cDNA structure and expression of calpactin, a peptide involved in Ca2(+)-dependent cell aggregation in sponges

Effect of dietary fat modification on subcutaneous white adipose tissue insulin sensitivity in patients with metabolic syndrome

SCOPE

To determine whether the insulin resistance that exists in metabolic syndrome (MetS) patients is modulated by dietary fat composition.

METHODS AND RESULTS

Seventy-five patients were randomly assigned to one of four diets for 12 wk: high-saturated fatty acids (HSFAs), high-MUFA (HMUFA), and two low-fat, high-complex carbohydrate (LFHCC) diets supplemented with long-chain n-3 (LFHCC n-3) PUFA or placebo. At the end of intervention, the LFHCC n-3 diet reduced plasma insulin, homeostasis model assessment of insulin resistance, and nonsterified fatty acid concentration (p < 0.05) as compared to baseline Spanish habitual (BSH) diet. Subcutaneous white adipose tissue (WAT) analysis revealed decreased EH-domain containing-2 mRNA levels and increased cbl-associated protein gene expression with the LFHCC n-3 compared to HSFA and HMUFA diets, respectively (p < 0.05). Moreover, the LFHCC n-3 decreased gene expression of glyceraldehyde-3-phosphate dehydrogenase with respect to HMUFA and BSH diets (p < 0.05). Finally, proteomic characterization of subcutaneous WAT identified three proteins of glucose metabolism downregulated by the LFHCC n-3 diet, including annexin A2. RT-PCR analysis confirmed the decrease of annexin A2 (p = 0.027) after this diet.

CONCLUSION

Our data suggest that the LFHCC n-3 diet reduces systemic insulin resistance and improves insulin signaling in subcutaneous WAT of MetS patients compared to HSFA and BSH diets consumption.

Cell surface complex of cathepsin B/annexin II tetramer in malignant progression

The cysteine protease cathepsin B is upregulated in a variety of tumors, particularly at the invasive edges. Cathepsin B can degrade extracellular matrix proteins, such as collagen IV and laminin, and can activate the precursor form of urokinase plasminogen activator (uPA), perhaps thereby initiating an extracellular proteolytic cascade. Recently, we demonstrated that procathepsin B interacts with the annexin II heterotetramer (AIIt) on the surface of tumor cells. AIIt had previously been shown to interact with the serine proteases: plasminogen/plasmin and tissue-type plasminogen activator (tPA). The AIIt binding site for cathepsin B differs from that for either plasminogen/plasmin or tPA. AIIt also interacts with extracellular matrix proteins, e.g., collagen I and tenascin-C, forming a structural link between the tumor cell surface and the extracellular matrix. Interestingly, cathepsin B, plasminogen/plasmin, t-PA and tenascin-C have all been linked to tumor development. We speculate that colocalization through AIIt of proteases and their substrates on the tumor cell surface may facilitate: (1) activation of precursor forms of proteases and initiation of proteolytic cascades; and (2) selective degradation of extracellular matrix proteins. The recruitment of proteases to specific regions on the cell surface, regions where potential substrates are also bound, could well function as a 'proteolytic center' to enhance tumor cell detachment, invasion and motility.

Cell adhesion and histocompatibility in sponges

Sponges are the lowest extant metazoan phylum and for about a century they have been used as a model system to study cell adhesion. There are three classes of molecules in the extracellular matrix of vertebrates: collagens, proteoglycans, and adhesive glycoproteins, all of them have been identified in sponges. Species-specific cell recognition in sponges is mediated by supramolecular proteoglycan-like complexes termed aggregation factors, still to be identified in higher animals. Polyvalent glycosaminoglycan interactions are involved in the species-specificity, representing one of the few known examples of a regulatory role for carbohydrates. Aggregation factors mediate cell adhesion via a bifunctional activity that combines a calcium-dependent self-interaction of aggregation factor molecules plus a calcium-independent heterophilic interaction with cell surface receptors. Important cases of cell adhesion are the phenomena involved in histocompatibility reactions. A long-standing prediction has been that the evolutionary ancestors of histocompatibility systems might be found among primitive cell-cell interaction molecules. A surprising characteristic of sponges, considering their low phylogenetic position, is that they possess an exquisitely sophisticated histocompatibility system. Any grafting between two different sponge individuals (allograft) is almost invariably incompatible in the many species investigated, exhibiting a variety of transitive qualitatively and quantitatively different responses, which can only be explained by the existence of a highly polymorphic gene system. Individual variability of protein and glycan components in the aggregation factor of the red beard sponge, Microciona prolifera, matches the elevated sponge alloincompatibility, suggesting an involvement of the cell adhesion system in sponge allogeneic reactions and, therefore, an evolutionary relationship between cell adhesion and histocompatibility systems.

A 35-kDa protein is the basic unit of the core from the 2 x 10(4)-kDa aggregation factor responsible for species-specific cell adhesion in the marine sponge Microciona prolifera

Dissociated sponge cells quickly reaggregate in a species-specific manner, differentiate, and reconstruct tissue, providing a very handy system to investigate the molecular basis of more complex intercellular recognition processes. Species-specific cell adhesion in the marine sponge Microciona prolifera is mediated by a supramolecular complex with a Mr = 2 x 10(7), termed aggregation factor. Guanidinium hydrochloride/cesium chloride dissociative gradients and rhodamine B isothiocyanate staining indicated the presence of several proteins with different degrees of glycosylation. Hyaluronate has been found to be associated with the aggregation factor. Chemical deglycosylation revealed a main component accounting for nearly 90% of the total protein. The cDNA-deduced amino acid sequence predicts a 35-kDa protein (MAFp3), the first sponge aggregation factor core protein ever described. The open reading frame is uninterrupted upstream from the amino terminus of the mature protein, and the deduced amino acid sequence for this region has been found to contain a long stretch sharing homology with the Na+-Ca2+ exchanger protein. A putative hyaluronic acid binding domain and several putative N- and O-glycosylation signals are present in MAFp3, as well as eight cysteines, some of them involved in intermolecular disulfide bridges. Northern blot data suggest variable expression, and Southern blot analysis reveals the presence of other related gene sequences. According to the respective molecular masses, one aggregation factor molecule would contain about 300 MAFp3 units, suggesting that sponge cell adhesion might be based on the assembly of multiple small glycosylated protein subunits.

Annexins in Paramecium cells. Involvement in site-specific positioning of secretory organelles

Annexins were isolated from Paramecium cell homogenates by standard ethylene glycol tetraacetic acid (EGTA) extraction and 100 000-g centrifugation. Two different antibodies (Abs) against synthetic peptides were used, Call-15 and B15, which in mammalian cells recognize a sequence of annexin II or a common sequence occurring in several annexins (except for annexin II), respectively. With anti-Call-15 Abs, western blots from EGTA extracts showed strongly reactive bands of 44.5 and 46 kDa and of higher values. Some of these bands bound to the 100 000-g pellet fraction when Ca(2+) was added. Immuno- and affinity labelling revealed selective, Ca(2+)-dependent labelling of the cell cortex, with enrichment around trichocyst docking sites (facing subplasmalemmal Ca(2+) stores). Cortical fluorescence labelling decreased in wild-type (7S) cells when trichocyst ghosts were detached after synchronous exocytosis. Similarly, cortical labelling was reduced when intact trichocysts were detached from the cell surface of non-discharge mutant cells (nd9-28 degrees C, showing identical bands on blots), which then contained numerous heavily labelled phagolysosomes. This strongly suggests annexin downregulation. All together, the dynamic labelling of cortical structures we observed strongly supports involvement of calpactin-like annexins in trichocyst docking. Anti-B15 Abs recognized a band of 51 kDa and some of higher values. These Abs selectively labelled the outlines of the cytoproct, the site of spent phagolysosome exocytosis. In conclusion, our data indicate involvement of specific sets of annexins in site-specific positioning and attachment of widely different secretory organelles at the cell surface in Paramecium cells.

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 annexins: specific markers of midline structures and sensory neurons in the developing murine central nervous system

The annexins are a family of cytoplasmic proteins that have been shown to have numerous actions within a cell. Recent evidence suggests that at least one of these proteins plays a role in the development of the central nervous system (CNS). The present study examines the temporal expression and spatial distribution of annexins I, II, IV, V, and VI during development and at maturity in the murine CNS by immunocytochemical analysis. The results demonstrate that annexins I, II and IV exhibit clear immunolabeling in the murine CNS with distinct patterns of temporal and spatial expression. Annexin IV is the first annexin to be expressed on embryonic day (E) 9.5 while annexin I is the last to be expressed (E11.5). Annexins I, II and IV are found in the floor plate region, but to differing rostrocaudal extents. Annexin I has a very restricted distribution, only present in the midline raphe of the brainstem. Annexin II is present in the spinal cord, brainstem and mesencephalon. Annexin IV has the widest midline distribution, being observed in the floor and roof plates of the developing CNS. Additionally, antibodies against annexin II and IV immunolabel most dorsal root and sensory ganglion cells and their axons. During early postnatal development, immunolabeling with each antibody gradually disappears in many structures, and only first order sensory neurons and their fibers are immunopositive for annexins II and IV at weaning. Three functions of the annexins are suggested by the present findings: (1) to help establish the midline structures of the floor and roof plates, (2) to help direct the decussation of sensory fibers, and (3) to regulate some aspect of sensory neuron processing, such as signal transduction.

Identification and partial sequence analysis of novel annexins in Lytechinus pictus oocytes

The annexins are a major class of calcium-binding proteins with unknown functions. In an attempt to define novel model systems in which to study members of the annexin family, we have investigated the expression of annexins in eggs from the sea urchin Lytechinus pictus. Western blot analysis of L. pictus eggs using antisera raised against human annexins I, V and VI revealed the presence of immunoreactive proteins of approximately 34 kDa, 35 kDa and 68 kDa respectively. The sea urchin annexins behaved similarly to their mammalian counterparts, both during purification and in their ability to bind calcium-dependently to anionic phospholipids. Of the three sea urchin annexins, the 34 kDa form was most abundant, yielding sufficient quantities for peptide microsequencing. The amino acid sequences derived in this way showed the L. pictus annexin to be closely related both to mammalian annexin I and to annexins IX, X and XII from Drosophila and Hydra. However, N-terminal sequence from the L. pictus annexin showed it to be a novel member of the annexin super-gene family. The results are interesting in view of the complex evolution of the annexin gene family, and also point to the potential usefulness of echinoderm eggs as a model system in which to study annexin function.

Differential tissue expression of Annexin VIII in human

The expression of Annexins V and VIII by human lung, liver, kidney, skin, heart, uterus, spleen and skeletal muscle was investigated by ELISA. All investigated tissues contained Annexin V. Its level varied with the tissue from around 5 microgram (skin) to approximately 120 micrograms (spleen) per g of wet tissue. Contradistinctionally Annexin VIII expression was less ubiquitous and less abundant. Only lung, skin, liver, and kidney expressed Annexin VIII. Its levels were approximately 100-fold less then the Annexin V levels. Immunohistochemical analysis of lung sections revealed Annexin VIII presence exclusively in the endothelia. Annexin V and VIII levels of cultured human umbilical vein endothelial cells, human arterial smooth muscle cells, human lung fibroblasts and HeLa cells were measured by ELISA. All cell types expressed Annexin V whereas only HeLa cells had detectable levels of Annexin VIII. The results indicate a tissue specific expression of Annexin VIII by lung endothelium, suggesting a highly specialised function.

Calcium-induced translocation of annexins to subcellular organelles of human neutrophils

The annexins are Ca(2+)-regulated, phospholipid-binding proteins which have been suggested to take part in cellular events such as exocytosis. The subcellular localization of annexins in human neutrophils was determined using monoclonal antibodies against annexins I, II, IV and VI and a polyclonal peptide antiserum against an annexin consensus sequence. Several annexins were translocated to the light membrane fraction enriched in plasma membranes and secretory vesicles. Annexins were associated also with the azurophil and specific granules. Whereas annexins I, IV and VI and one unidentified 35 kDa protein translocated to each of the isolated organelles, annexin II, a 66 kDa annexin IV-like protein, and a 38 kDa annexin I-like protein exhibited organelle-related differences in their association with membranes. The 38 kDa annexin associated only with specific granules and the secretory vesicles/plasma membrane but not with azurophil granules. Annexin II and the 66 kDa annexin IV-like protein associated with each of the neutrophil organelles, but the binding to specific granules and secretory vesicles/plasma membrane showed a Ca(2+)-dependency different from that of azurophil granules. This observation suggests that these proteins may contribute to the secretory process in neutrophils.

Identification of an annexin-like protein and its possible role in the Aplysia eye circadian system

Light and serotonin regulate the phase of the circadian rhythm of the isolated eye of Aplysia. To screen for possible protein components of the eye circadian oscillator, we identified a number of proteins whose synthesis was altered in opposite ways by light and serotonin. The cellular function of one of these proteins was investigated by obtaining a partial amino acid sequence of it and by examining its immunoreactivity. A 38-amino acid sequence was obtained from a 40-kDa (isoelectric point 5.6) protein. A greater than 60% amino acid identity existed between this sequence and sequences of a family of calcium/phospholipid-binding proteins called annexins. Furthermore, the 40-kDa protein reacted with antibodies generated against a conserved amino acid sequence of annexins and with antibodies raised against human annexin I. The identification of the 40-kDa, light- and serotonin-regulated protein as an annexin led us to hypothesize that arachidonic acid metabolism plays a role in the Aplysia eye circadian system. To test this hypothesis, we examined the ability of an inhibitor of the arachidonic acid metabolic pathway to perturb the eye rhythm. Pulse treatments of isolated eyes with a lipoxygenase inhibitor, nordihydroguaiaretic acid, phase shifted the rhythm. The phase-shifting ability of nordihydroguaiaretic acid suggests that arachidonic acid and some of its metabolites may play a role in the eye circadian system. The results of our studies raise the possibility that links may exist between the 40-kDa annexin-like protein, arachidonic acid metabolism, and the circadian oscillator.

The hinge region of chicken annexin I contains no site for tyrosine phosphorylation

Annexin I (AnxI) is a calcium-dependent membrane binding protein which has been implicated in various physiological activities. The region of the chicken anxI cDNA encoding the first 130 amino terminal residues was cloned by reverse transcription PCR in order to determine the relationship of its variable amino-terminal regulatory region with other known annexins. This nucleotide sequence shows 86% identity with pigeon AnxI isoforms, and 57% with its human homolog. The protein encoded by the chicken anxI cDNA lacks the canonical epidermal growth factor receptor/kinase phosphorylation site, which is present in AnxI of other species. In contrast, the putative protein kinase C phosphorylation site of the amino-terminus is present in the chicken AnxI. Whereas the pigeon genome contains two anxI genes, genomic Southern analysis shows that in the chicken AnxI is encoded by only a single gene. These data suggest that AnxI has undergone significant sequence variation in the avians, and clarifies the relationships of the avian anxI genes with their ancestral homologs.

Isolation, characterization and localization of annexin V from chicken liver

Annexin V has been purified from chicken liver; 40 mg of annexin V was obtained per kg of tissue. In contrast with mammalian liver, very little annexin VI was obtained. Surprisingly, chicken liver annexin V resembles mammalian annexin IV in its M(r) (32,500) and its isoelectric point (5.6), but amino-acid-sequence analysis demonstrates identity with chicken annexin V (anchorin CII). It binds to phospholipids in a Ca(2+)-dependent manner with free-Ca2+ concentrations for half-maximal binding to phosphatidylserine and phosphatidic acid of 10 microM; phosphatidylethanolamine of 32 microM and phosphatidylinositol of 90 microM. No binding to phosphatidylcholine was observed at Ca2+ concentrations up to 300 microM. In isolated liver membranes a significant proportion of annexin V was not extractable with EGTA but could only be extracted with Triton X-100, suggesting the existence of a tightly membrane-associated form of annexin V. A specific antiserum to chicken annexin V was used to localize the protein in adult and embryonic chicken liver. In the adult, annexin V was highly concentrated in epithelial cells lining the bile ducts, and along the bile canaliculi. In embryonic liver, strong staining of the bile-duct epithelial cells was again evident, and in addition, endothelial cells were strongly immunoreactive.

A growth-dependent post-translational modification of annexin VI

Annexin VI (p68, 67-kDa calelectrin) is a member of a family of Ca2+/phospholipid-binding proteins, that includes p35 (annexin I) and p36 (annexin II), the major cellular substrates for phosphorylation by the epidermal growth factor receptor and pp60v-src tyrosine kinase activities, respectively. We report here that like annexins I and II, annexin VI is phosphorylated in vivo, but that in contrast, annexin VI phosphorylation is associated with cell growth. In both Swiss 3T3 fibroblasts and human T-lymphoblasts the pattern of phosphorylation followed an almost identical profile. In particular, annexin VI was not phosphorylated in quiescent cells, but was phosphorylated on serine and to a lesser extent threonine, several hours following cell stimulation. Furthermore, annexin VI also incorporated phosphate in a growth-dependent manner, in a form other than a phosphoamino-acid. The phosphate was visualised following acid hydrolysis of immunoprecipitated annexin VI, as part of a complex having high mobility on 2-D thin-layer electrophoresis. The identity of this complex is not known. The results suggest that a post-translational modification other than direct protein phosphorylation may influence the activity of annexin VI and provide evidence linking cell growth with regulation of annexin VI function.

Distinct cellular expression pattern of annexins in Hydra vulgaris

The annexins are a structurally related family of Ca2+ and phospholipid binding proteins whose function has not been clearly defined. Further investigations of annexin function may be enhanced by studying simpler organisms that express fewer annexin gene products. We previously characterized annexin XII from the freshwater cnidarian Hydra vulgaris (Schlaepfer, D. D., D. A. Fisher, M. E. Brandt, H. R. Bode, J. Jones, and H. T. Haigler. 1992. J. Biol. Chem. 267:9529-9539). In this report, we detected one other hydra annexin (40 kD) by screening hydra cell extracts with antibodies raised against peptides from highly conserved regions of known annexins. The 40-kD protein was expressed at less than 1% of annexin XII levels. These biochemical studies indicate that hydra contain a very limited number of annexin gene products. The cellular hydra annexin distribution was analyzed by indirect immunofluorescence. Using affinity-purified antibodies to annexin XII, the epithelial battery cells were stained throughout the tentacle. A lower level of annexin XII staining was detected in peduncle region epithelial cells. No other cell types showed detectable annexin XII staining. The anti-peptide antibody that specifically detected the 40-kD hydra annexin, maximally stained the cytoplasm of nematocytes. The immunofluorescent results showed that annexin XII and the 40-kD annexin were not co-expressed in the same cells. Since the hydra annexins localized to specific subsets of the total hydra cell types, it is likely that these proteins perform specialized biological roles, and not general "housekeeping" functions which are part of the essential molecular machinery of all cells.