This study showed that the deficiency of KLHL23 in the invasive leading cancer cells is important for improving cell migration in UC. Currently, little is known about the underlying mechanisms of KLHL23-mediated cytoskeleton remodeling in the metastatic leading cells of tumors. Our findings showed that silencing of KLHL23 promotes cell migration in UC by regulating the translocation of focal adhesion proteins. Lack of KLHL23 causes abnormal formation of lamellipodia and increases the EMT phenotype and migration. Wound healing assay revealed that KLHL23 potentiates the actin bundles and intracellular focal adhesion protein formation in the invasive leading cells. Knockdown of KLHL23 abolishes the formation of actin stress fibers and translocalizes vinculin to the perimembrane, which enhances the mobility of cancer cells. To elucidate the mechanism, we found that during migration, KLHL23 appears in the leading cells in large numbers and binds to the actin stress fibers. A large amount of vinculin accumulated at both ends of the KLHL23/actin fibers, indicating an increase in cell anchorage. Thus, KLHL23 might play a critical role in enhancing actin fibers and promoting focal adhesion complex formation in the invasive leading cells. Analysis of the overall survival revealed that low KLHL23 is associated with poor survival in patients with bladder UC, indicating its clinical significance. We hypothesize that KLHL23 is involved in the formation of actin stress fibers and focal adhesion complexes in the invasive leading cells and may be associated with EMT progression and prognosis in UC patients.

LSP1-myosin1e bimolecular complex regulates focal adhesion dynamics and cell migration.

Several cytoskeleton-associated proteins and signaling pathways work in concert to regulate actin cytoskeleton remodeling, cell adhesion, and migration. Although the leukocyte-specific protein 1 (LSP1) has been shown to interact with the actin cytoskeleton, its function in the regulation of actin cytoskeleton dynamics is, as yet, not fully understood. We have recently demonstrated that the bimolecular complex between LSP1 and myosin1e controls actin cytoskeleton remodeling during phagocytosis. In this study, we show that LSP1 downregulation severely impairs cell migration, lamellipodia formation, and focal adhesion dynamics in macrophages. Inhibition of the interaction between LSP1 and myosin1e also impairs these processes resulting in poorly motile cells, which are characterized by few and small lamellipodia. Furthermore, cells in which LSP1-myosin1e interaction is inhibited are typically associated with inefficient focal adhesion turnover. Collectively, our findings show that the LSP1-myosin1e bimolecular complex plays a pivotal role in the regulation of actin cytoskeleton remodeling and focal adhesion dynamics required for cell migration.

MLK3 Is Associated With Poor Prognosis in Patients With Glioblastomas and Actin Cytoskeleton Remodeling in Glioblastoma Cells.

Mixed lineage kinase 3 (MLK3) has been implicated in human melanoma and breast cancers. However, the clinical significance of MLK3 in human gliomas and the underlying cellular and molecular mechanisms remain unclear. We found that MLK3 proteins were highly expressed in high-grade human glioma specimens and especially prevalent in primary and recurrent glioblastoma multiforme (GBM). High levels of MLK3 mRNA were correlated with poor prognosis in patients with isocitrate dehydrogenase (IDH)-wild-type (wt) gliomas. Furthermore, genetic ablation of MLK3 significantly suppressed the migration and invasion abilities of GBM cells and disrupted actin cytoskeleton organization. Importantly, MLK3 directly bound to epidermal growth factor receptor kinase substrate 8 (EPS8) and regulated the cellular location of EPS8, which is essential for actin cytoskeleton rearrangement. Overall, these findings provide evidence that MLK3 upregulation predicts progression and poor prognosis in human IDH-wt gliomas and suggest that MLK3 promotes the migration and invasion of GBM cells by remodeling the actin cytoskeleton via MLK3-EPS8 signaling.

Morphological and mechanical stability of bladder cancer cells in response to substrate rigidity.

BACKGROUND: Morphology of cells can be considered as an interplay between the accessibility of substrate anchoring sites, cytoskeleton properties and cellular deformability. To withstand tension induced by cell's environment, cells tend to spread out and, simultaneously, to remodel actin filament organization. METHODS: In this context, the use of polyacrylamide hydrogel substrates with a surface coated with laminin allows to trace remodeling of actin cytoskeleton during the interaction of cells with laminin-rich basement membrane. Reorganization of actin cortex can be quantified by a surface spreading area and deformability of single cells. RESULTS: In our study, we demonstrated that morphological and mechanical alterations of bladder cancer cells in response to altered microenvironment stiffness are of biphasic nature. Threshold-dependent relations are induced by mechanical properties of cell microenvironment. Initially, fast alterations in cellular capability to spread and to deform are followed by slow-rate changes. A switch provided by cellular deformability threshold, in the case of non-malignant cells, triggers the formation of thick actin bundles accompanied by matured focal adhesions. For cancer cells, cell spreading and deformability thresholds switch between slow and fast rate of changes with weak reorganization of actin filaments and focal adhesions formation. CONCLUSIONS: The presence of transition region enables the cells to achieve a morphological and mechanical stability, which together with altered expression of vinculin and integrins, can contribute to invasiveness of bladder cancers. GENERAL SIGNIFICANCE: Our findings show that morphological and mechanical stability is directly related to actin filament organization used by cancer cells to adapt to altered laminin-rich microenvironment.

Arf proteins in cancer cell migration.

Members of the ADP-ribosylation factor (Arf) family of small GTP-binding (G) proteins regulate several aspects of membrane trafficking, such as vesicle budding, tethering and cytoskeleton organization. Arf family members, including Arf-like (Arl) proteins have been implicated in several essential cellular functions, like cell spreading and migration. These functions are used by cancer cells to disseminate and invade the tissues surrounding the primary tumor, leading to the formation of metastases. Indeed, Arf and Arl proteins, as well as their guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) have been found to be abnormally expressed in different cancer cell types and human cancers. Here, we review the current evidence supporting the involvement of Arf family proteins and their GEFs and GAPs in cancer progression, focusing on 3 different mechanisms: cell-cell adhesion, integrin internalization and recycling, and actin cytoskeleton remodeling.

Proteomic comparison of the EWS-FLI1 expressing cells EF with NIH-3T3 and actin remodeling effect of (R/W)9 cell-penetrating peptide.

EWS-FLI1 expression in NIH-3T3 fibroblasts has a profound impact on the phenotype, resulting in the cytoskeleton and adhesive capacity disorganization (EF cells). Besides this, (R/W)9, a cell-penetrating peptide (CPP), has an intrinsic actin remodeling activity in EF cells. To evaluate the impact of the oncogenic protein EWS-FLI1 on proteins expression levels, a quantitative comparison of tumoral EF and non-tumoral 3T3 proteomes was performed. Then to see if we could link the EWS-FLI1 oncogenic transformation to the phenotype reversion induced by (R/W)9, (R/W)9 influence on EF cells proteome was assessed. To our knowledge no such â¿¿CPPomicâ¿¿ study has been performed before. BIOLOGICAL SIGNIFICANCE: Up to now very few global quantitative proteomic studies have been published to help understand the oncogenic transformation induced by EWS-FLI1 fusion protein and leading to Ewing sarcoma development and dissemination. The comparison we did in this study between a model tumoral cell line EF and its non-tumoral counterpart (3T3) allowed us to highlight several features either common to most tumor types or specific to Ewing sarcoma. Particularly, lack of actin cytoskeleton organization could very likely be explained by the down-regulation of many important actin binding proteins. These results are in accordance with the hypothesis of a passive/stochastic mode of dissemination conferring Ewing sarcoma tumoral cell a high metastatic potential.

Phosphorylation of filamin A by Cdk1 regulates filamin A localization and daughter cell separation.

In cell culture, many adherent mammalian cells undergo substantial actin cytoskeleton rearrangement prior to mitosis as they detach from the extracellular matrix and become spherical. At the end of mitosis, the actin cytoskeleton is required for cytokinesis and the reassembly of interphase structures as cells spread and reattach to substrate. To understand the processes regulating mitotic cytoskeletal remodeling, we studied how mitotic phosphorylation regulates filamin A (FLNa). FLNa is an actin-crosslinking protein that was previously identified as a cyclin-dependent kinase 1 (Cdk1) binding partner and substrate in vitro. Using quantitative label-based mass spectrometry, we find that FLNa serines 1084, 1459 and 1533 are phosphorylated in mitotic HeLa cells and all three sites match the phosphorylation consensus sequence of Cdk1. To investigate the functional role of mitotic FLNa phosphorylation, we mutated serines 1084, 1459 and 1533 to nonphosphorylatable alanine residues and expressed GFP-tagged FLNa(S1084A,S1459A,S1533A) (FLNa-AAA GFP) in a FLNa-deficient human melanoma cell line called M2. M2 cells expressing FLNa-AAA GFP have enhanced FLNa-AAA GFP and actin localization at sites of contact between daughter cells, impaired post-mitotic daughter cell separation and defects in cell migration. Therefore, mitotic phosphorylation of FLNa is important for successful cell division and interphase cell behavior.

Function and regulation of the Rho guanine nucleotide exchange factor Trio.

Rho GTPases oscillate between an inactive GDP-bound state and an active GTP-bound state. They are activated by Rho Guanine nucleotide Exchange Factors (GEF), which accelerate the GDP to GTP exchange. RhoGEFs fall into two different classes: the Dbl family and the DOCK family of proteins. In this review, we focus on the function and regulation of the Dbl family RhoGEF Trio. Trio and its paralog Kalirin are unique within this family in that they display two GEF domains of distinct specificity. Trio is a major regulator of neuronal development, and its function is conserved through evolution. Moreover, Trio plays an important role in cell adhesion and in signaling pathways elicited by Gαq protein-coupled receptors. Combined, these observations suggest that Trio has a major role in cellular physiology. Of note, Trio is an essential gene for mouse development, with a prominent role in the development of the nervous system. Finally, Trio expression is significantly increased in different types of tumors and it has been proposed that it could participate in oncogenesis.

Direct interaction of 14-3-3ζ with ezrin promotes cell migration by regulating the formation of membrane ruffle.

14-3-3 proteins have been shown to regulate the actin cytoskeleton remodeling, cell adhesion and migration. In this study, we identified ezrin, a cross-linker between plasma membrane and actin cytoskeleton, as a novel 14-3-3ζ interacting partner. The direct interaction between 14-3-3ζ and ezrin was validated in the cells and by in vitro assays. We showed that the 14-3-3ζ binding region in ezrin was located within the N-terminal and central α-helical domains and that the αG-to-αI helices of 14-3-3ζ are responsible for the binding to ezrin. Functional analyses revealed that the regulation of cell migration and membrane ruffling by 14-3-3ζ is ezrin dependent, for which the integrity of ezrin protein was required. Conversely, the knockdown of 14-3-3ζ abrogates also the stimulatory effect of ezrin on cell migration and membrane ruffling. Moreover, we found that the phosphorylation of Thr567 in ezrin facilitates the 14-3-3ζ-ezrin interaction and the formation of membrane ruffles. Taken together, these results suggest strongly that the functions of these two proteins in cell migration are linked and might be mediated by their direct physical interaction, which is important for the formation of membrane ruffles.

Structural features and interfacial properties of WH2, ß-thymosin domains and other intrinsically disordered domains in the regulation of actin cytoskeleton dynamics.

Many actin-binding proteins (ABPs) use complex multidomain architectures to integrate and coordinate multiple signals and interactions with the dynamic remodeling of actin cytoskeleton. In these proteins, small segments that are intrinsically disordered in their unbound native state can be functionally as important as identifiable folded units. These functional intrinsically disordered regions (IDRs) are however difficult to identify and characterize in vitro. Here, we try to summarize the state of the art in understanding the structural features and interfacial properties of IDRs involved in actin self-assembly dynamics. Recent structural and functional insights into the regulation of widespread, multifunctional WH2/ß-thymosin domains, and of other IDRs such as those associated with WASP/WAVE, formin or capping proteins are examined. Understanding the functional versatility of IDRs in actin assembly requires apprehending by multiple structural and functional approaches their large conformational plasticity and dynamics in their interactions. In many modular ABPs, IDRs relay labile interactions with multiple partners and act as interaction hubs in interdomain and protein-protein interfaces. They thus control multiple conformational transitions between the inactive and active states or between various active states of multidomain ABPs, and play an important role to coordinate the high turnover of interactions in actin self-assembly dynamics.

PtdIns5P: news and views of its appearance, disappearance and deeds.

Accumulated evidence indicates that PtdIns5P, one of the seven phosphoinositides, found now to be constitutively present in yeast, plants and metazoa, serves as a signaling molecule to modulate pleiotropic cellular functions in both the nucleus and the cytoplasm. The enzymatic routes in biogenesis of basal PtdIns5P have remained incompletely understood. The role for candidate kinase PIKfyve that is principally involved in PtdIns(3,5)P2 production, has been questioned. In this review article we scrutinize the past obstacles that prevented the definitive implication of PIKfyve in PtdIns5P biosynthesis from PtdIns and focus on the recent pharmacological and genetic advancements that now make this conclusion well supported. We further summarize our current knowledge of the diverse stimuli modulating PtdIns5P levels, binding partners and regulated cellular process, with particular reference to the available mechanistic insights for the relevant signaling pathways.