Characterization of the tyrosine phosphorylation of calpactin I (annexin II) induced by platelet-derived growth factor

FAXC interacts with ANXA2 and SRC in mitochondria and promotes tumorigenesis in cholangiocarcinoma

Cholangiocarcinoma (CCA) is one of the most difficult malignancies to treat as the therapeutic options are limited. Although several driver genes have been identified, most remain unknown. In this study, we identified a failed axon connection homolog (FAXC), whose function is unknown in mammals, by analyzing serially passaged CCA xenograft models. Knockdown of FAXC reduced subcutaneous tumorigenicity in mice. FAXC was bound to annexin A2 (ANXA2) and c-SRC, which are tumor-promoting genes. The FAXC/ANXA2/c-SRC complex forms in the mitochondria. FAXC enhances SRC-dependent ANXA2 phosphorylation at tyrosine-24, and the C-terminal amino acid residues (351-375) of FAXC are required for ANXA2 phosphorylation. Transcriptome data from a xenografted CCA cell line revealed that FAXC correlated with epithelial-mesenchymal transition, hypoxia, and KRAS signaling genes. Collectively, these findings advance our understanding of CCA tumorigenesis and provide candidate therapeutic targets.

Annexin A1, A2, A5, and A6 involvement in human pathologies

The human genome codes for 12 annexins with highly homologous membrane-binding cores and unique amino termini, which endow each protein with its specific biological properties. Not unique to vertebrate biology, multiple annexin orthologs are present in almost all eukaryotes. Their ability to combine either dynamically or constitutively with membrane lipid bilayers is hypothetically the key property that has led to their retention and multiple adaptation in eukaryotic molecular cell biology. Annexin genes are differentially expressed in many cell types but their disparate functions are still being discovered after more than 40 years of international research. A picture is emerging from gene knock down and knock out studies of individual annexins that these are important supporters rather than critical players in organism development and normal cell and tissue function. However, they appear to be highly significant "early responders" toward challenges arising from cell and tissue abiotic or biotic stress. In humans, recent focus has been on involvement of the annexin family for its involvement in diverse pathologies, especially cancer. From what has become an exceedingly broad field of investigation, we have selected four annexins in particular: AnxA1, 2, 5, and 6. Present both within and external to cells, these annexins are currently under intensive investigation in translational research as biomarkers of cellular dysfunction and as potential therapeutic targets for inflammatory conditions, neoplasia, and tissue repair. Annexin expression and release in response to biotic stress appears to be a balancing act. Under- or over-expression in different circumstances appears to damage rather than restore a healthy homeostasis. This review reflects briefly on what is already known of the structures and molecular cell biology of these selected annexins and considers their actual and potential roles in human health and disease.

Annexin A2 and Kidney Diseases

Annexin A2 is a Ca²⁺- and phospholipid-binding protein which is widely expressed in various types of cells and tissues. As a multifunctional molecule, annexin A2 is found to be involved in diverse cell functions and processes, such as cell exocytosis, endocytosis, migration and proliferation. As a receptor of plasminogen and tissue plasminogen activator, annexin A2 promotes plasmin generation and regulates the homeostasis of blood coagulation, fibrinolysis and matrix degradation. As an antigen expressed on cell membranes, annexin A2 initiates local inflammation and damage through binding to auto-antibodies. Annexin A2 also mediates multiple signaling pathways induced by various growth factors and oxidative stress. Aberrant expression of annexin A2 has been found in numerous kidney diseases. Annexin A2 has been shown to act as a co-receptor of integrin CD11b mediating NF-kB-dependent kidney inflammation, which is further amplified through annexin A2/NF-kB-triggered macrophage M2 to M1 phenotypic change. It also modulates podocyte cytoskeleton rearrangement through Cdc42 and Rac1/2/3 Rho pathway causing proteinuria. Thus, annexin A2 is implicated in the pathogenesis and progression of various kidney diseases. In this review, we focus on the current understanding of the role of annexin A2 in kidney diseases.

Protein phosphorylation and its role in the regulation of Annexin A2 function

BACKGROUND

Annexin A2 (AnxA2) is a multifunctional protein involved in endocytosis, exocytosis, membrane domain organisation, actin remodelling, signal transduction, protein assembly, transcription and mRNA transport, as well as DNA replication and repair.

SCOPE OF REVIEW

The current knowledge of the role of phosphorylation in the functional regulation of AnxA2 is reviewed. To provide a more comprehensive treatment of this topic, we also address in depth the phosphorylation process in general and discuss its possible conformational effects. Furthermore, we discuss the apparent limitations of the methods used to investigate phosphoproteins, as exemplified by the study of AnxA2.

MAJOR CONCLUSIONS

AnxA2 is subjected to complex regulation by post-translational modifications affecting its cellular functions, with Ser11, Ser25 and Tyr23 representing important phosphorylation sites. Thus, Ser phosphorylation of AnxA2 is involved in the recruitment and docking of secretory granules, the regulation of its association with S100A10, and sequestration of perinuclear, translationally inactive mRNP complexes. By contrast, Tyr phosphorylation of AnxA2 regulates its role in actin dynamics and increases its association with endosomal compartments. Modification of its three main phosphorylation sites is not sufficient to discriminate between its numerous functions. Thus, fine-tuning of AnxA2 function is mediated by the joint action of several post-translational modifications.

GENERAL SIGNIFICANCE

AnxA2 participates in malignant cell transformation, and its overexpression and/or phosphorylation is associated with cancer progression and metastasis. Thus, tight regulation of AnxA2 function is an integral aspect of cellular homeostasis. The presence of AnxA2 in cancer cell-derived exosomes, as well as the potential regulation of exosomal AnxA2 by phosphorylation or other PTMs, are topics of great interest.

Annexin II-dependent actin remodelling evoked by hydrogen peroxide requires the metalloproteinase/sphingolipid pathway

Actin remodeling is a dynamic process associated with cell shape modification occurring during cell cycle and proliferation. Oxidative stress plays a role in actin reorganization via various systems including p38MAPK. Beside, the mitogenic response evoked by hydrogen peroxide (H₂O₂) in fibroblasts and smooth muscle cells (SMC) involves the metalloproteinase (MMPs)/sphingomyelinase 2 (nSMase2) signaling pathway. The aim of this work was to investigate whether this system plays a role in actin remodeling induced by H₂O₂.

Low H₂O₂ dose (5 µM) rapidly triggered a signaling cascade leading to nSMase2 activation, src and annexin 2 (AnxA2) phosphorylation, and actin remodeling, in fibroblasts and SMC. These events were blocked by pharmacological inhibitors of MMPs (Ro28-2653) and p38MAPK (SB203580), and were lacking in MMP2^−/− and in nSMase2-mutant (fro) fibroblasts. Likewise, H₂O₂ was unable to induce actin remodeling in fro and MMP2^−/− fibroblasts or in cells pretreated with p38MAPK, or MMP inhibitors. Finally we show that nSMase2 activation by H₂O₂, depends on MMP2 and p38MAPK, and is required for the src-dependent phosphorylation of AnxA2, and actin remodeling.

Taken together, these findings indicate for the first time that AnxA2 phosphorylation and actin remodeling evoked by oxidative stress depend on the sphingolipid pathway, via MMP2 and p38MAPK.

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Low concentration of H₂O₂ activates matrix metalloproteinases MMP-2.

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MMP-2 activates p38MAPK, type 2 neutral sphingomyelinase.

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This signaling pathway induces annexin II phosphorylation via src.

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This pathway is involved in actin remodeling due to H₂O₂ stimulation.

Three are better than one: plasminogen receptors as cancer theranostic targets

Activation of plasminogen on the cell surface initiates a cascade of protease activity with important implications for several physiological and pathological events. In particular, components of the plasminogen system participate in tumor growth, invasion and metastasis. Plasminogen receptors are in fact expressed on the cell surface of most tumors, and their expression frequently correlates with cancer diagnosis, survival and prognosis. Notably, they can trigger multiple specific immune responses in cancer patients, highlighting their role as tumor-associated antigens. In this review, three of the most characterized plasminogen receptors involved in tumorigenesis, namely Annexin 2 (ANX2), Cytokeratin 8 (CK8) and alpha-Enolase (ENOA), are analyzed to ascertain an overall view of their role in the most common cancers. This analysis emphasizes the possibility of delineating new personalized therapeutic strategies to counteract tumor growth and metastasis by targeting plasminogen receptors, as well as their potential application as cancer predictors.

Identification of phosphoproteins in kidney tissues from patients with autosomal dominant polycystic kidney disease

Protein phosphorylation is a very important PTM. Phosphorylation/dephosphorylation of a protein can alter its behavior in almost every conceivable way. Previous studies indicate that abnormal phosphorylation is involved in the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD). However, large-scale proteomic analysis of altered phosphoproteins in ADPKD has not been reported. In this study, total proteins from ADPKD cystic kidney tissues (n = 5) and normal kidney tissues (n = 5) were extracted and phosphoproteins were enriched by phosphate metal affinity chromatography, then separated by 2-DE and identified by LC-MS/MS. Between the two groups, 48 protein spots showing more than a twofold difference were detected. Among them, 28 spots were up-regulated and 20 down-regulated in ADPKD kidney tissues. Of these, 38 different proteins were identified including cell signaling proteins, cytoskeleton proteins, mitochondria metabolic enzymes, antioxidant proteins, molecular chaperones, transcription factors and regulators. Two differential phosphoproteins, annexin II and tropomyosin, were further confirmed by immunoprecipitation and Western blot analysis. The results show that there are many kinds of abnormal phosphoproteins in ADPKD cystic kidney tissues. More studies on the functions of the differential phosphoproteins may provide us new clues for ADPKD pathogenesis and treatment.

Role of Annexin-II in GI cancers: interaction with gastrins/progastrins

The role of the gastrin peptide hormones (G17, G34) and their precursors (progastrins, PG; gly-extended gastrin, G-gly), in gastrointestinal (GI) cancers has been extensively reviewed in recent years [W. Rengifo-Cam, P. Singh, Role of progastrins and gastrins and their receptors in GI and pancreatic cancers: targets for treatment, Curr. Pharm. Des. 10 (19) (2004) 2345-2358; M. Dufresne, C. Seva, D. Fourmy, Cholecystokinin and gastrin receptors, Physiol. Rev. 86 (3) (2006) 805-847; A. Ferrand, T.C. Wang, Gastrin and cancer: a review, Cancer Lett. 238 (1) (2006) 15-29]. A possible important role of progastrin peptides in colon carcinogenesis has become evident from experiments with transgenic mouse models [W. Rengifo-Cam, P. Singh, (2004); A. Ferrand, T.C. Wang, (2006)]. It is now known that growth stimulatory and co-carcinogenic effects of gastrin/PG peptides are mediated by both proliferative and anti-apoptotic effects of the peptides on target cells [H. Wu, G.N. Rao, B. Dai, P. Singh, Autocrine gastrins in colon cancer cells Up-regulate cytochrome c oxidase Vb and down-regulate efflux of cytochrome c and activation of caspase-3, J. Biol. Chem. 275 (42) (2000) 32491-32498; H. Wu, A. Owlia, P. Singh, Precursor peptide progastrin(1-80) reduces apoptosis of intestinal epithelial cells and upregulates cytochrome c oxidase Vb levels and synthesis of ATP, Am. J. Physiol. Gastrointest. Liver Physiol. 285 (6) (2003) G1097-G1110]. Several receptor subtypes have been described that mediate growth effects of gastrin peptides [W. Rengifo-Cam, P. Singh (2004); M. Dufresne, C. Seva, D. Fourmy, (2006)]. Recently, we identified Annexin II as a high affinity binding protein for gastrin/PG peptides [P. Singh, H. Wu, C. Clark, A. Owlia, Annexin II binds progastrin and gastrin-like peptides, and mediates growth factor effects of autocrine and exogenous gastrins on colon cancer and intestinal epithelial cells, Oncogene (2006), doi:10.1038/sj.onc.1209798]. Importantly, the expression of Annexin II was required for mediating growth stimulatory effects of gastrin and PG peptides on intestinal epithelial and colon cancer cells [P. Singh, H. Wu, C. Clark, A. Owlia, Annexin II binds progastrin and gastrin-like peptides, and mediates growth factor effects of autocrine and exogenous gastrins on colon cancer and intestinal epithelial cells, Oncogene (2006), doi:10.1038/sj.onc.1209798], suggesting that Annexin-II may represent the elusive novel receptor for gastrin/PG peptides. The importance of this finding in relation to the structure and function of Annexin-II, especially in GI cancers, is described below. Since this surprising finding represents a new front in our understanding of the mechanisms involved in mediating growth effects of gastrin/PG peptides in GI cancers, our current understanding of the role of Annexin-II in proliferation and metastasis of cancer cells is additionally reviewed.

Annexin II binds progastrin and gastrin-like peptides, and mediates growth factor effects of autocrine and exogenous gastrins on colon cancer and intestinal epithelial cells

We and others have reported the presence of novel progastrin (PG)/gastrin receptors on normal and cancerous intestinal cells. We had earlier reported the presence of 33-36 kDa gastrin-binding proteins on cellular membranes of colon cancer cells. The goal of the current study was to identify the protein(s) in the 33-36 kDa band, and analyse its functional significance. A carbodiimide crosslinker was used for crosslinking radio-labeled gastrins to membrane proteins from gastrin/PG responsive cell lines. Native membrane proteins, crosslinked to the ligand, were solubulized and enriched by >1000-fold, and analysed by surface-enhanced laser desorption/ionization-time of flight-mass spectrometry. The peptide masses were researched against the NCBInr database using the ProFound search engine. Annexin II (ANX II) was identified, and confirmed by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry. As HCT-116 cells express autocrine PG, the in situ association of PG with ANX II was demonstrated in pulldown assays. Direct binding of PG with ANX II was confirmed in an in vitro binding assay. In order to confirm a functional importance of these observations, sense and anti-sense (AS) ANX II RNA-expressing clones of intestinal epithelial (IEC-18) and human colon cancer (HCT-116) cell lines were generated. AS clones demonstrated a significant loss in the growth response to exogenous (IEC-18) and autocrine (HCT-116) PG. We have thus discovered that membrane-associated ANX II binds PG/gastrins, and partially mediates growth factor effects of the peptides.

CEACAM1, a Cell-Cell Adhesion Molecule, Directly Associates with Annexin II in a Three-dimensional Model of Mammary Morphogenesis

The epithelial cell adhesion molecule CEACAM1 (carcinoembryonic antigen cell adhesion molecule-1) is down-regulated in colon, prostate, breast, and liver cancer. Here we show that CEACAM1-4S, a splice form with four Ig-like ectodomains and a short cytoplasmic domain (14 amino acids), directly associates with annexin II, a lipid raft-associated molecule, which is also down-regulated in many cancers. Annexin II was identified using a glutathione S-transferase pull-down assay in which the cytoplasmic domain of CEACAM-4S was fused to glutathione S-transferase, the fusion protein was incubated with cell lysates, and isolated proteins were sequenced by mass spectrometry. The interaction was confirmed first by reciprocal immunoprecipitations using anti-CEACAM1 and anti-annexin II antibodies and second by confocal laser microscopy showing co-localization of CEACAM1 with annexin II in mammary epithelial cells grown in Matrigel. In addition, CEACAM1 co-localized with p11, a component of the tetrameric AIIt complex at the plasma membrane, and with annexin II in secretory vesicles. Immobilized, oriented peptides from the cytoplasmic domain of CEACAM1-4S were shown to directly associate with bovine AIIt, which is 98% homologous to human AIIt, with average KD values of about 30 nM using surface plasmon resonance, demonstrating direct binding of functionally relevant AIIt to the cytoplasmic domain of CEACAM1-4S.

Expression of a releasable form of annexin II by human keratinocytes

Annexin II is a multifunctional calcium-dependent phospholipid binding protein whose presence in epidermis has previously been reported. However, like other members of annexin family, annexin II has been regarded as either an intracellular protein or associated with the cellular membrane. Here, we report the presence of a releasable annexin II and p11, two monomers of annexin II tetramer, in keratinocyte-conditioned medium (KCM). Proteins present in KCM were fractionated on a gel filtration column and following further evaluation, a releasable protein with apparent MW of 36 kDa was identified. Further characterization identified this protein as the p36 monomer of annexin II tetramer. The phospho-tyrosine antibody did not visualize this protein as the phosphorylated form of p36. Several experiments were conducted to examine whether this protein is soluble or associated with keratinocyte cell membranes in the conditioned medium. A centrifugation of conditioned medium was not able to bring this protein down into the pellet. Surprisingly, the results of Western analysis identified p36 and p11, two monomers of the annexin II tetramer, in conditioned medium derived from either keratinocytes cultured alone or keratinocytes co-cultured with fibroblasts. In contrast to the keratinocyte-conditioned medium in which annexin II was easily detectable, both monomers were barely detectable in conditioned medium collected from dermal fibroblasts. This finding was in contrast to the cell lysates in which p36 was detectable in both keratinocytes and fibroblasts. However, the amount of this protein was markedly higher in keratinocyte lysate relative to that of dermal fibroblasts. Conditioned medium derived from keratinocyte established from adult showed a higher level of annexin II compared to that of keratinocytes established from newborn babies. The expression of p11 seems to increase with differentiation of keratinocytes derived from either adult or newborn skin samples. When the site of annexin synthesis in human skin was examined by immunohistochemical staining, the antibody for p36 localized the annexin to the keratinocyte cell members in the basal and suprabasal keratinocytes. In conclusion, Western blot detection of both p36 and p11 in conditioned medium from skin cells revealed that human keratinocytes, but not fibroblasts, express a releasable monomer form of annexin II which is regulated by differentiation status of keratinocytes. This finding is consistent with the localization of annexin II detected by immunohistochemical staining.

Angiostatin binds to tyrosine kinase substrate annexin II through the lysine-binding domain in endothelial cells

Angiostatin(AS), an internal fragment of plasminogen, is one of the most potent specific inhibitors of angiogenesis. Angiostatin treatment has resulted in the complete regression of human tumors implanted subcutaneously into nude mice and has great therapeutic value (O'Reilly et al., Nat. Med. 2, 689-692, 1996). Despite promising therapeutic value in the treatment of cancer, the mechanism of its action is still unknown. We found that angiostatin binds to a 35-kDa protein in bovine aortic endothelial (BAE) cells (Sharma et al., Proc. Am. Assoc. Cancer Res. 42, 568, A3050, 2002). In an attempt to begin to understand angiostatin's mechanism of action, we have purified and characterized this 35-kDa protein from BAE cells. Internal peptide sequence analysis of purified protein demonstrated (SLYYIQQDTK, SYSPYDMLESIK, and ALLYLXGGDD) 100% sequence identity with tyrosine kinase substrate annexin II. Solid phase binding analysis suggests that angiostatin specifically bound to purified annexin II immobilized on 96-well plastic plates. Hundred-fold molar excess of unlabeled AS and anti-annexin II antibody inhibited bindings 85 and 55%, respectively, suggesting specific interaction. Annexin II is a predominant receptor for angiostatin, since neutralizing the angiostatin by soluble receptor (annexin II) effectively blocks angiostatin's anti-EC activity. Similarly, saturating the annexin II receptor by plasminogen in endothelial cells also blocks angiostatin's activity. Both angiostatin and plasminogen bind to purified annexin II in BAE cells saturably with apparent K(d) values of 101 and 164 nM, respectively, for purified annexin II and K(d) values of 83 and 125 nM, respectively, for BAE cells. Anti-annexin II monoclonal antibody inhibited angiostatin and plasminogen binding to endothelial cells by 68 and 62%, respectively, supporting our in vitro studies that annexin II is a receptor for angiostatin. Angiostatin-binding protein/annexin II specifically expressed in endothelial cells but not in fibroblasts suggests its EC-specific function. Epsilon-aminocaproic acid, a lys analogue, effectively blocks angiostatin and annexin II interaction, indicating that the lysine-binding domain of AS is required for binding to annexin II. These results suggest that the antiangiogenic action of angiostatin may be mediated via interaction with annexin II. Identification of annexin II as a receptor for angiostatin provides further evidence that clotting and fibrinolytic pathways are directly involved in the angiogenic process.

Annexin II overexpression correlates with stromal tenascin-C overexpression: a prognostic marker in colorectal carcinoma

BACKGROUND

Overexpression of annexin II, a calcium-dependent phospholipid-binding protein, has been reported in various carcinomas. One of its ligands is tenascin-C, an extracellular matrix glycoprotein with predominantly antiadhesive qualities that also has been reported to be a prognostic marker for several carcinomas. In the current study, the authors investigated the correlation between the overexpression of annexin II and tenascin-C in colorectal carcinoma.

METHODS

Western blot analysis of annexin II expression was examined in four human colorectal carcinoma cell lines. Using immunohistochemical methods, the authors also examined expression of annexin II and tenascin-C in 105 primary colorectal carcinoma cases.

RESULTS

Although annexin II was expressed in human colon carcinoma cell lines, there was no apparent correlation between its expression level and the metastatic potential of these cell lines. The authors observed overexpression of annexin II and tenascin-C proteins in 29.5% and 49.5%, respectively, of colorectal carcinoma cases. Overexpression of annexin II was found to be correlated significantly with histologic type, tumor size, depth of invasion, and pTNM stage, whereas tenascin-C overexpression was noted to be correlated significantly with histologic type, depth of invasion, lymphatic invasion, venous invasion, lymph node metastasis, and pTNM stage. Expression of annexin II was shown to be correlated significantly with that of tenascin-C. Multivariate analysis demonstrated that annexin II and tenascin-C cooverexpression was an independent factor of poor prognosis in patients with colorectal carcinoma.

CONCLUSIONS

The data from the current study suggest that both annexin II and tenascin-C are overexpressed in advanced colorectal carcinoma and that they may be related to the progression and metastatic spread of colorectal carcinoma.

Control of the nuclear-cytoplasmic partitioning of annexin II by a nuclear export signal and by p11 binding

This study investigated mechanisms controlling the nuclear-cytoplasmic partitioning of annexin II (AnxII). AnxII and its ligand, p11, were localized by immunofluorescence to the cytoplasmic compartment of U1242MG cells, with minimal AnxII or p11 detected within nuclei. Similarly, GFP-AnxII and GFP-p11 chimeras localized to the endogenous proteins. Likewise, GFP-AnxII(1-22) was excluded from nuclei, whereas GFP-AnxII(23-338) and GFP alone were distributed throughout the cells. Immunoprecipitation and biochemical studies showed that GFP-AnxII did not form heteromeric complexes with endogenous p11 and AnxII. Thus, the AnxII N-tail is necessary and sufficient to cause nuclear exclusion of the GFP fusion protein but this does not involve p11 binding. A nuclear export signal consensus sequence was found in the AnxII 3-12 region. The consensus mutant GFP-AnxII(L10A/L12A) confirmed that these residues are necessary for nuclear exclusion. The nuclear exclusion of GFP-AnxII(1-22) was temperature-dependent and reversible, and the nuclear export inhibitor leptomycin B (LmB) caused GFP-AnxII or overexpressed AnxII monomer to accumulate in nuclei. Therefore, AnxII monomer can enter the nucleus and is actively exported. However, LmB had little effect on the localization of AnxII/p11 complex in U1242MG cells, indicating that the complex is sequestered in the cytoplasm. By contrast, LmB treatment of v-src-transformed fibroblasts caused endogenous AnxII to accumulate in nuclei. The LmB-induced nuclear accumulation of AnxII was accelerated by pervanadate and inhibited by genistein, suggesting that phosphorylation promotes nuclear entry of AnxII. Thus, nuclear exclusion of AnxII results from nuclear export of the monomer and sequestration of AnxII/p11 complex, and may be modulated by phosphorylation.

Construction of recombinant adenoviral vector of annexin II

Annexin II is a member of the annexin family of calcium-dependent phospholipid binding proteins expressed in vascular endothelium. Recently this molecule was reported to play a role in control of fibrinolysis on the endothelial surface. To examine the role of annexin II in vascular endothelium critically, we developed a recombinant adenoviral vector containing the annexin II cDNA. A full-length annexin II cDNA was inserted into a shuttle vector, pAdRSV4, and co-transfected into 293 cells with a replication-deficient type 5 adenovirus, pJM17. Resulting plaques were isolated and checked for protein expression. The verified clone (AdRSV-ANII) was further analyzed. Characterization of this vector will facilitate the investigation of the mechanism of fibrinolysis on vascular endothelium.

Identification and immunohistochemical localization of annexin II in rat cornea

PURPOSE

We have identified annexin II mRNA expression in the rat cornea and demonstrated immunolocalization of annexin II in normal and injured corneas. Furthermore, to investigate possible interaction between annexin II and its extracellular ligand tenascin during corneal wound healing, we also examined tenascin expression simultaneously.

METHODS

Total RNA was extracted from the corneal tissue of male Wistar rats as well as from the cell cultures of corneal epithelial cells and keratocytes. cDNA was obtained by reverse transcription (RT). Annexin II mRNA expression was examined by polymerase chain reaction (PCR). Western blot analysis of annexin II protein was performed with protein samples that were obtained from the corneal tissue and cell cultures. In addition, the localization of annexin II and that of tenascin were clarified by immunohistochemical analysis, using both uninjured and epithelial scraped corneas.

RESULTS

RT-PCR analysis revealed that annexin II mRNA was expressed in corneal tissues, epithelial cells and keratocytes. Western blot analysis of corneal epithelium and keratocytes showed a 38kDa band that corresponded to the molecular weight of annexin II. Immunohistochemical study showed that annexin II was present in keratocytes as well as the basal cells of corneal epithelium in the central cornea, and basal/suprabasal cells of the limbal epithelium. Positive annexin II immunoreactivity is translocated from cytoplasm to the cell periphery/extracellular position during the epithelial wound healing process. Annexin II and tenascin are coexpressed on the basal surface of limbal epithelium and the leading edge of the healing epithelium. The reappearance of cytoplasmic annexin II staining at the periphery of the cornea correlated with the epithelial cell proliferation.

CONCLUSIONS

Annexin II is abundantly expressed in corneal tissue. The translocalization of annexin II protein suggests its role in the corneal epithelial migration during wound healing. The colocalization of annexin II and tenascin in migrating and proliferating corneal epithelial cells suggests that annexin II-tenascin interaction may play a role in epithelial wound healing.

Annexin II: a mediator of the plasmin/plasminogen activator system

The annexins constitute a family of calcium-dependent membrane binding proteins. Recently, annexin II has been shown to accelerate the activation of the clot-dissolving protease plasmin by complexing with the plasmin precursor plasminogen and with tissue plasminogen activator. Binding of plasminogen to annexin II is inhibited by the atherogenic lipoprotein, lipoprotein(a), while binding of tissue plasminogen activator to annexin II is blocked by the thiol amino acid homocysteine. Formation of the plasminogen/tissue plasminogen activator/annexin II complex may represent a key regulatory mechanism in fibrinolytic surveillance.

Lipocortin V may function as a signaling protein for vascular endothelial growth factor receptor-2/Flk-1

Binding of vascular endothelial growth factor (VEGF) to its receptor, VEGFR-2 (Flk-1/KDR), induces dimerization and activation of the tyrosine kinase domain of the receptor, resulting in autophosphorylation of cytoplasmic tyrosine residues used as docking sites for signaling proteins that relay the signals for cell proliferation, migration, and permeability enhancement. We explored the VEGF/receptor signaling pathway by performing a two-hybrid screen of a rat lung cDNA library in yeast using the intracellular domain of rat VEGFR-2 as bait. Two clones encoding lipocortin V were isolated. Subsequent studies with the yeast two-hybrid assay showed that the complete intracellular domain of VEGFR-2 was required for the interaction. Co-immunoprecipitation of translated proteins confirmed the interaction between the VEGF receptor and lipocortin V. VEGF induced a rapid tyrosine phosphorylation of lipocortin V in human umbilical vein endothelial cells (HUVEC). Pretreatment of HUVEC with antisense oligodeoxyribonucleotide (ODN) for lipocortin V significantly inhibited VEGF-induced cell proliferation, which was accompanied by a decrease in protein synthesis and tyrosine phosphorylation of lipocortin V. Our results indicate that lipocortin V may function as a signaling protein for VEGFR-2 by directly interacting with the intracellular domain of the receptor and appears to be involved in regulation of vascular endothelial cell proliferation mediated by VEGFR-2.

The Npc1 mutation causes an altered expression of caveolin-1, annexin II and protein kinases and phosphorylation of caveolin-1 and annexin II in murine livers

We have previously demonstrated (1) an increased expression of caveolin-1 in murine heterozygous and homozygous Niemann-Pick type C (NPC) livers, and (2) an increased concentration of unesterified cholesterol in a detergent insoluble caveolae-enriched fraction from homozygous livers. To define further the relationship between caveolin-1 function and the cholesterol trafficking defect in NPC, we examined the expression and distribution of additional caveolar and signal transduction proteins. The expression of annexin II was significantly increased in homozygous liver homogenates and the Triton X-100 insoluble floating fraction (TIFF). Phosphoamino acid analysis of caveolin-1 and annexin II from the homozygous TIFF demonstrated an increase in serine and tyrosine phosphorylation, respectively. To determine the basis for increased phosphorylation of these proteins, the expression and distribution of several protein kinases was examined. The expression of PKCalpha, PKCzeta and pp60-src (protein kinases) were significantly increased in both heterozygous and homozygous liver homogenates, while PKCdelta was increased only in homozygous livers. Of the protein kinases analyzed, only CK IIalpha was significantly enriched in the heterozygous TIFF. Finally, the concentration of diacylglycerol in the homozygous TIFF was significantly increased and this elevation may modulate PKC distribution and function. These results provide additional evidence for involvement of a caveolin-1 containing cellular fraction in the pathophysiology of NPC and also suggest that the Npc1 gene product may directly or indirectly, regulate the expression and distribution of signaling molecules.

Tyrosine phosphorylation of annexin II tetramer is stimulated by membrane binding

In the present article we have examined if the interaction of the Ca2+-binding protein, annexin II tetramer (AIIt) with the plasma membrane phospholipids or with the submembranous cytoskeleton, effects the accessibility of the tyrosine phosphorylation site of AIIt. In the presence of Ca2+, pp60(c-src) catalyzed the incorporation of 0.22 +/- 0.05 mol of phosphate/mol of AIIt (mean +/- S.D., n = 5). The Ca2+-dependent binding of AIIt to purified adrenal medulla plasma membrane or phosphatidylserine vesicles stimulated the pp60(c-src)-dependent phosphorylation of AIIt to 0.62 +/- 0.04 mol of phosphate/mol of AIIt (mean +/- S.D., n = 5) or 0.93 +/- 0.07 mol of phosphate/mol of AIIt (mean +/- S.D., n = 5), respectively. Phosphatidylserine- or phosphatidylinositol-containing vesicles but not vesicles composed of phosphatidylcholine or phosphatidylethanolamine, stimulated the phosphorylation of AIIt. In contrast, the binding of AIIt to F-actin resulted in the incorporation of only 0.04 +/- 0.04 mol of phosphate/mol of AIIt (mean +/- S.D., n = 5). These results suggest that the interaction of AIIt with plasma membrane and not the submembranous cytoskeleton, activates the tyrosine phosphorylation of AIIt by inducing a conformational change in the protein resulting in the enhanced exposure or accessibility of the tyrosine-phosphorylation site.

Annexin II is a novel player in insulin signal transduction. Possible association between annexin II phosphorylation and insulin receptor internalization

Annexin II is a Ca2+-, phospholipid-, and actin- binding protein that was implicated in the regulation of vesicular traffic and endosome fusion. It is a known substrate for protein kinases including the platelet-derived growth factor receptor, src protein-tyrosine kinase, and protein kinase C. In the present study we investigated the possible involvement of annexin II in insulin signal transduction. Phosphorylation of annexin II in response to insulin treatment of intact Chinese hamster ovary (CHO)-T cells was detected by 5 min and reached maximal levels after a 2-3-h incubation with the hormone. However, unlike other receptor substrates, annexin II failed to undergo insulin-induced Tyr phosphorylation under conditions where receptor internalization was inhibited. This was evident in CHO cells, overexpressing the insulin receptor, in which internalization was inhibited either by tyrosine kinase inhibitors or by lowering the temperature to 4 degrees C, and in CHO cells overexpressing various insulin receptor mutants in which normal internalization was impaired. Hence, Tyr phosphorylation of annexin II could be part of the internalization and sorting mechanism of the insulin receptor.

Detergent solubility defines an alternative itinerary for a subpopulation of PDGF beta receptors

Current models of platelet-derived growth factor (PDGF) beta receptor itinerary are based upon the properties of receptors recovered from nonionic detergent-solubilized cellular extracts. Comparing several commonly used cell extraction procedures, we have determined that up to 50% of immunoreactive PDGF beta receptors, reside in a Triton X-100 insoluble pool in a wide distribution of cultured cell lines, including Balb/c-3T3, NIH 3T3, and Swiss fibroblasts, primary murine and human fibroblasts, and primary human glial cells. Many properties of Triton insoluble receptors are distinct from the well-characterized PDGF beta receptors, including 1) delayed arrival of newly synthesized receptors into the Triton insoluble fraction, 2) prolonged half-life in the presence of PDGF, 3) increased abundance with increasing cell density, 4) inaccessibility to modification by extracellular compartment enzymes, 5) cofractionation with cytoskeletal proteins, and 6) a higher basal tyrosine phosphorylation state. PDGF stimulates accumulation of tyrosine phosphorylated PDGF beta receptors in the Triton X-100 insoluble fraction. Cell surface PDGF beta receptors modified by enzymatic desialylation redistribute to the insoluble fraction. These findings distinguish the itinerary of a large subpopulation of PDGF beta receptors from those characterized previously. Receptors in this fraction represent a long-lived tyrosine phosphorylated population that may effect responses for extended periods following ligand activation.

Effect of tyrosine mutations on the kinase activity and transforming potential of an oncogenic human insulin-like growth factor I receptor

The tyrosines in the cytoplasmic domain of an oncogenic human insulin-like growth factor I receptor (gag-IGFR) were systematically mutated to phenylalanines to investigate the role of those tyrosines in the enzymatic and biological function of the gag-IGFR. Our results indicate that tyrosines 1131, 1135, 1136, and 1221 are important for the receptor protein-tyrosine kinase (PTK) activity. However, mutation of Tyr-1136 only slightly affects the kinase activity but dramatically reduces the transforming ability and overall substrate phosphorylation, in particular, annexin II, which is strongly phosphorylated by the gag-IGFR but not by the Phe-1136 mutant. Single mutation of either Tyr-943 or Tyr-950 resulted in significantly reduced phosphorylation of the receptor but not on its PTK activity or transforming ability. Tyr-950 together with its surrounding sequence is involved in mediating the interaction between the gag-IGFR and insulin receptor substrate 1. Our data also suggest that Tyr-1316 is involved in phosphorylation of phospholipase C-gamma, which is, however, not important for cell transforming activity. Overall, our study has identified several tyrosine residues of IGFR important for its PTK activity and substrate interaction. The transforming potential of the gag-IGFR correlates well with its ability to phosphorylate overall cellular substrates and to activate phosphatidylinositol 3-kinase via insulin receptor substrate 1.

Annexin II tetramer: structure and function

The annexins are a family of proteins that bind acidic phospholipids in the presence of Ca2+. The interaction of these proteins with biological membranes has led to the suggestion that these proteins may play a role in membrane trafficking events such as exocytosis, endocytosis and cell-cell adhesion. One member of the annexin family, annexin II, has been shown to exist as a monomer, heterodimer or heterotetramer. The ability of annexin II tetramer to bridge secretory granules to plasma membrane has suggested that this protein may play a role in Ca(2+)-dependent exocytosis. Annexin II tetramer has also been demonstrated on the extracellular face of some metastatic cells where it mediates the binding of certain metastatic cells to normal cells. Annexin II tetramer is a major cellular substrate of protein kinase C and pp60src. Phosphorylation of annexin II tetramer is a negative modulator of protein function.

The effects of N-ras oncogene expression on PDGF-BB stimulated responses in cultured mouse myoblasts

The role of the ras oncogene in the signalling pathway triggered by platelet-derived growth factor BB (PDGF-BB) has been investigated in a cell line which normally differentiates into myotubes. Following the activation of the N-ras oncogene, however, the cells proliferate and form foci. PDGF-BB stimulated the phosphorylation of tyrosine in several cellular proteins of molecular weight 185, 160, 94, 54, 44, 42 kDa and furthermore Ca2+ was released from internal stores. Activation of the N-ras gene by treatment of cells with dexamethasone (DEX) inhibited these responses to PDGF-BB. On the other hand, both ras-induced and -non induced cells responded to bradykinin (BK), foetal calf serum (FCS) and ionomycin (ION) by releasing Ca2+ from intracellular stores. The inhibition of the response to PDGF-BB in ras-activated cells has been further investigated. The binding of [125I]-PDGF-BB to its receptors was low and western blotting showed a low level of PDGF-BB receptor protein. This was in marked contrast to the receptor number seen in cells grown in growth medium or fusion promoting medium. These results indicate that cells transformed with the N-ras oncogene fail to respond to platelet-derived growth factor and exhibit a very low level of PDGF receptors. This suggests a role for the ras oncogene in the earliest steps of the signalling pathway.

Tyrosine phosphorylation and activation of mitogen-activated protein kinase in the rat brain following transient cerebral ischemia

Activation of trophic factor receptors stimulates tyrosine phosphorylation on proteins and supports neuronal survival. We report that in the recovery phase following reversible cerebral ischemia, tyrosine phosphorylation increases in the membrane fraction of the resistant hippocampal CA3/dentate gyrus (DG) region, whereas in the sensitive CA1 region or striatum, tyrosine phosphorylation is less marked or decreases. In the cytosolic fractions, a 42-kDa protein, identified as mitogen-activated protein (MAP) kinase, is markedly phosphorylated and activated immediately following ischemia, in particular in CA3/DG, but not in striatum. In the CA1 region, phosphorylation of MAP kinase is less intense and decreases later during reperfusion, which could explain the delay of neuronal degeneration in this structure. The data suggest that in ischemia-resistant neurons the growth factor receptor-coupled signaling cascade is stimulated and, through its effects on DNA transcription and mRNA translation, supports neuronal survival.