Vascular endothelial growth factor-mediated activation of p38 is dependent upon Src and RAFTK/Pyk2

Role of LMCD1 in the Long-Term Effects of Angiotensin II in Vascular Smooth Muscle Cells

Excessive activity of the hormone angiotensin II (AngII) is known to contribute to the pathogenesis of multiple cardiovascular diseases, including atherosclerosis, vascular remodeling, and hypertension, primarily through inducing gene expression changes. In this study, we identified LMCD1 (LIM and cysteine-rich domains 1, also known as Dyxin), primarily recognized as a transcription co-factor involved in various oncogenic processes, cardiac hypertrophy, and vascular remodeling, as a potential key factor in AngII-mediated effects in vascular smooth muscle cells (VSMCs). We demonstrated that AngII upregulates LMCD1 expression in primary rat VSMCs through type 1 angiotensin receptor (AT1-R) activation, leading to calcium signaling and p38 MAPK pathway activation. Additionally, we also demonstrated in A7r5 vascular smooth muscle cells that LMCD1 protein overexpression results in enhanced cell proliferation and cell migration. Our findings provide insights into the mechanisms by which AngII mediates changes in LMCD1 expression. The elevated expression of LMCD1 enhanced the cell proliferation and migration in VSMCs in vitro experiments, suggesting that LMCD1 may be an important factor in vascular remodeling and the pathogenesis of severe cardiovascular diseases. These results raise the possibility that LMCD1 could be a promising pharmacological target in the cardiovascular dysfunctions associated with AT1-R overactivation.

Peptide RL-QN15 promotes wound healing of diabetic foot ulcers through p38 mitogen-activated protein kinase and smad3/miR-4482-3p/vascular endothelial growth factor B axis

Background

Wound management of diabetic foot ulcers (DFUs) is a complex and challenging task, and existing strategies fail to meet clinical needs. Therefore, it is important to develop novel drug candidates and discover new therapeutic targets. However, reports on peptides as molecular probes for resolving issues related to DFUs remain rare. This study utilized peptide RL-QN15 as an exogenous molecular probe to investigate the underlying mechanism of endogenous non-coding RNA in DFU wound healing. The aim was to generate novel insights for the clinical management of DFUs and identify potential drug targets.

Methods

We investigated the wound-healing efficiency of peptide RL-QN15 under diabetic conditions using in vitro and in vivo experimental models. RNA sequencing, in vitro transfection, quantitative real-time polymerase chain reaction, western blotting, dual luciferase reporter gene detection, in vitro cell scratches, and cell proliferation and migration assays were performed to explore the potential mechanism underlying the promoting effects of RL-QN15 on DFU repair.

Results

Peptide RL-QN15 enhanced the migration and proliferation of human immortalized keratinocytes (HaCaT cells) in a high-glucose environment and accelerated wound healing in a DFU rat model. Based on results from RNA sequencing, we defined a new microRNA (miR-4482-3p) related to the promotion of wound healing. The bioactivity of miR-4482-3p was verified by inhibiting and overexpressing miR-4482-3p. Inhibition of miR-4482-3p enhanced the migration and proliferation ability of HaCaT cells as well as the expression of vascular endothelial growth factor B (VEGFB). RL-QN15 also promoted the migration and proliferation ability of HaCaT cells, and VEGFB expression was mediated via inhibition of miR-4482-3p expression by the p38 mitogen-activated protein kinase (p38MAPK) and smad3 signaling pathways.

Conclusions

RL-QN15 is an effective molecule for the treatment of DFUs, with the underlying mechanism related to the inhibition of miR-4482-3p expression via the p38MAPK and smad3 signaling pathways, ultimately promoting re-epithelialization, angiogenesis and wound healing. This study provides a theoretical basis for the clinical application of RL-QN15 as a molecular probe in promoting DFU wound healing.

Therapeutic Targeting of NF-κB in Acute Lung Injury: A Double-Edged Sword

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a devastating disease that can be caused by a variety of conditions including pneumonia, sepsis, trauma, and most recently, COVID-19. Although our understanding of the mechanisms of ALI/ARDS pathogenesis and resolution has considerably increased in recent years, the mortality rate remains unacceptably high (~40%), primarily due to the lack of effective therapies for ALI/ARDS. Dysregulated inflammation, as characterized by massive infiltration of polymorphonuclear leukocytes (PMNs) into the airspace and the associated damage of the capillary-alveolar barrier leading to pulmonary edema and hypoxemia, is a major hallmark of ALI/ARDS. Endothelial cells (ECs), the inner lining of blood vessels, are important cellular orchestrators of PMN infiltration in the lung. Nuclear factor-kappa B (NF-κB) plays an essential role in rendering the endothelium permissive for PMN adhesion and transmigration to reach the inflammatory site. Thus, targeting NF-κB in the endothelium provides an attractive approach to mitigate PMN-mediated vascular injury, not only in ALI/ARDS, but in other inflammatory diseases as well in which EC dysfunction is a major pathogenic mechanism. This review discusses the role and regulation of NF-κB in the context of EC inflammation and evaluates the potential and problems of targeting it as a therapy for ALI/ARDS.

A microfluidic mammary gland coculture model using parallel 3D lumens for studying epithelial-endothelial migration in breast cancer

In breast cancer development, crosstalk between mammary epithelial cells and neighboring vascular endothelial cells is critical to understanding tumor progression and metastasis, but the mechanisms of this dynamic interplay are not fully understood. Current cell culture platforms do not accurately recapitulate the 3D luminal architecture of mammary gland elements. Here, we present the development of an accessible and scalable microfluidic coculture system that incorporates two parallel 3D luminal structures that mimic vascular endothelial and mammary epithelial cell layers, respectively. This parallel 3D lumen configuration allows investigation of endothelial-epithelial crosstalk and its effects of the comigration of endothelial and epithelial cells into microscale migration ports located between the parallel lumens. We describe the development and application of our platform, demonstrate generation of 3D luminal cell layers for endothelial cells and three different breast cancer cell lines, and quantify their migration profiles based on number of migrated cells, area coverage by migrated cells, and distance traveled by individual migrating cells into the migration ports. Our system enables analysis at the single-cell level, allows simultaneous monitoring of endothelial and epithelial cell migration within a 3D extracellular matrix, and has potential for applications in basic research on cellular crosstalk as well as drug development.

Sequential gene regulatory events leading to glucocorticoid-evoked apoptosis of CEM human leukemic cells:interactions of MAPK, MYC and glucocorticoid pathways

Gene expression responses to glucocorticoid (GC) in the hours preceding onset of apoptosis were compared in three clones of human acute lymphoblastic leukemia CEM cells. Between 2 and 20h, all three clones showed increasing numbers of responding genes. Each clone had many unique responses, but the two responsive clones showed a group of responding genes in common, different from the resistant clone. MYC levels and the balance of activities between the three major groups of MAPKs are known important regulators of glucocorticoid-driven apoptosis in several lymphoid cell systems. Common to the two sensitive clones were changed transcript levels from genes that decrease amounts or activity of anti-apoptotic ERK/MAPK1 and JNK2/MAPK9, or of genes that increase activity of pro-apoptotic p38/MAPK14. Down-regulation of MYC and several MYC-regulated genes relevant to MAPKs also occurred in both sensitive clones. Transcriptomine comparisons revealed probable NOTCH-GC crosstalk in these cells.

Lung Endothelial MicroRNA-1 Regulates Tumor Growth and Angiogenesis

RATIONALE

Vascular endothelial growth factor down-regulates microRNA-1 (miR-1) in the lung endothelium, and endothelial cells play a critical role in tumor progression and angiogenesis.

OBJECTIVES

To examine the clinical significance of miR-1 in non-small cell lung cancer (NSCLC) and its specific role in tumor endothelium.

METHODS

miR-1 levels were measured by Taqman assay. Endothelial cells were isolated by magnetic sorting. We used vascular endothelial cadherin promoter to create a vascular-specific miR-1 lentiviral vector and an inducible transgenic mouse. KRAS^{G12D mut}/Trp^53-/- (KP) mice, lung-specific vascular endothelial growth factor transgenic mice, Lewis lung carcinoma xenografts, and primary endothelial cells were used to test the effects of miR-1.

MEASUREMENTS AND MAIN RESULTS

In two cohorts of patients with NSCLC, miR-1 levels were lower in tumors than the cancer-free tissue. Tumor miR-1 levels correlated with the overall survival of patients with NSCLC. miR-1 levels were also lower in endothelial cells isolated from NSCLC tumors and tumor-bearing lungs of KP mouse model. We examined the significance of lower miR-1 levels by testing the effects of vascular-specific miR-1 overexpression. Vector-mediated delivery or transgenic overexpression of miR-1 in endothelial cells decreased tumor burden in KP mice, reduced the growth and vascularity of Lewis lung carcinoma xenografts, and decreased tracheal angiogenesis in vascular endothelial growth factor transgenic mice. In endothelial cells, miR-1 level was regulated through phosphoinositide 3-kinase and specifically controlled proliferation, de novo DNA synthesis, and ERK1/2 activation. Myeloproliferative leukemia oncogene was targeted by miR-1 in the lung endothelium and regulated tumor growth and angiogenesis.

CONCLUSIONS

Endothelial miR-1 is down-regulated in NSCLC tumors and controls tumor progression and angiogenesis.

Mechanisms and regulation of endothelial VEGF receptor signalling

Vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) are uniquely required to balance the formation of new blood vessels with the maintenance and remodelling of existing ones, during development and in adult tissues. Recent advances have greatly expanded our understanding of the tight and multi-level regulation of VEGFR2 signalling, which is the primary focus of this Review. Important insights have been gained into the regulatory roles of VEGFR-interacting proteins (such as neuropilins, proteoglycans, integrins and protein tyrosine phosphatases); the dynamics of VEGFR2 endocytosis, trafficking and signalling; and the crosstalk between VEGF-induced signalling and other endothelial signalling cascades. A clear understanding of this multifaceted signalling web is key to successful therapeutic suppression or stimulation of vascular growth.

Intracoronary Des-Acyl Ghrelin Acutely Increases Cardiac Perfusion Through a Nitric Oxide-Related Mechanism in Female Anesthetized Pigs

Des-acyl ghrelin (DAG), the most abundant form of ghrelin in humans, has been found to reduce arterial blood pressure and prevent cardiac and endothelial cell apoptosis. Despite this, data regarding its direct effect on cardiac function and coronary blood flow, as well as the related involvement of autonomic nervous system and nitric oxide (NO), are scarce. We therefore examined these issues using both in vivo and in vitro studies. In 20 anesthetized pigs, intracoronary 100 pmol/mL DAG infusion with a constant heart rate and aortic blood pressure, increased coronary blood flow and NO release, whereas reducing coronary vascular resistances (P < .05). Dose responses to DAG were evaluated in five pigs. No effects on cardiac contractility/relaxation or myocardial oxygen consumption were observed. Moreover, whereas the blockade of muscarinic cholinoceptors (n = 5) or α- and β-adrenoceptors (n = 5 each) did not abolish the observed responses, NO synthase inhibition (n = 5) prevented the effects of DAG on coronary blood flow and NO release. In coronary artery endothelial cells, DAG dose dependently increased NO release through cAMP signaling and ERK1/2, Akt, and p38 MAPK involvement as well as the phosphorylation of endothelial NO synthase. In conclusion, in anesthetized pigs, DAG primarily increased cardiac perfusion through the involvement of NO release. Moreover, the phosphorylation of ERK1/2 and Akt appears to play roles in eliciting the observed NO production in coronary artery endothelial cells.

Proline-rich tyrosine kinase 2 via enhancing signal transducer and activator of transcription 3-dependent cJun expression mediates retinal neovascularization

Despite the involvement of proline-rich tyrosine kinase 2 (Pyk2) in endothelial cell angiogenic responses, its role in pathological retinal angiogenesis is not known. In the present study, we show that vascular endothelial growth factor A (VEGFA) induces Pyk2 activation in mediating human retinal microvascular endothelial cell (HRMVEC) migration, sprouting and tube formation. Downstream to Pyk2, VEGFA induced signal transducer and activator of transcription 3 (STAT3) activation and cJun expression in the modulation of HRMVEC migration, sprouting and tube formation. Consistent with these observations, hypoxia induced activation of Pyk2-STAT3-cJun signaling axis and siRNA-mediated downregulation of Pyk2, STAT3 or cJun levels substantially inhibited hypoxia-induced retinal endothelial cell proliferation, tip cell formation and neovascularization. Together, these observations suggest that activation of Pyk2-mediated STAT3-cJun signaling is required for VEGFA-induced HRMVEC migration, sprouting and tube formation in vitro and hypoxia-induced retinal endothelial cell proliferation, tip cell formation and neovascularization in vivo.

Identification of an Endogenously Generated Cryptic Collagen Epitope (XL313) That May Selectively Regulate Angiogenesis by an Integrin Yes-associated Protein (YAP) Mechano-transduction Pathway

Extracellular matrix (ECM) remodeling regulates angiogenesis. However, the precise mechanisms by which structural changes in ECM proteins contribute to angiogenesis are not fully understood. Integrins are molecules with the ability to detect compositional and structural changes within the ECM and integrate this information into a network of signaling circuits that coordinate context-dependent cell behavior. The role of integrin αvβ3 in angiogenesis is complex, as evidence exists for both positive and negative functions. The precise downstream signaling events initiated by αvβ3 may depend on the molecular characteristics of its ligands. Here, we identified an RGD-containing cryptic collagen epitope that is generated in vivo. Surprisingly, rather than inhibiting αvβ3 signaling, this collagen epitope promoted αvβ3 activation and stimulated angiogenesis and inflammation. An antibody directed to this RGDKGE epitope but not other RGD collagen epitopes inhibited angiogenesis and inflammation in vivo. The selective ability of this RGD epitope to promote angiogenesis and inflammation depends in part on its flanking KGE motif. Interestingly, a subset of macrophages may represent a physiologically relevant source of this collagen epitope. Here, we define an endothelial cell mechano-signaling pathway in which a cryptic collagen epitope activates αvβ3 leading to an Src and p38 MAPK-dependent cascade that leads to nuclear accumulation of Yes-associated protein (YAP) and stimulation of endothelial cell growth. Collectively, our findings not only provide evidence for a novel mechano-signaling pathway, but also define a possible therapeutic strategy to control αvβ3 signaling by targeting a pro-angiogenic and inflammatory ligand of αvβ3 rather than the receptor itself.

[The Supernatant Obtained from Cultured Anip973 Cells Enhances the Biological Activities of HUVEC]

BACKGROUND AND OBJECTIVE

Unlike normal tissue-derived microvascular endothelial cells, tumor microvessel endothelial cells are highly reactive to growth factors and exhibit more adhesion molecules. Thus, vascular tumors are highly permeable and grow vigorously; this occurrence results in rapid growth and metastasis cancer cells. Therefore, understanding the characteristics of endothelial cells in the tumor microenvironment guides anti-angiogenic therapy. To this end, we explore the effect of the supernatant obtained from cultured Anip973 cells (high-metastatic human lung adenocarcinoma cells) on the biological behavior and on the cell surface markers of the human umbilical vein endothelial cell (HUVEC).

METHODS

The HUVEC that was cultured in a medium (RPMI-1640 + 10% fetal bovine serum) containing various concentrations of Anip973 supernatants was categorized into experimental groups. The HUVEC cultured in a medium without Anip973 supernatants served as the control group. Proliferation was determined with CCK-8; blood vessel formation was investigated with three-dimensional culture techniques in vitro; and HUVEC migration was observed via transwell assay. At the same time, the expressions of CD105, CD31, and the apoptotic marker of Annexin V were detected through flow cytometry for analyzing the relationship between the expression of cell surface markers and biological behavior.

RESULTS

Following incubation with the supernatant obtained from cultured Anip973 cells, HUVEC proliferated more than the control group did, and the proliferation rate was maximized when incubated in a supernatant concentration of 250 μL/mL for 24 h (P=0.002). In addition, the experimental groups exhibited varying degrees of migration and forms of vascular lumen sample structure, especially at supernatant concentrations of 125 µL/mL (P<0.001) and 250 µL/mL (P=0.002), respectively. CD105 expression was optimized at 250 μL/mL (P=0.028), and CD31 expression also increased with an increase in concentration. However, the percentage of apoptotic cells decreased. Correlation analysis results showed that cell proliferation, migration, and CD105 expression were significantly and positively correlated with one another. By contrast, no significant correlation was detected between CD31 expression and biological behavior.

CONCLUSIONS

Anip973 supernatants can promote HUVEC proliferation and migration, as well as angiogenesis. In addition, cell surface markers can change concurrently and relatively. To a certain extent, changes in CD105 expression can be attributed to shifts in its biological behavior.
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The Emerging Regulation of VEGFR-2 in Triple-Negative Breast Cancer

Vascular endothelial growth factor-A (VEGF) signals vascular development and angiogenesis mainly by binding to VEGF receptor family member 2 (VEGFR-2). Adaptor proteins mediate many VEGFR-2's functions in the development of blood vessels. Cancer cells secrete VEGF to activate VEGFR-2 pathway in their neighboring endothelial cells in the process of cancer-related angiogenesis. Interestingly, activation of VEGFR-2 signaling is found in breast cancer cells, but its role and regulation are not clear. We highlighted research advances of VEGFR-2, with a focus on VEGFR-2's regulation by mutant p53 in breast cancer. In addition, we reviewed recent Food and Drug Administration-approved tyrosine kinase inhibitor drugs that can inhibit the function of VEGFR-2. Ongoing preclinical and clinical studies might prove that pharmaceutically targeting VEGFR-2 could be an effective therapeutic strategy in treating triple-negative breast cancer.

Antidicer RNAse activity of monocyte chemotactic protein-induced protein-1 is critical for inducing angiogenesis

Inflammatory angiogenesis involves the induction of a novel gene ZC3H12A encoding monocyte chemoattractant protein-1 (MCP-1)-induced protein-1 (MCPIP1) that has deubiquitinase and antidicer RNAse activities. If and how these enzymatic activities of MCPIP1 mediate the biological functions of MCPIP1 are unknown. Present studies with human umbilical vein endothelial cells suggest that MCPIP-induced angiogenesis is mediated via hypoxia-inducible factor (HIF-1α), vascular endothelial growth factor (VEGF), and silent information regulator (SIRT-1) induction that results in the inhibition of angiogenesis inhibitor thrombospondin-1. MCPIP1 expression inhibited the production of the antiangiogenic microRNA (miR)-20b and -34a that repress the translation of HIF-1α and SIRT-1, respectively. The RNase-dead MCPIP mutant D141N not only did not induce angiogenesis but also failed to inhibit the production of miR-20b and -34a suggesting that the antidicer RNase activity of MCPIP1 is involved in MCPIP-mediated angiogenesis. Mimetics of miR-20b and -34a inhibited MCPIP1-induced angiogenesis confirming that MCPIP1 suppresses the biogenesis of miR-20b and -34a. Furthermore, our results indicate that MCPIP expression induces nuclear translocation of HIF-1α. We show that under hypoxia angiogenesis is mediated via induction of MCPIP1 and under normoxia, in vitro, MCPIP deubiquitinates ubiquitinated HIF-1α and the stabilized HIF-1α enters the nucleus to promote the transcription of its target genes, cyclooxygenase-2 and VEGF, suggesting that the deubiquitinase activity of MCPIP may also promote angiogenesis. The present results show for the first time that the antidicer RNase activity of MCPIP1 is critical in mediating a biological function of MCPIP, namely angiogenesis.

Vascular smooth muscle cell motility is mediated by a physical and functional interaction of Ca2+/calmodulin-dependent protein kinase IIδ2 and Fyn

In vascular smooth muscle (VSM) cells, Ca(2+)/calmodulin-dependent protein kinase IIδ2 (CaMKIIδ2) activates non-receptor tyrosine kinases and EGF receptor, with a Src family kinase as a required intermediate. siRNA-mediated suppression of Fyn, a Src family kinase, inhibited VSM cell motility. Simultaneous suppression of both Fyn and CaMKIIδ2 was non-additive, suggesting coordinated regulation of cell motility. Confocal immunofluorescence microscopy indicated that CaMKIIδ2 and Fyn selectively (compared with Src) co-localized with the Golgi in quiescent cultured VSM cells. Stimulation with PDGF resulted in a rapid (<5 min) partial redistribution and co-localization of both kinases in peripheral membrane regions. Furthermore, CaMKIIδ2 and Fyn selectively (compared with Src) co-immunoprecipitated, suggesting a physical interaction in a signaling complex. Stimulation of VSM cells with ionomycin, a calcium ionophore, resulted in activation of CaMKIIδ2 and Fyn and disruption of the complex. Pretreatment with KN-93, a pharmacological inhibitor of CaMKII, prevented activation-dependent disruption of CaMKIIδ2 and Fyn, implicating CaMKIIδ2 as an upstream mediator of Fyn. Overexpression of constitutively active CaMKII resulted in the dephosphorylation of Fyn at Tyr-527, which is required for Fyn activation. Taken together, these data demonstrate a dynamic interaction between CaMKIIδ2 and Fyn in VSM cells and indicate a mechanism by which CaMKIIδ2 and Fyn may coordinately regulate VSM cell motility.

LY2228820 dimesylate, a selective inhibitor of p38 mitogen-activated protein kinase, reduces angiogenic endothelial cord formation in vitro and in vivo

LY2228820 dimesylate is a highly selective small molecule inhibitor of p38α and p38β mitogen-activated protein kinases (MAPKs) that is currently under clinical investigation for human malignancies. p38 MAPK is implicated in a wide range of biological processes, in particular those that support tumorigenesis. One such process, angiogenesis, is required for tumor growth and metastasis, and many new cancer therapies are therefore directed against the tumor vasculature. Using an in vitro co-culture endothelial cord formation assay, a surrogate of angiogenesis, we investigated the role of p38 MAPK in growth factor- and tumor-driven angiogenesis using LY2228820 dimesylate treatment and by shRNA gene knockdown. p38 MAPK was activated in endothelial cells upon growth factor stimulation, with inhibition by LY2228820 dimesylate treatment causing a significant decrease in VEGF-, bFGF-, EGF-, and IL-6-induced endothelial cord formation and an even more dramatic decrease in tumor-driven cord formation. In addition to involvement in downstream cytokine signaling, p38 MAPK was important for VEGF, bFGF, EGF, IL-6, and other proangiogenic cytokine secretion in stromal and tumor cells. LY2228820 dimesylate results were substantiated using p38α MAPK-specific shRNA and shRNA against the downstream p38 MAPK effectors MAPKAPK-2 and HSP27. Using in vivo models of functional neoangiogenesis, LY2228820 dimesylate treatment reduced hemoglobin content in a plug assay and decreased VEGF-A-stimulated vascularization in a mouse ear model. Thus, p38α MAPK is implicated in tumor angiogenesis through direct tumoral effects and through reduction of proangiogenic cytokine secretion via the microenvironment.

Cytoskeletal architecture regulates cyclooxygenase-2 in human endothelial cells: autocrine modulation by prostacyclin

Endothelium is a highly dynamic tissue that controls vascular homeostasis. This requires constant rearrangements of the shape or function of endothelial cells that cannot set aside the role of the cytoskeleton. The aim of this study was to determine the mechanisms by means of which cytoskeletal alterations induce cyclooxygenase-2 (Cox-2) expression in human endothelial cells using compounds that interfere with microtubule or actin architecture. Microtubule disruption by nocodazole markedly increased Cox-2 expression and activity, and provoked paracellular gap formation, a cardinal feature of endothelial barrier dysfunction. The Cox-2 metabolite prostacyclin down-regulated Cox-2 through an autocrine receptor-mediated mechanism, and partially prevented the disassembly of endothelial monolayers. There was also an interaction between microtubules and actin filaments in nocodazole-induced Cox-2 expression. Nocodazole provoked the dissolution of the F-actin cortical ring and stress fiber formation, increased actin glutathionylation, and concomitantly lowered intracellular levels of reduced glutathione. The restoration of glutathione levels by N-acetylcysteine opposed Cox-2 expression and preserved the integrity of endothelial monolayers. Among the signaling pathways connecting microtubule disruption with Cox-2 up-regulation, crucial roles are played by Src family kinase activation, serine/threonine phosphatase 2A inhibition, and the phosphorylation of mitogen activated protein kinase p38. Our findings provide a mechanistic insight into the observation that Cox-2 is induced in endothelial cells under cytoskeleton-perturbing conditions such as those occurring in the presence of atherogenic/inflammatory stimuli and oxidative stress. In this scenario, Cox-2 up-regulation by endothelia exposed to noxious conditions can be considered protective of the vasodilatory and anti-thrombotic properties of the vessel wall.

Regulation of Rela/p65 and endothelial cell inflammation by proline-rich tyrosine kinase 2

We investigated the role of proline-rich tyrosine kinase 2 (Pyk2) in the mechanism of NF-κB activation and endothelial cell (EC) inflammation induced by thrombin, a procoagulant serine protease released in high amounts during sepsis and other inflammatory conditions. Stimulation of ECs with thrombin resulted in a time-dependent activation of Pyk2. RNA interference knockdown of Pyk2 attenuated thrombin-induced activity of NF-κB and expression of its target genes, vascular cell adhesion molecule-1 and monocyte chemoattractant protein-1. Pyk2 knockdown impaired thrombin-induced activation of IκB kinase (IKK) and phosphorylation (Ser32 and Ser36) of IkappaBα, but, surprisingly, failed to prevent IκBα degradation. However, depletion of IKKα or IKKβ was effective in inhibiting IκBα phosphorylation/degradation, as expected. Intriguingly, Pyk2 knockdown impaired nuclear translocation and DNA binding of RelA/p65, despite the inability to prevent IκBα degradation. In addition, Pyk2 knockdown was associated with inhibition of RelA/p65 phosphorylation at Ser536, which is important for transcriptional activity of RelA/p65. Depletion of IKKα or IKKβ each impaired RelA/p65 phosphorylation. Taken together, these data identify Pyk2 as a critical regulator of EC inflammation by virtue of engaging IKK to promote the release and the transcriptional capacity of RelA/p65, and, additionally, by its ability to facilitate the nuclear translocation of the released RelA/p65. Thus, specific targeting of Pyk2 may be an effective anti-inflammatory strategy in vascular diseases associated with EC inflammation and intravascular coagulation.

Pyk2 regulates H+-ATPase-mediated proton secretion in the outer medullary collecting duct via an ERK1/2 signaling pathway

Acid-secreting intercalated cells respond to changes in systemic pH through regulation of apical H(+) transporters. Little is known about the mechanism by which these cells sense changes in extracellular pH (pH(o)). Pyk2 is a nonreceptor tyrosine kinase activated by autophosphorylation at Tyr402 by cell-specific stimuli, including decreased pH, and is involved in the regulation of MAPK signaling pathways and transporter activity. We examined whether the Pyk2 and MAPK signaling pathway mediates the response of transport proteins to decreased pH in outer medullary collecting duct cells. Immunoblot analysis of phosphorylated Pyk2 (Tyr402), ERK1/2 (Thr202/Tyr204), and p38 (Thr180/Tyr182) was used to assay protein activation. To examine specificity of kinase activation and its effects, we used Pyk2 small interfering RNA to knockdown Pyk2 expression levels, the Src kinase inhibitor 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]-pyrimidine (PP 1) to inhibit Pyk2 phosphorylation, and the MEK inhibitor U0126 to inhibit ERK1/2 phosphorylation. The pH-sensitive fluorescent probe 2'-7'-bis(carboxyethyl)-5(6)-carboxyfluorescein-acetoxymethyl ester (BCECF-AM) was used to assay H(+) transporter activity. The activity of H(+) transporters was measured as the rate of intracellular pH (pH(i)) recovery after an NH(4)Cl prepulse. We show that Pyk2 is endogenously expressed and activated by acid pH in mouse-derived outer medullary collecting duct (mOMCD1) cells. Incubation of mOMCD1 cells in acid media [extracellular pH (pH(o)) 6.7] increased the phosphorylation of Pyk2, ERK1/2, and p38. Reduction in pH(i) induced by an NH(4)Cl prepulse also increased the phosphorylation of Pyk2, ERK1/2, and p38. Consistent with our previous studies, we found that mOMCD1 cells exhibit H(+)-ATPase and H(+),K(+)-ATPase activity. Pyk2 inhibition by Pyk2 siRNA and PP 1 prevented Pyk2 phosphorylation as well as H(+)-ATPase-mediated recovery in mOMCD1 cells. In addition, ERK1/2 inhibition by U0126 prevented acid-induced ERK1/2 phosphorylation and H(+)-ATPase-mediated pH(i) recovery but not phosphorylation of p38. We conclude that Pyk2 and ERK1/2 are required for increasing H(+)-ATPase, but not H(+),K(+)-ATPase, activity at decreased pH(i) in mOMCD1 cells.

High expression of proline-rich tyrosine kinase 2 is associated with poor survival of hepatocellular carcinoma via regulating phosphatidylinositol 3-kinase/AKT pathway

BACKGROUND

The peritumoral environment has been implicated to be important in the process of metastasis and recurrence in hepatocellular carcinoma (HCC). Our aims were to assess the prognostic value of proline-rich tyrosine kinase 2 (Pyk2) in HCC and investigate related molecular mechanism.

METHODS

Expression of Pyk2 was tested by immunohistochemistry in tissue microarrays containing 141 paired HCC samples. Correlation between Pyk2 and vascular endothelial growth factor (VEGF) expression in clinical samples was analyzed by Spearman rank correlation. Matrigel invasion, anchorage-independent growth assay and immunoblotting were performed to study the effect of Pyk2 on the invasion and progression of HCC cells and phosphoinositide 3-kinase (PI3K)/AKT pathway activation.

RESULTS

Higher Pyk2 density in both tumor and peritumor was associated with lower overall survival (P = 0.044; P = 0.041, respectively), serum AFP levels > 1,000 ng/ml (P = 0.013; P = 0.032, respectively) and postoperative distant metastasis (both P < 0.001). However, only higher peritumoral Pyk2 density was related to lower disease-free survival (P = 0.014) and vascular invasion (P = 0.035). A significant correlation between Pyk2 and VEGF density in tumor or peritumoral liver tissue was observed (r = 0. 3133, P = 0.0002; r = 0.5176, P < 0.0001, respectively). Immunoblotting showed that Pyk2 activated PI3K-AKT pathway to upregulate VEGF expression in HL-7702, SMMC-7721 and HepG2 cells.

CONCLUSIONS

High Pyk2, especially peritumoral Pyk2 was associated with poor survival, disease recurrence, and metastasis in HCC. PI3K-AKT pathway was involved in Pyk2-mediated VEGF expression during HCC progression and invasion.

Effect of dietary salt on regulation of TGF-β in the kidney

Dietary sodium chloride (salt) has long been considered injurious to the kidney by promoting the development of glomerular and tubulointerstitial fibrosis. Endothelial cells throughout the vasculature and glomeruli respond to increased dietary salt intake with increased production of transforming growth factor-β (TGF-β) and nitric oxide. High-salt intake activates large-conductance, voltage- and calcium-activated potassium (BK(Ca)) channels in endothelial cells. Activation of BK(Ca) channels promotes signaling through proline-rich tyrosine kinase-2, cellular-sarcoma (c-Src), Akt (also known as protein kinase B), and mitogen-activated protein kinase pathways that lead to endothelial production of TGF-β and nitric oxide. TGF-β signaling is broadly accepted as a strong stimulator of renal fibrosis. The classic description of TGF-β signaling pathology in renal disease involves signaling through Smad proteins resulting in extracellular matrix deposition and fibrosis. Active TGF-β1 also causes fibrosis by inducing epithelial-mesenchymal transition and apoptosis. By enhancing TGF-β signaling, increased dietary salt intake leads to progressive renal failure from nephron loss and glomerular and tubulointerstitial fibrosis.

Hck is a key regulator of gene expression in alternatively activated human monocytes

IL-13 is a Th2 cytokine that promotes alternative activation (M2 polarization) in primary human monocytes. Our studies have characterized the functional IL-13 receptor complex and the downstream signaling events in response to IL-13 stimulation in alternatively activated monocytes/macrophages. In this report, we present evidence that IL-13 induces the activation of a Src family tyrosine kinase, which is required for IL-13 induction of M2 gene expression, including 15-lipoxygenase (15-LO). Our data show that Src kinase activity regulates IL-13-induced p38 MAPK tyrosine phosphorylation via the upstream kinases MKK3 or MKK6. Our findings also reveal that the IL-13 receptor-associated tyrosine kinase Jak2 is required for the activation of both Src kinase as well as p38 MAPK. Further, we found that Src tyrosine kinase-mediated activation of p38 MAPK is required for Stat1 and Stat3 serine 727 phosphorylation in alternatively activated monocytes/macrophages. Additional studies identify Hck as the specific Src family member, stimulated by IL-13 and involved in regulating both p38 MAPK activation and p38 MAPK-mediated 15-LO expression. Finally we show that the Hck regulates the expression of other alternative state (M2)-specific genes (Mannose receptor, MAO-A, and CD36) and therefore conclude that Hck acts as a key regulator controlling gene expression in alternatively activated monocytes/macrophages.

Acetylation of a conserved lysine residue in the ATP binding pocket of p38 augments its kinase activity during hypertrophy of cardiomyocytes

Like phosphorylation, acetylation of lysine residues within a protein is considered a biologically relevant modification that controls the activity of target proteins. During stress of cells, massive protein acetylation takes place. Here, we show that p38 mitogen-activated protein kinase (MAPK), which controls many biological functions during stress, is reversibly acetylated by PCAF/p300 and HDAC3. We identified two acetylated lysine residues, K152 and K53, located in the substrate binding domain and in the ATP-binding pocket of p38, respectively. Acetylation of lysine 53 enhanced the activity of p38 by increasing its affinity for ATP binding. The enhanced acetylation and activation of p38 were found to be in parallel with reduced intracellular ATP levels in cardiomyocytes under stress, as well as in vivo models of cardiac hypertrophy. Thus, our data show, for the first time, that p38 activity is critically regulated by, in addition to phosphorylation, reversible acetylation of a lysine residue, which is conserved in other kinases, implying the possibility of a similar mechanism regulating their activity.

Pro-inflammatory angiogenesis is mediated by p38 MAP kinase

Chronic inflammation is tightly linked to diseases associated with endothelial dysfunction including aberrant angiogenesis. To better understand the endothelial role in pro-inflammatory angiogenesis, we analyzed signaling pathways in continuously activated endothelial cells, which were either chronically exposed to soluble TNF or the reactive oxygen species (ROS) generating H2O2, or express active transmembrane TNF. Testing in an in vitro capillary sprout formation assay, continuous endothelial activation increased angiogenesis dependent on activation of p38 MAP kinase, NADPH oxidase, and matrix metalloproteinases (MMP). p38 MAP kinase- and MMP-9-dependent angiogenesis in our assay system may be part of a positive feed forward autocrine loop because continuously activated endothelial cells displayed up-regulated ROS production and subsequent endothelial TNF expression. The pro-angiogenic role of the p38 MAP kinase in continuously activated endothelial cells was in stark contrast to the anti-angiogenic activity of the p38 MAP kinase in unstimulated control endothelial cells. In vivo, using an experimental prostate tumor, pharmacological inhibition of p38 MAP kinase demonstrated a significant reduction in tumor growth and in vessel density, suggesting a pro-angiogenic role of the p38 MAP kinase in pathological angiogenesis in vivo. In conclusion, our results suggest that continuous activation of endothelial cells can cause a switch of the p38 MAP kinase from anti-angiogenic to pro-angiogenic activities in conditions which link oxidative stress and autocrine TNF production.

PKG-I inhibition attenuates vascular endothelial growth factor-stimulated angiogenesis

Vascular endothelial growth factor (VEGF) stimulates nitric oxide (NO) production, which mediates many of its angiogenic actions. However, the angiogenic pathways that operate downstream of NO following VEGF treatment are not well characterized. Herein, we used DT-2 and DT-3, two highly selective cGMP-dependent protein kinase I peptide inhibitors to determine the contribution of PKG-I in VEGF-stimulated angiogenesis. Incubation of chicken chorioallantoic membranes (CAM) with PKG-I peptide inhibitors decreased vascular length in a dose-dependent manner, with DT-3 being more effective than DT-2. Moreover, inhibition of PKG-I with DT-3 abolished the angiogenic response elicited by VEGF in the rabbit eye cornea. PKG-I inhibition also blocked VEGF-stimulated vascular leakage. In vitro, treatment of cells with VEGF stimulated phosphorylation of the PKG substrate VASP through VEGFR2 activation; the VEGF-stimulated VASP phosphorylation was reduced by DT-2. Pre-treatment of cells with DT-2 or DT-3 inhibited VEGF-stimulated mitogen-activated protein kinase cascades (ERK1/2 and p38), growth, migration and sprouting of endothelial cells. The above observations taken together identify PKG-I as a downstream effector of VEGFR2 in EC and provide a rational basis for the use of PKG-I inhibitors in disease states characterized by excessive neovascularization.

Deciphering mechanisms controlling placental artery endothelial cell migration stimulated by vascular endothelial growth factor

Vascular endothelial growth factor (VEGF) stimulated fetoplacental artery endothelial (oFPAE) cell migration and activated multiple signaling pathways including ERK2/1, p38MAPK, Jun N-terminal kinase (JNK1/2), v-Akt murine thymoma viral oncogene homolog 1 (Akt1), and c-Src in oFPAE cells. VEGF-induced cell migration was blocked by specific kinase inhibitors of JNK1/2 (SP600125), c-Src (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d] pyrimidine), and phosphatidylinositol 3-kinase/Akt (wortmannin) but not ERK2/1 (U0126) and p38MAPK (SB203580). VEGF-induced cell migration was associated with dynamic actin reorganization and focal adhesion as evidenced by increased stress fiber formation and phosphorylation of cofilin-1 and focal adhesion kinase (FAK) and paxillin. Inhibition of JNK1/2, c-Src, and phosphatidylinositol 3-kinase/Akt suppressed VEGF-induced stress fiber formation and cofilin-1 phosphorylation. c-Src inhibition suppressed VEGF-induced phosphorylation of focal adhesion kinase, paxillin, and focal adhesion. VEGF-induced cell migration requires endogenous nitric oxide (NO) as: 1) VEGF-stimulated phosphorylation of endothelial NO synthase (eNOS) via activation of Akt, JNK1/2, and Src; 2) a NO donor diethylenetriamine-NO-stimulated cell migration; and 3) NO synthase inhibition blocked VEGF-induced cell migration. Targeted down-regulation and overexpression of caveolin-1 both inhibited VEGF-induced cell migration. Caveolin-1 down-regulation suppressed VEGF-stimulated phosphorylation of Akt, JNK, eNOS, c-Src, and FAK; however, basal activities of c-Src and FAK were elevated in parallel with increased stress fiber formation and focal adhesion. Caveolin-1 overexpression also inhibited VEGF-induced phosphorylation of Akt, JNK, c-Src, FAK, and eNOS. Thus, VEGF-induced placental endothelial cell migration requires activation of complex pathways that are paradoxically regulated by caveolin-1.

TrkB is highly expressed in NSCLC and mediates BDNF-induced the activation of Pyk2 signaling and the invasion of A549 cells

Background

Aberrant regulation in the invasion of cancer cells is closely associated with their metastatic potentials. TrkB functions as a receptor tyrosine kinase and is considered to facilitate tumor metastasis. Pyk2 is a non-receptor tyrosine kinase and integrates signals in cell invasion. However, little is known about the expression of TrkB in NSCLC and whether Pyk2 is involved in TrkB-mediated invasion of A549 cells.

Methods

The expression of TrkB was investigated in NSCLC by immunohistochemical staining. Both HBE and A549 cells were treated with BDNF. The expression of TrkB, Pyk2 and ERK phosphorylations were assessed by western blot. Besides, A549 cells were transfected with TrkB-siRNA or Pyk2-siRNA, or treated with ERK inhibitor where indicated. Transwell assay was performed to evaluate cell invasion.

Results

40 cases (66.7%) of NSCLC were found higher expression of TrkB and patients with more TrkB expression had significant metastatic lymph nodes (p = 0.028). BDNF facilitated the invasion of A549 cells and the activations of Pyk2 in Tyr402 and ERK. However, the effects of BDNF were not observed in HBE cells with lower expression of TrkB. In addition, the increased Pyk2 and ERK activities induced by BDNF were significantly inhibited by blocking TrkB expression, so was the invasion of A549 cells. Knockdown studies revealed the essential role of Pyk2 for BDNF-induced cell invasion, since the invasion of A549 cells was abolished by Pyk2-siRNA. The application of ERK inhibitor also showed the suppressed ERK phosphorylation and cell invasion.

Conclusion

These data indicated that higher expression of TrkB in NSCLC was closely correlated with lymph node metastasis, and BDNF probably via TrkB/Pyk2/ERK promoted the invasion of A549 cells.

Pigment epithelium-derived factor inhibits vascular endothelial growth factor-and interleukin-1beta-induced vascular permeability and angiogenesis in retinal endothelial cells

Increased vascular permeability associated with retinal vascular leakage is known to occur in patients with diabetes, and contributes to endothelial barrier dysfunction. The purpose of this study was to examine the effect of pigment epithelium-derived factor (PEDF) on signaling cascade in porcine retinal endothelial cells (PREC) related to permeability and angiogenesis induced by vascular endothelial growth factor (VEGF)-and interleukin-1beta (IL-1beta). PREC were exposed to VEGF, IL-1beta and PEDF at different concentrations, and in vitro permeability was assessed by solute flux assay using 70-kDa RITC-dextran. Angiogenic assays such as proliferation, migration and tube formation were determined by MTT, wound-scratch method and on-gel assay system respectively. To explore the signaling pathways behind VEGF-and IL-1beta-induced PREC permeability, an inhibitor assay was carried out using PP2, a Src kinase inhibitor. Further, Src activity was assessed by transient transfection assay using constitutively active (CA) and dominant negative (DN) Src mutants. We report that VEGF-and IL-1beta-stimulates permeability, in a dose and time-dependent manner and PEDF inhibits the VEGF-and IL-1beta-induced PREC permeability. In addition, PEDF inhibits the VEGF-and IL-1beta-induced endothelial cell proliferation, migration and tube formation. In addition, overexpression of DN Src blocked both VEGF-and IL-1beta-stimulation of permeability, proliferation and migration, while overexpression of CA Src overpowers the inhibitory action of PEDF on permeability, proliferation and migration. These results demonstrate that PEDF may inhibit the VEGF-and IL-1beta-induced permeability and angiogenesis via Src-dependent pathway.

Implications of vascular endothelial growth factor for postischemic neurovascular remodeling

Neurovascular remodeling has been recently recognized as a promising target for neurologic therapies. Hopes have emerged that, by stimulating vessel growth, it may be possible to stabilize brain perfusion, and at the same time promote neuronal survival, brain plasticity, and neurologic recovery. In this review, we outline the role of vascular endothelial growth factor (VEGF) in the ischemic brain, analyzing how this growth factor contributes to brain remodeling. Studies with therapeutic VEGF administration resulted in quite variable results depending on the route and time point of delivery. Local VEGF administration consistently enhanced neurologic recovery, whereas acute intravenous delivery exacerbated brain infarcts due to enhanced brain edema. Future studies should answer the following questions: (1) whether increased vessel density translates into improvements in blood flow in the hemodynamically compromised brain; (2) how VEGF influences brain plasticity and contributes to motor and nonmotor recovery; (3) what are the actions of VEGF not only in young animals with preserved vasculature, on which previous studies have been conducted, but also in aged animals and in animals with preexisting atherosclerosis; and (4) whether the effects of VEGF can be mimicked by pharmacological compounds or by cell-based therapies. Only on the basis of such information can more definite conclusions be made with regard to whether the translation of therapeutic angiogenesis into clinics is promising.

Involvement of MAPKs in Endostatin-Mediated Regulation of Blood-Retinal Barrier Function

PURPOSE

This study aimed to evaluate the effects of endostatin on tight junction (TJ) integrity in retinal microvascular endothelial cells (RMECs) in vitro and in vivo. Moreover, it was hypothesized that endostatin-induced occludin upregulation regulated VEGF165-mediated increases in endothelial cell permeability and involved activation of the MAPK signaling cascade. Endostatin is a 20-kDa fragment of collagen XVIII that has been shown to be efficacious in the eye by preventing retinal neovascularization. Endostatin is a specific inhibitor of endothelial cell proliferation, migration, and angiogenesis and has been reported to reverse VEGF-mediated increases in vasopermeability and to promote integrity of the blood-retinal barrier (BRB). In order to determine the mechanism of endostatin action on BRB integrity, we have examined the effects of endostatin on a number of intracellular pathways implicated in endothelial cell physiology.

METHODS

C57/Bl6 mice were injected with VEGF165 and/or endostatin, and the distribution of occludin staining was determined using retinal flatmounts. Western blot analysis of RMECs treated with VEGF165 and/or endostatin was used to determine changes in occludin expression and p38 MAPK and extracellular regulated kinase (ERK1/ERK2 MAPK) activation, while FD-4 flux across the RMEC monolayer was used to determine changes in paracellular permeability.

RESULTS

Endostatin prevented the discontinuous pattern of occludin staining observed at the retinal blood vessels of mice administered an intraocular injection of VEGF165. It was shown that endostatin activated p38 MAPK 5 min after addition to RMECs and continued to do so for approximately 30 min. Endostatin was also shown to activate ERK1/ERK2 5 min after addition and continued to do so, albeit with less potency, up to and including 15 min after addition. Inhibition of p38 MAPK and ERK1/ERK2 prevented endostatin's ability to upregulate levels of occludin expression. Inhibition of these key signaling molecules was shown to prevent endostatin's ability to protect against VEGF165-mediated increases in paracellular permeability in vitro. However, it appears that p38 MAPK may play a more important role in VEGF-mediated permeability, as inhibition of ERK1/ERK2 will not prevent VEGF165-mediated permeability compared with control (untreated) cells or cells treated with both a p38 MAPK inhibitor and VEGF165.

CONCLUSIONS

Occludin is important for the maintenance of tight junction integrity in vivo. In a p38 MAPK and ERK1/ERK2 dependent manner, endostatin was shown to upregulate the levels of expression of the tight junction protein occludin. Inhibition of these key MAPK components may prevent endostatin's ability to decrease VEGF165-induced paracellular permeability.

Src family kinases are necessary for cell migration induced by extracellular HMGB1

HMGB1 is a nuclear protein that signals tissue damage, as it is released by cells dying traumatically or secreted by activated innate immunity cells. Extracellular HMGB1 elicits the migration to the site of tissue damage of several cell types, including inflammatory cells and stem cells. The identity of the signaling pathways activated by extracellular HMGB1 is not known completely: We reported previously that ERK and NF-kappaB pathways are involved, and we report here that Src is also activated. The ablation of Src or inhibition with the kinase inhibitor PP2 blocks migration toward HMGB1. Src associates to and mediates the phosphorylation of FAK and the formation of focal adhesions.

Mechanism of dietary salt-mediated increase in intravascular production of TGF-beta1

Clinical and preclinical studies have demonstrated an important effect of arterial pathobiology on the progressive loss of renal function that occurs in chronic kidney disease. Chronic kidney disease, in turn, promotes alterations in vascular function. A modulating role for dietary salt has been suggested, with the amount of salt intake regulating endothelial cell production of transforming growth factor-beta1 (TGF-beta1), a fibrogenic growth factor that promotes arteriosclerosis and glomerulosclerosis. The purpose of the present studies was to determine how the interaction between dietary salt intake and vasculature promoted the production of TGF-beta1 in rats. Two different vascular tissues, aortic rings and glomeruli, were chosen for study. Dietary salt induced, in a dose-dependent fashion, activation of proline-rich tyrosine kinase-2 (Pyk2) and further identified c-Src as an important binding partner of Pyk2 in these tissues. Use of pharmacological inhibitors and dominant negative strategies confirmed that dietary salt induced complex formation of Pyk2 and c-Src with downstream activation of p38 and p42/44 mitogen-activated protein kinases and generation of TGF-beta1. The experiments defined the molecular signaling events that promoted the production of TGF-beta1, a key growth factor involved in the vascular response to increased salt intake.

Essential role of Pyk2 and Src kinase activation in neuropeptide-induced proliferation of small cell lung cancer cells

Neuropeptide hormones like bombesin/gastrin-releasing peptide, galanin or bradykinin, acting via auto and paracrine growth loops, represent the principal mitogens of small cell lung cancer (SCLC). These mitogenic neuropeptides activate G(q/11)-coupled receptors which stimulate phospholipase Cbeta activity, followed by rises of the intracellular calcium concentration ([Ca2+](i)) and activation of protein kinase C (PKC). We report here that proline-rich tyrosine kinase Pyk2 is highly expressed in SCLC cells and provides a functional link between neuropeptide-induced increases in [Ca2+](i) and tumor cell proliferation. Activation of Pyk2 and its association with Src kinases critically depends on the elevation of [Ca2+](i), but is independent of PKC. Src kinase activities are crucial for neuropeptide-mediated GTP-loading of Ras and activation of extracellular signal-regulated kinases in SCLC cells. Pyk2 and Src kinases essentially contribute to anchorage-independent proliferation of SCLC cells. Inhibition of either Pyk2 or Src kinases by lentiviral RNAi or pharmacological inhibition with PP2, respectively, attenuated basal and neuropeptide-elicited survival and proliferation of SCLC cells in liquid culture and in soft agar. Thus, neuropeptides stimulate anchorage-independent survival and proliferation of SCLC cells via pathways involving Pyk2 and Src kinases. Therefore, Ca2+-induced Pyk2/Src complex formation may be a rewarding molecular target for novel therapeutic strategies in SCLC cells.

Endothelial beta2 adrenergic signaling to AKT: role of Gi and SRC

We have recently demonstrated that endothelial beta(2) adrenergic receptors (beta(2)AR) regulate eNOS activity and consequently vascular tone, through means of PKB/AKT. In this work we explored the signal transduction pathway leading to AKT/eNOS activation in endothelial cells (EC). Using pharmacological and molecular inhibitors both in cultured EC cells and in ex vivo rat carotid preparations, we found that G(i) coupling of the beta(2)AR is needed for AKT activation and vasorelaxation. Since endothelial activation is sensitive to pertussis toxin but not to G(ibetagamma) inhibition by betaARKct, we conclude that G(alphai) mediates betaAR induced AKT activation. Downstream, betaAR signalling requires the soluble tyrosine kinase SRC, as both in cultured EC and rat carotid, the mutant dominant negative of SRC prevent beta(2)AR induced endothelial activation and vasodilation. In EC, G(alphai) directly interacts with SRC and this interaction leads to SRC activation and phosphorylation in a manner that is regulated by beta(2)AR stimulation. We propose a novel signal transduction pathway for beta(2)AR stimulation trough G(alphai) and SRC, leading to activation of AKT.

Role of p38 map kinase in glycine-induced hepatocyte resistance to hypoxic injury

BACKGROUND/AIMS

Glycine hepatoprotection is well known. However, the mechanisms involved are still poorly characterized.

METHODS

Glycine protection was investigated in isolated rat hepatocytes pretreated with 2 mmol/L glycine 15 min before incubation under hypoxic conditions.

RESULTS

Glycine significantly reduced Na+ overload and hepatocyte death caused by hypoxia. Glycine protection required the activation of a signal pathway involving Src, Pyk2 and p38 MAP kinases. Glycine treatment also induced a 11% increase of hepatocyte volume and transient ATP release. The prevention of cell swelling by hepatocyte incubation in a hypertonic medium as well as the degradation of extracellular ATP with apyrase or the block P2 purinergic receptors with suramin reverted glycine-induced cytoprotection and inhibited Src, Pyk2 and p38 MAPK activation. Glycine down-modulated Na+/H+ exchanger (NHE) activity, without affecting the development of intracellular acidosis during hypoxia. Such an effect was reverted by inhibiting p38 MAPK that also abolished glycine protection against Na+ overload caused by hypoxia.

CONCLUSIONS

Glycine-induced ATP release in response to a moderate hepatocyte swelling led to the autocrine stimulation of P2 receptors and to the activation of Src, Pyk2 and p38 MAPK that increased hepatocyte resistance to hypoxia by preventing Na+ influx through NHE.

The phosphodiesterase 5 inhibitor sildenafil stimulates angiogenesis through a protein kinase G/MAPK pathway

cGMP-degrading pathways have received little attention in the context of angiogenesis. In the present study we set out to determine whether cGMP-specific phosphodiesterase 5 (PDE5) inhibition affects new blood vessel growth. Incubation of chicken chorioallantoic membranes (CAMs) in vivo with sildenafil increased vascular length in a dose-dependent manner. Moreover, incubation of cultured endothelial cells (ECs) with the PDE5 inhibitor promoted proliferation, migration, and organization into tube-like structures. The effects of sildenafil on the angiogenesis-related properties of EC could be blocked by pre-treatment with the soluble guanylyl cyclase (sGC) inhibitor ODQ or the protein kinase G (PKG) I inhibitor DT-3. In addition, over-expression of sGC in EC led to an enhanced growth and migratory response to sildenafil. To study the signaling pathways implicated in the sildenafil-stimulated angiogenic responses we determined the phosphorylation status of mitogen-activated protein kinase (MAPK) members. Incubation of cells with sildenafil increased both extracellular signal regulated kinase 1/2 (ERK1/2) and p38 phosphorylation in a time-dependent manner. Inhibition of MEK by PD98059 and p38 with SB203580 blocked sildenafil-induced proliferation and migration, respectively, suggesting that these MAPK members are downstream of PDE5 and mediate the angiogenic effects of sildenafil. PDE5 inhibitors could, thus, be used in disease states where neo-vessel growth is desired.

Soluble guanylyl cyclase activation promotes angiogenesis

Soluble guanylyl cyclase (sGC) is a cGMP-generating enzyme carrying a heme prosthetic group that functions as a nitric oxide (NO) sensor. sGC is present in most cells types, including the vascular endothelium, where its biological functions remain largely unexplored. Herein, we have investigated the role of sGC in angiogenesis and angiogenesis-related properties of endothelial cells (EC). Initially, we determined that sGC was present and enzymatically active in the chicken chorioallantoic membrane (CAM) during the days of maximal angiogenesis. In the CAM, inhibition of endogenous sGC inhibited neovascularization, whereas activation promoted neovessel formation. Using zebrafish as a model for vascular development, we did not detect any effect on vasculogenesis upon sGC blockade, but we did observe an abnormal angiogenic response involving the cranial and intersegmental vessels, as well as the posterior cardinal vein. In vitro, pharmacological activation of sGC or adenovirus-mediated sGC gene transfer promoted EC proliferation and migration, whereas sGC inhibition blocked tube-like network formation. In addition, sGC inhibition blocked the migratory response to vascular EC growth factor. Cells infected with sGC-expressing adenoviruses exhibited increased extracellular signal-regulated kinase 1/2 and p38 MAPK activation that was sensitive to sGC inhibition by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, suggesting that these mitogen-activated protein kinases are downstream effectors of sGC in EC. A functional role for p38 in cGMP-stimulated migration was demonstrated using SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole]; pharmacological inhibition of p38 attenuated BAY 41-2272 [5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-pyrimidin-4-ylamine] and sGC overexpression-induced EC mobilization. We conclude that sGC activation promotes the expression of angiogenesis-related properties by EC and that sGC might represent a novel target to modulate neovessel formation.

Phosphorylation of Tyr1214 within VEGFR-2 triggers the recruitment of Nck and activation of Fyn leading to SAPK2/p38 activation and endothelial cell migration in response to VEGF

VEGFR-2 is the major receptor that regulates the different functions of VEGF in adults. We have previously reported that following VEGF treatment of endothelial cells, VEGFR-2 is phosphorylated on Tyr1214 upstream of the Cdc42-SAPK2/p38-MAPKAP K2 pathway. However, little is known of the earliest molecular events that compose the SAPK2/p38 pathway following VEGFR-2 activation. In this study, we address this question using HA-tagged constructs of either wild-type VEGFR-2 or Y1214F VEGFR-2 mutant in immunoprecipitation assays. We show that the Src family kinase member Fyn, but not c-Src itself, is recruited to VEGFR-2 and is activated in a p-Tyr1214-dependent manner. We also report that the SH2 domain-containing adapter molecule Nck, but not Grb2, is recruited to VEGFR-2 in a p-Tyr1214-dependent manner and that it associates with Fyn. Moreover, PAK-2 is phosphorylated in a Fyn-dependent manner. Using chemical and genetic inhibitors, we show that Fyn activity is required for SAPK2/p38 but not for FAK activation in response to VEGF. In contrast, c-Src permits activation of FAK, but not that of SAPK2/p38. In addition, Fyn is required for stress fiber formation and endothelial cell migration. We propose a model in which Fyn forms a molecular complex with Nck and PAK-2 and suggest that this complex assembles in a p-Tyr1214-dependent manner within VEGFR-2 following VEGF treatment. In turn, this triggers the activation of the SAPK2/p38 MAP kinase module, and promotes stress fiber formation and endothelial cell migration.

Role of Src in angiopoietin 1-induced capillary morphogenesis of endothelial cells: Effect of chronic hypoxia on Src inhibition by PP2

Signal transduction pathways leading to angiopoietin 1 (Ang1)-induced capillary morphogenesis by endothelial cells remain poorly defined. Angiogenic cellular responses by endothelial cells may be modulated in vivo by chronic hypoxia, such as that induced by tumors. Here, we studied Ang1-induced capillary morphogenesis in human umbilical-vein endothelial cells (HUVECs) cultured chronically under normoxic (21% oxygen) or hypoxic (1.5% oxygen) conditions. Downregulation of Src using a small interfering RNA (siRNA) inhibited Ang1-induced capillary morphogenesis of HUVECs cultured under both conditions by blocking cell spreading and protrusion. Ang1 upregulated the Src-dependent secretion of vascular endothelial growth factor-A (VEGF-A). Blockade of endogenous VEGF-A also inhibited Ang1-induced capillary morphogenesis. Addition of exogenous VEGF-A restored cell spreading and protrusion, leading to Ang1-induced capillary morphogenesis of Src siRNA-treated HUVECs, suggesting that Ang1-induced VEGF-A secretion through Src was required for capillary morphogenesis. PP2 inhibited both Ang1-induced capillary morphogenesis and Src activation in HUVECs cultured under normoxic conditions, but the PP2 activity was significantly impaired in HUVECs cultured under hypoxic conditions. Expression of multidrug resistance-associated protein 1 (MRP 1) was upregulated in hypoxic HUVECs, and treatment with MRP 1 siRNA restored the inhibitory action of PP2. Taken together, our results suggest that Ang1 induces capillary morphogenesis in HUVECs through Src-dependent upregulation of endogenous VEGF-A. Conditions of chronic hypoxia impaired the effect of PP2, possibly via MRP 1.

Angiotensin Type 1 Receptor Blocker Restores Podocyte Potential to Promote Glomerular Endothelial Cell Growth

Both podocytes and glomerular endothelial cells (GEN) are postulated to play important roles in the progression and potential regression of glomerulosclerosis. Inhibition of angiotensin is crucial in treatment of chronic kidney disease, presumably via effects on BP and extracellular matrix. This study aimed to investigate how angiotensin inhibition altered the interactions between podocytes and GEN. The effects of supernatants from primary cultured mouse podocytes, before or after sublethal injury by puromycin aminonucleoside, in the presence or absence of angiotensin type 1 receptor blocker (ARB), on GEN sprouting and growth were assessed. Supernatant from normal podocytes significantly increased GEN sprouting, whereas puromycin aminonucleoside-injured podocyte supernatant decreased these GEN responses. These effects were linked to decreased vascular endothelial growth factor A (VEGF-A) and angiopoietin-1 (Ang-1) protein from injured podocytes. This downregulation of VEGF-A and Ang-1 protein was reversed when injured podocytes were treated with ARB. Inhibition of VEGF-A or Ang-1 prevented this restored response by ARB. Activation of intracellular kinases (p38, extracellular signal-regulated kinase, and AKT) was suppressed in GEN that were treated with medium from injured podocytes but restored by medium from ARB-treated injured podocytes. Therefore, injured podocytes are ineffective in promoting GEN sprouting, and this effect is reversed by ARB treatment of the injured podocyte. These data support the idea that ARB effects on podocytes may mediate capillary remodeling in vivo.

HGF-induced capillary morphogenesis of endothelial cells is regulated by Src

The signal transduction pathway involved in hepatocyte growth factor (HGF)-induced capillary morphogenesis of endothelial cells was investigated. HGF-induced capillary morphogenesis of the murine spleen endothelial cell line MSS31 was inhibited by a Src family kinase inhibitor, PP2. Stable expression of kinase-inactive Src in MSS31 cells inhibited HGF-induced activation of Src as well as capillary morphogenesis. The HGF-induced capillary morphogenesis of human umbilical vein endothelial cells was also inhibited by PP2 and was reduced by the downregulation of Src by small interfering RNA. These results suggest that HGF induces capillary morphogenesis of endothelial cells through Src.

The role of VEGF receptors in angiogenesis; complex partnerships

Vascular endothelial growth factors (VEGFs) regulate blood and lymphatic vessel development and homeostasis but also have profound effects on neural cells. VEGFs are predominantly produced by endothelial, hematopoietic and stromal cells in response to hypoxia and upon stimulation with growth factors such as transforming growth factors, interleukins or platelet-derived growth factor. VEGFs bind to three variants of type III receptor tyrosine kinases, VEGF receptor 1, 2 and 3. Each VEGF isoform binds to a particular subset of these receptors giving rise to the formation of receptor homo- and heterodimers that activate discrete signaling pathways. Signal specificity of VEGF receptors is further modulated upon recruitment of coreceptors, such as neuropilins, heparan sulfate, integrins or cadherins. Here we summarize the knowledge accumulated since the discovery of these proteins more than 20 years ago with the emphasis on the signaling pathways activated by VEGF receptors in endothelial cells during cell migration, growth and differentiation.

Focal adhesion kinase is critical for entry of Kaposi's sarcoma-associated herpesvirus into target cells

Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8 (KSHV/HHV-8) interacts with cell surface alpha3beta1 integrin early during in vitro infection of human endothelial cells and fibroblasts and activates the focal adhesion kinase (FAK) that is immediately downstream in the outside-in signaling pathway by integrins, leading to the activation of several downstream signaling molecules. In this study, using real-time DNA and reverse transcription-PCR assays to measure total internalized viral DNA, viral DNA associated with infected nuclei, and viral gene expression, we examined the stage of infection at which FAK plays the most significant role. Early during KSHV infection, FAK was phosphorylated in FAK-positive Du17 mouse embryonic fibroblasts. The absence of FAK in Du3 (FAK(-/-)) cells resulted in about 70% reduction in the internalization of viral DNA, suggesting that FAK plays a role in KSHV entry. Expression of FAK in Du3 (FAK(-/-)) cells via an adenovirus vector augmented the internalization of viral DNA. Expression of the FAK dominant-negative mutant FAK-related nonkinase (FRNK) in Du17 cells significantly reduced the entry of virus. Virus entry in Du3 cells, albeit in reduced quantity, delivery of viral DNA to the infected cell nuclei, and expression of KSHV genes suggested that in the absence of FAK, another molecule(s) may be partially compensating for FAK function. Infection of Du3 cells induced the phosphorylation of the FAK-related proline-rich tyrosine kinase (Pyk2) molecule, which has been shown to complement some of the functions of FAK. Expression of an autophosphorylation site mutant of Pyk2 in which Y402 is mutated to F (F402 Pyk2) reduced viral entry in Du3 cells, suggesting that Pyk2 facilitates viral entry moderately in the absence of FAK. These results suggest a critical role for KSHV infection-induced FAK in the internalization of viral DNA into target cells.

Immunohistochemical study about the Flt-1/VEGFR1 expression in the gastrointestinal tract of mouse, rat, dog, swine and monkey

Fms-like tyrosine kinase 1 (Flt-1) performs a subordinate effector role in mesenchymal angiogenesis and potentially serves an equally important functional role as a self-contained receptor in epithelial cells. In both endothelial cells and epithelial cells, Flt-1/vascular endothelial growth factor receptor 1 (VEGFR1) downstream signalling is involved in regulating cellular processes such as cytoskeletal changes and cellular survival protection. Cellular renewal of the gastrointestinal mucosa is based on these processes and might involve Flt-1/VEGFR1 pathway activities; the molecular mechanisms regulating these cellular dynamics remain unclear. This study was performed to investigate the presence and distribution of Flt-1/VEGFR1 in epithelial cells of the gastrointestinal tract by immunohistochemistry (IHC). Gastrointestinal tissues were taken from eight anatomical sites from mouse, rat, dog, swine and monkey. Present results revealed a cytosolic Flt-1/VEGFR1 staining pattern in mucosal epithelial cells for all investigated species. Non-epithelial structures also displayed a distinct Flt-1/VEGFR1 positivity and included vascular smooth muscle walls, enteric smooth muscle layers, the enteric nervous system and capillary endothelial cells. Diverse intensities of the Flt-1/VEGFR1 binding reaction within each species were observed in the intestinal mucosa with a strong immunoreaction in enterocytes and with a low protein expression in the ileum in most species. Crypt cells in the large intestine were mostly negative for Flt-1/VEGFR1. A peculiar and mainly intranuclear antibody binding reaction was found in Brunner's gland epithelial cells of mouse and rat whereas Brunner's glands of dog, swine and monkey remained completely negative. These results indicate a potential involvement of Flt-1/VEGFR1 in normal restitution of gastrointestinal structures in the species studied. Additionally, intranuclear Flt-1/VEGFR1 antibody binding in Brunner's glands of rodents may suggest a nuclear translocation of the transmembrane VEGFR1 which has not previously been described.

CXCL-12/stromal cell-derived factor-1alpha transactivates HER2-neu in breast cancer cells by a novel pathway involving Src kinase activation

Experimental evidence suggests that CXCR4, a Gi protein-coupled receptor for the ligand CXCL12/stromal cell-derived factor-1alpha (SDF-1alpha), plays a role in breast cancer metastasis. Transactivation of HER2-neu by G protein-coupled receptor activation has been reported as a ligand-independent mechanism of activating tyrosine kinase receptors. We found that SDF-1alpha transactivated HER2-neu in the breast cancer cell lines MDA-MB-361 and SKBR3, which express both CXCR4 and HER2-neu. AMD3100, a CXCR4 inhibitor, PKI 166, an epidermal growth factor receptor/HER2-neu tyrosine kinase inhibitor, and PP2, a Src kinase inhibitor, each blocked SDF-1alpha-induced HER2-neu phosphorylation. Blocking Src kinase, with PP2 or using a kinase-inactive Src construct, and inhibiting epidermal growth factor receptor/HER2-neu signaling with PKI 166 each inhibited SDF-1alpha-stimulated cell migration. We report a novel mechanism of HER2-neu transactivation through SDF-1alpha stimulation of CXCR4 that involves Src kinase activation.

c-Src regulates constitutive and EGF-mediated VEGF expression in pancreatic tumor cells through activation of phosphatidyl inositol-3 kinase and p38 MAPK

OBJECTIVES

Multiple signaling proteins may be aberrantly activated and/or overexpressed in pancreatic tumors, including the nonreceptor protein tyrosine kinase Src. The goal of this study was to determine the role of Src in regulating VEGF expression and angiogenic potential in pancreatic cancer cell lines.

METHODS

Src activity was inhibited using the Src family kinase selective inhibitor PP2, and c-Src expression was down-regulated via siRNA. The activities of downstream signaling molecules phosphatidyl inositol 3'-kinase (PI3K) and p38 mitogen-activated protein kinase (MAPK) were disrupted via selective inhibitors. In vivo angiogenesis was assessed through the use of a gel-foam assay.

RESULTS

Inhibition of Src activity or expression decreases both constitutive and EGF-induced VEGF production. Both the PI3K/Akt and p38 MAPK pathways are activated in a Src family kinase-dependent fashion on EGF-R activation and are important for EGF-mediated VEGF production in pancreatic cancer cells. Additionally, media from Src-inhibited L3.6pl cells fail to promote angiogenesis into gel foams implanted subcutaneously into mice, whereas media from control cells promote a robust angiogenic response.

CONCLUSIONS

Src activity contributes to constitutive and EGF-induced VEGF expression and angiogenic potential in pancreatic cancer cells. Therefore, Src may be a viable target for antiangiogenesis therapy in pancreatic cancer.

Aspirin-triggered Lipoxin A4 inhibition of VEGF-induced endothelial cell migration involves actin polymerization and focal adhesion assembly

Angiogenesis, the growth of new capillaries from pre-existing ones, occurs through dynamic functions of the endothelial cells (EC), including migration, which is essential to achieve an organized formation of the vessel sprout. We demonstrated previously that an aspirin-triggered lipoxin analog, 15-epi-16-(para-fluoro)-phenoxy-lipoxin A4 (ATL-1), inhibits vascular endothelial growth factor (VEGF)-induced EC migration. In the present study, we investigated the effects of ATL-1 in the actin cytoskeleton reorganization of EC stimulated with VEGF. Pretreatment of EC with ATL-1 caused a reduction in VEGF-induced stress fibers and therefore reduced the intracellular content of filamentous actin. A concomitant impairment in stress-activated protein kinase (SAPK2/p38) phosphorylation suggests that ATL inhibition of VEGF-stimulated actin polymerization involves the SAPK2/p38 pathway. Moreover, ATL-1 treatment inhibited focal adhesion clustering due to inhibition of focal adhesion kinase (FAK) phosphorylation and the subsequent association of FAK with the actin cytoskeleton. This final event, which ultimately allows cell migration, was reverted by an LX receptor antagonist, but not by a cys-LT1R antagonist, indicating an effect via the G-protein-linked LXA4 receptor. Together our results provide evidence that ATL-1 inhibits EC migration via the concerted inhibition of actin polymerization and proper assembly of focal adhesions, supporting a role for these novel lipid mediators as angiogenesis modulators.