The cellular response to vascular endothelial growth factors requires co-ordinated signal transduction, trafficking and proteolysis

Endomucin selectively regulates vascular endothelial growth factor receptor-2 endocytosis through its interaction with AP2

The endothelial glycocalyx, located at the luminal surface of the endothelium, plays an important role in the regulation of leukocyte adhesion, vascular permeability, and vascular homeostasis. Endomucin (EMCN), a component of the endothelial glycocalyx, is a mucin-like transmembrane glycoprotein selectively expressed by venous and capillary endothelium. We have previously shown that knockdown of EMCN impairs retinal vascular development in vivo and vascular endothelial growth factor 165 isoform (VEGF165)-induced cell migration, proliferation, and tube formation by human retinal endothelial cells in vitro and that EMCN is essential for VEGF165-stimulated clathrin-mediated endocytosis and signaling of VEGF receptor 2 (VEGFR2). Clathrin-mediated endocytosis is an essential step in receptor signaling and is of paramount importance for a number of receptors for growth factors involved in angiogenesis. In this study, we further investigated the molecular mechanism underlying EMCN's involvement in the regulation of VEGF-induced endocytosis. In addition, we examined the specificity of EMCN's role in angiogenesis-related cell surface receptor tyrosine kinase endocytosis and signaling. We identified that EMCN interacts with AP2 complex, which is essential for clathrin-mediated endocytosis. Lack of EMCN did not affect clathrin recruitment to the AP2 complex following VEGF stimulation, but it is necessary for the interaction between VEGFR2 and the AP2 complex during endocytosis. EMCN does not inhibit VEGFR1 and FGFR1 internalization or their downstream activities since EMCN interacts with VEGFR2 but not VEGFR1 or FGFR1. Additionally, EMCN also regulates VEGF121-induced VEGFR2 phosphorylation and internalization.

Trafficking dynamics of VEGFR1, VEGFR2, and NRP1 in human endothelial cells

The vascular endothelial growth factor (VEGF) family of cytokines are key drivers of blood vessel growth and remodeling. These ligands act via multiple VEGF receptors (VEGFR) and co-receptors such as Neuropilin (NRP) expressed on endothelial cells. These membrane-associated receptors are not solely expressed on the cell surface, they move between the surface and intracellular locations, where they can function differently. The location of the receptor alters its ability to 'see' (access and bind to) its ligands, which regulates receptor activation; location also alters receptor exposure to subcellularly localized phosphatases, which regulates its deactivation. Thus, receptors in different subcellular locations initiate different signaling, both in terms of quantity and quality. Similarly, the local levels of co-expression of other receptors alters competition for ligands. Subcellular localization is controlled by intracellular trafficking processes, which thus control VEGFR activity; therefore, to understand VEGFR activity, we must understand receptor trafficking. Here, for the first time, we simultaneously quantify the trafficking of VEGFR1, VEGFR2, and NRP1 on the same cells-specifically human umbilical vein endothelial cells (HUVECs). We build a computational model describing the expression, interaction, and trafficking of these receptors, and use it to simulate cell culture experiments. We use new quantitative experimental data to parameterize the model, which then provides mechanistic insight into the trafficking and localization of this receptor network. We show that VEGFR2 and NRP1 trafficking is not the same on HUVECs as on non-human ECs; and we show that VEGFR1 trafficking is not the same as VEGFR2 trafficking, but rather is faster in both internalization and recycling. As a consequence, the VEGF receptors are not evenly distributed between the cell surface and intracellular locations, with a very low percentage of VEGFR1 being on the cell surface, and high levels of NRP1 on the cell surface. Our findings have implications both for the sensing of extracellular ligands and for the composition of signaling complexes at the cell surface versus inside the cell.

The role of microRNAs in the different phases of liver regeneration

INTRODUCTION

Since the first discovery of microRNAs (miRs) extensive evidence reveals their indispensable role in different patho-physiological processes. They are recognized as critical regulators of hepatic regeneration, as they modulate multiple complex signaling pathways affecting liver regeneration. MiR-related translational suppression and degradation of target mRNAs and proteins are not limited to one specific gene, but act on multiple targets.

AREAS COVERED

In this review, we are going to explore the role of miRs in the context of liver regeneration and discuss the regulatory effects attributed to specific miRs. Moreover, specific pathways crucial for liver regeneration will be discussed, with a particular emphasis on the involvement of miRs within the respective signaling cascades.

EXPERT OPINION

The considerable amount of studies exploring miR functions in a variety of diseases paved the way for the development of miR-directed therapeutics. Clinical implementation has already shown promising results, but additional research is warranted to assure safe and efficient delivery. Nevertheless, given the broad functional properties of miRs and their critical involvement during hepatic regeneration, they represent an attractive treatment target to promote liver recovery after hepatic resection.

Receptors that bind to PEDF and their therapeutic roles in retinal diseases

Retinal neovascular, neurodegenerative, and inflammatory diseases represented by diabetic retinopathy are the main types of blinding eye disorders that continually cause the increased burden worldwide. Pigment epithelium-derived factor (PEDF) is an endogenous factor with multiple effects including neurotrophic activity, anti-angiogenesis, anti-tumorigenesis, and anti-inflammatory activity. PEDF activity depends on the interaction with the proteins on the cell surface. At present, seven independent receptors, including adipose triglyceride lipase, laminin receptor, lipoprotein receptor-related protein, plexin domain-containing 1, plexin domain-containing 2, F1-ATP synthase, and vascular endothelial growth factor receptor 2, have been demonstrated and confirmed to be high affinity receptors for PEDF. Understanding the interactions between PEDF and PEDF receptors, their roles in normal cellular metabolism and the response the initiate in disease will be accommodating for elucidating the ways in which inflammation, angiogenesis, and neurodegeneration exacerbate disease pathology. In this review, we firstly introduce PEDF receptors comprehensively, focusing particularly on their expression pattern, ligands, related diseases, and signal transduction pathways, respectively. We also discuss the interactive ways of PEDF and receptors to expand the prospective understanding of PEDF receptors in the diagnosis and treatment of retinal diseases.

Bioactive phytoconstituents of ethanolic extract from Chromolaena odorata leaves interact with vascular endothelial growth factor and cyclooxygenase-2: A molecular docking study

Chromolaena odorata is an invasive plant with a broad spectrum of medicinal properties, including wound healing. This study aimed to evaluate the interaction of the already identified bioactive phytoconstituents from ethanolic extracts of C. odorata leaves with two angiogenesis-related proteins - vascular endothelial growth factor (VEGF) and cyclooxygenase-2 (COX-2) in silico. A molecular docking protocol was performed on AutoDock Vina employing the molecular structure of VEGF (3HNG) and COX-2 (3LN1) downloaded from the Protein Data Bank. The results reveal that most of the phytoconstituents possess strong binding affinity, where β-tocopherol and squalene have the highest values. In conclusion, it is highly possible that the phytoconstituents of C. odorata from the ethanolic leaf extract perform an interaction with VEGF and COX-2 and affect their activities.

VEGFR endocytosis: Implications for angiogenesis

The binding of vascular endothelial growth factor (VEGF) superfamily to VEGF receptor tyrosine kinases (VEGFRs) and co-receptors regulates vasculogenesis, angiogenesis and lymphangiogenesis. A recurring theme is that dysfunction in VEGF signaling promotes pathological angiogenesis, an important feature of cancer and pro-inflammatory disease states. Endocytosis of basal (resting) or activated VEGFRs facilitates signal attenuation and endothelial quiescence. However, increasing evidence suggest that activated VEGFRs can continue to signal from intracellular compartments such as endosomes. In this chapter, we focus on the evolving link between VEGFR endocytosis, signaling and turnover and the implications for angiogenesis. There is much interest in how such understanding of VEGFR dynamics can be harnessed therapeutically for a wide range of human disease states.

Promotion Effect of Angelica Sinensis Extract on Angiogenesis of Chicken Preovulatory Follicles in Vitro

Preovulatory follicles need a network of blood vessels to growth and maturation in hens (Gallus gallus). Angelica sinensis (Oliv.) (AS), a traditional Chinese herb, displays a novel pro-angiogenic activity. The molecular mechanisms underlying AS promoting preovulatory follicles angiogenesis are poorly understand. Several recent studies investigated the expression of vascular endothelial growth factor A (VEGF-A) in angiogenesis. In order to explore the promotion effect of AS extract on angiogenesis of chicken preovulatory follicles, we studied the effect of AS extract on follicle microvascular endothelial-like cells of chicken (FMEC) and granulosa cells (GC). The current study indicated that AS extract could promote the proliferation of FMECs and GCs. The assays of wounding healing, transwell invasion and tube formation showed that AS extract could enhance the invasion and migration ability of FMECs in vitro. The results of western blot and RT-PCR showed that AS extract promoted the phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR2) in FMECs by activating the PI3K/AKT signaling pathway. The AS extract activated PI3K/AKT signaling pathway and up-regulated the expressions of hypoxia-inducible factor 1-α (HIF1-α) and VEGF-A in GCs. In addition, treatment of FMECs and GCs with LY294002 (a PI3K inhibitor) significantly down-regulated the phosphorylation of VEGFR2, VEGF-A, and HIF1-α. The mRNA expression levels of PI3K, AKT, VEGF-A, VEGFR2, and HIF1-α were consistent with protein expression levels. In conclusion, our research showed that AS extract can promote the follicle angiogenesis in hens in vitro, providing a basis for application of the traditional Chinese herb AS in poultry production.

Blocking of VEGF-A is not sufficient to completely revert its long-term effects on the barrier formed by retinal endothelial cells

The VEGF-A-induced functional impairment of the barrier formed by retinal endothelial cells (REC) can be prevented and even - at least temporarily - reverted by trapping the growth factor in a complex with a VEGF-binding protein or by inhibiting the activity of the VEGF receptor 2 (VEGFR2). In an approach to emulate the clinically relevant situation of constant exposure to effectors, we investigated (1) whether prolonged exposure to VEGF-A₁₆₅ for up to six days results in a different type of disturbance of the barrier formed by immortalized bovine REC (iBREC) and (2) whether alterations of the barrier induced by VEGF-A₁₆₅ can indeed be sustainably reverted by subsequent treatment with the VEGF-A-binding proteins ranibizumab or brolucizumab. As a measure of barrier integrity, the cell index (CI) of iBREC cultivated on gold electrodes was monitored continuously. CI values declined shortly after addition of the growth factor and then remained low for more than six days over which considerable amounts of both extra- and intracellular VEGF-A were measured. Interestingly, the specific VEGFR2 inhibitor nintedanib normalized the lowered CI when added to iBREC pre-treated with VEGF-A₁₆₅ for one day, but failed to do so when cells had been exposed to the growth factor for six days. Expression of the tight junction (TJ) protein claudin-5 was unchanged early after addition of VEGF-A₁₆₅ but higher after prolonged treatment, whereas decreased amounts of the TJ-protein claudin-1 remained low, and increased expression of the plasmalemma vesicle-associated protein (PLVAP) remained high during further exposure. After two days, the characteristic even plasma membrane stainings of claudin-1 or claudin-5 appeared weaker or disordered, respectively. After six days the subcellular localization of claudin-5 was similar to that of control cells again, but claudin-1 remained relocated from the plasma membrane. To counteract these effects of VEGF-A₁₆₅, brolucizumab or ranibizumab was added after one day, resulting in recovery of the then lowered CI to normal values within a few hours. However, despite the VEGF antagonist being present, the CI declined again two days later to values that were just slightly higher than without VEGF inhibition during further assessment for several days. At this stage, neither the supernatants nor whole cell extracts from iBREC treated with VEGF-A₁₆₅ and its antagonists contained significant amounts of free VEGF-A. Treatment of VEGF-A₁₆₅-challenged iBREC with ranibizumab or brolucizumab normalized expression of claudin-1 and claudin-5, but not completely that of PLVAP. Interestingly, the characteristic VEGF-A₁₆₅-induced relocalization of claudin-1 from the plasma membrane was reverted within one day by any of the VEGF antagonists, but reappeared despite their presence after further exposure for several days. Taken together, barrier dysfunction induced by VEGF-A₁₆₅ results from deregulated para- and transcellular flow but the precise nature or magnitude of underlying changes on a molecular level clearly depend on the time of exposure, evolving into a stage of VEGF-A₁₆₅-independent barrier impairment. These findings also provide a plausible explanation for resistance to treatment with VEGF-A antagonists frequently observed in clinical practice.

Transient Exposure of Endothelial Cells to Doxorubicin Leads to Long-Lasting Vascular Endothelial Growth Factor Receptor 2 Downregulation

Doxorubicin (Dox) is an effective antineoplastic drug with serious cardiotoxic side effects that persist after drug withdrawal and can lead to heart failure. Dysregulation of vascular endothelium has been linked to the development of Dox-induced cardiotoxicity, but it is unclear whether and how transient exposure to Dox leads to long-term downregulation of Endothelial Vascular Endothelial Growth Factor Receptor type2 (VEGFR2), essential for endothelial cells function. Using an in vitro model devised to study the long-lasting effects of brief endothelial cells exposure to Dox, we show that Dox leads to sustained protein synthesis inhibition and VEGFR2 downregulation. Transient Dox treatment led to the development of long-term senescence associated with a reduction in VEGFR2 levels that persisted days after drug withdrawal. By analyzing VEGFR2 turnover, we ruled out that its downregulation was depended on Dox-induced autophagy. Conversely, Dox induced p53 expression, reduced mTOR-dependent translation, and inhibited global protein synthesis. Our data contribute to a mechanistic basis to the permanent damage caused to endothelial cells by short-term Dox treatment.

Increased Vascular Endothelial Growth Factor Serum Level and the Role of +936C/T Gene Polymorphism in Chronic Obstructive Pulmonary Disease

Background and Objectives: Chronic obstructive pulmonary disease (COPD) represents a debilitating disease, with rising morbidity and mortality. Vascular endothelial growth factor (VEGF) plays a major role in angiogenesis, vascular permeability, and airway remodeling. The purpose of this study was to investigate the relationship between VEGF serum levels and VEGF +936 C/T gene polymorphism (rs3025039) with COPD, for the first time in a Romanian population. Materials and Methods: In total, 120 participants from Transylvania were included in this case-control study. Serum levels of VEGF were determined using an enzyme-linked immune-sorbent assay and rs3025039 was investigated by high molecular weight genomic deoxyribonucleic acid (DNA). Spirometric values, arterial blood gas analysis, and the Six Minute Walk Test (6MWT) outcome were also determined. Results: The serum level of VEGF was higher in the COPD group versus controls (p < 0.001), with a positive correlation with the 6MWT outcome. No significant difference was observed in the VEGF serum levels between VEGF +936C/T genotypes. There was no difference in the VEGF +936C/T genotype between COPD patients and healthy subjects (chi2 test p = 0.92, OR = 1.04, 95%CI = 0.41–2.62), but the presence of the T allele was significantly linked to the presence of COPD (chi2 test p = 0.02, OR = 2.36, 95%CI = 1.12–4.97). Conclusions: Higher VEGF serum levels were found in moderate and severe COPD and were positively correlated with the distance in the 6MWT. No significant difference was found between CC, CT, and TT genotypes of rs3025039 and the presence of COPD. The presence of the T allele was found to be linked to COPD and also to the degree of airway obstruction.

Caffeic acid phenethyl ester mitigates infertility: A crucial role of metalloproteinase and angiogenic factor in cadmium-induced testicular damage

Cadmium (Cd) is expected to cause deleterious effects on most organs, especially on the male reproductive system. The current study was performed to assess the effect of Cd on fertility in Swiss mice and to evaluate the protective role of caffeic acid phenethyl ester (CAPE) in relieving the detrimental effect of Cd. The mice were divided into four groups of 10: normal Group I received distilled water. Group II, III, and IV were injected 3 mg/kg body weight with Cd intraperitoneally for four consecutive days. Group III received saline. Group IV was treated with 3 mg/kg/day CAPE intraperitoneally for 6 days. Results indicated that CAPE brings about a highly significant improvement in fertility parameters, spermatogenesis, and reduced apoptotic percent. Moreover, metalloprotease-3 (MMP-3) and vascular endothelial growth factor reduced significantly. Overall, our results strongly suggest that CAPE has a protective effect, counteracts the toxic effects of Cd, and prevents testicular injury.

CD146, from a melanoma cell adhesion molecule to a signaling receptor

CD146 was originally identified as a melanoma cell adhesion molecule (MCAM) and highly expressed in many tumors and endothelial cells. However, the evidence that CD146 acts as an adhesion molecule to mediate a homophilic adhesion through the direct interactions between CD146 and itself is still lacking. Recent evidence revealed that CD146 is not merely an adhesion molecule, but also a cellular surface receptor of miscellaneous ligands, including some growth factors and extracellular matrixes. Through the bidirectional interactions with its ligands, CD146 is actively involved in numerous physiological and pathological processes of cells. Overexpression of CD146 can be observed in most of malignancies and is implicated in nearly every step of the development and progression of cancers, especially vascular and lymphatic metastasis. Thus, immunotherapy against CD146 would provide a promising strategy to inhibit metastasis, which accounts for the majority of cancer-associated deaths. Therefore, to deepen the understanding of CD146, we review the reports describing the newly identified ligands of CD146 and discuss the implications of these findings in establishing novel strategies for cancer therapy.

VEGF-A in Cardiomyocytes and Heart Diseases

The vascular endothelial growth factor (VEGF), a homodimeric vasoactive glycoprotein, is the key mediator of angiogenesis. Angiogenesis, the formation of new blood vessels, is responsible for a wide variety of physio/pathological processes, including cardiovascular diseases (CVD). Cardiomyocytes (CM), the main cell type present in the heart, are the source and target of VEGF-A and express its receptors, VEGFR1 and VEGFR2, on their cell surface. The relationship between VEGF-A and the heart is double-sided. On the one hand, VEGF-A activates CM, inducing morphogenesis, contractility and wound healing. On the other hand, VEGF-A is produced by CM during inflammation, mechanical stress and cytokine stimulation. Moreover, high concentrations of VEGF-A have been found in patients affected by different CVD, and are often correlated with an unfavorable prognosis and disease severity. In this review, we summarized the current knowledge about the expression and effects of VEGF-A on CM and the role of VEGF-A in CVD, which are the most important cause of disability and premature death worldwide. Based on clinical studies on angiogenesis therapy conducted to date, it is possible to think that the control of angiogenesis and VEGF-A can lead to better quality and span of life of patients with heart disease.

Transport and fate of aflibercept in VEGF-A165-challenged retinal endothelial cells

Retinal vessels are at least in part involved in clearing of Fc terminus-containing proteins from the vitreous. In vitro, the Fc fusion protein aflibercept is transported through a monolayer of unchallenged immortalized bovine retinal endothelial cells (iBREC), mediated by the neonatal Fc receptor (FcRn), but part of the Fc fusion protein is also degraded. Aflibercept's target VEGF-A not only enhances the permeability of REC by destabilization of tight junctions (TJs) thereby allowing for paracellular flow, it may also lower the intracellular stability of the Fc fusion protein by changing its binding properties to the FcRn. Therefore, we investigated the transport and fate of aflibercept in VEGF-A₁₆₅-challenged iBREC. All cell culture media were supplemented with 5% fetal bovine serum (FBS) as its absence results in accumulation of aflibercept in iBREC due to deregulated expression of transport proteins. Early after exposure of a confluent iBREC monolayer cultivated on gold electrodes to 5% FBS, the cell index (CI) - assessed as a measure of barrier function, cell viability and cell adhesion - transiently declined but recovered again within a few hours to high values. These values remained stable for several days associated with a strong expression of the TJ-protein claudin-1, indicative of a functional barrier formed by the iBREC monolayer. Transient changes of the plasma membrane localizations of claudin-5 and vascular endothelial cadherin - both important for regulation of paracellular flow - accompanied the transient reduction of the CI not prevented by VEGF-binding proteins. Treatment of iBREC with 50 ng/ml VEGF-A₁₆₅ for one day resulted in a strong and persistent decline of the CI associated with a low expression level of the TJ-protein claudin-1; reversion to normal values was complete one day after aflibercept's addition at a final concentration of 250 μg/ml. Expressions of other proteins involved in regulation of paracellular flow or transcellular transport were not significantly changed. More aflibercept passed through the monolayer of iBREC cultivated on permeable membrane inserts pretreated with VEGF-A for one day, but this was not affected by a FcRn-inhibiting antibody. Subcellular localization of aflibercept was hardly changed in VEGF-A-exposed iBREC 3 h after its addition to the cells; inhibition of (non)-lysosomal or proteasomal proteases then only weakly affected the amount of internalized aflibercept. iBREC also internalized VEGF-A which was barely detectable as early as 2 h after addition of aflibercept. In contrast, blocking the tyrosine kinase activity of VEGF receptor(s) did not prevent VEGF-A's uptake. Inhibition of cellular proteases strongly increased the amount of internalized VEGF-A in the absence and presence of the Fc fusion protein. We therefore conclude that a FcRn-mediated transport plays a minor role in aflibercept's passage through a leaky barrier of REC. Even early after addition of aflibercept to VEGF-A-exposed iBREC, the levels of free intracellular VEGF-A are low, as aflibercept likely prevents binding of VEGF-A to its receptor. Interestingly, the growth factor's detrimental effects still persist for nearly one day.

The Noonan Syndrome Gene Lztr1 Controls Cardiovascular Function by Regulating Vesicular Trafficking

RATIONALE

Noonan syndrome (NS) is one of the most frequent genetic disorders. Bleeding problems are among the most common, yet poorly defined complications associated with NS. A lack of consensus on the management of bleeding complications in patients with NS indicates an urgent need for new therapeutic approaches.

OBJECTIVE

Bleeding disorders have recently been described in patients with NS harboring mutations of LZTR1 (leucine zipper-like transcription regulator 1), an adaptor for CUL3 (CULLIN3) ubiquitin ligase complex. Here, we assessed the pathobiology of LZTR1-mediated bleeding disorders.

METHODS AND RESULTS

Whole-body and vascular specific knockout of Lztr1 results in perinatal lethality due to cardiovascular dysfunction. Lztr1 deletion in blood vessels of adult mice leads to abnormal vascular leakage. We found that defective adherent and tight junctions in Lztr1-depleted endothelial cells are caused by dysregulation of vesicular trafficking. LZTR1 affects the dynamics of fusion and fission of recycling endosomes by controlling ubiquitination of the ESCRT-III (endosomal sorting complex required for transport III) component CHMP1B (charged multivesicular protein 1B), whereas NS-associated LZTR1 mutations diminish CHMP1B ubiquitination. LZTR1-mediated dysregulation of CHMP1B ubiquitination triggers endosomal accumulation and subsequent activation of VEGFR2 (vascular endothelial growth factor receptor 2) and decreases blood levels of soluble VEGFR2 in Lztr1 haploinsufficient mice. Inhibition of VEGFR2 activity by cediranib rescues vascular abnormalities observed in Lztr1 knockout mice Conclusions: Lztr1 deletion phenotypically overlaps with bleeding diathesis observed in patients with NS. ELISA screening of soluble VEGFR2 in the blood of LZTR1-mutated patients with NS may predict both the severity of NS phenotypes and potential responders to anti-VEGF therapy. VEGFR inhibitors could be beneficial for the treatment of bleeding disorders in patients with NS.

Photobiomodulation effect on angiogenic proteins produced and released by dental pulp cells

OBJECTIVE

To verify the photobiomodulation effect on angiogenic proteins produced and released by dental human pulpal fibroblasts (HPFs).

MATERIAL AND METHODS

HPFs were irradiated with 660-nm low-level laser at fluences of 2.5 J/cm² and 3.7 J/cm². The control group was not irradiated. MTT, crystal violet, and ELISA assays respectively verified viability, proliferation, and angiogenic protein (supernatant/lysate) at 6 h, 12 h, and 24 h after photobiomodulation. Capillary-like structure formation assay verified functional role. Two-way ANOVA/Tukey's test and ANOVA/Bonferroni's multiple comparisons test respectively verified cell viability/proliferation and intragroup and intergroup comparisons of protein synthesis (p < 0.05).

RESULTS

Irradiated and non-irradiated HPFs showed statistically similar cell viability and proliferation pattern. Intragroup comparisons showed similar patterns of protein synthesis for all groups: VEGF-A, VEGF-C, and vascular endothelial growth factor receptor 1 (VEGFR1) increased significantly in the supernatant, while FGF-2 and VEGF-A increased significantly in the lysate. The lower fluence significantly increased BMP-9 (6 h) in the supernatant and VEGFR1 (6 h and 12 h) and VEGF-D (24 h) in the lysate, while the higher fluence significantly increased BMP-9 (6 h) in the supernatant and VEGFR1 (12 h) in the lysate. Regardless of the time, both fluences statistically downregulated placental growth factor (PLGF) and PDGF secretion. Both fluences statistically decreased VEGF-A secretion (24 h) and PLGF production (6 h).

CONCLUSION

Photobiomodulation produced stimulatory effects on angiogenic protein secretion by pulp fibroblasts. In terms of photobiomodulation, over time, both fluences significantly increased the secretion of VEGF-A, VEGF-C, and VEGFR1 and significantly upregulated BMP-9 (6 h) in the supernatant; for capillary-like structure formation, the fluence of 2.5 J/cm² was better than the fluence of 3.7 J/cm².

CLINICAL RELEVANCE

This study results addressed effective photobiomodulation parameters tailored for pulp angiogenesis.

Does photobiomodulation change the synthesis and secretion of angiogenic proteins by different pulp cell lineages?

This study aimed to compare the synthesis and secretion of VEGF-A, VEGF-C, VEGF-D, VEGFR1, VEGFR2, and FGF-2 between pulp fibroblasts from human primary teeth (HPF) and stem cell from human deciduous teeth (SHED) before and after photobiomodulation. HPF were obtained from explant technique and characterized by immunohistochemistry, while SHED were obtained from digestion technique and characterized by flow cytometry. HPF (control group) and SHED were plated, let to adhere, and put on serum starvation to synchronize the cell cycles prior to photobiomodulation. Then, both cell lineages were irradiated with 660-nm laser according to the following groups: 2.5 and 3.7 J/cm². MTT and crystal violet assays respectively verified viability and proliferation. ELISA Multiplex Assay assessed the following proteins: VEGF-A, VEGF-C, VEGF-D, VEGFR1, VEGFR2, FGF-2, at 6, 12, and 24 h after photobiomodulation, in supernatant and lysate. Two-way ANOVA/Tukey test evaluated cell viability and proliferation, while angiogenic production and secretion values were analyzed by one-way ANOVA (P < .05). Statistically similar HPF and SHED viability and proliferation patterns occurred before and after photobiomodulation (P > .05). HPF exhibited statistically greater values of all angiogenic proteins than did SHED, at all study periods, except for FGF-2 (supernatant; 12 h); VEGFR1 (lysate; non-irradiated; 12 h); and VEGFR1 (lysate; non-irradiated; 24 h). Photobiomodulation changed the synthesis and secretion of angiogenic proteins by HPF. HPF produced and secreted greater values of all tested angiogenic proteins than did SHED before and after irradiation with both energy densities of 2.5 and 3.7 J/cm².

Sustain, Adapt, and Overcome-Hypoxia Associated Changes in the Progression of Lymphatic Neoplasia

Irregular perfusion and related tissue hypoxia is a common feature of solid tumors the role of which in the survival and progression cancer has been gradually recognized. Adaptation and selection mechanisms in hypoxic areas in solid tumors are regulated by Hypoxia Inducible transcriptional factor 1 (HIF1) and other hypoxia mediators and are associated with aggressive clinical behavior in a large spectrum of malignancies. Aggressive forms of lymphatic neoplasias present with solid tumor-like features, also including rapid cell growth, necrosis and angiogenesis, the clinical potential of which is still underestimated. While the role of regional hypoxia in normal B-cell maturation and malignant transformation is becoming evident, the impact of tissue hypoxia on their behavior is not well-understood. Compared to some of the common solid cancer types data for some of the key regulators, such as HIF1 and HIF2, and for their downstream effectors are available in a limited fashion. In the current review we aim to overview the physiological aspects of major hypoxia pathways during B-cell maturation and adaptation-related changes reported in lymphatic neoplasia covering important targets, such as carbonic anhydrases IX and XII (CAIX, CAXII), glucose transporter 1 (GLUT-1) and vascular endothelial growth factor (VEGF). In conclusion, experimental and clinical results direct to important but currently unexploited role of hypoxia-driven resistance mechanisms especially in aggressive forms of B-cell neoplasia.

ATF-2 and Tpl2 regulation of endothelial cell cycle progression and apoptosis

Cells respond to soluble and membrane-bound factors to activate signalling cascades that control cell proliferation and cell death. Vascular endothelial growth factor A (VEGF-A) is a soluble ligand that modulates a variety of cellular responses including cell proliferation and apoptosis. It is not well understood how VEGF-A signalling pathways regulate cell proliferation and cell death. To address this, we examined VEGF-A-regulated signalling pathways in the cytosol and nucleus and functional requirement for such cellular responses. The VEGF-A-regulated transcription factor, ATF-2, is required for cell cycle proteins such as p53, p21 and Cyclin D1. A cytosolic serine/threonine protein kinase (Tpl2) modulates ATF-2-regulated effects on the endothelial cell cycle. Such regulatory effects impact on endothelial cell proliferation, cell viability and apoptosis. These cellular effects influence complex cell-based organisation such as endothelial tubulogenesis. Our study now provides a framework for incorporating VEGF-A-stimulated signalling events from the cytosol to the nucleus which helps to understand how cell proliferation and apoptosis are controlled.

Receptor-Mediated Endocytosis of VEGF-A in Rat Liver Sinusoidal Endothelial Cells

Background and Aims

Vascular endothelial growth factor (VEGF) receptors (VEGFR1 and VEGFR2) bind VEGF-A with high affinity. This study sought to determine the relative contributions of these two receptors to receptor-mediated endocytosis of VEGF-A and to clarify their endocytic itineraries in rat liver sinusoidal endothelial cells (LSECs).

Methods

Isolated LSECs and radiolabeled VEGF-A were used to examine surface binding and receptor-mediated endocytosis. Quantitative real time RT-PCR (Q-RT-PCR) and Western blotting were applied to demonstrate receptor expression.

Results

Q-RT-PCR analysis showed that VEGFR1 and VEGFR2 mRNA were expressed in LSECs. Ligand saturation analysis at 4°C indicated two different classes of [¹²⁵I]-VEGFA binding sites on LSECs with apparent dissociation constants of 8 and 210 pM. At 37°C, LSECs efficiently took up and degraded [¹²⁵I]-VEGF-A for at least 2 hours. Uptake of [¹²⁵I]-VEGF-A by LSECs was blocked by dynasore that inhibits dynamin-dependent internalization, whereas inhibition of cysteine proteases by leupeptin inhibited degradation without affecting the uptake of [¹²⁵I]-VEGF-A, suggesting that it is degraded following transport to lysosomes. Incubation of LSECs in the continued presence of a saturating concentration of unlabeled VEGF-A at 37°C was associated with a loss of as much as 75% of the total VEGFR2 within 30 min as shown by Western blot analysis, whereas there was no appreciable decrease in protein levels for VEGFR1 after 120 min incubation, suggesting that VEGF-A stimulation downregulates VEGFR2, but not VEGFR1, in LSECs. This possibility was supported by the observation that a hexapeptide that specifically blocks VEGF-A binding to VEGFR1 caused a marked reduction in the uptake of [¹²⁵I]-VEGF-A, whereas a control peptide had no effect. Finally, live cell imaging studies using a fluorescently labeled anti-VEGFR2 antibody showed that VEGFR2 was transported via early and late endosomes to reach endolysosomes where degradation of the VEGFR2 takes place.

Conclusion

Our studies suggest that, subsequent to VEGF-A binding and internalization, the unoccupied VEGFR1 may recycle to the cell surface allowing its reutilization, whereas the majority of the internalized VEGFR2 is targeted for degradation.

Tpl2 is required for VEGF-A-stimulated signal transduction and endothelial cell function

New blood vessel sprouting (angiogenesis) and vascular physiology are fundamental features of metazoan species but we do not fully understand how signal transduction pathways regulate diverse vascular responses. The vascular endothelial growth factor (VEGF) family bind membrane-bound receptor tyrosine kinases (VEGFRs), which trigger multiple signal transduction pathways and diverse cellular responses. We evaluated whether the MAP3K family member and proto-oncoprotein Tpl2 (MAP3K8) regulates basal and VEGF-A-stimulated signal transduction in endothelial cells. Notably, stimulation with exogenous VEGF-A increased Tpl2 mRNA levels and consequently de novo protein synthesis. Depletion of Tpl2 levels reveals a role in both basal and VEGF-A-stimulated endothelial cell responses, including endothelial-leukocyte interactions, monolayer permeability and new blood vessel formation. Under basal conditions, Tpl2 modulates a signal transduction cascade resulting in phosphorylation of a nuclear transcription factor (ATF-2) and altered endothelial gene expression, a pathway previously identified as crucial in VEGF-dependent vascular responses. Loss of Tpl2 expression or activity impairs signal transduction through Akt, eNOS and ATF-2, broadly impacting on endothelial function. Our study now provides a mechanism for Tpl2 as a central component of signal transduction pathways in the endothelium.

Summary: Our study shows that the growth factor VEGF-A stimulates synthesis in endothelial cells of a proto-oncoprotein and protein kinase, Tpl2, and this is required for signal transduction and angiogenesis.

Alternative Splicing in Angiogenesis

Alternative splicing of pre-mRNA allows the generation of multiple splice isoforms from a given gene, which can have distinct functions. In fact, splice isoforms can have opposing functions and there are many instances whereby a splice isoform acts as an inhibitor of canonical isoform function, thereby adding an additional layer of regulation to important processes. Angiogenesis is an important process that is governed by alternative splicing mechanisms. This review focuses on the alternative spliced isoforms of key genes that are involved in the angiogenesis process; VEGF-A, VEGFR1, VEGFR2, NRP-1, FGFRs, Vasohibin-1, Vasohibin-2, HIF-1α, Angiopoietin-1 and Angiopoietin-2.

Microparticles from vascular endothelial growth factor pathway inhibitor-treated cancer patients mediate endothelial cell injury

Vascular endothelial growth factor pathway inhibitors (VEGFi), used as anti-angiogenic drugs to treat cancer are associated with cardiovascular toxicities through unknown molecular mechanisms. Endothelial cell-derived microparticles (ECMPs) are biomarkers of endothelial injury and are also functionally active since they influence downstream target cell signalling and function. We questioned whether microparticle (MP) status is altered in cancer patients treated with VEGFi and whether they influence endothelial cell function associated with vascular dysfunction. Plasma MPs were isolated from cancer patients before and after treatment with VEGFi (pazopanib, sunitinib, or sorafenib). Human aortic endothelial cells (HAECs) were stimulated with isolated MPs (106 MPs/mL). Microparticle characterization was assessed by flow cytometry. Patients treated with VEGFi had significantly increased levels of plasma ECMP. Endothelial cells exposed to post-VEGFi treatment ECMPs induced an increase in pre-pro-ET-1 mRNA expression, corroborating the increase in endothelin-1 (ET-1) production in HAEC stimulated with vatalanib (VEGFi). Post-VEGFi treatment MPs increased generation of reactive oxygen species in HAEC, effects attenuated by ETA (BQ123) and ETB (BQ788) receptor blockers. VEGFi post-treatment MPs also increased phosphorylation of the inhibitory site of endothelial nitric oxide synthase (eNOS), decreased nitric oxide (NO), and increased ONOO- levels in HAEC, responses inhibited by ETB receptor blockade. Additionally, gene expression of proinflammatory mediators was increased in HAEC exposed to post-treatment MPs, effects inhibited by BQ123 and BQ788. Our findings define novel molecular mechanism involving interplay between microparticles, the ET-1 system and endothelial cell pro-inflammatory and redox signalling, which may be important in cardiovascular toxicity and hypertension associated with VEGFi anti-cancer treatment. New and noteworthy: our novel data identify MPs as biomarkers of VEGFi-induced endothelial injury and important mediators of ET-1-sensitive redox-regulated pro-inflammatory signalling in effector endothelial cells, processes that may contribute to cardiovascular toxicity in VEGFi-treated cancer patients.

Targeting Receptor Kinases in Colorectal Cancer

Colorectal cancer is the third most common malignancy in men and the second most common cancer in women. Despite the success of screening programs and the development of adjuvant therapies, the global burden of colorectal cancer is expected to increase by 60% to more than 2.2 million new cases and 1.1 million deaths by 2030. In recent years, a great effort has been made to demonstrate the utility of protein kinase inhibitors for cancer treatment. Considering this heterogeneous disease is defined by mutations that activate different Receptor Tyrosine Kinases (RTKs) and affect downstream components of RTK-activated transduction pathways, in this review we analyze the potential utility of different kinase inhibitors for colorectal cancer treatment.

Recombinant RGD-disintegrin DisBa-01 blocks integrin αvβ3 and impairs VEGF signaling in endothelial cells

Background

Integrins mediate cell adhesion, migration, and survival by connecting the intracellular machinery with the surrounding extracellular matrix. Previous studies demonstrated the interaction between α_vβ₃ integrin and VEGF type 2 receptor (VEGFR2) in VEGF-induced angiogenesis. DisBa-01, a recombinant His-tag fusion, RGD-disintegrin from Bothrops alternatus snake venom, binds to α_vβ₃ integrin with nanomolar affinity blocking cell adhesion to the extracellular matrix. Here we present in vitro evidence of a direct interference of DisBa-01 with α_vβ₃/VEGFR2 cross-talk and its downstream pathways.

Methods

Human umbilical vein (HUVECs) were cultured in plates coated with fibronectin (FN) or vitronectin (VN) and tested for migration, invasion and proliferation assays in the presence of VEGF, DisBa-01 (1000 nM) or VEGF and DisBa-01 simultaneously. Phosphorylation of α_vβ₃/VEGFR2 receptors and the activation of intracellular signaling pathways were analyzed by western blotting. Morphological alterations were observed and quantified by fluorescence confocal microscopy.

Results

DisBa-01 treatment of endothelial cells inhibited critical steps of VEGF-mediated angiogenesis such as migration, invasion and tubulogenesis. The blockage of α_vβ₃/VEGFR2 cross-talk by this disintegrin decreases protein expression and phosphorylation of VEGFR2 and β₃ integrin subunit, regulates FAK/SrC/Paxillin downstream signals, and inhibits ERK1/2 and PI3K pathways. These events result in actin re-organization and inhibition of HUVEC migration and adhesion. Labelled-DisBa-01 colocalizes with α_vβ₃ integrin and VEGFR2 in treated cells.

Conclusions

Disintegrin inhibition of α_vβ₃ integrin blocks VEGFR2 signalling, even in the presence of VEGF, which impairs the angiogenic mechanism. These results improve our understanding concerning the mechanisms of pharmacological inhibition of angiogenesis.

Electronic supplementary material

The online version of this article (10.1186/s12964-019-0339-1) contains supplementary material, which is available to authorized users.

Molecular Pharmacology of VEGF-A Isoforms: Binding and Signalling at VEGFR2

Vascular endothelial growth factor-A (VEGF-A) is a key mediator of angiogenesis, signalling via the class IV tyrosine kinase receptor family of VEGF Receptors (VEGFRs). Although VEGF-A ligands bind to both VEGFR1 and VEGFR2, they primarily signal via VEGFR2 leading to endothelial cell proliferation, survival, migration and vascular permeability. Distinct VEGF-A isoforms result from alternative splicing of the Vegfa gene at exon 8, resulting in VEGFxxxa or VEGFxxxb isoforms. Alternative splicing events at exons 5⁻7, in addition to recently identified posttranslational read-through events, produce VEGF-A isoforms that differ in their bioavailability and interaction with the co-receptor Neuropilin-1. This review explores the molecular pharmacology of VEGF-A isoforms at VEGFR2 in respect to ligand binding and downstream signalling. To understand how VEGF-A isoforms have distinct signalling despite similar affinities for VEGFR2, this review re-evaluates the typical classification of these isoforms relative to the prototypical, “pro-angiogenic” VEGF165a. We also examine the molecular mechanisms underpinning the regulation of VEGF-A isoform signalling and the importance of interactions with other membrane and extracellular matrix proteins. As approved therapeutics targeting the VEGF-A/VEGFR signalling axis largely lack long-term efficacy, understanding these isoform-specific mechanisms could aid future drug discovery efforts targeting VEGF receptor pharmacology.

Tetrandrine suppresses lung cancer growth and induces apoptosis, potentially via the VEGF/HIF-1α/ICAM-1 signaling pathway

The present study investigated the effect of tetrandrine on lung cancer cell growth and apoptosis, and its possible underlying molecular mechanism. A549 human lung cancer cells were incubated with between 2.5 and 10 µM tetrandrine for 12, 24 and 48 h, following which the effect of tetrandrine on cell viability and apoptosis were assessed using an MTT assay and flow cytometry. ELISA and western blotting were used to analyze VEGF activity, and the expression of poly (ADP-ribose) polymerase (PARP), phosphorylated protein kinase B (Akt), Bcl-2-associated X protein (Bax), hypoxia inducible factor (HIF)-1α and inter-cellular adhesion molecule-1 (ICAM-1). Tetrandrine effectively suppressed the growth of and induced apoptosis in A549 lung cancer cells. The expression of PARP, Bax, intercellular adhesion molecule-1 (ICAM-1) and vascular endothelial growth factor (VEGF) was significantly upregulated, and the phosphorylation of Akt and expression of HIF-1α was significantly suppressed in A549 lung cancer cells. Therefore, tetrandrine may suppress cell viability and induce apoptosis via the VEGF/HIF-1α/ICAM-1 signaling pathway.

Effects of vascular endothelial growth factors and their receptors on megakaryocytes and platelets and related diseases

It is well known that vascular endothelial growth factors (VEGFs) and their receptors (vascular endothelial growth factor receptors, VEGFRs) are expressed in different tissues, and VEGF-VEGFR loops regulate a wide range of responses, including metabolic homeostasis, cell proliferation, migration and tubuleogenesis. As ligands, VEGFs act on three structurally related VEGFRs (VEGFR1, VEGFR2 and VEGFR3 [also termed FLT1, KDR and FLT4, respectively]) that deliver downstream signals. Haematopoietic stem cells (HSCs), megakaryocytic cell lines, cultured megakaryocytes (MKs), primary MKs and abnormal MKs express and secrete VEGFs. During the development from HSCs to MKs, VEGFR1, VEGFR2 and VEGFR3 are expressed at different developmental stages, respectively, and re-expressed, e.g., VEGFR2, and play different roles in commitment, differentiation, proliferation, survival and polyplodization of HSCs/MKs via autocrine, paracrine and/or even intracrine loops. Moreover, VEGFs and their receptors are abnormally expressed in MK-related diseases, including myeloproliferative neoplasms, myelodysplastic syndromes and acute megakaryocytic leukaemia (a rare subtype of acute myeloid leukaemia), and they lead to the disordered proliferation/differentiation of bone marrow cells and angiogenesis, indicating that they are closely related to these diseases. Thus, targeting VEGF-VEGFR loops may be of potential therapeutic value.

Expression of VEGFR-2 during Liver Regeneration after Partial Hepatectomy in a Bioluminescence Mouse Model

BACKGROUND

Liver regeneration requires the formation of new blood vessels. Endothelial cell proliferation is stimulated by vascular endothelial growth factor (VEGF) and its receptor tyrosine kinase VEGFR-2. The aim of this study was to investigate VEGFR-2 expression in vivo during liver regeneration after partial hepatectomy (PHx).

METHODS

Transgenic VEGFR-2-luc mice were used in which the luciferase reporter gene was under control of the VEGFR-2 promoter. Following 2/3 PHx, the mice underwent in vivo bioluminescence imaging until the 14th postoperative day. Additionally, liver tissue was analyzed by immunohistochemistry, in vitro luminescence assays, and quantitative RT-PCR.

RESULTS

In vivo bioluminescence imaging showed a significant increase in VEGFR-2 promoter activity after PHx. Maximum signal was recorded on the 3rd day; 8 days postoperatively the signal intensity decreased significantly. On the 14th day, bioluminescence signal reached almost baseline levels. Immunohistochemistry, quantitative RT-PCR, and in vitro luminescence confirmed a significant increase on the 3rd day following resection. The mRNA expression of VEGFR-2 was significantly higher on day 3 than preoperatively as well as on day 8.

CONCLUSION

In vivo bioluminescence imaging with transgenic VEGFR-2-luc mice is feasible and provides a convenient model for noninvasively studying VEGFR-2 expression during liver regeneration. This may facilitate further experiments with modulation of angiogenesis by different substances.

Ubiquitination of basal VEGFR2 regulates signal transduction and endothelial function

Cell surface receptors can undergo recycling or proteolysis but the cellular decision-making events that sort between these pathways remain poorly defined. Vascular endothelial growth factor A (VEGF-A) and vascular endothelial growth factor receptor 2 (VEGFR2) regulate signal transduction and angiogenesis, but how signaling and proteolysis is regulated is not well understood. Here, we provide evidence that a pathway requiring the E1 ubiquitin-activating enzyme UBA1 controls basal VEGFR2 levels, hence metering plasma membrane receptor availability for the VEGF-A-regulated endothelial cell response. VEGFR2 undergoes VEGF-A-independent constitutive degradation via a UBA1-dependent ubiquitin-linked pathway. Depletion of UBA1 increased VEGFR2 recycling from endosome-to-plasma membrane and decreased proteolysis. Increased membrane receptor availability after UBA1 depletion elevated VEGF-A-stimulated activation of key signaling enzymes such as PLCγ1 and ERK1/2. Although UBA1 depletion caused an overall decrease in endothelial cell proliferation, surviving cells showed greater VEGF-A-stimulated responses such as cell migration and tubulogenesis. Our study now suggests that a ubiquitin-linked pathway regulates the balance between receptor recycling and degradation which in turn impacts on the intensity and duration of VEGF-A-stimulated signal transduction and the endothelial response.

A Review of Anti-Angiogenic Targets for Monoclonal Antibody Cancer Therapy

Tumor angiogenesis is a key event that governs tumor progression and metastasis. It is controlled by the complicated and coordinated actions of pro-angiogenic factors and their receptors that become upregulated during tumorigenesis. Over the past several decades, vascular endothelial growth factor (VEGF) signaling has been identified as a central axis in tumor angiogenesis. The remarkable advent of recombinant antibody technology has led to the development of bevacizumab, a humanized antibody that targets VEGF and is a leading clinical therapy to suppress tumor angiogenesis. However, despite the clinical efficacy of bevacizumab, its significant side effects and drug resistance have raised concerns necessitating the identification of novel drug targets and development of novel therapeutics to combat tumor angiogenesis. This review will highlight the role and relevance of VEGF and other potential therapeutic targets and their receptors in angiogenesis. Simultaneously, we will also cover the current status of monoclonal antibodies being developed to target these candidates for cancer therapy.

VEGF isoforms have differential effects on permeability of human pulmonary microvascular endothelial cells

BACKGROUND

Alternative splicing of Vascular endothelial growth factor-A mRNA transcripts (commonly referred as VEGF) leads to the generation of functionally differing isoforms, the relative amounts of which have potentially significant physiological outcomes in conditions such as acute respiratory distress syndrome (ARDS). The effect of such isoforms on pulmonary vascular permeability is unknown. We hypothesised that VEGF₁₆₅a and VEGF₁₆₅b isoforms would have differing effects on pulmonary vascular permeability caused by differential activation of intercellular signal transduction pathways.

METHOD

To test this hypothesis we investigated the physiological effect of VEGF₁₆₅a and VEGF₁₆₅b on Human Pulmonary Microvascular Endothelial Cell (HPMEC) permeability using three different methods: trans-endothelial electrical resistance (TEER), Electric cell-substrate impedance sensing (ECIS) and FITC-BSA passage. In addition, potential downstream signalling pathways of the VEGF isoforms were investigated by Western blotting and the use of specific signalling inhibitors.

RESULTS

VEGF₁₆₅a increased HPMEC permeability using all three methods (paracellular and transcellular) and led to associated VE-cadherin and actin stress fibre changes. In contrast, VEGF₁₆₅b decreased paracellular permeability and did not induce changes in VE-cadherin cell distribution. Furthermore, VEGF₁₆₅a and VEGF₁₆₅b had differing effects on both the phosphorylation of VEGF receptors and downstream signalling proteins pMEK, p42/44MAPK, p38 MAPK, pAKT and peNOS. Interestingly specific inhibition of the pMEK, p38 MAPK, PI3 kinase and eNOS pathways blocked the effects of both VEGF₁₆₅a and VEGF₁₆₅b on paracellular permeability and the effect of VEGF₁₆₅a on proliferation/migration, suggesting that this difference in cellular response is mediated by an as yet unidentified signalling pathway(s).

CONCLUSION

This study demonstrates that the novel isoform VEGF₁₆₅a and VEGF₁₆₅b induce differing effects on permeability in pulmonary microvascular endothelial cells.

The Different Effects of VEGFA121 and VEGFA165 on Regulating Angiogenesis Depend on Phosphorylation Sites of VEGFR2

The effects of VEGFA isoforms on the vascular permeability and structure are still unclear. In this study, we found that VEGFA121 and VEGFA165, 2 isoforms of VEGFA, exerted the opposing effects of antiangiogenesis and proangiogenesis on regulating vascular endothelia cells proliferation and tube formation. The 2 isoforms affected the protein expression of Ras-related protein 1-GTPase-activating protein 1 (Rap1GAP) and thrombospondin 1, 2 important signal molecules of Rap1GAP/thrombospondin 1 signal pathway in primary human umbilical vein endothelial cells by regulating 2 different phosphorylating sites of VEGFR2, Tyr(1175) and Tyr(1214). We also found that VEGFA121 and VEGFA165 regulating angiogenesis was related to their regulating VEGFR2 and Rap1GAP/thrombospondin 1 signal pathway with the technology of RNA intervening the gene expression of VEGFR2 and Rap1GAP. Meanwhile, 2 inhibitors of VEGFR2, cabozantinib malate and ZM 323881 HCl (ZM), were used to investigate the relationship among VEGFA(121 and 165), VEGFR2, and angiogenesis. It was demonstrated that cabozantinib malate blocked VEGFA121 and VEGFA165 binding to VEGFR2 and inhibited angiogenesis by specifically binding to VEGFR2 rather than changing VEGFR2 phosphorylation or regulating the expression of VEGFR2. However, ZM antagonized the effect of VEGFA on angiogenesis by specifically reversing the phosphorylation induced by VEGFA121 and VEGFA165. The experiments in vivo also demonstrated that obvious abnormality of VEGFA121 and VEGFA165 presented in the serum of ulcerative colitis (UC) rats compared with that of the normal rats. ZM could promote the repairation of the injuries of the vessels and tissues of colonic mucosa of UC rats and caused mild inflammation in colonic mucosa of normal rats. On the contrary, cabozantinib malate caused injury of vessels and inflammation in the colonic mucosa of normal rats and aggravated the injuries of the vessels and inflammation in the colonic mucosa of UC rats. Hence, our data indicated that the activation of different phosphorylation sites of VEGFR2 leaded to VEGFA121 and VEGFA165 exerting opposing effects on angiogenesis, and it might be an underlying pathogenesis of UC and a potential target for UC treatment.

Antileukemic effects of midostaurin in acute myeloid leukemia - the possible importance of multikinase inhibition in leukemic as well as nonleukemic stromal cells

INTRODUCTION

Midostaurin is a multikinase inhibitor that inhibits receptor tyrosine kinases (Flt3, CD117/c-kit, platelet-derived growth factor receptor, vascular endothelial growth factor receptor 2) as well as non-receptor tyrosine kinases (Frg, Src, Syk, Protein kinase C). Combination of midostaurin with conventional intensive chemotherapy followed by one year maintenance monotherapy was recently reported to improve the survival of acute myeloid leukemia (AML) patients with Flt3 mutations. Areas covered: Relevant publications were identified through literature searches in the PubMed database. We searched for (i) original articles describing the results from clinical studies; (ii) published articles describing the importance of midostaurin-inhibited kinases for leukemogenesis and chemosensitivity. Expert opinion: Midostaurin monotherapy is well tolerated, combined with conventional chemotherapy gastrointestinal toxicity increases significantly. Midostaurin alters anthracycline pharmacokinetics. Furthermore, its antileukemic effects may not only be mediated through Flt3 inhibition alone; the inhibition of other kinases may also be important for the overall antileukemic effect. Midostaurin may then have direct effects on the leukemic cells but also indirect antileukemic effects through inhibition of the AML-supporting effects of neighboring stromal cells in the bone marrow microenvironment. Midostaurin may thus be used in combination with intensive chemotherapy, as maintenance treatment or as disease-stabilizing treatment for elderly unfit patients.

Modulating carbohydrate-protein interactions through glycoengineering of monoclonal antibodies to impact cancer physiology

Diverse glycans on proteins impact cell and organism physiology, along with drug activity. Since many protein-based biotherapeutics are glycosylated and these glycans have biological activity, there is a desire to engineer glycosylation for recombinant protein-based biotherapeutics. Engineered glycosylation can impact the recombinant protein efficacy and also influence many cell pathways by first changing glycan-protein interactions and consequently modulating disease physiologies. However, its complexity is enormous. Recent advances in glycoengineering now make it easier to modulate protein-glycan interactions. Here, we discuss how engineered glycans contribute to therapeutic monoclonal antibodies (mAbs) in the treatment of cancers, how these glycoengineered therapeutic mAbs affect the transformed phenotypes and downstream cell pathways. Furthermore, we suggest how systems biology can help in the next generation mAb glycoengineering process by aiding in data analysis and guiding engineering efforts to tailor mAb glycan and ultimately drug efficacy, safety and affordability.

VEGF-A isoforms program differential VEGFR2 signal transduction, trafficking and proteolysis

Vascular endothelial growth factor A (VEGF-A) binding to the receptor tyrosine kinase VEGFR2 triggers multiple signal transduction pathways, which regulate endothelial cell responses that control vascular development. Multiple isoforms of VEGF-A can elicit differential signal transduction and endothelial responses. However, it is unclear how such cellular responses are controlled by isoform-specific VEGF-A-VEGFR2 complexes. Increasingly, there is the realization that the membrane trafficking of receptor-ligand complexes influences signal transduction and protein turnover. By building on these concepts, our study shows for the first time that three different VEGF-A isoforms (VEGF-A165, VEGF-A121 and VEGF-A145) promote distinct patterns of VEGFR2 endocytosis for delivery into early endosomes. This differential VEGFR2 endocytosis and trafficking is linked to VEGF-A isoform-specific signal transduction events. Disruption of clathrin-dependent endocytosis blocked VEGF-A isoform-specific VEGFR2 activation, signal transduction and caused substantial depletion in membrane-bound VEGFR1 and VEGFR2 levels. Furthermore, such VEGF-A isoforms promoted differential patterns of VEGFR2 ubiquitylation, proteolysis and terminal degradation. Our study now provides novel insights into how different VEGF-A isoforms can bind the same receptor tyrosine kinase and elicit diverse cellular outcomes.