Role of phospholipase A2 in the stimulation of sponge cell proliferation by homologous lectin

Oogenesis and lipid metabolism in the deep-sea sponge Phakellia ventilabrum (Linnaeus, 1767)

Sponges contain an astounding diversity of lipids that serve in several biological functions, including yolk formation in their oocytes and embryos. The study of lipid metabolism during reproduction can provide information on food-web dynamics and energetic needs of the populations in their habitats, however, there are no studies focusing on the lipid metabolism of sponges during their seasonal reproduction. In this study, we used histology, lipidome profiling (UHPLC-MS), and transcriptomic analysis (RNA-seq) on the deep-sea sponge Phakellia ventilabrum (Demospongiae, Bubarida), a key species of North-Atlantic sponge grounds, with the goal to (i) assess the reproductive strategy and seasonality of this species, (ii) examine the relative changes in the lipidome signal and the gene expression patterns of the enzymes participating in lipid metabolism during oogenesis. Phakellia ventilabrum is an oviparous and most certainly gonochoristic species, reproducing in May and September in the different studied areas. Half of the specimens were reproducing, generating two to five oocytes per mm2. Oocytes accumulated lipid droplets and as oogenesis progressed, the signal of most of the unsaturated and monounsaturated triacylglycerides increased, as well as of a few other phospholipids. In parallel, we detected upregulation of genes in female tissues related to triacylglyceride biosynthesis and others related to fatty acid beta-oxidation. Triacylglycerides are likely the main type of lipid forming the yolk in P. ventilabrum since this lipid category has the most marked changes. In parallel, other lipid categories were engaged in fatty acid beta-oxidation to cover the energy requirements of female individuals during oogenesis. In this study, the reproductive activity of the sponge P. ventilabrum was studied for the first time uncovering their seasonality and revealing 759 lipids, including 155 triacylglycerides. Our study has ecological and evolutionary implications providing essential information for understanding the molecular basis of reproduction and the origins and formation of lipid yolk in early-branching metazoans.

Sponges: A Reservoir of Genes Implicated in Human Cancer

Recently, it was shown that the majority of genes linked to human diseases, such as cancer genes, evolved in two major evolutionary transitions—the emergence of unicellular organisms and the transition to multicellularity. Therefore, it has been widely accepted that the majority of disease-related genes has already been present in species distantly related to humans. An original way of studying human diseases relies on analyzing genes and proteins that cause a certain disease using model organisms that belong to the evolutionary level at which these genes have emerged. This kind of approach is supported by the simplicity of the genome/proteome, body plan, and physiology of such model organisms. It has been established for quite some time that sponges are an ideal model system for such studies, having a vast variety of genes known to be engaged in sophisticated processes and signalling pathways associated with higher animals. Sponges are considered to be the simplest multicellular animals and have changed little during evolution. Therefore, they provide an insight into the metazoan ancestor genome/proteome features. This review compiles current knowledge of cancer-related genes/proteins in marine sponges.

Exploring the antagonistic producer Streptomyces MSI051: implications of polyketide synthase gene type II and a ubiquitous defense enzyme phospholipase A2 in the host sponge Dendrilla nigra

To explore the functional role of the antagonistic producer strain Streptomyces dendra sp. nov. MSI051 in the host sponge Dendrilla nigra, hypothetical factors including the antagonistic potential of MSI051 against biofilm bacteria and a ubiquitous defense enzyme phospholipase A2 (PLA2) in host sponge as well as in bacterial symbiont MSI051 were determined. The host sponge D. nigra and associated bacterial symbiont MSI051 contained high levels of PLA2. The host sponge showed PLA2 activity to the extent of 1032 U/L, with a specific activity of 2021 U/g, and strain MSI051 showed similar activity. The findings of the present study suggest that PLA2 in the sponge-associated bacteria might have an integrated functional role in the host defense system of marine sponges. This report may be the first on the role of PLA2 activity in sponge-associated bacteria. Isolate MSI051 was a potential antagonistic producer which showed a broad spectrum of antibacterial activity. Polyketide synthase gene type II in MSI051 ultimately evidenced the antagonistic potential. Antimicrobial activity was found to be positively skewed toward biofilm bacteria. This implies a functional role of MSI051 in the protection of host sponge against fouling processes.

Formulation of a basal medium for primary cell culture of the marine sponge Hymeniacidon perleve

Marine sponge cell culture is a potential route for the sustainable production of sponge-derived bioproducts. Development of a basal culture medium is a prerequisite for the attachment, spreading, and growth of sponge cells in vitro. With the limited knowledge available on nutrient requirements for sponge cells, a series of statistical experimental designs has been employed to screen and optimize the critical nutrient components including inorganic salts (ferric ion, zinc ion, silicate, and NaCl), amino acids (glycine, glutamine, and aspartic acid), sugars (glucose, sorbitol, and sodium pyruvate), vitamin C, and mammalian cell medium (DMEM and RPMI 1640) using MTT assay in 96-well plates. The marine sponge Hymeniacidon perleve was used as a model system. Plackett-Burman design was used for the initial screening, which identified the significant factors of ferric ion, NaCl, and vitamin C. These three factors were selected for further optimization by Uniform Design and Response Surface Methodology (RSM), respectively. A basal medium was finally established, which supported an over 100% increase in viability of sponge cells.

Application of a MTT assay for screening nutritional factors in growth media of primary sponge cell culture

Marine sponges (Porifera) are producers of the largest variety of bioactive compounds among benthic marine organisms. In vitro culture of marine sponge cells has been proposed for the sustainable production of these pharmacologically interesting compounds from marine sponges but with limited success. The development of a suitable growth medium is an essential prerequisite for sponge cells grown in vitro. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was adapted to screen for potential nutritional factors in formulating a growth medium for primary cell culture of Suberites domuncula. In 96-well plates, the effects of nutritional factors including glutamine, pyruvate, iron citrate, silicon, RPMI 1640, and Marine Broth 2216 on the viable cell density were examined in primary cell culture of S. domuncula 36 h after inoculation. Ferric iron (Fe(3+)) and pyruvate were found to significantly improve cell viability in a dose-dependent manner. Silicon and glutamine showed limited improvements at certain concentrations. The supplement of RPMI 1640 and Marine Broth 2216 did not increase cell viability. As a result, several improved media able to maintain higher cell viability in a short-term culture of primary sponge cells could be formulated.

The hypothetical ancestral animal the Urmetazoa: Telomerase activity in sponges [Porifera]

Sponges (Porifera) represent the lowest metazoan phylum, characterized by a pronounced plasticity in the determination of cell lineages, and they are the closest related taxon to the hypothetical ancestral animal, the Urmetazoa, from which the metazoan lineages diverged. In a first approach to elucidate the molecular mechanisms controlling the switch from the cell lineage with a putative indefinite growth capacity to senescent, somatic cells, the activity of the telomerase as an indicator for immortality has been determined. The studies were performed with the marine demosponges Suberites domuncula and Geodia cydonium, in vivo with tissue but also in vitro using the primmorph system. Primmorphs are formed from dissociated cells which have retained their proliferation potency. It was found that the activity of telomerase in tissue of both sponges is high. Based on this and additional findings it is assumed that the separation of the senescent sponge cell lineage from the immortal germ-/somatic cell lineage is triggered by the loss of contact to cell adhesion factors. First evidence is included which suggests that the final progress of the senescent telomerase- negative cells to cell death is caused by apoptosis.

Quantitative assessment of marine sponge cells in vitro: development of improved growth medium

As sources of natural products with potential human therapeutic value, marine sponges are important subjects for cell culture studies. A critical component of any cell culture system is its growth medium. Proceeding from the hypotheses that the thawed, cryopreserved, primary cells would display detectable differential responses and that those responses could be comparatively quantified, this study has established that multiwell screening assays are useful tools for improving medium formulations in cell cultures of the marine sponge, Teichaxinella morchella. Fluorescent probe signals were correlated with known cell densities and viabilities in a 96-well format. Analysis of variance and post-test methods were applied to judge the significance of signal differences seen in a variety of medium formulations. Results from a series of experiments suggested that reducing glutamine and selenium concentrations in the standard medium would result in greater DNA, protein, and esterase activity signals. This was confirmed by the direct comparison of the standard and improved medium formulations. Significantly higher protein content and esterase activity were associated with the improved medium. DNA content was also higher, though not significantly. The result is a new medium formulation that may be more able to support cell growth and division, providing an improved cell culture system for marine sponge cell studies. The assays can be used in additional studies to further improve the in vitro conditions for marine sponge cell culture.

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.

Sponges (Porifera) model systems to study the shift from immortal to senescent somatic cells: the telomerase activity in somatic cells

Sponges (Porifera) represent the lowest metazoan phylum, characterized by a pronounced plasticity in the determination of cell lineages. In a first approach to elucidate the molecular mechanisms controlling the switch from the cell lineage with a putative indefinite growth capacity to senescent, somatic cells, the activity of the telomerase as an indicator for immortality has been determined. The studies were performed with the marine demosponges Suberites domuncula and Geodia cydonium. It was found that the activity for the telomerase in the tissue of both sponges is high; a quantitative analysis revealed that the extract from S. domuncula contained 10.3 TPG units per 5000 cell equivalents and the one from G. cydonium 8.3 TPG units; hence the activity reached approximately 30-20% of the activity seen in telomerase-positive reference cells. In contrast, dissociated spherulous cells from G. cydonium, after an incubation period of 24 h, contained no detectable telomerase activity. From earlier studies it is known that isolated sponge cells do not proliferate. Based on these findings it is assumed that the separation of the senescent sponge cell lineage from the immortal germ/somatic cell lineage is triggered by the loss of contact with cell adhesion factors. First evidence is included which suggests that the final progress of the senescent, telomerase-negative cells to cell death is caused by apoptosis.

Purification and characterization of two exopolyphosphatases from the marine sponge Tethya lyncurium

Two exopolyphosphatases (exopolyphosphatase I and II; EC 3.6.1.11) which release orthophosphate from inorganic polyphosphates have been detected and purified for the first time from a marine sponge. Tethya lyncurium. Exopolyphosphatase I has a molecular mass of 45 kDa, a pH optimum of 5.0 and does not require divalent cations for activity, while exopolyphosphatase II has a molecular mass of 70 kDa, a pH optimum of 7.5 and displays optimal activity in the presence of Mg2+ ions. Final purification of the enzymes could be achieved by affinity chromatography on polyphosphate-modified zirconia. The mode of action of both enzymes was found to be processive. Orthophosphate is the sole product formed by exopolyphosphatase I, while degradation of linear polyphosphates by exopolyphosphatase II occurs to pyrophosphate as end product, which is hydrolyzed, if at all, only very slowly. Significant amounts of polyphosphate (approximately 30 micrograms/g wet weight) were found to be present in the sponge organism. Polyphosphate is shown to inhibit the formation of ATP by adenylate kinase activity present in T. lyncurium extracts in a competitive manner. The inhibitory effect of long-chain polyphosphates was higher than that of short-chain polyphosphate, suggesting a potential role of polyphosphate metabolism in regulating intracellular concentrations of adenylate nucleotides.

Immunoglobulin-like domain is present in the extracellular part of the receptor tyrosine kinase from the marine sponge Geodia cydonium

We have isolated and characterized two cDNAs from the marine sponge Geodia cydonium coding for a new member of a receptor tyrosine kinase of class II. The deduced amino acid sequence shows two characteristic domains: (i) the tyrosine kinase domain; and (ii) an immunoglobulin-like domain. The latter part shows high homology to the vertebrate C2 type immunoglobulin domain. This result demonstrates that immunoglobulin domains are not recent achievements of higher animals but exist also in those animals which have diverged from other organisms about 800 million years ago.

Possible involvement of arachidonic acid and eicosanoids in metamorphic events in Hydractinia echinata (Coelenterata; Hydrozoa)

Upon induction of metamorphosis, larvae of the marine hydroid Hydractinia echinata release [14C]-arachidonic acid from previously labeled endogenous sources. The lipoxygenase inhibitors nordihydroguaiaretic acid and 5,8,11,14-eicosatetraynoic acid inhibited metamorphosis induced by Cs+ and 1,2-sn-dioctanoylglycerol, whereas the inhibitors of cyclooxygenase, indomethacin, and acetylsalicylic acid were ineffective, suggesting a role for lipoxygenase metabolites of arachidonic acid in induction of metamorphosis. Lipoxygenase products in Hydractinia echinata were isolated and identified by gas chromatography/mass spectrometry. 8- and 12-HETE were the most abundant metabolites. In cytosolic fractions from larvae activity of an arachidonic acid metabolizing enzyme, presumably a lipoxygenase, was found. The metabolic product was identified by 1H-NMR and chiral phase HPLC as 8(R)-HETE. Its production was strongly inhibited by NDGA, but not by indomethacin.

Molecular cloning of a tyrosine kinase gene from the marine sponge Geodia cydonium: a new member belonging to the receptor tyrosine kinase class II family

We have isolated and characterized a cDNA from the marine sponge Geodia cydonium coding for a new member of the tyrosine protein kinase (TK) family. The cDNA encodes a protein of M(r) = 68,710, termed GCTK, which is homologous to class II receptor tyrosine kinases (RTKs). GCTK contains conserved amino acids (aa) characteristic of all protein kinases, and the sequences DLATRN and PIRWMATE which are highly specific for TKs. Furthermore, the sequence N-L-Y-x(3)-Y-Y-R is highly homologous to the sequence D-[LIV]-Y-x(3)-Y-Y-R found only in class II RTKs. The sponge TK, when compared with mammalian class II RTKs, shows maximum 31% homology in the TK domain indicating that this the oldest member of class II RTK started to diverge from the common ancestral protein kinase approximately 650 million years ago. Using GCTK as a probe we identified three mRNA signals ranging from 2.6 to 0.6 kb. Kinase activity was localized only in the cell membranes from G. cydonium (M(r) = 65,000), and was not detected in the cytosol of this organism. Antibodies raised against a synthetic peptide, corresponding to the aa residues within the catalytic domain of the sponge TK, recognized strongly two proteins of M(r) = 65,000; these proteins, present in membrane fractions, also bound to the antiphosphotyrosine antibody. These data suggest that the TK cloned from the sponge is a membrane-associated 65 kDa protein. Moreover these results demonstrate that RTKs are present from the lowest group of multicellular eukaryotes, sponges, to mammals, and may suggest that RTKs are involved in a signal transduction pathway.

Cloning of the polyubiquitin cDNA from the marine sponge Geodia cydonium and its preferential expression during reaggregation of cells

Ubiquitination of proteins is a critical step in the controlled degradation process of many polypeptides. Here we show that sponges, the simplest multicellular group of eukaryotic organisms, are also equipped with the ubiquitin pathway. The polyubiquitin cDNA was isolated and characterized from the marine sponge Geodia cydonium. The open reading frame contains six ubiquitin moieties, which are lined up head to tail without spacers. A comparison of the predicted amino acid sequence of the six sponge ubiquitin-coding units with those from other organisms revealed a high degree of homology (> 93%). The ubiquitin gene is expressed to almost the same extent in the two main compartments of the sponge, the cortex and the medulla. However, only in the cortex are detectable amounts of the ubiquitin protein synthesized. The ubiquitin protein isolated from the sponge organism was found to initiate protein degradation in the heterologous reticulocyte system in the same manner as bovine ubiquitin. In vitro studies with dissociated sponge cells revealed that the homologous aggregation factor causes (i) a strong increase in the steady-state level of mRNA coding for ubiquitin and (ii) a drastic increase in ubiquitin protein synthesis, while the homologous lectin failed to display that effect in isolated cells. These data suggest that ubiquitin may play a role in sponge morphogenesis.

Phospholipase A2 and arthritis

Over the last 30 years, interest in PLA2 has grown beyond its enzymatic capacity to cleave phospholipids. It has been recognized as the rate-limiting step in the release of arachidonic acid and subsequent formation of prostaglandins, leukotrienes, and other bioactive lipids. Subsequently, PLA2 has not only been found to be present in high concentrations in inflammatory arthritis, but also to induce inflammation when injected into animals. At the same time, investigators into mechanisms of signal transduction demonstrated that a variety of cytokines including IL-1 and TNF, which are found in high concentrations in synovial fluid from patients with RA, stimulate PLA2 activity. These investigations demonstrated further the central role for PLA2 in inflammatory events, especially inflammatory arthritis. Numerous other PLA2 proteins, in addition to the low molecular weight synovial fluid/platelet enzyme, also have been characterized. Their clinical role in arthritis is yet to be elucidated. Human proteins which either inhibit or stimulate PLA2 have also been identified, characterized, and cloned. More recently, exciting investigations, primarily from biotechnology and pharmaceutical companies, into inhibitors of PLA2 have been reported. New PLA2-regulating compounds, which will hopefully move from the laboratory and through clinical trials and then be used to treat patients with arthritis, are on the horizon.

Purification and characterization of a pore-forming protein from the marine sponge Tethya lyncurium

A pore-forming protein was detected and purified for the first time from a marine sponge (Tethya lyncurium). The purified protein has a polypeptide molecular mass of 21 kDa and a pI of 6.4. Tethya pore-forming protein (also called Tethya hemolysin) rapidly lysed erythrocytes from a variety of organisms. After binding to target membranes, the hemolysin resisted elution with EDTA, salt or solutions of low ionic strength and hence resembled an integral membrane protein. Erythrocytes could be protected from hemolysis induced by Tethya hemolysin by addition of 30 mM dextran 4 (4-6 kDa; equivalent hydrodynamic diffusion radius, 1.75-2.3 nm) to the extracellular medium, but not by addition of uncharged molecules of smaller size [sucrose, raffinose and poly(ethylene glycol) 1550; equivalent hydrodynamic diffusion radii, 0.46, 0.57 and 1.2 nm, respectively]. This result indicates that hemolysin is able to form stable transmembrane pores with an effective diameter of about 2-3 nm. Treatment of osmotically protected erythrocytes with Tethya hemolysin caused a rapid efflux of intracellular K+ and ATP, and a rapid influx of extracellularly added Ca2+ and sucrose. In negative-staining electron microscopy, target erythrocyte membranes exposed to purified Tethya hemolysin displayed ultrastructural lesions but without visible pores.

Avarol restores the altered prostaglandin and leukotriene metabolism in monocytes infected with human immunodeficiency virus type 1

Infection of monocytes with human immunodeficiency virus type 1 (HIV-1) (strain Ada-M) caused increased levels of leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) in vitro. These two products result from the activities of the two enzymes cyclooxygenase and 5-lipoxygenase. The addition of the sesquiterpenoid hydroquinone Avarol, an HIV inhibitor, strongly reduced the levels of LTB4 and PGE2 via inhibition of both cyclooxygenase and lipoxygenase in monocytes. The 50% inhibition concentrations (IC50) for the enzymes were determined to be 2.26 microM (cyclooxygenase) and 1.97 microM (lipoxygenase). A 50% reduction of the extent of PGE2 and LTB4 production in HIV-infected monocytes was measured at a concentration of 0.9 microM Avarol, a dose which caused an 80% anti-HIV effect in vitro (50% inhibition of virus release from infected cells: 0.3 microM). We conclude that Avarol inhibits the enzymes cyclooxygenase and lipoxygenase and suggest that, in general, inhibitors of these enzymes are promising anti-HIV compounds.

Possible involvement of a lipocortin in the initiation of DNA synthesis by human endothelial cells

This work focused on three themes. First, evidence was obtained for the presence of proteins of 34, 35, 32, and 69 kDa immunologically related to lipocortins I, II, V, and VI, respectively, in human umbilical vein endothelial (HUVE) cells. The 69-kDa protein (p69), but not proteins related to lipocortins I, II, and V, exhibited an increased phosphorylation after exposure of cells to basic fibroblast growth factor (bFGF) and phorbol ester PMA. Second, treatment of HUVE cell particulate fractions with EGTA and hydrophobic affinity chromatography in combination with conventional techniques provided extracts rich in p69 and purified p69. p69 from control cells and extracts from control, bFGF-treated, and PMA-treated cells were found to possess anti-phospholipase A2 (PLA2) activity of lipocortin. In contrast, a striking reverse effect occurred when extracts were obtained from cells exposed to bFGF plus PMA. Third, the combination of bFGF and PMA induced a stimulated PLA2-catalyzed release of arachidonic acid in HUVE cells. This arachidonate production was shown to be involved in the decision of cells to enter into DNA synthesis. Taken together, the present results suggest that phosphorylation of p69 is causally involved in the control of commitment to growth in HUVE cells by acting as a coupling mechanism between surface stimuli and arachidonate pathways.

Isolation and characterization of three inhibitors of thymidine incorporation into bovine fetal liver cells

During the isolation and purification of erythroid cell-stimulating factors from fetal tissues and blood, we found that they were almost invariably contaminated with substances that inhibited thymidine incorporation into erythroid cells of fetal bovine liver. We have isolated and partially sequenced three of these inhibitory factors. The first one was a 46-kDa heparin-binding protein from fetal bovine serum with 80% sequence identity with human apolipoprotein H (apo H). Although human apo H had no inhibitory activity on thymidine incorporation, the bovine apo H-like protein inhibited thymidine incorporation with an ID50 of 36 nM. It probably belongs to a group of heparin-binding apolipoproteins such as apo B and E, which have been reported to inhibit hematopoietic cells. The second inhibitor isolated from fetal bovine serum was clearly cytotoxic at a concentration of 1 nM. This 11-kDa peptide seems to be structurally related to the anaphylatoxins. The third inhibitor was isolated from human fetal intestine. The amino-terminal sequence of this protein was nearly identical to the amino-terminal sequence of human phospholipase A2 isolated from pancreas or lung. Bovine liver erythroid cell membranes are particularly sensitive to phospholipases. Since the synthesis and secretion of phospholipase A2 has been reported to be under the control of interleukin-1 or tumor necrosis factor in different cells, it is possible that this enzyme may be secreted locally and play an important role in tissue remodeling during injury or fetal development.

Immunoregulatory effects of phospholipase A2 (PLA2) on the proliferation of human lymphocytes

Extracellular phospholipase A2 (PLA2) is a proinflammatory enzyme found especially in the inflammatory exudate to modulate blood flow to areas of antigen stimulation. In this study we found that PLA2 exerted a biphasic effect on the proliferation of phytohemagglutinin (PHA)-stimulated human mononuclear cells (PHA MNC). At low concentrations range from 0.001 to 1 U/ml, PLA2 enhanced the proliferation of PHA MNC (maximal increase was 37.0 +/- 5.67%). Conversely, at concentrations over 10 U/ml, PLA2 markedly suppressed the PHA-induced MNC proliferation (maximal decrease was 88.86 +/- 2.89%). PLA2 was non-toxic to lymphocytes after three days culture, unless the concentration was higher than 100 U/ml. The membrane polarization of PHA-stimulated lymphocytes was also increased by PLA2 at a low concentration. In addition, PLA2 displayed a similar effect on the proliferation of streptokinase-streptodornase (SK/SD) or allogeneic cell stimulated lymphocytes. The change of lymphocyte proliferation by PLA2, was parallel to the change of percentage of helper T cells. Furthermore--a CD4-rich population was proved more susceptible to PLA2 effect than a CD8-rich population. Para-bromophenacyl bromide (pBPB), an irreversible inhibitor of PLA2, abrogated the biphasic effect of PLA2 on PHA MNC proliferation. These results suggest that PLA2 plays a regulatory role on immune reactions by modulating the percentage of helper T cells.

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

Aggregation of cells of the marine sponge Geodia cydonium is mediated by an aggregation factor (AF) particle of Mr 1.3 X 10(8). It is now reported that the AF particle is associated with calpactin, which was ascribed a role in the cell-adhesion process. In order to identify the sequence similarity to other members of the lipocortin family, the cDNA of sponge calpactin was cloned and found to display an 80% sequence similarity to vertebrate calpactin II but only a 47% similarity to calpactin I. The calpactin gene, which contains the consensus sequence coding for the amino acids G-T-D-E, was expressed in Escherichia coli and subsequently purified to a 37000-Mr polypeptide. Both the p32 and the p37 are provided with approximately two Ca2+ ions/molecule and the property to bind to phospholipids. The dissociation constant (calpactin-Ca2+) was in the absence of phospholipids in the range 500-700 microM-Ca2+ but in their presence about 20-30 microM-Ca2+. On the basis of (i) inhibition studies with antibodies to calelectrin and (ii) competition experiments with soluble phospholipids (both chemically defined as well as total homologous membrane lipids) we conclude that the AF-associated calpactin and plasma-membrane-bound phospholipid(s) are involved in cell-cell aggregation in sponges.

Regulated expression and phosphorylation of the 23-26-kDa ras protein in the sponge Geodia cydonium

We have cloned, sequenced and examined the sponge Geodia cydonium cDNA encoding a protein homologous to ras proteins. The sponge ras protein has a more conserved N-terminal region and a less conserved C-terminal region, especially in comparison to Dictyostelium discoideum; the similarity to human c-Ha-ras-1 and to Saccharomyces cerevisiae is less pronounced. The sponge ras cDNA comprises five TAG triplets; at the translational level these UAG termination codons are suppressed by a Gln-tRNA. The sponge ras protein was isolated and partially purified (23-26 kDa) and found to undergo phosphorylation at a threonine moiety, when dissociated cells were incubated in the presence of a homologous aggregation factor and insulin. Insulin-mediated phosphorylation of the ras protein resulted in a decrease in its Kd with GTP from 2 microM to 80 nM. The activated ras protein displayed high GTPase activity if the partially purified protein was incubated with homologous lectin and lectin receptor molecules. These results suggest that in the sponge, ras is activated by the insulin/insulin(insulin-like)-receptor system. This transition enables the ras protein to interact with the lectin-receptor/lectin complex, a process which may ultimately lead to an initiation of an intracellular signal-transduction chain.

Inhibition of intrinsic protein tyrosine kinase activity of EGF-receptor kinase complex from human breast cancer cells by the marine sponge metabolite (+)-aeroplysinin-1

1. (+)-Aeroplysinin-1, a naturally occurring tyrosine metabolite from the marine sponge Verongia aerophoba, was found to inhibit the phosphorylation of lipocortin-like proteins by a highly purified preparation of the epidermal growth factor (EGF) receptor-tyrosine protein kinase complex from MCF-7 breast carcinoma cells. 2. (+)-Aeroplysinin-1 blocked the EGF-dependent proliferation of both MCF-7 and ZR-75-1 human breast cancer cells and inhibited the ligand-induced endocytosis of the EGF receptor in vitro. 3. Treatment with aeroplysinin-1 in the concentration range at 0.25-0.5 microM resulted in a time- and dose-dependent total tumor cell death in vitro. 4. At a 10-fold higher concentration the compound did not reveal any cytostatic activity in normal human fibroblasts. 5. From these data we conclude that (+)-aeroplysinin-1 represents a compound which displays a strong anti-tumor effect on EGF-dependent tumor cell lines.

Intracellular signal transduction pathways in sponges

Sponges are the lowest multicellular eukaryotic organisms. Due to the relatively low specialization, and concomitantly the high differentiation and dedifferentiation potency of their cells, the sponge cell system has proven to be a useful model to study the mechanism of cell-cell adhesion on molecular levels. Results of detailed biochemical and cell biological studies with the main cell adhesion molecules, the aggregation factor (AF) and the aggregation receptor, led to the formation of the modulation theory of cell adhesion. The events of cell adhesion are contigent on a multiplicity of precisely coordinated intracellular signal transduction pathways. Using the marine sponge Geodia cydonium we showed that during the initial phase of cell-cell contact the AF causes a rapid stimulation of the phosphatidylinositol pathway, resulting in an activation of protein kinase C and a subsequent phosphorylation of DNA topoisomerase II. As one consequence of these processes, the cells undergo a phase of high DNA synthesis. However, at later stages, the AF loses its mitogenic activity; this function is then taken over by the matrix lectin. During this switch, the lectin receptor associates in the plasma membrane with the ras oncogene product. The description of these processes is subject of this review article.