Centrosome-organized plasma membrane infoldings linked to growth of a cortical actin domain.

Regulated cell shape change requires the induction of cortical cytoskeletal domains. Often, local changes to plasma membrane (PM) topography are involved. Centrosomes organize cortical domains and can affect PM topography by locally pulling the PM inward. Are these centrosome effects coupled? At the syncytial Drosophila embryo cortex, centrosome-induced actin caps grow into dome-like compartments for mitoses. We found the nascent cap to be a collection of PM folds and tubules formed over the astral centrosomal MT array. The localized infoldings require centrosome and dynein activities, and myosin-based surface tension prevents them elsewhere. Centrosome-engaged PM infoldings become specifically enriched with an Arp2/3 induction pathway. Arp2/3 actin network growth between the infoldings counterbalances centrosomal pulling forces and disperses the folds for actin cap expansion. Abnormal domain topography with either centrosome or Arp2/3 disruption correlates with decreased exocytic vesicle association. Together, our data implicate centrosome-organized PM infoldings in coordinating Arp2/3 network growth and exocytosis for cortical domain assembly.

PI 3-Kinase and the Histone Methyl-Transferase KMT2D Collaborate to Induce Arp2/3-Dependent Migration of Mammary Epithelial Cells.

Breast cancer develops upon sequential acquisition of driver mutations in mammary epithelial cells; however, how these mutations collaborate to transform normal cells remains unclear in most cases. We aimed to reconstitute this process in a particular case. To this end, we combined the activated form of the PI 3-kinase harboring the H1047R mutation with the inactivation of the histone lysine methyl-transferase KMT2D in the non-tumorigenic human mammary epithelial cell line MCF10A. We found that PI 3-kinase activation promoted cell-cycle progression, especially when growth signals were limiting, as well as cell migration, both in a collective monolayer and as single cells. Furthermore, we showed that KMT2D inactivation had relatively little influence on these processes, except for single-cell migration, which KMT2D inactivation promoted in synergy with PI 3-kinase activation. The combination of these two genetic alterations induced expression of the ARPC5L gene that encodes a subunit of the Arp2/3 complex. ARPC5L depletion fully abolished the enhanced migration persistence exhibited by double-mutant cells. Our reconstitution approach in MCF10A has thus revealed both the cell function and the single-cell migration, and the underlying Arp2/3-dependent mechanism, which are synergistically regulated when KMT2D inactivation is combined with the activation of the PI 3-kinase.

Nuclear actin structure regulates chromatin accessibility.

Polymerized ß-actin may provide a structural basis for chromatin accessibility and actin transport into the nucleus can guide mesenchymal stem cell (MSC) differentiation. Using MSC, we show that using CK666 to inhibit Arp2/3 directed secondary actin branching results in decreased nuclear actin structure, and significantly alters chromatin access measured with ATACseq at 24 h. The ATAC-seq results due to CK666 are distinct from those caused by cytochalasin D (CytoD), which enhances nuclear actin structure. In addition, nuclear visualization shows Arp2/3 inhibition decreases pericentric H3K9me3 marks. CytoD, alternatively, induces redistribution of H3K27me3 marks centrally. Such alterations in chromatin landscape are consistent with differential gene expression associated with distinctive differentiation patterns. Further, knockdown of the non-enzymatic monomeric actin binding protein, Arp4, leads to extensive chromatin unpacking, but only a modest increase in transcription, indicating an active role for actin-Arp4 in transcription. These data indicate that dynamic actin remodeling can regulate chromatin interactions.

SOX4 induces cytoskeleton remodeling and promotes cell motility via N-wasp/ARP2/3 pathway in colorectal cancer cells.

Filopodia are thin, actin-rich projection from the plasma membrane that promote cancer cell invasion and migration. Sex-determining region Y-related high-mobility group-box 4 (SOX4) is a crucial transcription factor that plays a role in the development and metastasis of colorectal cancer (CRC). However, the involvement of SOX4 in cytoskeleton remodeling in CRC remains unknown. For the first time, we demonstrate that SOX4 is a potent regulator of filopodia formation in CRC cells. Overexpression of SOX4 protein enhances both migration and invasion ability of HCT116, and CACO2 cells, which is relevant to the metastasis. Furthermore, through phalloidin staining, cytoskeleton re-assembly was observed in SOX4-modified cell lines. Enhanced expression of SOX4 increased the number and length of filopodia on cell surface. In contrast, silencing SOX4 in SW620 cells with higher endogenous expression of SOX4, impeded the filopodia formation. Moreover, SOX4 was found to be positively regulating the expression of central regulators of actin cytoskeleton - N-Wiskott-Aldrich syndrome protein (N-WASP); WAVE2; Actin related proteins, ARP2 and ARP3. Inhibiting the N-WASP/ARP2/3 pathway diminishes the filopodia formation and the migration of CRC cells. These results indicate the crucial role of SOX4 in the regulation of filopodia formation mediated by N-WASP/ARP2/3 pathway in CRC cells.

Oleate Promotes Triple-Negative Breast Cancer Cell Migration by Enhancing Filopodia Formation through a PLD/Cdc42-Dependent Pathway.

Breast cancer, particularly triple-negative breast cancer (TNBC), poses a global health challenge. Emerging evidence has established a positive association between elevated levels of stearoyl-CoA desaturase 1 (SCD1) and its product oleate (OA) with cancer development and metastasis. SCD1/OA leads to alterations in migration speed, direction, and cell morphology in TNBC cells, yet the underlying molecular mechanisms remain elusive. To address this gap, we aim to investigate the impact of OA on remodeling the actin structure in TNBC cell lines, and the underlying signaling. Using TNBC cell lines and bioinformatics tools, we show that OA stimulation induces rapid cell membrane ruffling and enhances filopodia formation. OA treatment triggers the subcellular translocation of Arp2/3 complex and Cdc42. Inhibiting Cdc42, not the Arp2/3 complex, effectively abolishes OA-induced filopodia formation and cell migration. Additionally, our findings suggest that phospholipase D is involved in Cdc42-dependent filopodia formation and cell migration. Lastly, the elevated expression of Cdc42 in breast tumor tissues is associated with a lower survival rate in TNBC patients. Our study outlines a new signaling pathway in the OA-induced migration of TNBC cells, via the promotion of Cdc42-dependent filopodia formation, providing a novel insight for therapeutic strategies in TNBC treatment.

The NADPH oxidase 2 subunit p47phox binds to the WAVE regulatory complex and p22phox in a mutually exclusive manner.

The actin cytoskeleton and reactive oxygen species (ROS) both play crucial roles in various cellular processes. Previous research indicated a direct interaction between two key components of these systems: the WAVE1 subunit of the WAVE regulatory complex (WRC), which promotes actin polymerization and the p47phox subunit of the NADPH oxidase 2 complex (NOX2), which produces ROS. Here, using carefully characterized recombinant proteins, we find that activated p47phox uses its dual Src homology 3 domains to bind to multiple regions within the WAVE1 and Abi2 subunits of the WRC, without altering WRC's activity in promoting Arp2/3-mediated actin polymerization. Notably, contrary to previous findings, p47phox uses the same binding pocket to interact with both the WRC and the p22phox subunit of NOX2, albeit in a mutually exclusive manner. This observation suggests that when activated, p47phox may separately participate in two distinct processes: assembling into NOX2 to promote ROS production and engaging with WRC to regulate the actin cytoskeleton.

Liquid-like condensates mediate competition between actin branching and bundling.

Cellular remodeling of actin networks underlies cell motility during key morphological events, from embryogenesis to metastasis. In these transformations, there is an inherent competition between actin branching and bundling, because steric clashes among branches create a mechanical barrier to bundling. Recently, liquid-like condensates consisting purely of proteins involved in either branching or bundling of the cytoskeleton have been found to catalyze their respective functions. Yet in the cell, proteins that drive branching and bundling are present simultaneously. In this complex environment, which factors determine whether a condensate drives filaments to branch or become bundled? To answer this question, we added the branched actin nucleator, Arp2/3, to condensates composed of VASP, an actin bundling protein. At low actin to VASP ratios, branching activity, mediated by Arp2/3, robustly inhibited VASP-mediated bundling of filaments, in agreement with agent-based simulations. In contrast, as the actin to VASP ratio increased, addition of Arp2/3 led to formation of aster-shaped structures, in which bundled filaments emerged from a branched actin core, analogous to filopodia emerging from a branched lamellipodial network. These results demonstrate that multi-component, liquid-like condensates can modulate the inherent competition between bundled and branched actin morphologies, leading to organized, higher-order structures, similar to those found in motile cells.

LINC00869 Promotes Hepatocellular Carcinoma Metastasis via Protrusion Formation.

Coordination of filament assembly and membrane remodeling is required for the directional migration of cancer cells. The Wiskott-Aldrich syndrome protein (WASP) recruits the actin-related protein (ARP) 2/3 complex to assemble branched actin networks. The goal of our study was to assess the potential regulatory role exerted by the novel long noncoding RNA (lncRNA) LINC00869 on hepatocellular carcinoma (HCC) cells. We used HCC cells to overexpress or knockdown LINC00869, analyzed patient data from publicly available databases and Cancer Hospital Affiliated with Zhengzhou University, and used a xenograft mouse model of HCC to study the molecular mechanism associated with LINC00869 expression. We found that high levels of LINC00869 expression were associated with poor prognosis in patients with HCC. Next, we detected an interaction between LINC00869 and both WASP and ARP2 in HCC cells, and observed a modulatory effect of LINC00869 on the phosphorylation of WASP at Y291 and the activity of cell division control protein 42 (CDC42). These modulatory roles were required for WASP/CDC42 activity on F-actin polymerization to enhance membrane protrusion formation and maintain persistent cell polarization. This, in turn, promoted the migration and invasion abilities of HCC cells. Finally, we confirmed the role of LINC00869in vivo, using the tumor xenograft mouse model; and identified a positive correlation between LINC00869 expression levels and the phosphorylation levels of WASP in HCC samples. Overall, our findings suggest a unique mechanism by which LINC00869 orchestrates membrane protrusion during migration and invasion of HCC cells. IMPLICATIONS: LncRNA LINC00869 regulates the activity of CDC42-WASP pathway and positively affects protrusion formation in HCC cells, which expands the current understanding of lncRNA functions as well as gives a better understanding of carcinogenesis.

ARPC5 acts as a potential prognostic biomarker that is associated with cell proliferation, migration and immune infiltrate in gliomas.

BACKGROUND: Gliomas are the most common malignant brain tumors, with powerful invasiveness and an undesirable prognosis. Actin related protein 2/3 complex subunit 5 (ARPC5) encodes a component of the Arp2/3 protein complex, which plays a significant role in regulating the actin cytoskeleton. However, the prognostic values and biological functions of ARPC5 in gliomas remain unclear. METHODS: Based on the TCGA, GEO, HPA, and UALCAN database, we determined the expression of ARPC5 in glioma. The results were verified by immunohistochemistry and Western blot analysis of glioma samples. Moreover, Kaplan-Meier curves, ROC curves, Cox regression analyses, and prognostic nomograms were used to observe the correlation between the ARPC5 expression and the prognosis of glioma patients. GO and KEGG enrichment analyses were conducted to identify immune-related pathways involved with the differential expression of ARPC5. Subsequently, the TCGA database was used to estimate the relationship between ARPC5 expression and immunity-related indexes, such as immune scores, infiltrating immune cells, and TMB. The TCIA database was used to assess the correlation between ARPC5 with immunotherapy. The association between ARPC5 and T cells marker CD3 was also evaluated through immunohistochemistry methods. The correlation between ARPC5 and T cell, as well as the prognosis of patients, was also evaluated using immunological methods. Moreover, the effect of ARPC5 on the biological characteristics of LN229 and U251 cells was determined by MTT, clone formation, and transwell migration assay. RESULTS: The high degree of ARPC5 was correlated with worse prognosis and unfavorable clinical characteristics of glioma patients. In the analysis of GO and KEGG, it is shown that ARPC5 was strongly correlated with multiple immune-related signaling pathways. The single-cell analysis revealed that ARPC5 expression was increased in astrocytes, monocytes and T cells. In addition, ARPC5 expression was strongly associated with immune scores, infiltrating immune cells, TMB, MSI, immune biomarkers, and immunotherapy. In experimental analysis, we found that ARPC5 was significantly overexpressed in gliomas and closely correlated with patient prognosis and CD3 expression. Functionally, the knockout of ARPC5 significantly reduced the proliferation and invasion of LN229 and U251 cells. CONCLUSIONS: Our study revealed that the high expression level of ARPC5 may serve as a promising prognostic biomarker and be associated with tumor immunity in glioma.

ARP2/3 complex associates with peroxisomes to participate in pexophagy in plants.

Actin-related protein (ARP2/3) complex is a heteroheptameric protein complex, evolutionary conserved in all eukaryotic organisms. Its conserved role is based on the induction of actin polymerization at the interface between membranes and the cytoplasm. Plant ARP2/3 has been reported to participate in actin reorganization at the plasma membrane during polarized growth of trichomes and at the plasma membrane-endoplasmic reticulum contact sites. Here we demonstrate that individual plant subunits of ARP2/3 fused to fluorescent proteins form motile spot-like structures in the cytoplasm that are associated with peroxisomes in Arabidopsis and tobacco. ARP2/3 is found at the peroxisome periphery and contains the assembled ARP2/3 complex and the WAVE/SCAR complex subunit NAP1. This ARP2/3-positive peroxisomal domain colocalizes with the autophagosome and, under conditions that affect the autophagy, colocalization between ARP2/3 and the autophagosome increases. ARP2/3 subunits co-immunoprecipitate with ATG8f and peroxisome-associated ARP2/3 interact in vivo with the ATG8f marker. Since mutants lacking functional ARP2/3 complex have more peroxisomes than wild type, we suggest that ARP2/3 has a novel role in the process of peroxisome degradation by autophagy, called pexophagy.

Polymerization force-regulated actin filament-Arp2/3 complex interaction dominates self-adaptive cell migrations.

Cells migrate by adapting their leading-edge behaviors to heterogeneous extracellular microenvironments (ECMs) during cancer invasions and immune responses. Yet it remains poorly understood how such complicated dynamic behaviors emerge from millisecond-scale assembling activities of protein molecules, which are hard to probe experimentally. To address this gap, we establish a spatiotemporal "resistance-adaptive propulsion" theory based on the interactions between Arp2/3 complexes and polymerizing actin filaments and a multiscale dynamic modeling system spanning from molecular proteins to the cell. We quantitatively find that cells can accurately self-adapt propulsive forces to overcome heterogeneous ECMs via a resistance-triggered positive feedback mechanism, dominated by polymerization-induced actin filament bending and the bending-regulated actin-Arp2/3 binding. However, for high resistance regions, resistance triggers a negative feedback, hindering branched filament assembly, which adapts cellular morphologies to circumnavigate the obstacles. Strikingly, the synergy of the two opposite feedbacks not only empowers the cell with both powerful and flexible migratory capabilities to deal with complex ECMs but also enables efficient utilization of intracellular proteins by the cell. In addition, we identify that the nature of cell migration velocity depending on ECM history stems from the inherent temporal hysteresis of cytoskeleton remodeling. We also show that directional cell migration is dictated by the competition between the local stiffness of ECMs and the local polymerizing rate of actin network caused by chemotactic cues. Our results reveal that it is the polymerization force-regulated actin filament-Arp2/3 complex binding interaction that dominates self-adaptive cell migrations in complex ECMs, and we provide a predictive theory and a spatiotemporal multiscale modeling system at the protein level.

PPP2R1A regulates migration persistence through the NHSL1-containing WAVE Shell Complex.

The RAC1-WAVE-Arp2/3 signaling pathway generates branched actin networks that power lamellipodium protrusion of migrating cells. Feedback is thought to control protrusion lifetime and migration persistence, but its molecular circuitry remains elusive. Here, we identify PPP2R1A by proteomics as a protein differentially associated with the WAVE complex subunit ABI1 when RAC1 is activated and downstream generation of branched actin is blocked. PPP2R1A is found to associate at the lamellipodial edge with an alternative form of WAVE complex, the WAVE Shell Complex, that contains NHSL1 instead of the Arp2/3 activating subunit WAVE, as in the canonical WAVE Regulatory Complex. PPP2R1A is required for persistence in random and directed migration assays and for RAC1-dependent actin polymerization in cell extracts. PPP2R1A requirement is abolished by NHSL1 depletion. PPP2R1A mutations found in tumors impair WAVE Shell Complex binding and migration regulation, suggesting that the coupling of PPP2R1A to the WAVE Shell Complex is essential to its function.

The overexpression of actin related protein 2/3 complex subunit 1B(ARPC1B) promotes the ovarian cancer progression via activation of the Wnt/ß-catenin signaling pathway.

Introduction: Ovarian cancer is one of the most fatal malignancies of the female reproductive system. The purpose of this study is to explore the mechanism of Actin Related Protein 2/3 Complex Subunit 1B(ARPC1B) in the progression of ovarian cancer. Methods: The expressions and prognostic value of ARPC1B in ovarian cancer were identified using the GEPIA database and the Kaplan-Meier Plotter database. The expression of ARPC1B was manipulated to evaluate its impact on the malignant phenotypes of ovarian cancer. The cell proliferation ability was analyzed through CCK-8 assay and clone formation assay. The cell migration and invasion capacity was evaluated through wound healing assay and trans well assay. Mice xenografts were conducted to measure the effects of ARPC1B on tumor development in vivo. Results: Our data suggested that ARPC1B was overexpressed in ovarian cancer, which was correlated with a poorer survival compared to low mRNA expression of ARPC1B in ovarian cancer patients. The overexpression of ARPC1B promoted cell proliferation, migration, and invasion of ovarian cancer cells. Conversely, the knockdown of ARPC1B resulted in the opposite effect. Additionally, ARPC1B expression could activate Wnt/ß-catenin signaling pathway. The administration of the ß-catenin inhibitor XAV-939 abolished the promotion of cell proliferation, migration, and invasion activities induced by ARPC1B overexpression in vitro. Conclusions: ARPC1B was overexpressed in ovarian cancer and was correlated with poor prognosis. ARPC1B promoted ovarian cancer progression through activation of Wnt/ß-catenin Signaling Pathway.

CPEB2 enhances cell growth and angiogenesis by upregulating ARPC5 mRNA stability in multiple myeloma.

BACKGROUND: The process of multiple myeloma (MM) is the result of the combined action of multiple genes. This study aims to explore the role and mechanism of cytoplasmic polyadenylation element binding protein2 (CPEB2) in MM progression. METHODS: The mRNA and protein expression levels of CPEB2 and actin-related protein 2/3 complex subunit 5 (ARPC5) were assessed by quantitative real-time PCR and western blot analysis. Cell function was determined by cell counting kit 8 assay, soft-agar colony formation assay, flow cytometry and tube formation assay. Fluorescent in situ hybridization assay was used to analyze the co-localization of CPEB2 and ARPC5 in MM cells. Actinomycin D treatment and cycloheximide chase assay were performed to assess the stability of ARPC5. The interaction between CPEB2 and ARPC5 was confirmed by RNA immunoprecipitation assay. RESULTS: CPEB2 and ARPC5 mRNA and protein expression levels were upregulated in CD138+ plasma cells from MM patients and cells. CPEB2 downregulation reduced MM cell proliferation, angiogenesis, and increased apoptosis, while its overexpression had an opposite effect. CPEB2 and ARPC5 were co-localized at cell cytoplasm and could positively regulate ARPC5 expression by mediating its mRNA stability. ARPC5 overexpression reversed the suppressive effect of CPEB2 knockdown on MM progression, and it knockdown also abolished CPEB2-promoted MM progression. Besides, CPEB2 silencing also reduced MM tumor growth by decreasing ARPC5 expression. CONCLUSION: Our results indicated that CPEB2 increased ARPC5 expression through promoting its mRNA stability, thereby accelerating MM malignant process.

Role and mechanism of actin-related protein 2/3 complex signaling in cancer invasion and metastasis: A review.

The actin 2/3 complex (Arp2/3) regulates actin polymerization and nucleation of actin filaments, is associated with cell motility, and has been shown to play a key role in the invasion and migration of cancer cells. nucleation-promoting factor (NPF) such as N-WASP (neural-WASP famly verprolin-homologous protein family), WAVE (WASP famly verprolin-homologous protein family), and WASH (WASP and Scar homologue) undergo conformational changes upon receipt of multiple upstream signals including Rho family GTPases, cdc42 (Cell division control protein 42 homolog), and phosphatidylinositol 4,5-bisphosphate (PtdIns 4,5 P2) to bind and activate the Arp2/3 complex. Once activated, the Arp2/3 complex forms actin-based membrane protrusions necessary for cancer cells to acquire an invasive phenotype. Therefore, how to influence the invasion and migration of cancer cells by regulating the activity of the Arp2/3 complex has attracted great research interest in recent years. Several studies have explored the effects of phosphorylation modifications of cortactin and several NPFs (Nucleation Promoting Factor) including N-WASP and WAVE on the activity of the Arp2/3 complex and ultimately on cancer cell invasiveness, and have attempted to suggest new strategies for antiinvasive therapy as a result. Other studies have highlighted the potential of targeting genes encoding partial or complete proteins of the Arp2/3 complex as a therapeutic strategy to prevent cancer cell invasion and metastasis. This article reviews the role of the Arp2/3 complex in the development, invasion, and metastasis of different types of cancer and the mechanisms regulating the activity of the Arp2/3 complex.

ERK3/MAPK6 dictates CDC42/RAC1 activity and ARP2/3-dependent actin polymerization.

The actin cytoskeleton is tightly controlled by RhoGTPases, actin binding-proteins and nucleation-promoting factors to perform fundamental cellular functions. We have previously shown that ERK3, an atypical MAPK, controls IL-8 production and chemotaxis (Bogueka et al., 2020). Here, we show in human cells that ERK3 directly acts as a guanine nucleotide exchange factor for CDC42 and phosphorylates the ARP3 subunit of the ARP2/3 complex at S418 to promote filopodia formation and actin polymerization, respectively. Consistently, depletion of ERK3 prevented both basal and EGF-dependent RAC1 and CDC42 activation, maintenance of F-actin content, filopodia formation, and epithelial cell migration. Further, ERK3 protein bound directly to the purified ARP2/3 complex and augmented polymerization of actin in vitro. ERK3 kinase activity was required for the formation of actin-rich protrusions in mammalian cells. These findings unveil a fundamentally unique pathway employed by cells to control actin-dependent cellular functions.

Actin-rich lamellipodia-like protrusions contribute to the integrity of epithelial cell-cell junctions.

Metastasis-suppressor 1 (MTSS1) is a membrane-interacting scaffolding protein that regulates the integrity of epithelial cell-cell junctions and functions as a tumor suppressor in a wide range of carcinomas. MTSS1 binds phosphoinositide-rich membranes through its I-BAR domain and is capable of sensing and generating negative membrane curvature in vitro. However, the mechanisms by which MTSS1 localizes to intercellular junctions in epithelial cells and contributes to their integrity and maintenance have remained elusive. By carrying out EM and live-cell imaging on cultured Madin-Darby canine kidney cell monolayers, we provide evidence that adherens junctions of epithelial cells harbor lamellipodia-like, dynamic actin-driven membrane folds, which exhibit high negative membrane curvature at their distal edges. BioID proteomics and imaging experiments demonstrated that MTSS1 associates with an Arp2/3 complex activator, the WAVE-2 complex, in dynamic actin-rich protrusions at cell-cell junctions. Inhibition of Arp2/3 or WAVE-2 suppressed actin filament assembly at adherens junctions, decreased the dynamics of junctional membrane protrusions, and led to defects in epithelial integrity. Together, these results support a model in which membrane-associated MTSS1, together with the WAVE-2 and Arp2/3 complexes, promotes the formation of dynamic lamellipodia-like actin protrusions that contribute to the integrity of cell-cell junctions in epithelial monolayers.

ARPC5 is transcriptionally activated by KLF4, and promotes cell migration and invasion in prostate cancer via up-regulating ADAM17 : ARPC5 serves as an oncogene in prostate cancer.

BACKGROUND: Prostate cancer (PCa) is one of the most common cancers in men worldwide. Actin-related protein 2/3 complex subunit 5 (ARPC5) has been validated as a critical regulator in several kinds of human tumors. However, whether ARPC5 is implicated in PCa progression remains largely unknown. METHODS: PCa specimens and PCa cell lines were obtained for detecting gene expressions using western blot and quantitative reverse transcriptase PCR (qRT-PCR). PCa cells transfected with ARPC5 shRNA or a disintegrin and metalloprotease 17 (ADAM17) overexpressed plasmids were harvested for assessing cell proliferation, migration and invasion by using cell counting kit-8 (CCK-8), colony formation and transwell assays, respectively. The interaction relationship between molecules was testified with chromatin immunoprecipitation and luciferase reporter assay. Xenograft mice model was conducted for confirming the role of ARPC5/ADAM17 axis in vivo. RESULTS: Upregulated ARPC5 was observed in PCa tissues and cells, as well as forecasted poor prognosis of PCa patients. Depletion of ARPC5 inhibited PCa cell proliferation, migration and invasion. Krüppel-like factor 4 (KLF4) was identified to be a transcriptional activator of ARPC5 via binding with its promoter region. Furthermore, ADAM17 served as a downstream effector of ARPC5. ADAM17 overexpression overturned ARPC5 knockdown-induced repressive impacts on PCa progression in vitro and in vivo. CONCLUSION: Collectively, ARPC5 was activated by KLF4 and upregulated ADAM17 to promote PCa progression, which might act as a promising therapeutic target and prognostic biomarker for PCa.

The Arp2/3 complex enhances cell migration on elastic substrates.

Cell migration on soft surfaces occurs in both physiological and pathological processes such as corticogenesis during embryonic development and cancer invasion and metastasis. The Arp2/3 complex in neural progenitor cells was previously demonstrated to be necessary for cell migration on soft elastic substrate but not on stiff surfaces, but the underlying mechanism was unclear. Here, we integrate computational and experimental approaches to elucidate how the Arp2/3 complex enables cell migration on soft surfaces. We found that lamellipodia comprised of a branched actin network nucleated by the Arp2/3 complex distribute forces over a wider area, thus decreasing stress in the substrate. Additionally, we found that interactions between parallel focal adhesions within lamellipodia prolong cell-substrate interactions by compensating for the failure of neighboring adhesions. Together with decreased substrate stress, this leads to the observed improvements in migratory ability on soft substrates in cells utilizing lamellipodia-dependent mesenchymal migration when compared with filopodia-based migration. These results show that the Arp2/3 complex-dependent lamellipodia provide multiple distinct mechanical advantages to gliomas migrating on soft 2D substrates, which can contribute to their invasive potential.

An actin filament branching surveillance system regulates cell cycle progression, cytokinesis and primary ciliogenesis.

Dysfunction of cell cycle control and defects of primary ciliogenesis are two features of many cancers. Whether these events are interconnected and the driving mechanism coordinating them remains elusive. Here, we identify an actin filament branching surveillance system that alerts cells of actin branching insufficiency and regulates cell cycle progression, cytokinesis and primary ciliogenesis. We find that Oral-Facial-Digital syndrome 1 functions as a class II Nucleation promoting factor to promote Arp2/3 complex-mediated actin branching. Perturbation of actin branching promotes OFD1 degradation and inactivation via liquid-to-gel transition. Elimination of OFD1 or disruption of OFD1-Arp2/3 interaction drives proliferating, non-transformed cells into quiescence with ciliogenesis by an RB-dependent mechanism, while it leads oncogene-transformed/cancer cells to incomplete cytokinesis and irreversible mitotic catastrophe via actomyosin ring malformation. Inhibition of OFD1 leads to suppression of multiple cancer cell growth in mouse xenograft models. Thus, targeting OFD1-mediated actin filament branching surveillance system provides a direction for cancer therapy.