Annexin A4 trimers are recruited by high membrane curvatures in giant plasma membrane vesicles

The plasma membrane (PM) of eukaryotic cells consists of a crowded environment comprised of a high diversity of proteins in a complex lipid matrix. The lateral organization of membrane proteins in the PM is closely correlated with biological functions such as endocytosis, membrane budding and other processes which involve protein mediated shaping of the membrane into highly curved structures. Annexin A4 (ANXA4) is a prominent player in a number of biological functions including PM repair. Its binding to membranes is activated by Ca2+ influx and it is therefore rapidly recruited to the cell surface near rupture sites where Ca2+ influx takes place. However, the free edges near rupture sites can easily bend into complex curvatures and hence may accelerate recruitment of curvature sensing proteins to facilitate rapid membrane repair. To analyze the curvature sensing behavior of curvature inducing proteins in crowded membranes, we quantifify the affinity of ANXA4 monomers and trimers for high membrane curvatures by extracting membrane nanotubes from giant PM vesicles (GPMVs). ANXA4 is found to be a sensor of negative membrane curvatures. Multiscale simulations, in which we extract molecular information from atomistic scale simulations as input to our macroscopic scale simulations, furthermore predicted that ANXA4 trimers generate membrane curvature upon binding and have an affinity for highly curved membrane regions only within a well defined membrane curvature window. Our results indicate that curvature sensing and mobility of ANXA4 depend on the trimer structure of ANXA4 which could provide new biophysical insight into the role of ANXA4 in membrane repair and other biological processes.

Annexin A4 inhibits sulfatide-induced activation of coagulation factor XII

BACKGROUND

Factor XII (FXII) is a plasma serine protease that initiates the intrinsic pathway of blood coagulation upon contact with anionic substances, such as the sulfated glycolipid sulfatide. Annexins (ANXs) have been implicated in the regulation of the blood coagulation reaction by binding to anionic surfaces composed of phospholipids and sulfated glycoconjugates, but their physiological importance is only partially understood.

OBJECTIVE

To test the hypothesis that ANXs are involved in suppressing the intrinsic pathway initiated by sulfatide, we examined the effect of eight recombinant ANX proteins on the intrinsic coagulation reaction and their sulfatide binding activities.

METHODS

Recombinant ANXs were prepared in Escherichia coli expression systems and their anticoagulant effects on the intrinsic pathway initiated by sulfatide were examined using plasma clotting assay and chromogenic assay. ANXA4 active sites were identified by alanine scanning and fold deletion in the core domain.

RESULTS AND CONCLUSIONS

We found that ANXA3, ANXA4, and ANXA5 strongly inhibited sulfatide-induced plasma coagulation. Wild-type and mutated ANXA4 were used to clarify the molecular mechanism involved in inhibition. ANXA4 inhibited sulfatide-induced auto-activation of FXII to FXIIa and the conversion of its natural substrate FXI to FXIa but showed no effect on the protease activity of FXIIa or FXIa. Alanine scanning showed that substitution of the Ca2+ -binding amino acid residue in the fourth fold of the core domain of ANXA4 reduced anticoagulant activity, and deletion of the entire fourth fold of the core domain resulted in complete loss of anticoagulant activity.

[Pathologic features of fallopian tubal fimbriae in patients with endometrial serous carcinoma]

OBJECTIVE

To discuss the potential relationship between endometrial serous carcinoma (ESC) and tubal epithelial lesions by pathologic examination of fallopian tubes with ESC.

METHODS

A total of 30 cases of typical ESC were reexamined and chosen by the pathologist. In each case, bilateral fallopian tubes were submitted to examination of pathologic morphology and immunostaining for p53, annexin IV (ANX-IV), human epidermal growth factor receptor 2 (HER2)/neu, and high-mobility group protein A2 (HMGA2).

RESULTS

Fallopian tubal epithelial lesions were found in 15 cases, including 9 cases tubal serous carcinoma, 2 cases serous tubal intraepithelial carcinoma (STIC) and 2 cases epithelial hyperplasia. Both sides of tubal serous carcinoma and STIC were found in 1 case. The results showed the positive expression for p53 in 26 (87%) out of 30 endometrial malignant specimens tissues and 9 (30%) tubal tissues samples (P > 0.05). Twenty-five (83%) endometrial malignant specimens tissues and 6 (20%) tubal tissues samples showed the positive expression of ANX-IV. Twenty-one (70%) endometrial malignant tissues and 7 (23%) tubal tissues showed the positive expression of HER2/neu. Twenty-five (83%) endometrial malignant tissues and 6 (20%) tubal tissues showed the positive expression of HMGA2. While, there were significant differences among the expression of three proteins between endometrium and the fallopian tube site (all P < 0.05).

CONCLUSIONS

STIC may be associated with the occurrence of ESC. The expression of p53 was positively correlated between the fallopian tube and the endometrium. ANX-IV, HER2/neu and HMGA2 were extensively expressed in ESC.

Proteomic analysis of pycnogenol effects in RAW 264.7 macrophage reveals induction of cathepsin D expression and enhancement of phagocytosis

Pycnogenol, polyphenolic compounds extracted from the pine bark, is beneficial for human health. To understand more of its effects, the present study is to explore the protein expression pattern induced by pycnogenol in RAW 264.7 cells. Global analysis using two-dimensional gel electrophoresis indicated that treatment with pycnogenol induces upregulation of four proteins, whose identities were revealed by mass spectrometry as cathepsin D, keratinocyte lipid-binding protein, proteasome subunit alpha type 1, and annexin IV. The pycnogenol effect displayed a time- and concentration-dependent manner. Unlike pycnogenol, N-acetyl cysteine and vitamin C had no effect on cathepsin D expression. Further studies showed that cathepsin D induction is correlated with an increase of lysosomal staining and enhancement of phagocytosis. These results reveal the novel effects of pycnogenol on protein expression and phagocytic functions and illustrate the advantage of proteomics-based strategy in unveiling the molecular basis of phytochemicals.

Expression of carbohydrate-binding protein p33/41 in human tumor cell lines

We previously reported a new type of lectin, p33/41 (annexin IV), which was isolated from a bovine tissue extract [Kojima, K. et al. (1992) J. Biol. Chem. 267, 20536-20539]. When the expression of p33/41 (annexin IV) was surveyed in the lysates of 39 human tumor cell lines by SDS-PAGE, followed by Western blot analysis with polyclonal anti-bovine p33/41 and monoclonal anti-annexin IV (Z016, Zymed) antibodies, 21 cell lines were found to be reactive with the polyclonal antibody, whereas all 39 cell lines were stained with Z016. These results together with those obtained with standard proteins, annexins IV and V, suggested that the monoclonal antibody, Z016, recognizes annexin V, but not p33/41 (annexin IV). Therefore, we performed cDNA cloning of human p33/41 (annexin IV) to prepare a recombinant protein and raised monoclonal antibodies against the protein. Northern blot analysis with the cDNA as a probe showed that a human colon cancer cell line, HT29, contains p33/41 (annexin IV) mRNA of two sizes, 2.0 and 3.0 kb. The two monoclonal antibodies, AS11 and AS17, against the recombinant protein generated were useful for flow cytometric analysis, ELISA, Western blot analysis and immunoprecipitation. Flow cytometric analysis with AS17 showed that p33/41 (annexin IV) is located in the cytoplasm of HT29 cells, but not on the cell surface. However, one of the cell surface proteins first labeled with biotin and then solubilized with a detergent was immunoprecipitated with AS17. The results suggest the existence of a membrane spanning form of p33/41 (annexin IV).

Virulence of transparent and opaque colony types of Neisseria gonorrhoeae for the genital tract of mice

The virulence of transparent (Tr) and opaque (Op) colony types of Neisseria gonorrhoeae in the genital tract of female mice was evaluated at two stages of oestrous. Isogenic pairs of Tr and Op variants were isolated from N. gonorrhoeae strain 57-120. Both variants exhibited a T2 morphology, but only the Op variant possessed protein II (P.II) in outer-membrane fractions. When administered by intravaginal inoculation Op gonococci were highly infective only for mice in late pro-oestrous, whereas Tr gonococci were virulent for mice at both late pro-oestrous and dioestrous. Gonococci recovered from the uterus were of both Tr and Op phenotypes in equal proportions when mice were infected at dioestrous with Tr cells. In contrast, greater than 90% of recovered colonies were of Op phenotype when mice were infected at late pro-oestrous with either Op or Tr cells. These results indicate that the virulence of gonococci for the genital tract of female mice differs from that for the chicken embryo. Furthermore, gonococcal survival in the female genital tract might be attributable to phase variation from Tr to Op phenotypes.

Lipocortin IV is a basolateral cytoskeleton constituent of rabbit enterocytes

A monoclonal antibody, BL7B1, which specifically recognized rabbit lipocortin IV, was produced. The BL7B1 epitope is localized between the methionine residues that occupy positions 148 and 259 in human lipocortin IV. Immunofluorescence and subcellular fractionation studies showed that in the rabbit enterocytes, lipocortin IV is specifically associated with the basolateral membranes. When these membranes are solubilized by Triton X-100 in the presence of 1 mM of Ca2+ the lipocortin IV, like the cytoskeleton, remained insoluble suggesting that it might be associated with this structure in vivo. No lipocortin IV was detected in the brush border using immunofluorescence techniques and less than 10% of the amount present in the purified basolateral membranes was detected in the brush border membrane fraction.

Identification and characterization of phospholipase A2 inhibitory proteins in human mononuclear cells

Calcium-dependent phospholipid binding and phospholipase A2 inhibitory proteins were isolated from human mononuclear cells. Lipocortins I and II were present whereas lipocortin IV (endonexin I) was not. The other proteins were purified to homogeneity and shown to have molecular masses of 35, 36, 32 and 73 kDa. The 36-kDa and 73-kDa proteins are related, the smaller appears to be part of the larger. The 73-kDa protein is related to the 67-kDa calelectrin and to lipocortin VI; the 32-kDa protein is different from endonexin I but related to chromobindin 7 and to lipocortin V. The 35-kDa protein has been identified by tryptic peptide sequencing as lipocortin III. All these proteins inhibit phospholipase A2 activity in vitro and the three smaller ones inhibit the [3H]arachidonic acid release from prelabelled monocytes induced by the calcium ionophore A23187 in a dose-dependent manner.

Characterization of Ca2(+)-dependent phospholipid binding, vesicle aggregation and membrane fusion by annexins

The annexins are a family of structurally similar, Ca2(+)-dependent, phospholipid-binding proteins. We compared six members of this family (calpactin I heavy chain, lipocortins I and III, endonexin II, p68 and protein II) to determine their phospholipid-binding specificities, as well as their ability to promote aggregation and fusion of phospholipid vesicles. The Ca2+ requirement for all of the proteins was lowest for binding to vesicles composed of phosphatidic acid, followed by phosphatidylserine and then phosphatidylinositol. Only protein II, p68, lipocortin III and endonexin II bound to vesicles composed of phosphatidylethanolamine, and none bound to phosphatidylcholine. Both calpactin I heavy chain and lipocortin I promoted aggregation of phosphatidylserine- or phosphatidylinositol-containing vesicles in the presence of less than 10 microM-Ca2+. Lipocortin I promoted fusion of liposome membranes by lowering threshold Ca2+ concentrations. Although calpactin I heavy chain did not affect threshold Ca2+ concentrations, it did increase the rate and extent of spontaneous fusion. In contrast, p68 inhibited fusion at threshold Ca2+ concentrations. Whereas previous reports have emphasized properties that the annexins have in common, these findings reveal quantitative and qualitative differences among the annexins which may relate to distinct intracellular functions.

Characterization of annexins in mammalian brain

Three annexins--p68, endonexin, and p32--have been isolated from porcine brain using their calcium-dependent affinity for membranes. Large amounts (20-50 mg/kg of tissue) of p68 and p32 can be isolated from cerebrum and cerebellum. The p68 is present as up to 0.3% of total porcine brain protein. The p68 and p32 from porcine brain bind to phosphatidic acid (half-maximal binding at 6 and 34 microM free calcium, respectively) and to phosphatidylserine (8 and 34 microM, respectively). They do not bind to phosphatidylcholine at calcium concentrations up to 1 mM. Two other major proteins (Mr 180,000 and Mr 76,000) were isolated with the annexins in a calcium-dependent manner but do not bind to phospholipids. The 180-kilodalton protein is the heavy chain of clathrin. From immunohistochemical studies, p68 is strongly associated with the plasma membranes of Purkinje cell bodies and dendrites in porcine cerebellum. It is also an intracellular component of Purkinje cells localized to perinuclear structures. Staining of axons in the white matter and granule cell layer was also seen. In contrast, p32 is completely absent from Purkinje cells and their dendrites; it is predominantly located in the molecular layer and in white matter of the cerebellar folds. The distribution of p32 may be consistent with a predominantly glial localization.

Biosynthesis, secretion and extracellular localization of anchorin CII, a collagen-binding protein of the calpactin family

The amino acid sequence of anchorin CII, a collagen-binding protein isolated originally from chondrocyte membranes, was previously determined by sequencing of cDNA and proteolytic fragments of the protein. Computer analysis of the protein sequence revealed four internal repeats of approximately 70-80 residues, each containing a highly conserved consensus sequence of 17 residues. These repeats show considerable homology with sequences in human and bovine calpactin, lipocortin, endonexin and protein II, which are members of a family of Ca2+- and phospholipid-binding proteins, as well as major substrates of tyrosine kinases. While these proteins have been located at the inner side of the plasma membrane of fibroblasts and epithelial cells, here we present experimental evidence that anchorin CII is at least partially released from cells and binds to the outer cell surface. Biosynthesis studies in cell-free systems and in cell culture indicate that anchorin CII is not processed, which is consistent with the absence of signal sequences from the protein. Yet, pulse-chase experiments show that anchorin is released into the culture medium of fibroblasts after 30 min, and in chondrocyte cultures after 20 h. Anchorin CII was located to the outer cell surface of chondrocytes by lactoperoxidase-catalyzed cell surface iodination as well as by antibody labeling both at light- and electron-microscopical level. The pericellular localization of anchorin CII is consistent with the notion that this protein is involved in the interaction of chondrocytes and fibroblasts with extracellular collagen.

The amino acid sequence of protein II and its phosphorylation site for protein kinase C; the domain structure Ca2+-modulated lipid binding proteins

Protein II isolated from porcine intestinal epithelium is a Ca2+-modulated lipid-binding protein. The amino acid sequence of porcine protein II reported here sheds new light on the properties of a multigene protein family which includes the tyrosine kinase substrates of the sarc gene (p36) and of the EGF-receptor (p35). The sequence consolidates the structural principle in which an amino-terminal tailpiece of variable length is followed by a core built from four internally homologous segments for those proteins in the 35-40 kd range. Sequence data also show that the core can now be described as two domains each containing one low and one high homology segment. This view accounts for two Ca2+ sites, lipid aggregation and F-actin bundling--when present--and suggests that properties of the cores in which protein II differs from p36 and p35 arise primarily from segments 1 and 2. The protease-sensitive tailpiece of protein II is very short and lacks the phosphorylatable tyrosine present in the larger tail domains of p36 and p35. It harbors, however, like the p36 domain, the major site for in vitro phosphorylation by the Ca2+- and lipid-activated protein kinase C. In protein II this site is most likely threonine 6. The sequence alignment also explains why protein II does not interact with a unique p11, a property probably specific for p36. Our results further suggest that liver endonexin may reflect two protein species both closely related to protein II.

Calcium binding protein from porcine intestine binds to phosphatidylserine vesicles in the presence of calcium

Protein II, a 32K cytoskeleton-associated protein isolated from porcine intestinal epithelium, binds to vesicles composed of phosphatidylserine in the presence, but not the absence, of 10 microM Ca2+. Binding was saturable and was specifically inhibited by chelation of free Ca2+ with EGTA. Binding was also inhibited by trifluophenothiazine. Vesicles composed of dimyristoylphosphatidylcholine did not bind protein II, suggesting that interaction with phosphatidylserine was selective. These properties are consistent with a possible role for protein II in Ca-regulated cytoskeleton-cell membrane events.