RanBPM associates with CD39 and modulates ecto-nucleotidase activity

CD39/ecto-NTPDase 1 (nucleoside triphosphate diphosphohydrolase 1) is an ecto-nucleotidase that influences P2 receptor activation to regulate vascular and immune cell adhesion and signalling events pivotal in inflammation. Whether CD39 interacts with other membrane or cytoplasmic proteins has not been established to date. Using the yeast two-hybrid system, we note that the N-terminus of CD39 binds to RanBPM (Ran binding protein M; also known as RanBP9), a multi-adaptor scaffolding membrane protein originally characterized as a binding protein for the small GTPase Ran. We confirm formation of complexes between CD39 and RanBPM in transfected mammalian cells by co-immunoprecipitation studies. Endogenous CD39 and RanBPM are also found to be co-expressed and abundant in cell membranes of B-lymphocytes. NTPDase activity of recombinant CD39, but not of N-terminus-deleted-CD39 mutant, is substantially diminished by RanBPM co-expression in COS-7 cells. The conserved SPRY [repeats in splA and RyR (ryanodine receptor)] moiety of RanBPM is insufficient alone for complete physical and functional interactions with CD39. We conclude that CD39 associations with RanBPM have the potential to regulate NTPDase catalytic activity. This intermolecular interaction may have important implications for the regulation of extracellular nucleotide-mediated signalling.     

A novel p53-inducible apoptogenic gene,PRG3, encodes a homologue of the apoptosis-inducing factor (AIF)

The p53 tumor suppressor protein induces cell cycle arrest or apoptosis in response to cellular stresses. We have identified PRG3 (p53-responsive gene 3), which is induced specifically under p53-dependent apoptotic conditions in human colon cancer cells, and encodes a novel polypeptide of 373 amino acids with a predicted molecular mass of 40.5 kDa. PRG3 has significant homology to bacterial oxidoreductases and the apoptosis-inducing factor, AIF, and the gene was assigned to chromosome 10q21.3-q22.1. Expression of PRG3 was induced by the activation of endogenous p53 and it contains a p53-responsive element. Unlike AIF, PRG3 localizes in the cytoplasm and its ectopic expression induces apoptosis. An amino-terminal deletion mutant of PRG3 that lacks a putative oxidoreductase activity retains its apoptotic activity, suggesting that the oxidoreductase activity is dispensable for the apoptotic function of PRG3. The PRG3 gene is thus a novel p53 target gene in a p53-dependent apoptosis pathway.     

Sources of Vibrio mimicus Contamination of Turtle Eggs

Vibrio mimicus contamination of sand increased significantly during the arrival of the olive ridley sea turtles (Lepidochelys olivacea) at Ostional anidation beach, Costa Rica. Statistical analysis supports that eggs are contaminated with V. mimicus by contact with the sand nest. V. mimicus was isolated from eggs of all nests tested, and ctxA⁺ strains were found in 31% of the nests, all of which were near the estuary.     

Apolipoprotein M expression increases the size of nascent pre�� HDL formed by ATP binding cassette transporter A1

Apolipoprotein M (apoM) is a novel apolipoprotein that is reportedly necessary for preβ HDL formation; however, its detailed function remains unknown. We investigated the biogenesis and properties of apoM and its effects on the initial steps of nascent preβ HDL assembly by ABCA1 in HEK293 cells. Transiently transfected apoM was localized primarily in the endomembrane compartment. Pulse-chase analyses demonstrated that apoM is inefficiently secreted, relative to human serum albumin, and that ∼50% remains membrane-associated after extraction with sodium carbonate, pH 11.5. To investigate the role of apoM in nascent preβ HDL formation, ABCA1-expressing or control cells, transfected with empty vector, apoM, or C-terminal epitope-tagged apoM (apoM-C-FLAG), were incubated with ¹²⁵I-apoA-I for 24 h. Conditioned media were harvested and fractionated by fast-protein liquid chromatography (FPLC) to monitor HDL particle size. Preβ HDL particles were formed effectively in the absence of apoM expression; however, increased apoM expression stimulated the formation of larger-sized nascent preβ HDLs. Immunoprecipitation with anti-apoA-I antibody followed by apoM Western blot analysis revealed that little secreted apoM was physically associated with preβ HDL. Our results suggest that apoM is an atypical secretory protein that is not necessary for ABCA1-dependent preβ HDL formation but does stimulate the formation of larger-sized preβ HDL. We propose that apoM may function catalytically at an intracellular site to transfer lipid onto preβ HDL during or after their formation by ABCA1.     

Flexibility in Red Sea Tridacna maxima‐Symbiodiniaceae associations supports environmental niche adaptation

Giant clams (Tridacninae) are important members of Indo‐Pacific coral reefs and among the few bivalve groups that live in symbiosis with unicellular algae (Symbiodiniaceae). Despite the importance of these endosymbiotic dinoflagellates for clam ecology, the diversity and specificity of these associations remain relatively poorly studied, especially in the Red Sea. Here, we used the internal transcribed spacer 2 (ITS2) rDNA gene region to investigate Symbiodiniaceae communities associated with Red Sea Tridacna maxima clams. We sampled five sites spanning 1,300 km (10° of latitude, from the Gulf of Aqaba, 29°N, to the Farasan Banks, 18°N) along the Red Sea''s North‐South environmental gradient. We detected a diverse and structured assembly of host‐associated algae with communities demonstrating region and site‐specificity. Specimens from the Gulf of Aqaba harbored three genera of Symbiodiniaceae, Cladocopium, Durusdinium, and Symbiodinium, while at all other sites clams associated exclusively with algae from the Symbiodinium genus. Of these exclusively Symbiodinium‐associating sites, the more northern (27° and 22°) and more southern sites (20° and 18°) formed two separate groupings despite site‐specific algal genotypes being resolved at each site. These groupings were congruent with the genetic break seen across multiple marine taxa in the Red Sea at approximately 19°, and along with our documented site‐specificity of algal communities, contrasted the panmictic distribution of the T. maxima host. As such, our findings indicate flexibility in T. maxima‐Symbiodiniaceae associations that may explain its relatively high environmental plasticity and offers a mechanism for environmental niche adaptation.