Domains I and IV of annexin A2 affect the formation and integrity of in vitro capillary-like networks

Annexin A2 promotes development of retinal neovascularization through PI3K/ AKT signaling pathway

PURPOSE

Retinal Neovascularization (RNV) is a pathological characteristic of ocular diseases. Annexin A2 (ANXA2) plays important roles in RNV while the mechanism remains unclear. The study aimed to explore relationship between ANXA2 and PI3K/AKT signaling pathway in RNV.

METHODS

We used human retinal vascular endothelial cells (HRECs) and oxygen-induced retinopathy (OIR) mice model to show ANXA2 can promote the development of RNV through PI3K/AKT signaling pathway. We divided HRECs into six groups by infecting lentivirus containing appropriate plasmid and adding corresponding solution. Assays showing ability of HRECs were performed in vitro. Mice were randomly divided into three groups and treated accordingly.

RESULTS

Expression of ANXA2 and activity of PI3K/AKT signaling pathway in HRECs were detected. RNV and expression of ANXA2 in mice retinas were detected. Results showed that ANXA2 expression is positively related with RNV-forming ability of HRECs in vitro and development of RNV in vivo while low activity of PI3K/AKT signaling pathway could attenuate the role of ANXA2.

CONCLUSIONS

We can make ANXA2 and PI3K/ AKT signaling pathway as a promising target for the regulation of pathological neovascularization of the retina, which also provides a novel idea for effective prevention and treatment of diseases related to RNV in future.

Recombinant annexin A2 inhibits peripheral leukocyte activation and brain infiltration after traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is a significant cause of death and disability worldwide. The TLR4-NFκB signaling cascade is the critical pro-inflammatory activation pathway of leukocytes after TBI, and modulating this signaling cascade may be an effective therapeutic target for treating TBI. Previous studies indicate that recombinant annexin A2 (rA2) might be an interactive molecule modulating the TLR4-NFκB signaling; however, the role of rA2 in regulating this signaling pathway in leukocytes after TBI and its subsequent effects have not been investigated.

METHODS

C57BL/6 mice were subjected to TBI and randomly divided into groups that received intraperitoneal rA2 or vehicle at 2 h after TBI. The peripheral leukocyte activation and infiltrating immune cells were examined by flow cytometry, RT-qPCR, and immunostaining. The neutrophilic TLR4 expression on the cell membrane was examined by flow cytometry and confocal microscope, and the interaction of annexin A2 with TLR4 was assessed by co-immunoprecipitation coupled with Western blotting. Neuroinflammation was measured via cytokine proteome profiler array and RT-qPCR. Neurodegeneration was determined by Western blotting and immunostaining. Neurobehavioral assessments were used to monitor motor and cognitive function. Brain tissue loss was assessed via MAP2 staining.

RESULTS

rA2 administration given at 2 h after TBI significantly attenuates neutrophil activation and brain infiltration at 24 h of TBI. In vivo and in vitro data show that rA2 binds to and reduces TLR4 expression on the neutrophil surface and suppresses TLR4/NFκB signaling pathway in neutrophils at 12 h after TBI. Furthermore, rA2 administration also reduces pro-inflammation of brain tissues within 24 h and neurodegeneration at 48 h after TBI. Lastly, rA2 improves long-term sensorimotor ability and cognitive function, and reduces brain tissue loss at 28 days after TBI.

CONCLUSIONS

Systematic rA2 administration at 2 h after TBI significantly inhibits activation and brain infiltration of peripheral leukocytes, especially neutrophils at the acute phase. Consequently, rA2 reduces the detrimental brain pro-inflammation-associated neurodegeneration and ultimately ameliorates neurological deficits after TBI. The underlying molecular mechanism might be at least in part attributed to rA2 bindings to pro-inflammatory receptor TLR4 in peripheral leukocytes, thereby blocking NFκB signaling activation pathways following TBI.

The role of microenvironment in tumor angiogenesis

Tumor angiogenesis is necessary for the continued survival and development of tumor cells, and plays an important role in their growth, invasion, and metastasis. The tumor microenvironment—composed of tumor cells, surrounding cells, and secreted cytokines—provides a conducive environment for the growth and survival of tumors. Different components of the tumor microenvironment can regulate tumor development. In this review, we have discussed the regulatory role of the microenvironment in tumor angiogenesis. High expression of angiogenic factors and inflammatory cytokines in the tumor microenvironment, as well as hypoxia, are presumed to be the reasons for poor therapeutic efficacy of current anti-angiogenic drugs. A combination of anti-angiogenic drugs and antitumor inflammatory drugs or hypoxia inhibitors might improve the therapeutic outcome.

Annexin A3 is necessary for parallel artery-vein alignment in the mouse retina

BACKGROUND

Annexin A3 (Anxa3) is a member of the calcium-regulated, cell membrane-binding family of annexin proteins. We previously confirmed that Anxa3 is expressed in the endothelial lineage in vertebrates and that loss of anxa3 in Xenopus laevis leads to embryonic blood vessel defects. However, the biological function of Anxa3 in mammals is completely unknown. In order to investigate Anxa3 vascular function in mammals, we generated an endothelial cell-specific Anxa3 conditional knockout mouse model (Anxa3f/f ;Tie2-Cre).

RESULTS

Anxa3f/f ;Tie2-Cre mice are born at Mendelian ratios and display morphologically normal blood vessels during development. However, loss of Anxa3 leads to artery-vein (AV) misalignment characterized by atypical AV crossovers in the postnatal and adult retina.

CONCLUSIONS

Anxa3 is not essential for embryonic blood vessel formation but is required for proper parallel AV alignment in the murine retina. AV crossovers associated with Anxa3f/f ;Tie2-Cre mice are similar to AV intersections observed in patients with branch retinal vein occlusion (BRVO), although we did not observe occluded vessels. This new Anxa3 mouse model may provide a basis for understanding AV crossover formation associated with BRVO.

Domain IV of Annexin A5 Is Critical for Binding Calcium and Guarantees Its Maximum Binding to the Phosphatidylserine Membrane

Background: Although domain IV of annexin A5 (anxA5) may be less effective in binding phosphatidylserine (PS), the four domains together may guarantee the maximum binding of anxA5 to the PS membrane. Additionally, previous research has shown that annexin mutants lacking one or more domain(s) have different biological activities compared to the wild-type. The present research mainly aims to study the role of domain IV in the crucial PS-binding function of anxA5. Methods: The domain IV-truncated anxA5 protein was constructed and purified. Isothermal titration calorimetry, flow cytometry and activated partial thromboplastin time were adopted to examine the function of domain IV in anxA5-PS binding directly or indirectly. Results: The domain IV-truncated form of anxA5 is impaired in binding PS liposome and apoptotic cells, and anticoagulation activity. The mutant cannot bind calcium, but binds PS only in the presence of calcium. Conclusions: Truncation of domain IV of anxA5 destroys its calcium-binding ability and impairs its PS-binding activity. Truncation of domain IV may induce conformation change of anxA5 or reduce the hydrophobic interactions between protein and membrane, which may explain the decrease of PS-binding affinity of the mutant.

Molecular Regulation of Sprouting Angiogenesis

The term angiogenesis arose in the 18th century. Several studies over the next 100 years laid the groundwork for initial studies performed by the Folkman laboratory, which were at first met with some opposition. Once overcome, the angiogenesis field has flourished due to studies on tumor angiogenesis and various developmental models that can be genetically manipulated, including mice and zebrafish. In addition, new discoveries have been aided by the ability to isolate primary endothelial cells, which has allowed dissection of various steps within angiogenesis. This review will summarize the molecular events that control angiogenesis downstream of biochemical factors such as growth factors, cytokines, chemokines, hypoxia-inducible factors (HIFs), and lipids. These and other stimuli have been linked to regulation of junctional molecules and cell surface receptors. In addition, the contribution of cytoskeletal elements and regulatory proteins has revealed an intricate role for mobilization of actin, microtubules, and intermediate filaments in response to cues that activate the endothelium. Activating stimuli also affect various focal adhesion proteins, scaffold proteins, intracellular kinases, and second messengers. Finally, metalloproteinases, which facilitate matrix degradation and the formation of new blood vessels, are discussed, along with our knowledge of crosstalk between the various subclasses of these molecules throughout the text. Compr Physiol 8:153-235, 2018.

Anti-angiogenic agents for the treatment of solid tumors: Potential pathways, therapy and current strategies - A review

Recent strategies for the treatment of cancer, other than just tumor cell killing have been under intensive development, such as anti-angiogenic therapeutic approach. Angiogenesis inhibition is an important strategy for the treatment of solid tumors, which basically depends on cutting off the blood supply to tumor micro-regions, resulting in pan-hypoxia and pan-necrosis within solid tumor tissues. The differential activation of angiogenesis between normal and tumor tissues makes this process an attractive strategic target for anti-tumor drug discovery. The principles of anti-angiogenic treatment for solid tumors were originally proposed in 1972, and ever since, it has become a putative target for therapies directed against solid tumors. In the early twenty first century, the FDA approved anti-angiogenic drugs, such as bevacizumab and sorafenib for the treatment of several solid tumors. Over the past two decades, researches have continued to improve the performance of anti-angiogenic drugs, describe their drug interaction potential, and uncover possible reasons for potential treatment resistance. Herein, we present an update to the pre-clinical and clinical situations of anti-angiogenic agents and discuss the most recent trends in this field.

Post-translational modifications of Annexin A2 are linked to its association with perinuclear nonpolysomal mRNP complexes

Various post‐translational modifications (PTMs) regulate the localisation and function of the multifunctional protein Annexin A2 (AnxA2). In addition to its various tasks as a cytoskeletal‐ and membrane‐associated protein, AnxA2 can function as a trans‐acting protein binding to cis‐acting sequences of specific mRNAs. In the present study, we have examined the role of Ser25 phosphorylation in subcellular localisation of AnxA2 and its interaction with mRNP complexes. Subcellular fractionation and confocal microscopy of rat neuroendocrine PC12 cells showed that Ser25‐phosphorylated AnxA2 (pSer25AnxA2) is absent from the nucleus and mainly localised to the perinuclear region, evidently associating with both membranes and cytoskeletal elements. Perinuclear targeting of AnxA2 was abolished by inhibition of protein kinase C activity, which resulted in cortical enrichment of the protein. Although oligo(dT)‐affinity purification of mRNAs revealed that pSer25AnxA2 associates with nonpolysomal, translationally inactive mRNP complexes, it displayed only partial overlap with a marker of P‐bodies. The phosphorylated protein is present as high‐molecular‐mass forms, indicating that it contains additional covalent PTMs, apparently triggered by its Ser25 phosphorylation. The subcellular distributions of these forms clearly differ from the main form of AnxA2 and are also distinct from that of Tyr23‐phosphorylated AnxA2. Immunoprecipitation verified that these high‐molecular‐mass forms are due to ubiquitination and/or sumoylation. Moreover, these results indicate that Ser25 phosphorylation and ubiquitin/SUMO1 conjugation of AnxA2 promote its association with nonpolysomal mRNAs, providing evidence of a possible mechanism to sequester a subpopulation of mRNAs in a translationally inactive and transport competent form at a distinct subcellular localisation.

Angiogenesis inhibitors as therapeutic agents in cancer: Challenges and future directions

Angiogenesis has become an attractive target for cancer therapy since the US Food and Drug Administration (FDA) approved the first angiogenesis inhibitor (bevacizumab) for the treatment of metastatic colorectal cancer in 2004. In following years, a large number of angiogenesis inhibitors have been discovered and developed, ranging from monoclonal antibodies, endogenous peptides, to small organic molecules and microRNAs. Many of them are now entering the clinical trial, or achieving approval for clinical use. However, major limitations have been observed about angiogenesis inhibitors by continued clinical investigations, such as resistance, enhancing tumor hypoxia and reducing delivery of chemotherapeutic agents, which might be the main reason for poor improvement in overall survival after angiogenesis inhibitor administration in clinic. Therefore, optimal anti-angiogenic therapy strategies become critical. The present review summarizes recent researches in angiogenesis inhibitors, and proposes a perspective on future directions in this field.

Reactive oxygen species exert opposite effects on Tyr23 phosphorylation of the nuclear and cortical pools of annexin A2

Annexin A2 (AnxA2) is a multi-functional and -compartmental protein whose subcellular localisation and functions are tightly regulated by its post-translational modifications. AnxA2 and its Tyr23-phosphorylated form (pTyr23AnxA2) are involved in malignant cell transformation, metastasis and angiogenesis. Here, we show that H₂O₂ exerts rapid, simultaneous and opposite effects on the Tyr23 phosphorylation status of AnxA2 in two distinct compartments of rat pheochromocytoma (PC12) cells. Reactive oxygen species induce dephosphorylation of pTyr23AnxA2 located in the PML bodies of the nucleus, whereas AnxA2 associated with F-actin at the cell cortex is Tyr23 phosphorylated. The H₂O₂-induced responses in both compartments are transient and the pTyr23AnxA2 accumulating at the cell cortex is subsequently incorporated into vesicles and then released to the extracellular space. Blocking nuclear export by leptomycin B does not affect the nuclear pool of pTyr23AnxA2, but increases the amount of total AnxA2 in this compartment, indicating that the protein might have several functions in the nucleus. These results suggest that Tyr23 phosphorylation can regulate the function of AnxA2 at distinct subcellular sites.

Summary: Reactive oxygen species cause two opposite and transient Tyr23-based modifications of annexin A2; its dephosphorylation in the nucleus and phosphorylation at the cell cortex, resulting in release of the protein in exosomes.

Atorvastatin protects endothelial colony‑forming cells against H2O2‑induced oxidative damage by regulating the expression of annexin A2

Endothelial dysfunction and injury are central events in the pathogenesis of ischemic vascular disorders. Endothelial progenitor cells (EPCs) are mobilized from the bone marrow into the peripheral circulation, where they locate to sites of injured endothelium and are involved in endothelial repair and vascular regeneration. During these processes, EPCs are exposed to oxidative stress, a crucial pathological condition, which occurs during vascular injury and limits the efficacy of EPCs in the repair of injured endothelium. Statins are effective inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase, and are commonly used to manage and prevent ischemic vascular disease by reducing plasma cholesterol levels. In addition to lowering cholesterol, statins have also been reported to exert pleiotropic actions, including anti-inflammatory and anti-oxidative activities. The present study aimed to investigate the ability of atorvastatin to protect endothelial colony-forming cells (ECFCs), a homogeneous subtype of EPCs, from hydrogen peroxide (H₂O₂)-induced oxidative damage, and to determine the mechanism underlying this protective action. MTT assay, acridine orange/ethidium bromide staining, reactive oxygen species assay, western blot analysis and tube formation assay were employed. The results demonstrated that H₂O₂ induced cell death and decreased the tube-forming ability of the ECFCs, in a concentration-dependent manner; however, these effects were partially attenuated following administration of atorvastatin. The reversion of the quantitative and qualitative impairment of the H₂O₂-treated ECFCs appeared to be mediated by the regulation of annexin A2, as the expression levels of annexin A2 were decreased following treatment with H₂O₂ and increased following treatment with atorvastatin. These results indicated that annexin A2 may be involved in the H₂O₂-induced damage of ECFCs, and in the protective activities of atorvastatin in response to oxidative stress.

The native structure of annexin A2 peptides in hydrophilic environment determines their anti-angiogenic effects

The progression of aggressive cancer occurs via angiogenesis and metastasis makes these processes important targets for the development of anti-cancer agents. However, recent studies have raised the concern that selective inhibition of angiogenesis results in a switch towards increased tumour growth and metastasis. Since Annexin A2 (AnxA2) is involved in both angiogenesis and metastasis, it may serve as an ideal target for the simultaneous inhibition of both processes. Based on the discovery that domains I (D(I)) and IV (D(IV)) of AnxA2 are potent inhibitors of angiogenesis, we designed seven peptides derived from these domains based on AnxA2 crystal structures. The peptides were expressed as fusion peptides to increase their folding and solubility. Light scattering, far-UV circular dichroism and thermal transition analyses were employed to investigate their aggregation tendencies, α-helical propensity and stability, respectively. 2,2,2-trifluoroethanol (50%) increased the α-helical propensities of all peptides, indicating that they may favour a hydrophobic environment, but did not enhance their thermal stability. D(I)-P2 appears to be the most stable and folded peptide in a hydrophilic environment. The secondary structure of D(I)-P2 was confirmed by nuclear magnetic resonance spectra. The effect of the seven AnxA2 peptides on the formation and integrity of capillary-like networks was studied in a co-culture system mimicking many of the angiogenesis-related processes. Notably, D(I)-P2 inhibited significantly network formation in this system, indicating that the folded D(I)-P2 peptide interferes with vascular endothelial growth factor-dependent pro-angiogenic processes. Thus, this peptide has the potential of being developed further as an anti-angiogenic drug.

Association of annexin A2 with cancer development (Review)

Annexin A2 (ANXA2) is a well-known calcium-dependent phospholipid binding protein widely distributed in the nucleus, cytoplasm and extracellular surface of various eukaryotic cells. It has been recognized as a pleiotropic protein affecting a wide range of molecular and cellular processes. Dysregulation and abnormal expression of ANXA2 are linked to a large number of prevalent diseases, including autoimmune and neurodegenerative disease, antiphospholipid syndrome, inflammation, diabetes mellitus and a series of cancers. Accumulating data suggest that ANXA2 is aberrantly expressed in a wide spectrum of cancers, and exerts profound effects on tumor cell adhesion, proliferation, apoptosis, invasion and metastasis as well as tumor neovascularization via different modes of action. However, despite significant research, our knowledge of the mechanism by which ANXA2 participates in cancer development remains fragmented. The present review systematically summarizes the effects of ANXA2 on tumor progression, in an attempt to gain an improved understanding of the underlying mechanisms and to provide a potential effective target for cancer therapy.