Rac1-dependent lamellipodial motility in prostate cancer PC-3 cells revealed by optogenetic control of Rac1 activity

Optogenetic modulation of guanine nucleotide exchange factors of Ras superfamily proteins directly controls cell shape and movement

In this article, we provide detailed protocols on using optogenetic dimerizers to acutely perturb activities of guanine nucleotide exchange factors (GEFs) specific to Ras, Rac or Rho small GTPases of the migratory networks in various mammalian and amoeba cell lines. These GEFs are crucial components of signal transduction networks which link upstream G-protein coupled receptors to downstream cytoskeletal components and help cells migrate through their dynamic microenvironment. Conventional approaches to perturb and examine these signaling and cytoskeletal networks, such as gene knockout or overexpression, are protracted which allows networks to readjust through gene expression changes. Moreover, these tools lack spatial resolution to probe the effects of local network activations. To overcome these challenges, blue light-inducible cryptochrome- and LOV domain-based dimerization systems have been recently developed to control signaling or cytoskeletal events in a spatiotemporally precise manner. We illustrate that, within minutes of global membrane recruitment of full-length GEFs or their catalytic domains only, widespread increases or decreases in F-actin rich protrusions and cell size occur, depending on the particular node in the networks targeted. Additionally, we demonstrate localized GEF recruitment as a robust assay system to study local network activation-driven changes in polarity and directed migration. Altogether, these optical tools confirmed GEFs of Ras superfamily GTPases as regulators of cell shape, actin dynamics, and polarity. Furthermore, this optogenetic toolbox may be exploited in perturbing complex signaling interactions in varied physiological contexts including mammalian embryogenesis.

SH3BP1 Regulates Melanoma Progression Through Race1/Wace2 Signaling Pathway

Background

SH3-domain binding protein-1 (SH3BP1), which specifically inactivates Rac1 and its target protein Wave2, has been shown to be an important regulator of cancer metastasis. However, the effects of SH3BP1 in melanoma progression remain unclear. The current study aimed to explore the function of SH3BP1 in melanoma and its possible molecular mechanism.

Methods

TCGA database was used to analyze the expression of SH3BP1 in melanoma. Then, reverse transcription-quantitative polymerase chain reaction was performed to detect the expression of SH3BP1 in melanoma tissues and cells. Next, genes related to SH3BP1 were analyzed by LinkedOmics database, and protein interactions were analyzed by STRING database. These genes were further subjected to Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis. In addition, the signaling pathway of SH3BP1 action was screened by bioinformatics analysis. Finally, the function of SH3BP1 and its mediated signaling pathway in melanoma progression were investigated in vitro and in vivo.

Results

SH3BP1 was significantly upregulated in melanoma tissues and cells. The pathways regulated by SH3BP1 are closely related to the occurrence and development of tumors. And we found that overexpression of SH3BP1 promoted the proliferation, migration, and invasion of melanoma cells by increasing Rac1 activity and Wave2 protein levels in vitro. Similarly, overexpression of SH3BP1 facilitated melanoma progression by upregulating Wave2 protein expression in vivo.

Conclusion

In summary, this study revealed for the first time that SH3BP1 promoted melanoma progression through Rac1/Wave2 signaling pathway, providing a new therapeutic target for melanoma.

A‑kinase interacting protein 1 regulates the cell proliferation, invasion, migration and angiogenesis of clear cell renal cell carcinoma cells and affects the ERK/c‑Myc signaling pathway by binding to Rac1

A-kinase interacting protein 1 (AKIP1) has previously been demonstrated to be overexpressed in clear cell renal cell carcinoma (ccRCC) tissues and is associated with patient prognosis. The aim of the present study was to explore whether AKIP1 can affect the proliferation, invasion, migration and angiogenesis of ccRCC cells via its interaction with Rac1. Furthermore, the influence of AKIP1 and therefore Rac1 on the expression of the downstream ERK/cellular (c)-Myc signaling pathway was explored. The interaction between AKIP1 and Rac1 was determined using co-immunoprecipitation. The mRNA and protein expression levels of AKIP1 and Rac1 in normal renal epithelial cell lines and ccRCC cell lines were detected using reverse transcription-quantitative PCR (RT-qPCR) and western blotting, respectively. The transfection efficiency of small interfering RNA-AKIP1 and the Rac1 overexpression vector were also confirmed using RT-qPCR and western blotting. The viability, proliferation, invasion and migration of ccRCC cells following transfection were analyzed using the Cell Counting Kit-8, 5-ethynyl-2'-deoxyuridine staining, Transwell and wound healing assays, respectively. The tube formation ability of HUVECs was assessed using the tube formation assay. The protein expression levels of proliferation, invasion, migration and tube-formation-associated proteins as well as proteins associated with the ERK/c-Myc signaling pathway, were detected via western blotting. The results demonstrated that AKIP1 expression levels were increased in ccRCC cell lines. AKIP1 knockdown inhibited the proliferation, invasion and migration of ccRCC cells and HUVEC tube-formation. In addition, AKIP1 was demonstrated to bind to Rac1 in ccRCC cells and AKIP1 downregulation inhibited Rac1 expression. Furthermore, Rac1 overexpression reversed the effects of AKIP1 knockdown on ccRCC cells. AKIP1 knockdown also suppressed the ERK/c-Myc signaling pathway, which was reversed by Rac1 overexpression. In conclusion, AKIP1 knockdown potentially suppressed the proliferation, invasion, migration and angiogenesis of ccRCC cells and inhibited the ERK/c-Myc signaling pathway by binding to Rac1.

Optogenetic control of intracellular flows and cell migration: A comprehensive mathematical analysis with a minimal active gel model

The actin cytoskeleton of cells is in continuous motion due to both polymerization of new filaments and their contraction by myosin II molecular motors. Through adhesion to the substrate, such intracellular flow can be converted into cell migration. Recently, optogenetics has emerged as a new powerful experimental method to control both actin polymerization and myosin II contraction. While optogenetic control of polymerization can initiate cell migration by generating protrusion, it is less clear if and how optogenetic control of contraction can also affect cell migration. Here we analyze the latter situation using a minimal variant of active gel theory into which we include optogenetic activation as a spatiotemporally constrained perturbation. The model can describe the symmetrical flow of the actomyosin system observed in optogenetic experiments, but not the long-lasting polarization required for cell migration. Motile solutions become possible if cytoskeletal polymerization is included through the boundary conditions. Optogenetic activation of contraction can then initiate locomotion in a symmetrically spreading cell and strengthen motility in an asymmetrically polymerizing one. If designed appropriately, it can also arrest motility even for protrusive boundaries.

The Role of WAVE2 Signaling in Cancer

The Wiskott–Aldrich syndrome protein (WASP) and WASP family verprolin-homologous protein (WAVE)—WAVE1, WAVE2 and WAVE3 regulate rapid reorganization of cortical actin filaments and have been shown to form a key link between small GTPases and the actin cytoskeleton. Upon receiving upstream signals from Rho-family GTPases, the WASP and WAVE family proteins play a significant role in polymerization of actin cytoskeleton through activation of actin-related protein 2/3 complex (Arp2/3). The Arp2/3 complex, once activated, forms actin-based membrane protrusions essential for cell migration and cancer cell invasion. Thus, by activation of Arp2/3 complex, the WAVE and WASP family proteins, as part of the WAVE regulatory complex (WRC), have been shown to play a critical role in cancer cell invasion and metastasis, drawing significant research interest over recent years. Several studies have highlighted the potential for targeting the genes encoding either part of or a complete protein from the WASP/WAVE family as therapeutic strategies for preventing the invasion and metastasis of cancer cells. WAVE2 is well documented to be associated with the pathogenesis of several human cancers, including lung, liver, pancreatic, prostate, colorectal and breast cancer, as well as other hematologic malignancies. This review focuses mainly on the role of WAVE2 in the development, invasion and metastasis of different types of cancer. This review also summarizes the molecular mechanisms that regulate the activity of WAVE2, as well as those oncogenic pathways that are regulated by WAVE2 to promote the cancer phenotype. Finally, we discuss potential therapeutic strategies that target WAVE2 or the WAVE regulatory complex, aimed at preventing or inhibiting cancer invasion and metastasis.

SCF FBXW17 E3 ubiquitin ligase regulates FBXL19 stability and cell migration

The Skp1-Cul1-F-box protein (SCF) E3 ligase complex is one of the largest ubiquitin E3 ligase families. FBXL19, a F-box protein in SCF^FBXL19 E3 ligase complex, regulates a variety of cellular responses including cell migration. We have shown that FBXL19 is not stable and its degradation is mediated by the ubiquitin-proteasome system, while the ubiquitin E3 ligase for FBXL19 ubiquitination and degradation has not been identified. In the study, we discovered that a new ubiquitin E3 ligase, SCF^FBXW17 , ubiquitinates and induces FBXL19 degradation. Exogenous FBXW17 targets FBXL19 for its ubiquitination and degradation. Lysine 114 in FBXL19 is a potential ubiquitin acceptor site. Acetylation of FBXL19 attenuated SCF^FBXW17 -mediated FBXL19 degradation. SCF^FBXL19 E3 ligase reduced Rac1 levels and cell migration, while the effects were attenuated by exogenous FBXW17. Downregulation of FBXW17 attenuated lysophosphatidic acid-induced lamellipodia formation and Rac1 accumulation at migration leading edge. Taken together with our previous studies, FBXL19 is degraded by the ubiquitin-proteasome system and its site-specific ubiquitination is mediated by SCF^FBXW17 E3 ligase, which promotes cell migration.

Actin dynamics during tumor cell dissemination

The actin cytoskeleton is a dynamic network that regulates cellular behavior from development to disease. By rearranging the actin cytoskeleton, cells are capable of migrating and invading during developmental processes; however, many of these cellular properties are hijacked by cancer cells to escape primary tumors and disseminate to distant organs in the body. In this review article, we highlight recent work describing how cancer cells regulate the actin cytoskeleton to achieve efficient invasion and metastatic colonization. We also review new imaging technologies that are capable of revealing the complex architecture and regulation of the actin cytoskeleton during motility and invasion of tumor cells.

A novel DENND1B-localized structure found at the basal side of adherent cells

Rab35 is a small G protein involved in various cellular events including clathrin-dependent endocytosis, phagocytosis, and autophagy. DENND1B, a DENN family member, acts as a guanine nucleotide exchange factor (GEF) for Rab35 to convert it to the GTP-bound active form from the GDP-bound inactive form. DENND1B contains the DENN domain which harbors GEF activity for Rab35 in the N-terminus, while the clathrin binding motif and adaptor protein-2-interaction motif are at the C-terminus. In this study, we investigated the intracellular localization of DENN1B in various cell types and found novel DENND1B-localized gathered line structures in BS-C-1 cells and in some other cell types. The localization of DENND1B to gathered line structures was dependent on a specific region located in the C-terminus of DENND1B protein. DENND1B-localized gathered lines were partially associated with microtubules but not with F-actin; instead, F-actin bundles surrounded the assembly of gathered lines. We also show that the gathered line structures appeared at the bottom of spreading lamellipodia and disappeared at the retracting site during cell motility in EGF-stimulated BS-C-1 cells. These results shed light on a new role for DENND1B in the regulation of cell migration.

Lights, cytoskeleton, action: Optogenetic control of cell dynamics

Cell biology is moving from observing molecules to controlling them in real time, a critical step towards a mechanistic understanding of how cells work. Initially developed from light-gated ion channels to control neuron activity, optogenetics now describes any genetically encoded protein system designed to accomplish specific light-mediated tasks. Recent photosensitive switches use many ingenious designs that bring spatial and temporal control within reach for almost any protein or pathway of interest. This next generation optogenetics includes light-controlled protein-protein interactions and shape-shifting photosensors, which in combination with live microscopy enable acute modulation and analysis of dynamic protein functions in living cells. We provide a brief overview of various types of optogenetic switches. We then discuss how diverse approaches have been used to control cytoskeleton dynamics with light through Rho GTPase signaling, microtubule and actin assembly, mitotic spindle positioning and intracellular transport and highlight advantages and limitations of different experimental strategies.

Effects of Arf6 downregulation on biological characteristics of human prostate cancer cells

Objective

To evaluate the effects of Arf6 downregulation on human prostate cancer cells.

Materials and Methods

The effects of Arf6 downregulation on cell proliferation, migration, invasion and apoptosis were assessed by MTT, BrdU, scratch, Transwell assays and flow cytometry respectively. AKT, p-AKT, ERK1/2, p-ERK1/2 and Rac1 protein expressions were detected by Western blot.

Results

Downregulating Arf6 by siRNA interference suppressed the mRNA and protein expressions of Arf6. The proliferation capacities of siRNA group at 48h, 72h, and 96h were significantly lower than those of control group (P <0.05). The migration distance of siRNA group at 18h was significantly shorter than that of control group (P <0.01). The number of cells penetrating Transwell chamber membrane significantly decreased in siRNA group compared with that of control group (P <0.01). After 24h, negative control and normal control groups had similar apoptotic rates (P >0.05) which were both significantly lower than that of siRNA group (P <0.01). After Arf6 expression was downregulated, p-ERK1/2 and Rac1 protein expressions were significantly lower than those of control group (P <0.05).

Conclusion

Downregulating Arf6 expression can inhibit the proliferation, migration and invasion of prostate cancer cells in vitro, which may be related to ERK1/2 phosphorylation and Rac1 downregulation.

Differential roles and activation of mammalian target of rapamycin complexes 1 and 2 during cell migration in prostate cancer cells

BACKGROUND

Mammalian target of rapamycin (mTOR) is a downstream substrate activated by PI3K/AKT pathway and it is essential for cell migration. It exists as two complexes: mTORC1 and mTORC2. mTORC1 is known to be regulated by active AKT, but the activation of mTORC2 is poorly understood. In this study, we investigated the roles and differential activation of the two mTOR complexes during cell migration in prostate cancer cells.

METHODS

We used small interfering RNA to silence the expression of Rac1 and the main components of mTOR complexes (regulatory associated protein of mTOR [RAPTOR] and rapamycin-insensitive companion of mTOR [RICTOR]) in LNCaP, DU145, and PC3 prostate cancer cell lines. We performed transwell migration assay to evaluate the migratory capability of the cells, and Western blot analysis to study the activation levels of mTOR complexes.

RESULTS

Specific knockdown of RAPTOR and RICTOR caused a decrease of cell migration, suggesting their essential role in prostate cancer cell movement. Furthermore, epidermal growth factor (EGF) treatments induced the activation of both the mTOR complexes. Lack of Rac1 activity in prostate cancer cells blocked EGF-induced activation of mTORC2, but had no effect on mTORC1 activation. Furthermore, the overexpression of constitutively active Rac1 resulted in significant increase in cell migration and activation of mTORC2 in PC3 cells, but had no effect on mTORC1 activation. Active Rac1 was localized in the plasma membrane and was found to be in a protein complex, with RICTOR, but not RAPTOR.

CONCLUSION

We suggest that EGF-induced activation of Rac1 causes the activation of mTORC2 via RICTOR. This mechanism plays a critical role in prostate cancer cell migration.

PI(3,4)P2 Signaling in Cancer and Metabolism

The phosphatidylinositide 3 kinases (PI3Ks) and their downstream mediators AKT and mammalian target of rapamycin (mTOR) are central regulators of glycolysis, cancer metabolism, and cancer cell proliferation. At the molecular level, PI3K signaling involves the generation of the second messenger lipids phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3] and phosphatidylinositol 3,4-bisphosphate [PI(3,4)P2]. There is increasing evidence that PI(3,4)P2 is not only the waste product for the removal of PI(3,4,5)P3 but can also act as a signaling molecule. The selective cellular functions for PI(3,4)P2 independent of PI(3,4,5)P3 have been recently described, including clathrin-mediated endocytosis and mTOR regulation. However, the specific spatiotemporal dynamics and signaling role of PI3K minor lipid messenger PI(3,4)P2 are not well-understood. This review aims at highlighting the biological functions of this lipid downstream of phosphoinositide kinases and phosphatases and its implication in cancer metabolism.

The Small GTPase Rac1 Increases Cell Surface Stiffness and Enhances 3D Migration Into Extracellular Matrices

Membrane ruffling and lamellipodia formation promote the motility of adherent cells in two-dimensional motility assays by mechano-sensing of the microenvironment and initiation of focal adhesions towards their surroundings. Lamellipodium formation is stimulated by small Rho GTPases of the Rac subfamily, since genetic removal of these GTPases abolishes lamellipodium assembly. The relevance of lamellipodial or invadopodial structures for facilitating cellular mechanics and 3D cell motility is still unclear. Here, we hypothesized that Rac1 affects cell mechanics and facilitates 3D invasion. Thus, we explored whether fibroblasts that are genetically deficient for Rac1 (lacking Rac2 and Rac3) harbor altered mechanical properties, such as cellular deformability, intercellular adhesion forces and force exertion, and exhibit alterations in 3D motility. Rac1 knockout and control cells were analyzed for changes in deformability by applying an external force using an optical stretcher. Five Rac1 knockout cell lines were pronouncedly more deformable than Rac1 control cells upon stress application. Using AFM, we found that cell-cell adhesion forces are increased in Rac1 knockout compared to Rac1-expressing fibroblasts. Since mechanical deformability, cell-cell adhesion strength and 3D motility may be functionally connected, we investigated whether increased deformability of Rac1 knockout cells correlates with changes in 3D motility. All five Rac1 knockout clones displayed much lower 3D motility than Rac1-expressing controls. Moreover, force exertion was reduced in Rac1 knockout cells, as assessed by 3D fiber displacement analysis. Interference with cellular stiffness through blocking of actin polymerization by Latrunculin A could not further reduce invasion of Rac1 knockout cells. In contrast, Rac1-expressing controls treated with Latrunculin A were again more deformable and less invasive, suggesting actin polymerization is a major determinant of observed Rac1-dependent effects. Together, we propose that regulation of 3D motility by Rac1 partly involves cellular mechanics such as deformability and exertion of forces.

Non-canonical Notch Signaling Regulates Actin Remodeling in Cell Migration by Activating PI3K/AKT/Cdc42 Pathway

Tumor cell migration is a critical step in cancer metastasis. Over-activated Notch pathway can promote the migration of cancer cells, especially in the breast cancer. However, the underlying mechanism of non-canonical Notch signaling in modulating the migration has not yet been clearly characterized. Here we demonstrated that DAPT, a gamma secretase inhibitor, inhibited protrusion formation and cell motility, and then reduced the migration of triple-negative breast cancer cells, through increasing the activity of Cdc42 by non-canonical Notch pathway. Phosphorylation of AKT on S473 was surprisingly increased when Notch signaling was inhibited by DAPT. Inhibition of PI3K and AKT by LY294002 and MK2206, respectively, or knockdown of AKT expression by siRNA blocked DAPT-induced activation of Cdc42. Moreover, immunofluorescence staining further showed that DAPT treatment reduced the formation of lamellipodia and induced actin cytoskeleton remodeling. Taken together, these results indicated that DAPT inhibited Notch signaling and consequently activated PI3K/AKT/Cdc42 signaling by non-canonical pathway, facilitated the formation of filopodia and inhibited the assembly of lamellipodia, and finally resulted in the decrease of migration activity of breast cancer cells.

Transient localization of the Arp2/3 complex initiates neuronal dendrite branching in vivo

The formation of neuronal dendrite branches is fundamental for the wiring and function of the nervous system. Indeed, dendrite branching enhances the coverage of the neuron's receptive field and modulates the initial processing of incoming stimuli. Complex dendrite patterns are achieved in vivo through a dynamic process of de novo branch formation, branch extension and retraction. The first step towards branch formation is the generation of a dynamic filopodium-like branchlet. The mechanisms underlying the initiation of dendrite branchlets are therefore crucial to the shaping of dendrites. Through in vivo time-lapse imaging of the subcellular localization of actin during the process of branching of Drosophila larva sensory neurons, combined with genetic analysis and electron tomography, we have identified the Actin-related protein (Arp) 2/3 complex as the major actin nucleator involved in the initiation of dendrite branchlet formation, under the control of the activator WAVE and of the small GTPase Rac1. Transient recruitment of an Arp2/3 component marks the site of branchlet initiation in vivo These data position the activation of Arp2/3 as an early hub for the initiation of branchlet formation.

TRPV2 suppresses Rac1 and RhoA activation and invasion in rheumatoid arthritis fibroblast-like synoviocytes

The TRPV2 cation channel has been recently implicated in the regulation of arthritis severity, joint damage, and in the invasive behavior of the fibroblast-like synoviocyte (FLS). However, its mechanism of action was unknown. In this study we characterize the cell signaling events mediating the TRPV2 suppressive activity in FLS invasiveness. Studies with FLS cell lines derived from patients with RA revealed that TRPV2-specific stimulation significantly reduced FLS adhesion to different extracellular matrices that shared binding to αν, β1 and β3 integrins. Localization of these integrins to the plasma membrane and numbers of thick and organized actin filaments were diminished by TRPV2 specific stimulation, and cells developed a round and non-polarized morphology. TRPV2 stimulation significantly reduced levels of activated RhoA, Rac1 and cofilin. RhoA activators were able to overcome the TRPV2-induced suppression on both RhoA activation and invasion. These new discoveries suggest that TRPV2 regulates key intracellular processes implicated in cell invasion in arthritis and other processes such as cancer, and has the potential to become a useful target for drug development.

Modulation of CD44, EGFR and RAC Pathway Genes (WAVE Complex) in Epithelial Cancers

Cancer hallmarks help in understanding the diversity of various neoplasms. Epithelial cancers play an immense role in the tumor biology through Epithelial-Mesenchymal Transition (EMT) process. Receptor tyrosine kinase, as well as phosphatidyl ionositol-3 kinase pathways, play an important role in the regulation of cell proliferation, survival, and differentiation during EMT. Till date, numerous studies have shown modulation in the expression profile of potential targets like CD44, EGFR, and Rac in epithelial cancers. CD44 interacts with EGFR and recruits other molecules which further activate the Rac pathway intermediates. This review mainly focused on modulation of genes like CD44, EGFR, and Rac pathway intermediates which play a crucial role in the tumor progression, metastasis, proliferation, and invasion characteristics in epithelial cancers with EMT properties. Hence, targeting Rac pathway might be a more strategically relevant approach in treating epithelial cancers.

Cullin-3/KCTD10 E3 complex is essential for Rac1 activation through RhoB degradation in human epidermal growth factor receptor 2-positive breast cancer cells

Rho GTPase Rac1 is a central regulator of F‐actin organization and signal transduction to control plasma membrane dynamics and cell proliferation. Dysregulated Rac1 activity is often observed in various cancers including breast cancer and is suggested to be critical for malignancy. Here, we showed that the ubiquitin E3 ligase complex Cullin‐3 (CUL3)/KCTD10 is essential for epidermal growth factor (EGF)‐induced/human epidermal growth factor receptor 2 (HER2)‐dependent Rac1 activation in HER2‐positive breast cancer cells. EGF‐induced dorsal membrane ruffle formation and cell proliferation that depends on both Rac1 and HER2 were suppressed in CUL3‐ or KCTD10‐depleted cells. Mechanistically, CUL3/KCTD10 ubiquitinated RhoB for degradation, another Rho GTPase that inhibits Rac1 activation at the plasma membrane by suppressing endosome‐to‐plasma membrane traffic of Rac1. In HER2‐positive breast cancers, high expression of Rac1 mRNA significantly correlated with poor prognosis of the patients. This study shows that this novel molecular axis (CUL3/KCTD10/RhoB) positively regulates the activity of Rac1 in HER2‐positive breast cancers, and our findings may lead to new treatment options for HER2‐ and Rac1‐positive breast cancers.

Huntingtin-interacting protein 1 (HIP1) regulates arthritis severity and synovial fibroblast invasiveness by altering PDGFR and Rac1 signalling

OBJECTIVES

While new treatments for rheumatoid arthritis (RA) have markedly improved disease control by targeting immune/inflammatory pathways, current treatments rarely induce remission, underscoring the need for therapies that target other aspects of the disease. Little is known about the regulation of disease severity and joint damage, which are major predictors of disease outcome, and might be better or complementary targets for therapy. In this study, we aimed to discover and characterise a new arthritis severity gene.

METHODS

An unbiased and phenotype-driven strategy including studies of unique congenic rat strains was used to identify new arthritis severity and joint damage genes. Fibroblast-like synoviocytes (FLS) from rats and patients with RA expressing or not Huntingtin-interacting protein 1 (HIP1) were studied for invasiveness, morphology and cell signalling. HIP1 knockout mice were used in in vivo confirmatory studies. Paired t-test was used.

RESULTS

DNA sequencing and subcongenic strains studied in pristane-induced arthritis identified a new amino acid changing functional variant in HIP1. HIP1 was required for the increased invasiveness of FLS from arthritic rats and from patients with RA. Knocking down HIP1 expression reduced receptor tyrosine kinase-mediated responses in RA FLS, including RAC1 activation, affecting actin cytoskeleton and cell morphology and interfering with the formation of lamellipodia, consistent with reduced invasiveness. HIP1 knockout mice were protected in KRN serum-induced arthritis and developed milder disease.

CONCLUSION

HIP1 is a new arthritis severity gene and a potential novel prognostic biomarker and target for therapy in RA.

The role of the oncogenic Rab35 in cancer invasion, metastasis, and immune evasion, especially in leukemia

The study of cancer has allowed researchers to describe some biological characteristics that tumor cells acquire during their development, known as the “hallmarks of cancer” but more research is needed to expand our knowledge about cancer biology and to generate new strategies of treatment. The role that RabGTPases might play in some hallmarks of cancer represents interesting areas of study since these proteins are frequently altered in cancer. However, their participation is not well known. Recently, Rab35was recognized as an oncogenic RabGTPase and and because of its association with different cellular functions, distinctly important in immune cells, a possible role of Rab35 in leukemia can be suggested. Nevertheless, the involvement of Rab35 in cancer remains poorly understood and its possible specific role in leukemia remains unknown. In this review, we analyze general aspects of the participation of RabGTPases in cancer, and especially, the plausible role of Rab35 in leukemia.

Blockade of ITGA2 Induces Apoptosis and Inhibits Cell Migration in Gastric Cancer

Background

Gastric cancer is currently the fourth leading cause of cancer-related death worldwide. Gastric cancer is often diagnosed at advanced stages and the outcome of the treatment is often poor. Therefore, identifying new therapeutic targets for this cancer is urgently needed. Integrin alpha 2 (ITGA2) subunit and the beta 1 subunit form a heterodimer for a transmembrane receptor for extracellular matrix, is an important molecule involved in tumor cell proliferation, survival and migration. Integrin α2β1 is over-expressed on a variety of cancer cells, but is low or absent in most normal organs and resting endothelial cells.

Results

In this report, we assessed the ITGA2 as the potential therapeutic target with the bioinformatics tools from the TCGA dataset in which composed of 375 gastric cancer tissues and 32 gastric normal tissues. According to the information from the Cancer Cell Line Encyclopedia (CCLE) database, the AGS cell line with ITGA2 high expression and the SUN-1 cell line with low expression were chosen for the further investigation. Interestingly, the anti-ITGA2 antibody (at 3 μg/ml) inhibited approximately 50% survival of the AGS cells (over-expressed ITGA2), but had no effect in SNU-1 cells (ITGA2 negative). The extents of antibody-mediated cancer inhibition positively correlated with the expression levels of the ITGA2. We further showed that the anti-ITGA2 antibody induced apoptosis by up-regulating the RhoA-p38 MAPK signaling to promote the expressions of Bim, Apaf-1 and Caspase-9, whereas the expressions of Ras and Bax/Bcl-2 were not affected. Moreover, blocking ITGA2 by the specific antibody at lower doses also inhibited cell migration of gastric cancer cells. Blockade of ITGA2 by a specific antibody down-regulated the expression of N-WASP, PAK and LIMK to impede actin organization and cell migration of gastric cancer cells.

Conclusions

Here, we showed that the mRNA expression levels of ITGA2 comparing to normal tissues significantly increased. In addition, the results revealed that targeting integrin alpha 2 subunit by antibodies did not only inhibit cell migration, but also induce apoptosis effect on gastric cancer cells. Interestingly, higher expression level of ITGA2 led to significant effects on apoptosis progression during anti-ITGA2 antibody treatment, which indicated that ITGA2 expression levels directly correlate with their functionality. Our findings suggest that ITGA2 is a potential therapeutic target for gastric cancer.

Visualizing the spatiotemporal map of Rac activation in bovine aortic endothelial cells under laminar and disturbed flows

Disturbed flow can eliminate the alignment of endothelial cells in the direction of laminar flow, and significantly impacts on atherosclerosis in collateral arteries near the bifurcation and high curvature regions. While shear stress induced Rac polarity has been shown to play crucial roles in cell polarity and migration, little is known about the spatiotemporal map of Rac under disturbed flow, and the mechanism of flow-induced cell polarity still needs to be elucidated. In this paper, disturbed flow or laminar flow with 15 dyn/cm2 of average shear stress was applied on bovine aortic endothelial cells (BAECs) for 30 minutes. A genetically-encoded PAK-PBD-GFP reporter was transfected into BAECs to visualize the real-time activation of Rac in living cell under fluorescence microscope. The imaging of the fluorescence intensity was analyzed by Matlab and the normalized data was converted into 3D spatiotemporal map. Then the changes of data upon chemical interference were fitted with logistic curve to explore the rule and mechanism of Rac polarity under laminar or disturbed flow. A polarized Rac activation was observed at the downstream edge along the laminar flow, which was enhanced by benzol alcohol-enhanced membrane fluidity but inhibited by nocodazole-disrupted microtubules or cholesterol-inhibited membrane fluidity, while no obvious polarized Rac activation could be found upon disturbed flow application. It is concluded that disturbed flow inhibits the flow-induced Rac polarized activation, which is related to the interaction of cell membrane and cytoskeleton, especially the microtubules.

Conditionally reprogrammed normal and primary tumor prostate epithelial cells: a novel patient-derived cell model for studies of human prostate cancer

Our previous study demonstrated that conditional reprogramming (CR) allows the establishment of patient-derived normal and tumor epithelial cell cultures from a variety of tissue types including breast, lung, colon and prostate. Using CR, we have established matched normal and tumor cultures, GUMC-29 and GUMC-30 respectively, from a patient's prostatectomy specimen. These CR cells proliferate indefinitely in vitro and retain stable karyotypes. Most importantly, only tumor-derived CR cells (GUMC-30) produced tumors in xenografted SCID mice, demonstrating maintenance of the critical tumor phenotype. Characterization of cells with DNA fingerprinting demonstrated identical patterns in normal and tumor CR cells as well as in xenografted tumors. By flow cytometry, both normal and tumor CR cells expressed basal, luminal, and stem cell markers, with the majority of the normal and tumor CR cells expressing prostate basal cell markers, CD44 and Trop2, as well as luminal marker, CD13, suggesting a transit-amplifying phenotype. Consistent with this phenotype, real time RT-PCR analyses demonstrated that CR cells predominantly expressed high levels of basal cell markers (KRT5, KRT14 and p63), and low levels of luminal markers. When the CR tumor cells were injected into SCID mice, the expression of luminal markers (AR, NKX3.1) increased significantly, while basal cell markers dramatically decreased. These data suggest that CR cells maintain high levels of proliferation and low levels of differentiation in the presence of feeder cells and ROCK inhibitor, but undergo differentiation once injected into SCID mice. Genomic analyses, including SNP and INDEL, identified genes mutated in tumor cells, including components of apoptosis, cell attachment, and hypoxia pathways. The use of matched patient-derived cells provides a unique in vitro model for studies of early prostate cancer.

Mechanochemical feedback underlies coexistence of qualitatively distinct cell polarity patterns within diverse cell populations

Cell polarization and directional cell migration can display random, persistent, and oscillatory dynamic patterns. However, it is not clear whether these polarity patterns can be explained by the same underlying regulatory mechanism. Here, we show that random, persistent, and oscillatory migration accompanied by polarization can simultaneously occur in populations of melanoma cells derived from tumors with different degrees of aggressiveness. We demonstrate that all of these patterns and the probabilities of their occurrence are quantitatively accounted for by a simple mechanism involving a spatially distributed, mechanochemical feedback coupling the dynamically changing extracellular matrix (ECM)-cell contacts to the activation of signaling downstream of the Rho-family small GTPases. This mechanism is supported by a predictive mathematical model and extensive experimental validation, and can explain previously reported results for diverse cell types. In melanoma, this mechanism also accounts for the effects of genetic and environmental perturbations, including mutations linked to invasive cell spread. The resulting mechanistic understanding of cell polarity quantitatively captures the relationship between population variability and phenotypic plasticity, with the potential to account for a wide variety of cell migration states in diverse pathological and physiological conditions.

Rac1 switching at the right time and location is essential for Fcγ receptor-mediated phagosome formation

Lamellipodia are sheet-like cell protrusions driven by actin polymerization mainly through Rac1, a GTPase molecular switch. In Fcγ receptor-mediated phagocytosis of IgG-opsonized erythrocytes (IgG-Es), Rac1 activation is required for lamellipodial extension along the surface of IgG-Es. However, the significance of Rac1 deactivation in phagosome formation is poorly understood. Our live-cell imaging and electron microscopy revealed that RAW264 macrophages expressing a constitutively active Rac1 mutant showed defects in phagocytic cup formation, while lamellipodia were formed around IgG-Es. Because the activated Rac1 reduced the phosphorylation levels of myosin light chain, failure of the cup formation were probably due to inhibition of actin/myosin II contractility. Reversible photo-manipulation of the Rac1 switch in macrophages fed with IgG-Es could phenocopy two lamellipodial motilities: outward-extension and cup-constriction by Rac1 ON and OFF, respectively. In conjunction with FRET imaging of Rac1 activity, we provide a novel mechanistic model of phagosome formation spatiotemporally controlled by Rac1 switching within a phagocytic cup.

CD147 regulates cancer migration via direct interaction with Annexin A2 and DOCK3-β-catenin-WAVE2 signaling

The acquisition of inappropriate migratory feature is crucial for tumor metastasis. It has been suggested that CD147 and Annexin A2 are involved in regulating tumor cell movement, while the regulatory mechanisms are far from clear. In this study, we demonstrated that CD147 physically interacted with the N-terminal domain of Annexin A2 and decreased Annexin A2 phosphorylation on tyrosine 23. In vitro kinase assay showed that the I domain of CD147 was indispensable for CD147-mediated downregulation of Annexin A2 phosphorylation by Src. Furthermore, we determined that p-Annexin A2 promoted the expression of dedicator of cytokinesis 3 (DOCK3) and DOCK3 blocked β-catenin nuclear translocation, resulting in inhibition of β-catenin signaling. In addition, DOCK3 inhibited lamellipodium dynamics and tumor cell movement. Also, we found that β-catenin signaling increased WAVE2 expression. Therefore, DOCK3 was characterized as a negative regulator of WAVE2 expression via inhibiting β-catenin signaling. Our study provides the first evidence that CD147 promotes tumor cell movement and metastasis via direct interaction with Annexin A2 and DOCK3-β-catenin-WAVE2 signaling axis.

Central role of PI3K-SYK interaction in fibrinogen-induced lamellipodia and filopodia formation in platelets

The WAVE complex‐1, a complex of WAVE, Abi1, NAP1, PIR121, HSPC300, RacGTP and Arp2/3 proteins, and WASP complex‐1, a complex of WASP, Cdc42, PIP2, and Arp2/3 proteins, are involved in lamellipodia and filopodia formation, respectively. It is known that the two complexes have opposite dynamics. Furthermore, Rac has two guanine nucleotide exchange factors, Vav and Sos, whose role in activating Rac is not well understood. In this work, by the construction of signaling network, analysis, and mathematical modeling, I show that Sos generates a pulse of WAVE complex‐1, decreasing the response time of WAVE complex‐1 formation upon the stimulation of platelets by fibrinogen. Furthermore, I also show that the dynamics of WAVE and WASP complexes depends on PI3K–SYK interaction. In the absence of this interaction, the WAVE complex‐1 does not form and the WASP complex‐1 remains at the initial, sustained level. Thus, I show the significance of the two protein/protein complexes: Sos and PI3K–SYK interaction, in fibrinogen‐induced lamellipodia and filopodia formation in platelets.

Determination of cell uptake pathways for tumor inhibitor lysyl oxidase propeptide

The lysyl oxidase propeptide (LOX-PP) is derived from pro-lysyl oxidase (Pro-LOX) by extracellular biosynthetic proteolysis. LOX-PP inhibits breast and prostate cancer xenograft tumor growth and has tumor suppressor activity. Although, several intracellular targets and molecular mechanisms of action of LOX-PP have been identified, LOX-PP uptake pathways have not been reported. Here we demonstrate that the major uptake pathway for recombinant LOX-PP (rLOX-PP) is PI3K-dependent macropinocytosis in PWR-1E, PC3, SCC9, MDA-MB-231 cell lines. A secondary pathway appears to be dynamin- and caveola dependent. The ionic properties of highly basic rLOX-PP provide buffering capacity at both high and low pHs. We suggest that the buffering capacity of rLOX-PP, which serves to limit endosomal acidification, sustains PI3K-dependent macropinocytosis in endosomes which in turn is likely to facilitate LOX-PP endosomal escape into the cytoplasm and its observed interactions with cytoplasmic targets and nuclear uptake.