Rho, Rac, Pak and angiogenesis: old roles and newly identified responsibilities in endothelial cells

Phloridzin Docosahexaenoate, an Omega-3 Fatty Acid Ester of a Flavonoid Precursor, Inhibits Angiogenesis by Suppressing Endothelial Cell Proliferation, Migration, and Differentiation

Angiogenesis is a normal physiological process that also contributes to diabetic retinopathy-related complications and facilitates tumor metastasis by promoting the hematogenic dissemination of malignant cells from solid tumors. Here, we investigated the in vitro, ex vivo, and in vivo anti-angiogenic activity of phloridzin docosahexaenoate (PZ-DHA), a novel ω-3 fatty acid ester of a flavonoid precursor. Human umbilical vein endothelial cells (HUVEC) and human dermal microvascular endothelial cells (HMVEC) treated with a sub-cytotoxic concentration of PZ-DHA to assess in vitro anti-angiogenic activity showed impaired tubule formation on a Matrigel matrix. Ex vivo angiogenesis was measured using rat thoracic aortas, which exhibited reduced vessel sprouting and tubule formation in the presence of PZ-DHA. Female BALB/c mice bearing VEGF165- and basic fibroblast growth factor-containing Matrigel plugs showed a significant reduction in blood vessel development following PZ-DHA treatment. PZ-DHA inhibited HUVEC and HMVEC proliferation, as well as the migration of HUVECs in gap closure and trans-well cell migration assays. PZ-DHA inhibited upstream and downstream components of the Akt pathway and vascular endothelial growth factor (VEGF165)-induced overexpression of small molecular Rho GTPases in HUVECs, suggesting a decrease in actin cytoskeletal-mediated stress fiber formation and migration. Taken together, these findings reveal the potential of combined food biomolecules in PZ-DHA to inhibit angiogenesis.

Rhogef17: A novel target for endothelial barrier function

ARHGEF17 encodes the protein RhoGEF17, which is highly expressed in vascular endothelial cells. It is a guanine nucleotide exchange factor (GEF) that accelerates the exchange of GDP with GTP on many small GTPases through its Dbl homology (DH) domain, enabling the activation of Rho-GTPases such as RhoA, RhoB, and RhoC. Rho GTPase-regulated changes in the actin cytoskeleton and cell adhesion kinetics are the main mechanisms mediating many endothelial cell (EC) alterations, including cell morphology, migration, and division changes, which profoundly affect EC barrier function. This review focuses on ARHGEF17 expression, activation and biological functions in ECs, linking its regulation of cellular morphology, migration, mitosis and other cellular behaviors to disease onset and progression. Understanding ARHGEF17 mechanisms of action will contribute to the design of therapeutic approaches targeting RhoGEF17, a potential drug target for the treatment of various endothelium-related diseases, Such as vascular inflammation, carcinogenesis and transendothelial metastasis of tumors.

PAK in Pancreatic Cancer-Associated Vasculature: Implications for Therapeutic Response

Angiogenesis has been associated with numbers of solid tumours. Anti-angiogenesis drugs starve tumours of nutrients and oxygen but also make it difficult for a chemo reagent to distribute into a tumour, leading to aggressive tumour growth. Anti-angiogenesis drugs do not appear to improve the overall survival rate of pancreatic cancer. Vessel normalisation is merging as one of the new approaches for halting tumour progression by facilitating the tumour infiltration of immune cells and the delivery of chemo reagents. Targeting p21-activated kinases (PAKs) in cancer has been shown to inhibit cancer cell growth and improve the efficacy of chemotherapy. Inhibition of PAK enhances anti-tumour immunity and stimulates the efficacy of immune checkpoint blockades. Inhibition of PAK also improves Car-T immunotherapy by reprogramming the vascular microenvironment. This review summarizes current research on PAK's role in tumour vasculature and therapeutical response, with a focus on pancreatic cancer.

RHOJ as a novel mechanosensitive modulator of endothelial inflammation

Physiological high shear stress (HSS), a frictional force generated by flowing blood, is essential for endothelial homeostasis under normal physiological conditions. HSS suppresses atherosclerosis by inhibiting endothelial inflammation. However, the molecular mechanisms underlying this process have not been fully elucidated. Here, we report that HSS downregulated the mRNA and protein levels of ras homolog family member J (RHOJ) in endothelial cells (ECs). Silencing endogenous RHOJ expression decreased the mRNA and protein levels of proinflammatory vascular cell adhesion molecule 1 (VCAM-1) and intercellular cell adhesion molecule 1 (ICAM-1) in ECs, leading to a reduction in monocyte adhesion to ECs. Conversely, the overexpression of RHOJ had the opposite effect. RNA-sequencing analysis uncovered several differentially expressed genes (such as yes-associated protein 1 (YAP1),heme oxygenase-1 (HO1), and monocyte chemoattractant protein-1 (MCP1)) and pathways (such as nuclear factor-kappa B (NF-κB), fluid shear stress and atherosclerosis, and cell adhesion pathways) as RHOJ targets. Additionally, HSS was observed to alleviate endothelial inflammation by inhibiting RHOJ expression. Finally, methylated RNA immunoprecipitation sequencing (MeRIP-seq) illustrated that fluid shear stress regulates RHOJ expression in an N6-methyladenosine (m6A)-dependent manner. Mechanistically, the RNA m6A writer, methyltransferase 3 (METTL3), and the RNA m6A readers, YTH N6-methyladenosine RNA-binding protein F 3 (YTHDF3) and YTH N6-methyladenosine RNA-binding protein C 1/2 (YTHDC1/2), are involved in this process. Taken together, our data demonstrate that HSS-induced downregulation of RHOJ contributes to endothelial homeostasis by suppressing endothelial inflammation and that RHOJ inhibition in ECs is a promising therapeutic strategy for endothelial dysfunction.

Single-cell transcriptional analysis of human endothelial colony-forming cells from patients with low VWF levels

von Willebrand factor (VWF) plays a key role in normal hemostasis, and deficiencies of VWF lead to clinically significant bleeding. We sought to identify novel modifiers of VWF levels in endothelial colony-forming cells (ECFCs) using single-cell RNA sequencing (scRNA-seq). ECFCs were isolated from patients with low VWF levels (plasma VWF antigen levels between 30 and 50 IU/dL) and from healthy controls. Human umbilical vein endothelial cells were used as an additional control cell line. Cells were characterized for their Weibel Palade body (WPB) content and VWF release. scRNA-seq of all cell lines was performed to evaluate for gene expression heterogeneity and for candidate modifiers of VWF regulation. Candidate modifiers identified by scRNA-seq were further characterized with small-interfering RNA (siRNA) experiments to evaluate for effects on VWF. We observed that ECFCs derived from patients with low VWF demonstrated alterations in baseline WPB metrics and exhibit impaired VWF release. scRNA-seq analyses of these endothelial cells revealed overall decreased VWF transcription, mosaicism of VWF expression, and genes that are differentially expressed in low VWF ECFCs and control endothelial cells (control ECs). An siRNA screen of potential VWF modifiers provided further evidence of regulatory candidates, and 1 such candidate, FLI1, alters the transcriptional activity of VWF. In conclusion, ECFCs from individuals with low VWF demonstrate alterations in their baseline VWF packaging and release compared with control ECs. scRNA-seq revealed alterations in VWF transcription, and siRNA screening identified multiple candidate regulators of VWF.

Molecular Genetic Features of Cerebral Cavernous Malformations (CCM) Patients: An Overall View from Genes to Endothelial Cells

Cerebral cavernous malformations (CCMs) are vascular lesions that affect predominantly microvasculature in the brain and spinal cord. CCM can occur either in sporadic or familial form, characterized by autosomal dominant inheritance and development of multiple lesions throughout the patient's life. Three genes associated with CCM are known: CCM1/KRIT1 (krev interaction trapped 1), CCM2/MGC4607 (encoding a protein named malcavernin), and CCM3/PDCD10 (programmed cell death 10). All the mutations identified in these genes cause a loss of function and compromise the protein functions needed for maintaining the vascular barrier integrity. Loss of function of CCM proteins causes molecular disorganization and dysfunction of endothelial adherens junctions. In this review, we provide an overall vision of the CCM pathology, starting with the genetic bases of the disease, describing the role of the proteins, until we reach the cellular level. Thus, we summarize the genetics of CCM, providing a description of CCM genes and mutation features, provided an updated knowledge of the CCM protein structure and function, and discuss the molecular mechanisms through which CCM proteins may act within endothelial cells, particularly in endothelial barrier maintenance/regulation and in cellular signaling.

Cucurbitacin IIa: A review of phytochemistry and pharmacology

Cucurbitacin IIa was first found in plants and it belongs to tetracyclo triterpenoids. It is one of the most important active components in cucurbitaceae plants. Studies have found that cucurbitacin IIa has a variety of pharmacological effects, such as antitumor, antiinflammatory, antibacterial, antihepatitis B virus, inhibition of human immunodeficiency virus replication, and antidepressant effect. However, the underlying mechanisms, intracellular targets, and structure-activity relationships of cucurbitacin IIa remain to be completely elucidated. This review summarizes the current advances concerning the phytochemistry and pharmacology of cucurbitacin IIa. Electronic databases such as PubMed, Web of Science, Google Scholar, Science Direct, and CNKI were used to find relevant information about cucurbitacin IIa using keywords such as "Cucurbitacin IIa," "Pharmacology," and "Phytochemistry." These pharmacological effects involve the actin cytoskeleton aggregation, the regulation of JAK2/STAT3, ERBB-MAPK, CaMKII α/CREB/BDNF signal pathways, as well as the regulation of survivin, caspases, and other cell cycles, apoptosis, autophagy-related cytokines, and kinases. It has high development and use value.

Lipid Signaling in Ocular Neovascularization

Vasculogenesis and angiogenesis play a crucial role in embryonic development. Pathological neovascularization in ocular tissues can lead to vision-threatening vascular diseases, including proliferative diabetic retinopathy, retinal vein occlusion, retinopathy of prematurity, choroidal neovascularization, and corneal neovascularization. Neovascularization involves various cellular processes and signaling pathways and is regulated by angiogenic factors such as vascular endothelial growth factor (VEGF) and hypoxia-inducible factor (HIF). Modulating these circuits may represent a promising strategy to treat ocular neovascular diseases. Lipid mediators derived from membrane lipids are abundantly present in most tissues and exert a wide range of biological functions by regulating various signaling pathways. In particular, glycerophospholipids, sphingolipids, and polyunsaturated fatty acids exert potent pro-angiogenic or anti-angiogenic effects, according to the findings of numerous preclinical and clinical studies. In this review, we summarize the current knowledge regarding the regulation of ocular neovascularization by lipid mediators and their metabolites. A better understanding of the effects of lipid signaling in neovascularization may provide novel therapeutic strategies to treat ocular neovascular diseases and other human disorders.

The Role of Rho GTPases in VEGF Signaling in Cancer Cells

Vascular endothelial growth factors (VEGFs) consist of five molecules (VEGFA through D as well as placental growth factor) which are crucial for regulating key cellular and tissue functions. The role of VEGF and its intracellular signaling and downstream molecular pathways have been thoroughly studied. Activation of VEGF signal transduction can be initiated by the molecules' binding to two classes of transmembrane receptors: (1) the VEGF tyrosine kinase receptors (VEGF receptors 1 through 3) and (2) the neuropilins (NRP1 and 2). The involvement of Rho GTPases in modulating VEGFA signaling in both cancer cells and endothelial cells has also been well established. Additionally, different isoforms of Rho GTPases, namely, RhoA, RhoC, and RhoG, have been shown to regulate VEGF expression as well as blood vessel formation. This review article will explore how Rho GTPases modulate VEGF signaling and the consequences of such interaction on cancer progression.

Computational insight into the mechanisms of action and selectivity of Afraxis PAK inhibitors

Aim: The p21-activated kinases (PAKs) are involved in many important biological activity regulations. FRAX019, FRAX414, FRAX597, FRAX1036 and G-5555 were identified as PAKs inhibitors. Their detailed inhibitory mechanisms deserve further investigation. Results: Molecular dynamics simulations and further calculations for the PAK1/inhibitor and PAK4/inhibitor complexes indicate that their binding free energies are basically consistent with the trend of experimental activity data. Conclusion: The anchoring of residues Leu347^PAK1 and Leu398^PAK4 is the structural basis for designing Afraxis PAK inhibitors. This study discloses the inhibitory mechanisms of FRAX019, FRAX414, FRAX597, FRAX1036 and G-5555 toward PAK1 and PAK4 and some clues to enhance kinase activities and selectivities, which will provide valuable information to the development of more potent and selective PAK inhibitors.

Hypoxia and EGF Stimulation Regulate VEGF Expression in Human Glioblastoma Multiforme (GBM) Cells by Differential Regulation of the PI3K/Rho-GTPase and MAPK Pathways

Glioblastoma multiforme (GBM) is one of the most common and deadly cancers of the central nervous system (CNS). It is characterized by the presence of hypoxic regions, especially in the core, leading to an increase in vascularity. This increased vascularization is driven by the expression of the major angiogenic inducer VEGF and the indirect angiogenic inducer Epidermal growth factor (EGF), which stimulates VEGF expression. In this study, we examine the regulation of VEGF by both hypoxia and the EGF signaling pathway. We also examine the involvement of pathways downstream from EGF signaling, including the mitogen-activated protein kinase/extracellular regulated kinase (MAPK/ERK) pathway and the Phosphatidylinositol-3-kinase/RhoA/C (PI3K/RhoA/C) pathway in this regulation. Our results show that VEGF expression and secretion levels increase following either hypoxia or EGF stimulation, with the two stimuli signaling in parallel. We also observed an increase in ERK and protein kinase B (Akt) phosphorylation, in response to EGF stimulation, with kinetics that correlated with the kinetics of the effect on VEGF. Using pharmacological inhibitors against ERK and PI3K and small interfering RNAs (siRNAs) against RhoA and RhoC, we found that both the ERK and the PI3K/RhoA/C pathways have to cooperate in order to lead to an increase in VEGF expression, downstream from EGF. In response to hypoxia, however, only ERK was involved in the regulation of VEGF. Hypoxia also led to a surprising decrease in the activation of PI3K and RhoA/C. Finally, the decrease in the activation of these Rho-GTPases was found to be mediated through a hypoxia-driven overexpression of the Rho-GTPase GTPase activating protein (GAP), StarD13. Therefore, while under normoxic conditions, EGF stimulates the activation of both the PI3K and the MAPK pathways and the induction of VEGF, in glioblastoma cells, hypoxic conditions lead to the suppression of the PI3K/RhoA/C pathway and an exclusive switch to the MAPK pathway.

Chromosomal Heterogeneity of the G-401 Rhabdoid Tumor Cell Line: Unusual Partial 7p Trisomy

Rhabdoid tumor is a very aggressive and hardly curable pediatric malignancy. It commonly starts in the kidneys but also can occur in the brain, liver, and other organs. The treatment of this tumor usually involves a combination of surgery, radiation, and chemotherapy. Because this tumor is rare, there is still limited experience with a defined standard of care. Cytogenetic analysis is an important routine method to monitor chromosomal aberrations. We have analyzed metaphases of the G-401 rhabdoid tumor cell line. In these cells we have observed metaphases with derivative chromosome 12 arising from partial trisomy 7p. With increasing passage number the numbers of metaphases having this derivative chromosome 12 were found to be higher. In passage number 2 only one metaphase had this pathological chromosome 12. By passage number 10 and passage number 15 about 25 and 95% of this derivative chromosome 12 were found, respectively. We were able to subclone G-401 cells by limiting dilutions and successfully separated cells having apparently normal karyotypes from cells having derivative chromosome 12. Using the cell proliferation assay we showed that clones possessing the derivative chromosome 12 grew more rapidly than clones with normal chromosomes. The cell cycle analysis confirmed this observation. Overall, in this study we describe for the first time a 7p triplication in a rare rhabdoid tumor of kidney. Both types of clones described in this study could be used as a preclinical model to study the involvement of partial chromosome 7 alterations in the development of rhabdoid tumors.

RHO Family GTPases in the Biology of Lymphoma

RHO GTPases are a class of small molecules involved in the regulation of several cellular processes that belong to the RAS GTPase superfamily. The RHO family of GTPases includes several members that are further divided into two different groups: typical and atypical. Both typical and atypical RHO GTPases are critical transducers of intracellular signaling and have been linked to human cancer. Significantly, both gain-of-function and loss-of-function mutations have been described in human tumors with contradicting roles depending on the cell context. The RAS family of GTPases that also belong to the RAS GTPase superfamily like the RHO GTPases, includes arguably the most frequently mutated genes in human cancers (K-RAS, N-RAS, and H-RAS) but has been extensively described elsewhere. This review focuses on the role of RHO family GTPases in human lymphoma initiation and progression.

RAC1 Takes the Lead in Solid Tumors

Three GTPases, RAC, RHO, and Cdc42, play essential roles in coordinating many cellular functions during embryonic development, both in healthy cells and in disease conditions like cancers. We have presented patterns of distribution of the frequency of RAC1-alteration(s) in cancers as obtained from cBioPortal. With this background data, we have interrogated the various functions of RAC1 in tumors, including proliferation, metastasis-associated phenotypes, and drug-resistance with a special emphasis on solid tumors in adults. We have reviewed the activation and regulation of RAC1 functions on the basis of its sub-cellular localization in tumor cells. Our review focuses on the role of RAC1 in cancers and summarizes the regulatory mechanisms, inhibitory efficacy, and the anticancer potential of RAC1-PAK targeting agents.

RHOG Activates RAC1 through CDC42 Leading to Tube Formation in Vascular Endothelial Cells

Angiogenesis is a hallmark of cancer cell malignancy. The role of the RHO family GTPase RHOG in angiogenesis in vascular endothelial cells has recently been elucidated. However, the regulation of RHOG during this process, as well as its cross-talk with other RHO GTPases, have yet to be fully examined. In this study, we found that siRNA-mediated depletion of RHOG strongly inhibits tube formation in vascular endothelial cells (ECV cells), an effect reversed by transfecting dominant active constructs of CDC42 or RAC1 in the RHOG-depleted cells. We also found CDC42 to be upstream from RAC1 in these cells. Inhibiting either Phosphatidyl inositol (3) kinase (PI3K) with Wortmannin or the mitogen-activated protein kinase extracellular-regulated kinase (MAPK ERK) with U0126 leads to the inhibition of tube formation. While knocking down either RHO, GTPase did not affect p-AKT levels, and p-ERK decreased in response to the knocking down of RHOG, CDC42 or RAC1. Recovering active RHO GTPases in U0126-treated cells also did not reverse the inhibition of tube formation, placing ERK downstream from PI3K-RHOG-CDC42-RAC1 in vascular endothelial cells. Finally, RHOA and the Rho activated protein kinases ROCK1 and ROCK2 positively regulated tube formation independently of ERK, while RHOC seemed to inhibit the process. Collectively, our data confirmed the essential role of RHOG in angiogenesis, shedding light on a potential new therapeutic target for cancer malignancy and metastasis.

Ovarian Tumor Microenvironment Signaling: Convergence on the Rac1 GTPase

The tumor microenvironment for epithelial ovarian cancer is complex and rich in bioactive molecules that modulate cell-cell interactions and stimulate numerous signal transduction cascades. These signals ultimately modulate all aspects of tumor behavior including progression, metastasis and therapeutic response. Many of the signaling pathways converge on the small GTPase Ras-related C3 botulinum toxin substrate (Rac)1. In addition to regulating actin cytoskeleton remodeling necessary for tumor cell adhesion, migration and invasion, Rac1 through its downstream effectors, regulates cancer cell survival, tumor angiogenesis, phenotypic plasticity, quiescence, and resistance to therapeutics. In this review we discuss evidence for Rac1 activation within the ovarian tumor microenvironment, mechanisms of Rac1 dysregulation as they apply to ovarian cancer, and the potential benefits of targeting aberrant Rac1 activity in this disease. The potential for Rac1 contribution to extraperitoneal dissemination of ovarian cancer is addressed.

Cgnl1, an endothelial junction complex protein, regulates GTPase mediated angiogenesis

Aims

The formation of cell–cell and cell–extra cellular matrix (ECM) contacts by endothelial cells (ECs) is crucial for the stability and integrity of a vascular network. We previously identified cingulin-like 1 (Cgnl1) in a transcriptomic screen for new angiogenic modulators. Here we aim to study the function of the cell–cell junction associated protein Cgnl1 during vessel formation.

Methods and results

Unlike family member cingulin, Cgnl1 expression is enriched in ECs during vascular growth. Cgnl1 is important for the formation of multicellular tubule structures, as shown in vitro using loss-of function assays in a 3D matrix co-culture system that uses primary human ECs and supporting mural cells. Further studies revealed that Cgnl1 regulates vascular growth by promoting Ve-cadherin association with the actin cytoskeleton, thereby stabilizing adherens junctions. Cgnl1 also regulates focal adhesion assembly in response to ECM contact, promoting vinculin and paxillin recruitment and focal adhesion kinase signalling. In vivo, we demonstrate in a postnatal retinal vascular development model in mice that Cgnl1 function is crucial for sustaining neovascular growth and stability.

Conclusions

Our data demonstrate a functional relevance for Cgnl1 as a defining factor in new vessel formation both in vitro and in vivo.

RHO GTPases in cancer: known facts, open questions, and therapeutic challenges

RHO GTPases have been traditionally associated with protumorigenic functions. While this paradigm is still valid in many cases, recent data have unexpectedly revealed that RHO proteins can also play tumor suppressor roles. RHO signaling elements can also promote both pro- and antitumorigenic effects using GTPase-independent mechanisms, thus giving an extra layer of complexity to the role of these proteins in cancer. Consistent with these variegated roles, both gain- and loss-of-function mutations in RHO pathway genes have been found in cancer patients. Collectively, these observations challenge long-held functional archetypes for RHO proteins in both normal and cancer cells. In this review, I will summarize these data and discuss new questions arising from them such as the functional and clinical relevance of the mutations found in patients, the mechanistic orchestration of those antagonistic functions in tumors, and the pros and cons that these results represent for the development of RHO-based anticancer drugs.

VEGF-neuropilin-2 signaling promotes stem-like traits in breast cancer cells by TAZ-mediated repression of the Rac GAP β2-chimaerin

The role of vascular endothelial growth factor (VEGF) signaling in cancer is not only well known in the context of angiogenesis but also important in the functional regulation of tumor cells. Autocrine VEGF signaling mediated by its co-receptors called neuropilins (NRPs) appears to be essential for sustaining the proliferation and survival of cancer stem cells (CSCs), which are implicated in mediating tumor growth, progression, and drug resistance. Therefore, understanding the mechanisms involved in VEGF-mediated support of CSCs is critical to successfully treating cancer patients. The expression of the Hippo effector TAZ is associated with breast CSCs and confers stem cell-like properties. We found that VEGF-NRP2 signaling contributed to the activation of TAZ in various breast cancer cells, which mediated a positive feedback loop that promoted mammosphere formation. VEGF-NRP2 signaling activated the GTPase Rac1, which inhibited the Hippo kinase LATS, thus leading to TAZ activity. In a complex with the transcription factor TEAD, TAZ then bound and repressed the promoter of the gene encoding the Rac GTPase-activating protein (Rac GAP) β2-chimaerin. By activating GTP hydrolysis, Rac GAPs effectively turn off Rac signaling; hence, the TAZ-mediated repression of β2-chimaerin resulted in sustained Rac1 activity in CSCs. Depletion of β2-chimaerin in non-CSCs increased Rac1 activity, TAZ abundance, and mammosphere formation. Analysis of a breast cancer patient database revealed an inverse correlation between β2-chimaerin and TAZ expression in tumors. Our findings highlight an unexpected role for β2-chimaerin in a feed-forward loop of TAZ activation and the acquisition of CSC properties.

Oncogenic epithelial cell-derived exosomes containing Rac1 and PAK2 induce angiogenesis in recipient endothelial cells

The metastatic cascade describes the escape of primary tumour cells to distant secondary sites. Cells at the leading tumour edge are thought to undergo epithelial-mesenchymal transition (EMT), to enhance their motility and invasion for spreading. Whether EMT cells directly promote tumour angiogenesis, and the role of exosomes (30-150 nm extracellular vesicles) remains largely unknown. We examined the functional effects of exosomes from MDCK cells, MDCK cells stably expressing YBX1 (MDCK^YBX1, intermediate EMT), and Ras-transformed MDCK cells (21D1 cells, complete EMT). 2F-2B cell motility and tube formation (length and branching) was significantly increased following supplementation with MDCK^YBX1 or 21D1 exosomes, but not MDCK exosomes. Next, Matrigel™ plugs containing exosome-supplemented 2F-2B cells were subcutaneously injected into mice. Systemic perfusion was only observed for plugs supplemented with MDCK^YBX1 or 21D1 exosomes. Comparative proteomics revealed that 21D1 exosomes contained VEGF-associated proteins, while MDCK^YBX1 exosomes were enriched with activated Rac1 and PAK2. To validate, 2F-2B cells and HUVECs were pre-treated with PAK inhibitors prior to exosome supplementation. PAK inhibition nullified the effects of MDCK^YBX1 exosomes by reducing the tube length and branching to baseline levels. By contrast, the effects of 21D1 exosomes were not significantly decreased. Our results demonstrate for the first time that oncogenic cells undergoing EMT can communicate with endothelial cells via exosomes, and establish exosomal Rac1/PAK2 as angiogenic promoters that may function from early stages of the metastatic cascade.

Small G protein Rac GTPases regulate the maintenance of glioblastoma stem-like cells in vitro and in vivo

Glioblastoma is the most common and aggressive malignant brain tumor in adults. The existence of glioblastoma stem cells (GSCs) or stem-like cells (stemloids) may account for its invasiveness and high recurrence. Rac proteins belong to the Rho small GTPase subfamily which regulates cell movement, proliferation, and survival. To investigate whether Rac proteins can serve as therapeutic targets for glioblastoma, especially for GSCs or stemloids, we examined the potential roles of Rac1, Rac2 and Rac3 on the properties of tumorspheres derived from glioblastoma cell lines. Tumorspheres are thought to be glioblastoma stem-like cells. We showed that Rac proteins promote the STAT3 and ERK activation and enhance cell proliferation and colony formation of glioblastoma stem-like cells. Knockdown of Rac proteins reduces the expression of GSC markers, such as CD133 and Sox2. The in vivo effects of Rac proteins in glioblastoma were further studied in zebrafish and in the mouse xenotransplantation model. Knocking-down Rac proteins abolished the angiogenesis effect induced by the injected tumorspheres in zebrafish model. In the CD133+-U373-tumorsphere xenotransplanted mouse model, suppression of Rac proteins decreased the incidence of tumor formation and inhibited the tumor growth. Moreover, knockdown of Rac proteins reduced the sphere forming efficiency of cells derived from these tumors. In conclusion, not only Rac1 but also Rac2 and 3 are important for glioblastoma tumorigenesis and can serve as the potential therapeutic targets against glioblastoma and its stem-like cells.

Phosphatase POPX2 Exhibits Dual Regulatory Functions in Cancer Metastasis

Cancer metastasis is a complex mechanism involving multiple processes. Previously, our integrative proteome, transcriptome, and phosphoproteome study reported that the levels of serine/threonine phosphatase POPX2 were positively correlated with cancer cell motility through modulating MAPK signaling. Surprisingly, here we found that POPX2 knockdown cells induced more numerous and larger tumor nodules in lungs in longer term animal studies. Interestingly, our analysis of DNA microarray data from cancer patient samples that are available in public databases shows that low POPX2 expression is linked to distant metastasis and poor survival rate. These observations suggest that lower levels of POPX2 may favor tumor progression in later stages of metastasis. We hypothesize that POPX2 may do so by modulation of angiogenesis. Secretome analysis of POPX2-knockdown MDA-MB-231 cells using LC-MS/MS-based SILAC quantitative proteomics and cytokine array show that silencing of POPX2 leads to increased secretion of exosomes, which may, in turn, induce multiple pro-angiogenic cytokines. This study, combined with our previous findings, suggests that a single ubiquitously expressed phosphatase POPX2 influences cancer metastasis via modulating multiple biological processes including MAPK signaling and exosome cytokine secretion.

Endothelial Cells Require CD98 for Efficient Angiogenesis-Brief Report

OBJECTIVE

CD98 regulates integrin signaling and is critical for tumor cell proliferation. It is also expressed on endothelial cells (EC), but its role in angiogenesis is unclear.

APPROACH AND RESULTS

We used specific genetic targeting and antibody blockade approaches to examine the function of CD98 in EC proliferation, blood vessel growth, and tumor angiogenesis. It is upregulated on angiogenic ECs, and EC-specific deletion of CD98 in mice inhibited tumor growth, retinal angiogenesis, and EC proliferation. Reconstitution with CD98 mutants showed that integrin and CD98 interaction is necessary for EC survival and growth. Moreover, anti-CD98 treatment inhibited vessel formation and reversed EC-assisted tumor growth.

CONCLUSIONS

Our findings demonstrate a requirement for CD98 in EC growth and suggest that CD98-specific reagents could have a dual anticancer effect: directly by inhibiting tumor cell proliferation and indirectly by preventing tumor angiogenesis.

Tenascin-C induces resistance to apoptosis in pancreatic cancer cell through activation of ERK/NF-κB pathway

As a glycol-protein located in extracellular matrix (ECM), tenascin-C (TNC) is absent in most normal adult tissues but is highly expressed in the majority of malignant solid tumors. Pancreatic cancer is characterized by an abundant fibrous tissue rich in TNC. Although it was reported that TNC's expression increased in the progression from low-grade precursor lesions to invasive cancer and was associated with tumor differentiation in human pancreatic cancer, studies on the relations between TNC and tumor progression in pancreatic cancer were rare. In this study, we performed an analysis to determine the effects of TNC on modulating cell apoptosis and chemo-resistance and explored its mechanisms involving activation in pancreatic cancer cell. The expressions of TNC, ERK1/2/p-ERK1/2, Bcl-xL and Bcl-2 were detected by immunohistochemistry and western blotting. Then the effects of exogenous and endogenous TNC on the regulation of tumor proliferation, apoptosis and gemcitabine cytotoxicity were investigated. The associations among the TNC knockdown, TNC stimulation and expressions of ERK1/2/NF-κB/p65 and apoptotic regulatory proteins were also analyzed in cell lines. The mechanism of TNC on modulating cancer cell apoptosis and drug resistant through activation of ERK1/2/NF-κB/p65 signals was evaluated. The effect of TNC on regulating cell cycle distribution was also tested. TNC, ERK1/2/p-ERK1/2, and apoptotic regulatory proteins Bcl-xL and Bcl-2 were highly expressed in human pancreatic cancer tissues. In vitro, exogenous TNC promoted pancreatic cancer cell growth also mediates basal as well as starved and drug-induced apoptosis in pancreatic cancer cells. The effects of TNC on anti-apoptosis were induced by the activation state of ERK1/2/NF-κB/p65 signals in pancreatic cell. TNC phosphorylate ERK1/2 to induce NF-κB/p65 nucleus translocation. The latter contributes to promote Bcl-xL, Bcl-2 protein expressions and reduce caspase activity, which inhibit cell apoptotic processes. TNC mediated gemcitabine chemo-resistance via modulating cell apoptosis in pancreatic cancer. TNC resulted in the enrichment of pancreatic cancer cells in S-phase with a concomitant decrease in number of cells in G1 phase. The present study indicated TNC in cellular matrix induces an activation of ERK1/2/NF-κB/p65 signaling cascade and thereby mediates resistance to apoptosis in pancreatic cancer. TNC could serve as a diagnostic marker and predictor of gemcitabine response and potentially as a target for chemotherapy of pancreatic cancer.

Overexpression of P21-activated kinase 4 is associated with poor prognosis in non-small cell lung cancer and promotes migration and invasion

BACKGROUND

P21-activated kinase 4 (PAK4), an effector of the Rho family protein Cdc42, is an important oncogene whose expression is increased in many human cancers and is generally positively correlated with advanced disease and decreased survival. However, little is known about the expression and biological function of PAK4 in human non-small cell lung cancer (NSCLC).

METHODS

PAK4 expression in NSCLC tissues and adjacent non-tumor tissues were assessed by immunohistochemistry, real-time PCR, and western blotting. Prognostic value of PAK4 expression was evaluated by Kaplan-Meier analysis and Cox regression. siRNA-mediated gene silencing and protein kinase assay was applied to demonstrate the role and the mechanism of PAK4 in lung cancer cell migration, invasion.

RESULTS

The results showed that PAK4 was overexpressed in NSCLC cell lines and human NSCLC tissues. PAK4 expression was detected both in the membranes and cytoplasm of NSCLC cancer cells in vivo. Moreover, increased expression of PAK4 was associated with metastasis, shorter overall survival, advanced stage of NSCLC. Furthermore, PAK4 expression was positively correlated with phosphorylation of LIMK1 expression levels. Knockdown of PAK4 in NSCLC cell lines led to reduce the phosphorylation of LIMK1, which resulted in decrease of the cell migration and invasion. In addition, PAK4 bound to LIMK1 directly and activated it via phosphorylation.

CONCLUSIONS

These data demonstrate that PAK4 mediated LIMK1 phosphorylation regulates the migration and invasion in NSCLC. Therefore, PAK4 might be a significant prognostic marker and potential therapeutic molecular target in NSCLC.

Kaposi's sarcoma-associated herpesvirus microRNAs repress breakpoint cluster region protein expression, enhance Rac1 activity, and increase in vitro angiogenesis

MicroRNAs (miRNAs) are small, ∼ 22-nucleotide-long RNAs that regulate gene expression posttranscriptionally. Kaposi's sarcoma-associated herpesvirus (KSHV) encodes 12 pre-miRNAs during latency, and the functional significance of these microRNAs during KSHV infection and their cellular targets have been emerging recently. Using a previously reported microarray profiling analysis, we identified breakpoint cluster region mRNA (Bcr) as a cellular target of the KSHV miRNA miR-K12-6-5p (miR-K6-5). Bcr protein levels were repressed in human umbilical vein endothelial cells (HUVECs) upon transfection with miR-K6-5 and during KSHV infection. Luciferase assays wherein the Bcr 3' untranslated region (UTR) was cloned downstream of a luciferase reporter showed repression in the presence of miR-K6-5, and mutation of one of the two predicted miR-K6-5 binding sites relieved this repression. Furthermore, inhibition or deletion of miR-K6-5 in KSHV-infected cells showed increased Bcr protein levels. Together, these results show that Bcr is a direct target of the KSHV miRNA miR-K6-5. To understand the functional significance of Bcr knockdown in the context of KSHV-associated disease, we hypothesized that the knockdown of Bcr, a negative regulator of Rac1, might enhance Rac1-mediated angiogenesis. We found that HUVECs transfected with miR-K6-5 had increased Rac1-GTP levels and tube formation compared to HUVECs transfected with control miRNAs. Knockdown of Bcr in latently KSHV-infected BCBL-1 cells increased the levels of viral RTA, suggesting that Bcr repression by KSHV might aid lytic reactivation. Together, our results reveal a new function for both KSHV miRNAs and Bcr in KSHV infection and suggest that KSHV miRNAs, in part, promote angiogenesis and lytic reactivation.

IMPORTANCE

Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) infection is linked to multiple human cancers and lymphomas. KSHV encodes small nucleic acids (microRNAs) that can repress the expression of specific human genes, the biological functions of which are still emerging. This report uses a variety of approaches to show that a KSHV microRNA represses the expression of the human gene called breakpoint cluster region (Bcr). Repression of Bcr correlated with the activation of a protein previously shown to cause KS-like lesions in mice (Rac1), an increase in KS-associated phenotypes (tube formation in endothelial cells and vascular endothelial growth factor [VEGF] synthesis), and modification of the life cycle of the virus (lytic replication). Our results suggest that KSHV microRNAs suppress host proteins and contribute to KS-associated pathogenesis.

Dexamethasone increases Cdc42 expression in human TM-1 cells

PURPOSE

Changes in the cytoskeletal organization of the human trabecular meshwork (HTM) is thought to be responsible for primary open-angle glaucoma (POAG) pathologies. Cdc42 is a Rho GTPase; Rho GTPases are important modulatory agents of the cytoskeleton. This study aimed to investigate the effects of dexamethasone (DEX) on Cdc42 in a transformed HTM cell line, TM-1 to understand the molecular pathologies underlying POAG.

METHODS

TM-1 cells were cultured in vitro. The cultures were treated with DEX at 10(-6) and 10(-7) M for 1-4 days. Cdc42 was silenced using small interfering RNA (siRNA). The expression levels of Cdc42 in the TM-1 cells were measured using reverse transcription (RT)-PCR, western blotting analysis and immunofluorescence. Its downstream effectors, p21-activated kinase phosphorylation (phospho-PAK) and myosin light chain kinase (MLCK), were measured using western blotting analysis. In addition, the F-actin of TM-1 cells was stained using phalloidin.

RESULTS

The mRNA and protein levels of Cdc42 showed an increase in TM-1 cells with DEX treatment and a decrease in TM-1 cells transfected with Cdc42 siRNA. Moreover, phospho-PAK levels increased, whereas MLCK levels appeared to decrease, with DEX treatment. The F-actin of DEX-treated TM-1 cells displayed a rearrangement. Cdc42 siRNA decreased the expression of Cdc42 and its related proteins, resulting in an attenuation of the effects of DEX on Cdc42 and F-actin organization in TM-1 cells.

CONCLUSIONS

DEX increases Cdc42 expression in TM-1. This may represent a potential mechanism of DEX-induced HTM cytoskeletal rearrangement.

Repression of choroidal neovascularization through actin cytoskeleton pathways by microRNA-24

Actin cytoskeleton is critical for cell motility and division, both of which are important for angiogenesis. MicroRNAs (miRNA/miR) are emerging as pivotal modulators of vascular development and disease. How miRNAs regulate actin cytoskeleton dynamics in endothelial cells (EC) and neovascularization is still unclear. Here, we report that miR-24 regulates actin dynamics in ECs through targeting multiple members downstream of Rho signaling, including Pak4, Limk2, and Diaph1 proteins. Overexpression of miR-24 in ECs blocks stress fiber and lamellipodia formation, represses EC migration, proliferation, and tube formation in vitro, as well as angiogenesis in an ex vivo aortic ring assay. Moreover, subretinal delivery of miR-24 mimics represses laser-induced choroidal neovascularization (CNV) in vivo. Mechanistically, knockdown of miR-24 target protein LIMK2 or PAK4 inhibits stress fiber formation and tube formation in vitro, mimicking miR-24 overexpression phenotype in angiogenesis, while overexpression of LIMK2 and PAK4 by adenoviruses partially rescued the tube formation defects in miR-24 overexpressing ECs. Taken together, these findings suggest that miR-24 represses angiogenesis by simultaneously regulating multiple components in the actin cytoskeleton pathways. Manipulation of actin cytoskeleton pathways by miR-24 may represent an attractive therapeutic solution for the treatment of wet age-related macular degeneration (AMD) and other vascular diseases.

Thy-1-induced migration inhibition in vascular endothelial cells through reducing the RhoA activity

Our previous study indicated that Thy-1, which is expressed on blood vessel endothelium in settings of pathological and a specific of physiological, but not during embryonic, angiogenesis, may be used as a marker for angiogenesis. However, the function of Thy-1 during angiogenesis is still not clear. Here, we demonstrate that knock-down of the endogenous Thy-1 expression by Thy-1 siRNA transfection promoted the migration of human umbilical vein endothelial cells (HUVEC). In contrast, treatment with interleukin-1β (IL-1β) or phorbol-12-myristate-13-acetate (PMA) increased the level of Thy-1 protein and reduced the migration of HUVEC. These effects were abolished by pre-transfection of HUVEC with Thy-1 siRNA to knock-down the expression of Thy-1. Moreover, over-expression of Thy-1 by transfection of HUVEC with Thy-1 pcDNA3.1 decreased the activity of RhoA and Rac-1 and inhibited the adhesion, migration and capillary-like tube formation of these cells. These effects were prevented by co-transfection of the cell with constitutively active RhoA construct (RhoA V14). On the other hand, pre-treatment with a ROCK (a kinase associated with RhoA for transducing RhoA signaling) inhibitor, Y27632, abolished the RhoA V14-induced prevention effect on the Thy-1-induced inhibition of endothelial cell migration and tube formation. Taken together, these results indicate that suppression of the RhoA-mediated pathway might participate in the Thy-1-induced migration inhibition in HUVEC. In the present study, we uncover a completely novel role of Thy-1 in endothelial cell behaviors.

The vascular-disrupting agent combretastatin impairs splitting and sprouting forms of physiological angiogenesis

OBJECTIVE

Vascular-disrupting agents like combretastatin (CA-4-P), used to attenuate tumor blood flow in vivo, exert anti-mitotic and anti-migratory effects on endothelial cells in vitro. We tested whether anti-vascular or anti-angiogenic effects of CA-4-P are evident with physiological angiogenesis in skeletal muscle (EDL) due to sustained hyperemia (intraluminal splitting) and chronic muscle overload (abluminal sprouting).

METHODS

CA-4-P was given i.v. (25 mg/kg on alternate days for 14 days) to mice subjected to angiogenic stimuli (prazosin or synergist extirpation). The responses of femoral artery blood flow as well as capillarity, capillary ultrastructure, and levels of Rho GTPase were measured.

RESULTS

Blood flow was unaffected in the sprouting angiotype, but decreased in the splitting angiotype, by CA-4-P. In contrast, CA-4-P attenuated the capillarity increase in both models, associated with reduced lamellipodia and filopodia formation. Muscle overload, but not hyperemia, was accompanied by an increase in Rho GTPase with CA-4-P.

CONCLUSIONS

CA-4-P impaired the angiogenic response in both experimental models. This inhibitory effect was associated with a lower increase in femoral blood flow in splitting, whereas sprouting angiogenesis was accompanied by higher Rho activity consistent with the interruption of actin polymerization. Thus, CA-4-P may exert context-dependent anti-vascular and anti-angiogenic effects in vivo under physiological conditions.

Angiogenesis is a link between atherosclerosis and tumorigenesis: role of LOX-1

Angiogenesis is defined as the formation of new blood vessels sprouting from pre-existing vessels. It plays an important role not only in physiological situations such as embryonic vascular development and wound healing, but also in pathological conditions including atherogenesis and evolution and spread of certain tumors. Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), a receptor for oxidized low density lipoprotein (ox-LDL), is mainly expressed in endothelial cells. It has diverse physiological functions and it could be a link between atherogenesis and tumorigenesis. The risk factors for atherosclerosis like hypertension, diabetes mellitus and hyperlipidemia are associated with LOX-1. Dyslipidemia and obesity are also being recognized as risk factor for certain tumors. LOX-1 is also found to be important for maintaining the transformed state in developmentally diverse cancer cell lines and for tumor growth. There is emerging evidence that LOX-1 plays an important role in the angiogenesis process. In this review, we outline the roles of angiogenesis in atherogenesis and tumorigenesis, and describe the role of LOX-1 as a potential molecular target for blocking angiogenesis.

Prolactin-stimulated activation of ERK1/2 mitogen-activated protein kinases is controlled by PI3-kinase/Rac/PAK signaling pathway in breast cancer cells

There is strong evidence that deregulation of prolactin (PRL) signaling contributes to pathogenesis and chemoresistance of breast cancer. Therefore, understanding cross-talk between distinct signal transduction pathways triggered by activation of the prolactin receptor (PRL-R), is essential for elucidating the pathogenesis of metastatic breast cancer. In this study, we applied a sequential inhibitory analysis of various signaling intermediates to examine the hierarchy of protein interactions within the PRL signaling network and to evaluate the relative contributions of multiple signaling branches downstream of PRL-R to the activation of the extracellular signal-regulated kinases ERK1 and ERK2 in T47D and MCF-7 human breast cancer cells. Quantitative measurements of the phosphorylation/activation patterns of proteins showed that PRL simultaneously activated Src family kinases (SFKs) and the JAK/STAT, phosphoinositide-3 (PI3)-kinase/Akt and MAPK signaling pathways. The specific blockade or siRNA-mediated suppression of SFK/FAK, JAK2/STAT5, PI3-kinase/PDK1/Akt, Rac/PAK or Ras regulatory circuits revealed that (1) the PI3-kinase/Akt pathway is required for activation of the MAPK/ERK signaling cascade upon PRL stimulation; (2) PI3-kinase-mediated activation of the c-Raf-MEK1/2-ERK1/2 cascade occurs independent of signaling dowstream of STATs, Akt and PKC, but requires JAK2, SFKs and FAK activities; (3) activated PRL-R mainly utilizes the PI3-kinase-dependent Rac/PAK pathway rather than the canonical Shc/Grb2/SOS/Ras route to initiate and sustain ERK1/2 signaling. By interconnecting diverse signaling pathways PLR may enhance proliferation, survival, migration and invasiveness of breast cancer cells.

Examining the role of Rac1 in tumor angiogenesis and growth: a clinically relevant RNAi-mediated approach

Angiogenesis, the sprouting of new blood vessels from the pre-existing vasculature, is a well established target in anti-cancer therapy. It is thought that the Rho GTPase Rac1 is required during vascular endothelial growth factor (VEGF)-mediated angiogenesis. In the present study, we have used a clinically relevant RNA interference approach to silence Rac1 expression. Human umbilical vein endothelial cells were transiently transfected with non-specific control siRNA (siNS) or Rac1 siRNA (siRac1) using electroporation or Lipofectamine 2000. Functional assays with transfected endothelial cells were performed to determine the effect of Rac1 knockdown on angiogenesis in vitro. Silencing of Rac1 inhibited VEGF-mediated tube formation, cell migration, invasion and proliferation. In addition, treatment with Rac1 siRNA inhibited angiogenesis in an in vivo Matrigel plug assay. Intratumoral injections of siRac1 almost completely inhibited the growth of grafted Neuro2a tumors and reduced tumor angiogenesis. Together, these data indicate that Rac1 is an important regulator of VEGF-mediated angiogenesis. Knockdown of Rac1 may represent an attractive approach to inhibit tumor angiogenesis and growth.

cGMP-dependent protein kinases as potential targets for colon cancer prevention and treatment

In recent years, several antitumor signaling pathways mediated by the cGMP-dependent protein kinases have been identified in colon cancer cells. This review aims to present the mounting evidence in favor of cGMP/protein kinase G (PKG) signaling as a therapeutic strategy in colon cancer. The homeostatic and tumor suppressive effects of cGMP in the intestine are uncontested, but the signaling details are not understood. PKG is the central cGMP effector, and can block proliferation and tumor angiogenesis by inhibiting β-catenin/TCF and SOX9 signaling. Therapeutic activation of cGMP/PKG offers a promising avenue for the prevention and treatment of colon cancer, but additional preclinical studies are needed to fully understand the potential of this system.

IRX1 influences peritoneal spreading and metastasis via inhibiting BDKRB2-dependent neovascularization on gastric cancer

The overexpression of IRX1 gene correlates with the growth arrest in gastric cancer. Furthermore, overexpression of IRX1 gene suppresses peritoneal spreading and long distance metastasis. To explore the precise mechanisms, we investigated whether restoring IRX1 expression affects the angiogenesis or vasculogenic mimicry (VM). Human umbilical vein endothelial cells (HUVECs) and chick embryo and SGC-7901 gastric cancer cells were used for angiogenesis and VM analysis. Small interfering RNA was used for analyzing the function of BDKRB2, a downstream target gene of IRX1. As results, the remarkable suppression on peritoneal spreading and pulmonary metastasis of SGC-7901 cells by IRX1 transfectant correlates to reduced angiogenesis as well as VM formation. Using the supernatant from SGC-7901/IRX1 cells, we found a strong inhibiting effect on angiogenesis both in vitro and in chick embryo. SGC-7901/IRX1 cells revealed strong inhibiting effect on VM formation too. By gene-specific RNA interference for BDKRB2, or its effector PAK1, we got an effective inhibition on tube formation, cell proliferation, cell migration and invasion in vitro. In conclusion, enforcing IRX1 expression effectively suppresses peritoneal spreading and pulmonary metastasis via anti-angiogenesis and anti-VM mechanisms, in addition to previously found cell growth and invasion. BDKRB2 and its downstream effector might be potential targets for anti-cancer strategy.

Rac1-dependent intracellular superoxide formation mediates vascular endothelial growth factor-induced placental angiogenesis in vitro

Vascular endothelial growth factor (VEGF) is one of the best characterized angiogenic factors controlling placental angiogenesis; however, how VEGF regulates placental angiogenesis has not yet completely understood. In this study, we found that all the components of assembling a functional NADPH oxidase (NOX2, p22(phox), p47(phox), p67(phox), and Rac1) are expressed in ovine fetoplacental artery endothelial cells (oFPAECs) in vitro and ex vivo. Treatment with VEGF (10 ng/ml) rapidly and transiently activated Rac1 in oFPAECs in vitro and increased Rac1 association with p67(phox) in 5 min. Intracellular superoxide formation began to significantly increase after 25-30 min of VEGF stimulation, which was mediated by both VEGFR1 and VEGFR2. VEGF also stimulated oFPAE cell proliferation and migration and enhanced the formation of tube-like structures on Matrigel matrix. In oFAPEC transfected with specific Rac1 small interfering RNA (siRNA, 40 nm), VEGF-induced intracellular superoxide formation was completely abrogated in association with a 78% reduction of endogenous Rac1. In oFPAE cells transfected with the specific Rac1 siRNA, but not with transfection reagent alone or scrambled control siRNA, VEGF-induced cell proliferation, migration, and tube-like structure formation were dramatically inhibited. Pretreatment of an NADPH oxidase inhibitor apocynin also abrogates the VEGF-stimulated intracellular superoxide production and DNA synthesis in oFPAECs. Taken together, our results demonstrated that a Rac1/Nox2-based NADPH oxidase system is present in placental endothelial cells. This NADPH oxidase system appears to generate the second messenger superoxide that plays a critical role in the signaling control of the VEGF-induced placental angiogenesis.

Suppression of uPA and uPAR attenuates angiogenin mediated angiogenesis in endothelial and glioblastoma cell lines

Background

In our earlier reports, we showed that downregulation of uPA and uPAR inhibited glioma tumor angiogenesis in SNB19 cells, and intraperitoneal injection of a hairpin shRNA expressing plasmid targeting uPA and uPAR inhibited angiogenesis in nude mice. The exact mechanism by which inhibition of angiogenesis takes place is not clearly understood.

Methodology/Principal Findings

In the present study, we have attempted to investigate the mechanism by which uPA/uPAR downregulation by shRNA inhibits angiogenesis in endothelial and glioblastoma cell lines. uPA/uPAR downregulation by shRNA in U87 MG and U87 SPARC co-cultures with endothelial cells inhibited angiogenesis as assessed by in vitro angiogenesis assay and in vivo dorsal skin-fold chamber model in nude mice. Protein antibody array analysis of co-cultures of U87 and U87 SPARC cells with endothelial cells treated with pU2 (shRNA against uPA and uPAR) showed decreased angiogenin secretion and angiopoietin-1 as well as several other pro-angiogenic molecules. Therefore, we investigated the role of angiogenin and found that nuclear translocation, ribonucleolytic and 45S rRNA synthesis, which are all critical for angiogenic function of angiogenin, were significantly inhibited in endothelial cells transfected with uPA, uPAR and uPA/uPAR when compared with controls. Moreover, uPA and uPAR downregulation significantly inhibited the phosphorylation of Tie-2 receptor and also down regulated FKHR activation in the nucleus of endothelial cells via the GRB2/AKT/BAD pathway. Treatment of endothelial cells with ruPA increased angiogenin secretion and angiogenin expression as determined by ELISA and western blotting in a dose-dependent manner. The amino terminal fragment of uPA down regulated ruPA-induced angiogenin in endothelial cells, thereby suggesting that uPA plays a critical role in positively regulating angiogenin in glioblastoma cells.

Conclusions/Significance

Taken together, our results suggest that uPA/uPAR downregulation suppresses angiogenesis in endothelial cells induced by glioblastoma cell lines partially by downregulation of angiogenin and by inhibition of the angiopoietin-1/AKT/FKHR pathway.

RhoA phosphorylation induces Rac1 release from guanine dissociation inhibitor alpha and stimulation of vascular smooth muscle cell migration

Although overactivation of RhoA is recognized as a common component of vascular disorders, the molecular mechanisms regulating RhoA activity in vascular smooth muscle cells (VSMC) are still unclear. We have previously shown that in VSMC, RhoA is phosphorylated on Ser188 by nitric oxide (NO)-stimulated cGMP-dependent kinase (PKG), which leads to RhoA-Rho kinase pathway inhibition. In this study, we showed that expression of phosphoresistant RhoA mutants prevented the stimulation of VSMC migration and adhesion induced by NO-PKG pathway activation. In contrast, under basal conditions, phosphomimetic RhoA mutants stimulated VSMC adhesion and migration through a signaling pathway requiring Rac1 and the Rho exchange factor Vav3. RhoA phosphorylation or phosphomimetic RhoA mutants induced Rac1 activation but did not activate Vav3. Indeed, phosphorylated RhoA or phosphomimetic mutants trapped guanine dissociation inhibitor α (GDIα), leading to the release of Rac1 and its translocation to the membrane, where it was then activated by the basal Vav3 nucleotide exchange activity. In vivo, RhoA phosphorylation induced by PKG activation in the aortas of rats treated with sildenafil induced dissociation of Rac1 from GDIα and activation of the Rac1 signaling pathway. These results suggest that the phosphorylation of RhoA represents a novel potent and physiological GDIα displacement factor that leads to Rac1 activation and regulation of Rac1-dependent VSMC functions.

Prediction of sphingosine 1-phosphate-stimulated endothelial cell migration rates using biochemical measurements

The ability to predict endothelial cell migration rates may aid in the design of biomaterials that endothelialize following implantation. However, the complexity of the signaling response to migration-promoting stimuli such as sphingosine 1-phosphate (S1P) makes such predictions quite challenging. A number of signaling pathways impact S1P-mediated cell migration, including the Akt and Src pathways, which both affect activation of the small GTPase Rac. Rac activation promotes the formation of lamellipodia, and thus should be intimately linked to cell migration rates. In immortalized endothelial cells, expression of proteins that inhibit Akt, Src, and Rac (PTEN, CSK, and beta2-chimaerin, respectively) was decreased using RNA interference, resulting in increases in the basal level of activation of Akt, Src, and Rac. Cells were scrape-wounded and stimulated with 1 microM S1P. The timecourse of Akt, Src, and Rac activation was followed over 2 h in the perturbed cells, while migration into the scrape wound was measured over 6 h. Rac activation at 120 min post-stimulation was highly correlated with the mean migration rate of cells, but only in cells stimulated with S1P. Using partial least squares regression, the migration rate of cells into the scrape wound was found to be highly correlated with the magnitude of the early Akt peak (e.g., 5-15 min post-stimulation). These results demonstrated that biochemical measurements might be useful in predicting rates of endothelial cell migration.

The PI3K p110alpha isoform regulates endothelial adherens junctions via Pyk2 and Rac1

Endothelial cell-cell junctions control efflux of small molecules and leukocyte transendothelial migration (TEM) between blood and tissues. Inhibitors of phosphoinositide 3-kinases (PI3Ks) increase endothelial barrier function, but the roles of different PI3K isoforms have not been addressed. In this study, we determine the contribution of each of the four class I PI3K isoforms (p110alpha, -beta, -gamma, and -delta) to endothelial permeability and leukocyte TEM. We find that depletion of p110alpha but not other p110 isoforms decreases TNF-induced endothelial permeability, Tyr phosphorylation of the adherens junction protein vascular endothelial cadherin (VE-cadherin), and leukocyte TEM. p110alpha selectively mediates activation of the Tyr kinase Pyk2 and GTPase Rac1 to regulate barrier function. Additionally, p110alpha mediates the association of VE-cadherin with Pyk2, the Rac guanine nucleotide exchange factor Tiam-1 and the p85 regulatory subunit of PI3K. We propose that p110alpha regulates endothelial barrier function by inducing the formation of a VE-cadherin-associated protein complex that coordinates changes to adherens junctions with the actin cytoskeleton.

Angiopoietin-like protein 2 promotes chronic adipose tissue inflammation and obesity-related systemic insulin resistance

Recent studies of obesity have provided new insights into the mechanisms underlying insulin resistance and metabolic dysregulation. Numerous efforts have been made to identify key regulators of obesity-linked adipose tissue inflammation and insulin resistance. We found that angiopoietin-like protein 2 (Angptl2) was secreted by adipose tissue and that its circulating level was closely related to adiposity, systemic insulin resistance, and inflammation in both mice and humans. Angptl2 activated an inflammatory cascade in endothelial cells via integrin signaling and induced chemotaxis of monocytes/macrophages. Constitutive Angptl2 activation in vivo induced inflammation of the vasculature characterized by abundant attachment of leukocytes to the vessel walls and increased permeability. Angptl2 deletion ameliorated adipose tissue inflammation and systemic insulin resistance in diet-induced obese mice. Conversely, Angptl2 overexpression in adipose tissue caused local inflammation and systemic insulin resistance in nonobese mice. Thus, Angptl2 is a key adipocyte-derived inflammatory mediator that links obesity to systemic insulin resistance.

Rasip1 is required for endothelial cell motility, angiogenesis and vessel formation

Ras proteins are small GTPases that regulate cellular growth and differentiation. Components of the Ras signaling pathway have been shown to be important during embryonic vasculogenesis and angiogenesis. Here, we report that Rasip1, which encodes a novel Ras-interacting protein, is strongly expressed in vascular endothelial cells throughout development, in both mouse and frog. Similar to the well-characterized vascular markers VEGFR2 and PECAM, Rasip1 is specifically expressed in angioblasts prior to vessel formation, in the initial embryonic vascular plexus, in the growing blood vessels during angiogenesis and in the endothelium of mature blood vessels into the postnatal period. Rasip1 expression is undetectable in VEGFR2 null embryos, which lack endothelial cells, suggesting that Rasip1 is endothelial specific. siRNA-mediated reduction of Rasip1 severely impairs angiogenesis and motility in endothelial cell cultures, and morpholino knockdown experiments in frog embryos demonstrate that Rasip1 is required for embryonic vessel formation in vivo. Together, these data identify Rasip1 as a novel endothelial factor that plays an essential role in vascular development.

Formation of endothelial lumens requires a coordinated PKCepsilon-, Src-, Pak- and Raf-kinase-dependent signaling cascade downstream of Cdc42 activation

In this study, we present data showing that Cdc42-dependent lumen formation by endothelial cells (ECs) in three-dimensional (3D) collagen matrices involves coordinated signaling by PKCepsilon in conjunction with the Src-family kinases (SFKs) Src and Yes. Activated SFKs interact with Cdc42 in multiprotein signaling complexes that require PKCepsilon during this process. Src and Yes are differentially expressed during EC lumen formation and siRNA suppression of either kinase, but not Fyn or Lyn, results in significant inhibition of EC lumen formation. Concurrent with Cdc42 activation, PKCepsilon- and SFK-dependent signaling converge to activate p21-activated kinase (Pak)2 and Pak4 in steps that are also required for EC lumen formation. Pak2 and Pak4 further activate two Raf kinases, B-Raf and C-Raf, leading to ERK1 and ERK2 (ERK1/2) activation, which all seem to be necessary for EC lumen formation. This work reveals a multicomponent kinase signaling pathway downstream of integrin-matrix interactions and Cdc42 activation involving PKCepsilon, Src, Yes, Pak2, Pak4, B-Raf, C-Raf and ERK1/2 to control EC lumen formation in 3D collagen matrices.

Host deficiency in Vav2/3 guanine nucleotide exchange factors impairs tumor growth, survival, and angiogenesis in vivo

Vav guanine nucleotide exchange factors modulate changes in cytoskeletal organization through activation of Rho, Rac, and Cdc42 small GTPases. Although Vav1 expression is restricted to the immune system, Vav2 and Vav3 are expressed in several tissues, including highly vascularized organs. Here, we provide the first evidence that Vav2 and Vav3 function within the tumor microenvironment to promote tumor growth, survival, and neovascularization. Host Vav2/3 deficiency reduced microvascular density, as well as tumor growth and/or survival, in transplanted B16 melanoma and Lewis lung carcinoma models in vivo. These defects were due in part to Vav2/3 deficiency in endothelial cells. Vav2/3-deficient endothelial cells displayed reduced migration in response to tumor cells in coculture migration assays, and failed to incorporate into tumor vessels and enhance tumor volume in tumor-endothelial cotransplantation experiments. These data suggest that Vav2/3 guanine nucleotide exchange factors play a critical role in host-mediated tumor progression and angiogenesis, particularly in tumor endothelium.

RNF13: a novel RING-type ubiquitin ligase over-expressed in pancreatic cancer

Protein ubiquitination by E3 ubiquitin ligases plays an important role in cancer development. In this study, we provide experimental evidence that a RING-finger-containing protein RNF13 is an ER/Golgi membrane-associated E3 ubiquitin ligase and its RING finger domain is required for the ubiquitin ligase activity. Immunohistochemical analysis of pancreatic ductal adenocarcinoma (PDAC) and paracancerous normal tissues from 72 patients documented RNF13 over-expression in 30 tumor samples (41.7%, 30/72), and its expression was significantly associated with histological grading (P = 0.024). In addition, RNF13 was detected in precancerous lesions: tubular complexes in chronic pancreatitis (CP) and pancreatic intraepithelial neoplasia (PanIN) (79.3%, 23/29 and 62.8%, 22/35, respectively). Moreover, RNF13 staining was significantly correlated with Tenascin-C expression (P = 0.004) in PDAC samples, further supporting the role of RNF13 in cancer progression. Over-expression of wild type but not RING domain-mutant RNF13 in pancreatic MiaPaca-2 cancer cells increased invasive potential and gelatinolytic activity by matrix metalloproteinase-9. Taken together, these findings reveal that RNF13 is a novel E3 ubiquitin ligase involved in pancreatic carcinogenesis; ubiquitin-mediated modification of proteins by RNF13 may participate in pancreatic cancer development.

Phosphodiesterase 2 mediates redox-sensitive endothelial cell proliferation and angiogenesis by thrombin via Rac1 and NADPH oxidase 2

Cyclic nucleotide phosphodiesterases (PDEs) control the levels of the second messengers cAMP and cGMP in many cell types including endothelial cells. Although PDE2 has the unique property to be activated by cGMP but to hydrolyze cAMP, its role in endothelial function is only poorly understood. Reactive oxygen species (ROS) have been recognized as signaling molecules controlling many endothelial functions. We thus investigated whether PDE2 would link to ROS generation and proliferative responses in human umbilical vein endothelial cells in response to thrombin. Thrombin stimulated the GTPase Rac1, known to activate NADPH oxidases, and enhanced ROS formation, whereas PDE2 inhibition or depletion by short hairpin (sh)RNA prevented these responses. Similar observations were made with 8-Br-cGMP or atrial natriuretic peptide. In agreement, thrombin elevated cGMP but decreased cAMP levels, whereas db-cAMP or forskolin diminished Rac1 activity and ROS production. Subsequently, PDE2 overexpression activated Rac1, increased ROS generation, and enhanced proliferation and in vitro capillary formation. These responses were not observed in the presence of inactive Rac1 or shRNA against the NADPH oxidase subunit NOX2. Inhibition or depletion of PDE2 also prevented thrombin-induced proliferation and capillary formation. Importantly, downregulation of PDE2 by lentiviral shRNA or PDE2 inhibition prevented vessel sprouting from mouse aortic explants and in vivo angiogenesis in a mouse model, respectively. In summary, PDE2 promotes activation of NADPH oxidase-dependent ROS production and subsequent endothelial proliferation and angiogenesis. Targeting PDE2 may provide a new therapeutic approach in diseases associated with endothelial dysfunction, oxidative stress, vascular proliferation, and angiogenesis.

Erbin and the NF2 tumor suppressor Merlin cooperatively regulate cell-type-specific activation of PAK2 by TGF-beta

Transforming growth factor beta (TGF-beta) family ligands are pleotropic proteins with diverse cell-type-specific effects on growth and differentiation. For example, PAK2 activation is critical for the proliferative/profibrotic action of TGF-beta on mesenchymal cells, and yet it is not responsive to TGF-beta in epithelial cells. We therefore investigated the regulatory constraints that prevent inappropriate PAK2 activation in epithelial cultures. The results show that the epithelial-enriched protein Erbin controls the function of the NF2 tumor suppressor Merlin by determining the output of Merlin's physical interactions with active PAK2. Whereas mesenchymal TGF-beta signaling induces PAK2-mediated inhibition of Merlin function in the absence of Erbin, Erbin/Merlin complexes bind and inactivate GTPase-bound PAK2 in epithelia. These results not only identify Erbin as a key determinant of epithelial resistance to TGF-beta signaling, they also show that Erbin controls Merlin tumor suppressor function by switching the functional valence of PAK2 binding.

14-3-3beta-Rac1-p21 activated kinase signaling regulates Akt1-mediated cytoskeletal organization, lamellipodia formation and fibronectin matrix assembly

Akt1 belongs to the three-gene Akt family and functions as a serine-threonine kinase regulating phosphorylation of an array of substrates and mediating cellular processes such as cell migration, proliferation, survival, and cell cycle. Our previous studies have established the importance of Akt1 in angiogenesis and absence of Akt1 resulted in impaired integrin activation, adhesion, migration, and extracellular matrix assembly by endothelial cells and fibroblasts. In this study, we identify the downstream signaling pathways activated by Akt1 in the regulation of these cellular events. We demonstrate here that Akt1 is necessary for the growth factor stimulated activation of 14-3-3beta-Rac1-p21 activated kinase (Pak) pathway in endothelial cells and fibroblasts. While activation of Akt1 resulted in translocation of Rac1 to membrane ruffles, enhanced Rac1 activity, Pak1 phosphorylation, and lamellipodia formation, resulting in enhanced adhesion and assembly of fibronectin, inhibition of Akt1 resulted in inhibition of these processes due to impaired Rac1-Pak signaling. Formation of lamellipodia, adhesion, and fibronectin assembly by myristoylated Akt1 expression in NIH 3T3 fibroblasts was inhibited by co-expression with either dominant negative Rac1 or dominant negative Pak1. In contrast, impaired lamellipodia formation, adhesion, and fibronectin assembly by dominant negative-Akt1 expression was rescued by co-expression with either constitutively active-Rac1 or -Pak1. Moreover, previously reported defects in adhesion and extracellular matrix assembly by Akt1(-/-) fibroblasts could be rescued by expression with either active-Rac1 or -Pak1, implying the importance of Rac1-Pak signaling in growth factor stimulated cytoskeletal assembly, lamellipodia formation and cell migration in endothelial cells and fibroblasts downstream of Akt1 activation.