Relative actin nucleation promotion efficiency by WASP and WAVE proteins in endothelial cells

The conserved Pelado/ZSWIM8 protein regulates actin dynamics by promoting linear actin filament polymerization

Actin filament polymerization can be branched or linear, which depends on the associated regulatory proteins. Competition for actin monomers occurs between proteins that induce branched or linear actin polymerization. Cell specialization requires the regulation of actin filaments to allow the formation of cell type-specific structures, like cuticular hairs in <i>Drosophila</i>, formed by linear actin filaments. Here, we report the functional analysis of CG34401/<i>pelado</i>, a gene encoding a SWIM domain-containing protein, conserved throughout the animal kingdom, called ZSWIM8 in mammals. Mutant <i>pelado</i> epithelial cells display actin hair elongation defects. This phenotype is reversed by increasing actin monomer levels or by either pushing linear actin polymerization or reducing branched actin polymerization. Similarly, in hemocytes, Pelado is essential to induce filopodia, a linear actin-based structure. We further show that this function of Pelado/ZSWIM8 is conserved in human cells, where Pelado inhibits branched actin polymerization in a cell migration context. In summary, our data indicate that the function of Pelado/ZSWIM8 in regulating actin cytoskeletal dynamics is conserved, favoring linear actin polymerization at the expense of branched filaments.

Elucidating the molecular signaling pathways of WAVE3

Cancer metastasis is a complex, multistep process that requires tumor cells to evade from the original site and form new tumors at a distant site or a different organ, often via bloodstream or the lymphatic system. Metastasis is responsible for more than 90% of cancer-related deaths. WAVE3 belongs to the Wiskott-Aldrich syndrome protein (WASP) family, which regulate actin cytoskeleton remodeling as well as several aspects of cell migration, invasion, and metastasis. In fact, WAVE3 has been established as a driver of tumor progression and metastasis in cancers from several origins, including triple negative breast cancers (TNBCs), which are classified as the most lethal subtype of breast cancer, due to their resistance to standard of care therapy and highly metastatic behavior. In this review, we will attempt to summarize the recent advances that have been made to understand how WAVE3 contributes to the molecular mechanisms that control cancer progression and metastasis. We will also review the signaling pathways that are involved in the regulation of WAVE3 expression and function to identify potential therapeutic options targeted against WAVE3 for the treatment of patients with metastatic tumors.

MicroRNA-1253 Regulation of WASF2 (WAVE2) and its Relevance to Racial Health Disparities

The prevalence of hypertension among African Americans (AAs) in the US is among the highest of any demographic and affects over two-thirds of AA women. Previous data from our laboratory suggest substantial differential gene expression (DGE) of mRNAs and microRNAs (miRNAs) exists within peripheral blood mononuclear cells (PBMCs) isolated from AA and white women with or without hypertension. We hypothesized that DGE by race may contribute to racial differences in hypertension. In a reanalysis of our previous dataset, we found that the Wiskott-Aldrich syndrome protein Verprolin-homologous protein 2 (WASF2 (also known as WAVE2)) is differentially expressed in AA women with hypertension, along with several other members of the actin cytoskeleton signaling pathway that plays a role in cell shape and branching of actin filaments. We performed an in silico miRNA target prediction analysis that suggested miRNA miR-1253 regulates WASF2. Transfection of miR-1253 mimics into human umbilical vein endothelial cells (HUVECs) and human aortic endothelial cells (HAECs) significantly repressed WASF2 mRNA and protein levels (p < 0.05), and a luciferase reporter assay confirmed that miR-1253 regulates the WASF2 3' UTR (p < 0.01). miR-1253 overexpression in HUVECs significantly increased HUVEC lamellipodia formation (p < 0.01), suggesting the miR-1253-WASF2 interaction may play a role in cell shape and actin cytoskeleton function. Together, we have identified novel roles for miR-1253 and WASF2 in a hypertension-related disparities context. This may ultimately lead to the discovery of additional actin-related genes which are important in the vascular-related complications of hypertension and influence the disproportionate susceptibility to hypertension among AAs in general and AA women in particular.

Comparative transcriptional analysis and RNA interference reveal immunoregulatory pathways involved in growth of the oriental river prawn Macrobrachium nipponense

A source of premium animal protein, crustaceans are widely distributed and cultivated around the world. Short-term or long-term starvation events occur frequently owing to natural environment changes or manual management strategies in the life cycle of crustaceans. The result induced by starvation is that somatic growth of crustaceans will be retarded, while the immune mechanism is activated in this process. The aim of this study was to investigate whether the immune regulatory pathways are involved in the growth of crustaceans. Twelve muscle tissue transcriptomes of the oriental river prawn Macrobrachium nipponense were sequenced across four fasting stages lasting 0, 7, 14 and 21 d. The results showed that three immune-related pathways were involved in the growth of M. nipponense by regulating actin expression inducing the chemokine signaling pathway, the leukocyte transendothelial migration pathway and the FcR-mediated phagocytosis pathway. Furthermore, we employed RNA interference (RNAi) to further verify the effects that genes involved in the pathways had on regulating growth of M. nipponense. Comparative transcriptional analysis and RNA interference reveal that VASP and WAVE positively regulated the expression of actin; however, WASP negatively regulated the expression of actin. This is the first report that the immune regulatory pathways play key roles in the growth of crustaceans. Our results will not only provide an entirely new understanding of the immune mechanism of crustaceans from a unique angle but also further enrich and develop the theory of growth and developmental biology in crustaceans.

Drosophila comes of age as a model system for understanding the function of cytoskeletal proteins in cells, tissues, and organisms

For the last 100 years, Drosophila melanogaster has been a powerhouse genetic system for understanding mechanisms of inheritance, development, and behavior in animals. In recent years, advances in imaging and genetic tools have led to Drosophila becoming one of the most effective systems for unlocking the subcellular functions of proteins (and particularly cytoskeletal proteins) in complex developmental settings. In this review, written for non-Drosophila experts, we will discuss critical technical advances that have enabled these cell biological insights, highlighting three examples of cytoskeletal discoveries that have arisen as a result: (1) regulation of Arp2/3 complex in myoblast fusion, (2) cooperation of the actin filament nucleators Spire and Cappuccino in establishment of oocyte polarity, and (3) coordination of supracellular myosin cables. These specific examples illustrate the unique power of Drosophila both to uncover new cytoskeletal structures and functions, and to place these discoveries in a broader in vivo context, providing insights that would have been impossible in a cell culture model or in vitro. Many of the cellular structures identified in Drosophila have clear counterparts in mammalian cells and tissues, and therefore elucidating cytoskeletal functions in Drosophila will be broadly applicable to other organisms.

Knockdown of WAVE3 impairs HGF induced migration and invasion of prostate cancer cells

Background

The WASP (Wiskott-Aldrich syndrome protein) and WAVE (WASP Verpolin homologous) family of proteins are structurally related and responsible for regulation of actin polymerization through their interaction with actin related proteins 2&3 (ARP 2/3). WAVE-3 has exhibited an association with disease progression and poorer prognosis of certain malignancies. In the current study, we determined the role of WAVE-3 in hepatocyte growth factor induced cellular changes including cell matrix interaction, invasion and cellular motility, and pathways that may be responsible for the changes in prostate cancer cells.

Methods

We used hammer head ribozymes to knock down the expression of WAVE-3 in PC-3 prostate cancer cell line. In vitro cellular functional assays including growth, invasion, adhesion, motility and invasion, were performed to assess the effects of WAVE-3 knock down. Further experimentation was performed to investigate the role of different pathway through expression and phosphorylation status of various intermediate proteins.

Results

WAVE-3 knockdown reduced invasive potential and motility of prostate cancer cells. Following addition of HGF, control cells showed significantly increased invasion and motility (p value <0.5) and marked increase in cellular growth. However, WAVE-3 knockdown cell line failed to show any increase in these trends (p value <0.5) except increased growth compared with control cells. Further experiments revealed that HGF-induced activation of Paxillin was weakened by the knockdown of WAVE-3. Our study also indicated that reduced invasiveness following WAVE-3 knockdown, may be related to reduce activity of MMP-2.

Conclusions

Our studies suggest a vital role of WAVE-3 in HGF induced invasion and migration in which Paxillin and MMP-2 are involved. Further study will shed light on its potential as therapeutic target to suppress local invasion and metastasis of prostate cancer cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12935-015-0203-3) contains supplementary material, which is available to authorized users.

A novel role for WAVE1 in controlling actin network growth rate and architecture

A novel functional role for WAVE1 is found that is lacking in N-WASP and WAVE2. Through its unique WH2 domain, WAVE1 dramatically reduces the rate of actin filament elongation independently of its interactions with the Arp2/3 complex. These findings help explain how cells build actin networks with distinct geometries and growth rates.

Branched actin filament networks in cells are assembled through the combined activities of Arp2/3 complex and different WASP/WAVE proteins. Here we used TIRF and electron microscopy to directly compare for the first time the assembly kinetics and architectures of actin filament networks produced by Arp2/3 complex and dimerized VCA regions of WAVE1, WAVE2, or N-WASP. WAVE1 produced strikingly different networks from WAVE2 or N-WASP, which comprised unexpectedly short filaments. Further analysis showed that the WAVE1-specific activity stemmed from an inhibitory effect on filament elongation both in the presence and absence of Arp2/3 complex, which was observed even at low stoichiometries of WAVE1 to actin monomers, precluding an effect from monomer sequestration. Using a series of VCA chimeras, we mapped the elongation inhibitory effects of WAVE1 to its WH2 (“V”) domain. Further, mutating a single conserved lysine residue potently disrupted WAVE1's inhibitory effects. Taken together, our results show that WAVE1 has unique activities independent of Arp2/3 complex that can govern both the growth rates and architectures of actin filament networks. Such activities may underlie previously observed differences between the cellular functions of WAVE1 and WAVE2.

WAVE1 gene silencing via RNA interference reduces ovarian cancer cell invasion, migration and proliferation

OBJECTIVE

Wiskott-Aldrich syndrome protein family verprolin-homologous protein 1 (WAVE1) has been implicated in cancer cell migration and invasion. We have previously shown that the overexpression of WAVE1 in epithelial ovarian cancer (EOC) tissues is associated with a poor prognosis. However, the mechanism of WAVE1 regulating the malignant behaviors in EOC remains unclear.

METHODS

In the present study, we knocked down WAVE1 expression in SKOV3 and OVCAR-3 cells through RNA interference to detect the cell biology and molecular biology changes. Moreover, western-blot was used to investigate the underlying mechanism of WAVE1 regulating the proliferative and invasive malignant behaviors in ovarian cancer cells.

RESULTS

The down-regulation of WAVE1 had a significant effect on cell morphological changes. WAVE1 silencing decreased cell migration, cell invasion, cell adhesion, colony formation and cell proliferation in vitro. In addition, we found that down-regulation of WAVE1 inhibited malignant behaviors in vivo. Furthermore, our study also indicated that the PI3K/AKT and p38MAPK signaling pathways might contribute to WAVE1 promotion of ovarian cancer cell proliferation, migration, and invasion.

CONCLUSIONS

WAVE1 might promote the proliferative and invasive malignant behaviors through the activation of the PI3K/AKT and p38MAPK signaling pathways in EOC.

The Src substrate SKAP2 regulates actin assembly by interacting with WAVE2 and cortactin proteins

In our attempt to screen for substrates of Src family kinases in glioblastoma, Src kinase-associated phosphoprotein 2 (SKAP2) was identified. Although SKAP2 has been suggested to be associated with integrin-mediated adhesion of hematopoietic cells, little is known about its molecular function and the effects in other types of cells and tumors. Here, we demonstrate that SKAP2 physically associates with actin assembly factors WAVE2 and cortactin and inhibits their interaction. Cortactin is required for the membrane localization of WAVE2, and SKAP2 suppresses actin polymerization mediated by WAVE2 and cortactin in vitro. Knockdown of SKAP2 in NIH3T3 accelerated cell migration and enhanced translocation of WAVE2 to the cell membrane, and those effects of SKAP2 depend on the binding activity of SKAP2 to WAVE2. Furthermore, reduction of SKAP2 in the glioblastoma promoted tumor invasion both in ex vivo organotypic rat brain slices and immune-deficient mouse brains. These results suggest that SKAP2 negatively regulates cell migration and tumor invasion in fibroblasts and glioblastoma cells by suppressing actin assembly induced by the WAVE2-cortactin complex, indicating that SKAP2 may be a novel candidate for the suppressor of tumor progression.

The ability of LCRMP-1 to promote cancer invasion by enhancing filopodia formation is antagonized by CRMP-1

Metastasis is a predominant cause of death in patients with cancer. It is a complex multistep process that needs to be better understood if we are to develop new approaches to managing tumor metastasis. Tumor cell invasion of the local stroma is suppressed by collapsin response mediator protein-1 (CRMP-1). Recently, we identified a long isoform of CRMP-1 (LCRMP-1), expression of which correlates with cancer cell invasiveness and poor clinical outcome in patients with non-small-cell lung cancer (NSCLC). Here, we report that LCRMP-1 overexpression in noninvasive human cell lines enhanced filopodia formation, cancer cell migration, and invasion via stabilization of actin. This effect required a highly conserved N-terminal region of LCRMP-1 as well as the WASP family verprolin-homologous protein-1/actin nucleation pathway (WAVE-1/actin nucleation pathway). Furthermore, LCRMP-1 appeared to act downstream of Cdc42, a Rho family protein known to be involved in actin rearrangement. In addition, LCRMP-1 associated with CRMP-1, which downregulated cancer cell metastasis by interrupting the association of LCRMP-1 and WAVE-1. Finally, we found that high-level expression of LCRMP-1 and low-level expression of CRMP-1 were associated with lymph node metastasis and poor survival in patients with NSCLC. In sum, we show that LCRMP-1 and CRMP-1 have opposing functions in regulating cancer cell invasion and metastasis and propose that this pathway may serve as a potential anticancer target.

WAVE3, an actin remodeling protein, is regulated by the metastasis suppressor microRNA, miR-31, during the invasion-metastasis cascade

WAVE3, an actin cytoskeleton remodeling protein, is highly expressed in advanced stages of breast cancer and influences tumor cell invasion. Loss of miR-31 has been associated with cancer progression and metastasis. Here, we show that the activity of WAVE3 to promote cancer cell invasion is regulated by miR-31. An inverse correlation was demonstrated between expression levels of WAVE3 and miR-31 in invasive versus noninvasive breast cancer cell lines. miR-31 directly targeted the 3'-UTR of the WAVE3 mRNA and inhibited its expression in the invasive cancer cells, i.e., miR-31-mediated down-regulation of WAVE3 resulted in a significant reduction in the invasive phenotype of cancer cells. This relationship was specific to the loss of WAVE3 expression because re-expression of a miR-31-resistant form of WAVE3 reversed miR-31-mediated inhibition of cancer cell invasion. Furthermore, expression of miR-31 correlates inversely with breast cancer progression in humans, where an increase in expression of miR-31 target genes was observed as the tumors progressed to more aggressive forms. In conclusion, a novel mechanism for the regulation of WAVE3 expression in cancer cells has been identified, which controls the invasive properties of cancer cells. The study also identifies a critical role for WAVE3, downstream of miR-31, in the invasion-metastasis cascade.