Galectin 9 is the sugar-regulated urate transporter/channel UAT

UAT, also designated galectin 9, is a multifunctional protein that can function as a urate channel/transporter, a regulator of thymocyte-epithelial cell interactions, a tumor antigen, an eosinophil chemotactic factor, and a mediator of apoptosis. We review the evidence that UAT is a transmembrane protein that transports urate, describe our molecular model for this protein, and discuss the evidence from epitope tag and lipid bilayer studies that support this model of the transporter. The properties of recombinant UAT are compared with those of urate transport into membrane vesicles derived from proximal tubule cells in rat kidney cortex. In addition, we review channel functions predicted by our molecular model that resulted in the novel finding that the urate channel activity is regulated by sugars and adenosine. Finally, the presence and possible functions of at least 4 isoforms of UAT and a closely related gene hUAT2 are discussed. Published in 2004.     

Social Reinforcement Delays in Free-Flying Honey Bees (Apis mellifera L.)

Free-flying honey bees (Apis mellifera L.) reactions were observed when presented with varying schedules of post-reinforcement delays of 0 s, 300 s, or 600 s. We measured inter-visit-interval, response length, inter-response-time, and response rate. Honey bees exposed to these post-reinforcement delay intervals exhibit one of several patterns compared to groups not encountering delays, and had longer inter-visit-intervals. We observed no group differences in inter-response time. Honey bees with higher response rates tended to not finish the experiment. The removal of the delay intervals increased response rates for those subjects that completed the trials.     

The ATP-dependent interaction of eukaryotic initiation factors with mRNA

The interaction of three protein synthesis initiation factors, eukaryotic initiation factor (eIF)-4A, -4B, and -4F, with mRNA has been examined. Three assays specifically designed to evaluate this interaction are RNA-dependent ATP hydrolysis, retention of mRNAs on nitrocellulose filters, and cross-linking to periodate-oxidized mRNAs. The ATPase activity of eIF-4A is only activated by RNA which is lacking in secondary structure, and the minimal size of an oligonucleotide capable of effecting an optimal activation is 12-18 bases. In the presence of ATP, eIF-4A is capable of binding mRNA. Consistent with the ATPase activity, this binding shows a definite preference for single-stranded RNA. In the absence of ATP, eIF-4F is the only factor to bind capped mRNAs, and this binding, unlike that of eIF-4A, is sensitive to m7GDP inhibition. The activities of both eIF-4A and eIF-4F are stimulated by eIF-4B, which seems to have no specific independent activity in our assays. Evidence from the cross-linking studies indicates that in the absence of ATP, only the 24,000-dalton polypeptide of eIF-4F binds to the 5' cap region of the mRNA. From the data presented in conjunction with the current literature, a suggested sequence of factor binding to mRNA is: eIF-4F is the first initiation factor to bind mRNA ind an ATP-independent fashion; eIF-4B then binds to eIF-4F, if in fact it was not already bound prior to mRNA binding; and finally, eIF-4A binds to the eIF-4F X eIF-4B X mRNA complex and functions in an ATP-dependent manner to allow unwinding of the mRNA.     

Dissociation of double-stranded polynucleotide helical structures by eukaryotic initiation factors, as revealed by a novel assay

A new technique has been applied to the study of the RNA secondary structure unwinding activity of the eukaryotic initiation factors (eIFs) 4F, 4A, and 4B. Secondary structures were generated at the 5' ends of reovirus and globin mRNA molecules by hybridization with 32P-labeled cDNA molecules 15 nucleotide residues long. The dissociation of the labeled cDNAs from the mRNAs was assayed by a gel filtration chromatography procedure which separates the free cDNAs from mRNAs and mRNA/cDNA hybrids. When the three factors were tested alone, only eIF-4F stimulated dissociation of hybrids. The combination of eIF-4A plus eIF-4B also exhibited a strong hybrid dissociating activity, which was markedly temperature dependent. Under optimum conditions, up to 90% of the hybrid structures are disrupted in 60 min. These results demonstrate for the first time that stable double-stranded regions can be melted and dissociated by eIFs. They also characterize more precisely the first step in the structure unwinding reaction.     

Dissociation between increased surface expression of gp165/95 and homotypic neutrophil aggregation

Whether homotypic neutrophil aggregation depends on the quantitative increase of gp165/95 molecules (Mac 1, CR3) recruited to the cell surface during activation was studied using mAb of the CD11b group that recognize distinct epitopes encoded by the alpha-subunit of this glycoprotein. After the addition of antibody MN41, neutrophils did not aggregate in response to a chemoattractant, FMLP. Blockade of preexisting surface gp165/95 by mAb MN41, followed by removal of the excess antibody from the mixture, was used to show that the molecules of gp165/95 newly expressed in response to stimulation by a chemoattractant were incapable of effectively mediating the induced cell-cell interactions of aggregation. Flow cytometry studies confirmed that binding of unlabeled antibody MN41 did not block further increases in surface expression of gp165/95 after stimulation with FMLP. These data suggest that molecules of gp165/95 exhibit two functionally distinct forms, one, present on the surface of freshly isolated neutrophils, that becomes competent to mediate the aggregation response upon activation by a stimulus and a second form that can be translocated to the cell surface by the stimulus but is greatly diminished if not lacking in the ability to participate in that aggregation event.     

Induction of eIF-4E phosphorylation by the addition of L-pyrroline-5-carboxylic acid to rabbit reticulocyte lysate

Addition of L-pyrroline-5-carboxylic acid to reticulocyte lysates inhibits protein synthesis and induced phosphoproteins of 25 and 14 kDa. The 25 kDa phosphoprotein had the same Mr and pI as phosphorylated eIF-4E. Incubation of lysates with L-pyrroline-5-carboxylic acid did not alter the crosslinking of eIF-4E to reovirus mRNA caps. These results suggest that modifications of the translational apparatus other than eIF-4E phosphorylation may mediate the inhibitory effect seen with L-pyrroline-5-carboxylic acid and/or that phosphorylation of eIF-4E may effect functions subsequent to its interaction with the mRNA cap such as protein-protein interactions with other cap-specific translation factors.     

Biochemical evidence supporting a mechanism for cap-independent and internal initiation of eukaryotic mRNA

The role of eukaryotic initiation factor (eIF)4B in translation is somewhat uncertain, although it appears to stimulate a variety of activities of eIF-4A and eIF-4F. Using the model RNA-dependent ATP hydrolysis assay, the ability of eIF-4B to stimulate eIF-4A and eIF-4F was investigated. The most dramatic effect of eIF-4B is to increase the affinity of eIF-4A for RNA; no effect is seen on the affinity of eIF-4A for ATP. This is not the case for eIF-4F where stimulation occurs primarily through an increase in Vmax and not a change in the affinity for RNA. The finding that eIF-4A and eIF-4B can bind to an mRNA (lacking in secondary structure), with essentially the same degree of effectiveness and affinity as would occur for natural mRNAs in the presence of eIF-4A, eIF-4B, and eIF-4F, suggests a possible role for eIF-4A and eIF-4B in both cap-independent and internal initiation.     

Effect of temperature on the rate of pupal-adult development of the noctuid moth,Mamestra configurata Wlk.: evidence for differential effects on the initiation of development and subsequent metamorphic development

Summary Moths eclosed earlier from pupae of the bertha armyworm,Mamestra configurata, that were exposed briefly (1 to 5 days) to a warm temperature (15 or 20°C) at the beginning of postdiapause pupal-adult metamorphosis and then incubated at 10 or 12.5°C than from pupae incubated at 10 or 12.5°C throughout metamorphosis. The differences were greater than could be explained by the additional thermal units received at the higher temperature. Analyses of the times of peak concentrations of ecdysteroids (insect growth and development hormones) in metamorphosing pupae and of moth eclosion after exposure to various combinations of temperatures indicated that the warm termperature effect was not on the rate metamorphic development but on an earlier neuroendocrine process concerned with the initiation of development.The magnitude of the difference in eclosion time between pupac receiving a brief warm temperature trigger and the control suggests that the differential effect of temperature on the initiation of development and subsequent metamorphic development is of biological significance and should be considered in the construction of models of insect development under natural conditions.Contirbution No. 1188, Agriculture Canada Research Station, Winnipeg, Manitoba     

Properties of beta-adrenergic receptors of cultured mammalian cells. Interaction of receptors with a guanine nucleotide-binding protein in membranes prepared from L6 myoblasts and from wild-type and cyc- S49 lymphoma cells

The radiolabeled agonist [3H]hydroxybenzylisoproterenol ([3H]HBI) and antagonist [125I]iodopindolol ([125I]IPIN) were used to investigate the properties of beta-adrenergic receptors on membranes prepared from L6 myoblasts and S49 lymphoma cells. The high affinity binding of (-)-[3H]HBI to membranes prepared from L6 myoblasts was stereoselectively inhibited by the active isomers of isoproterenol and propranolol. The density of receptors determined with (-)-[3H]HBI was less than that determined with [125I]IPIN. The binding of (-)-[3H]HBI was inhibited by guanine nucleotides, suggesting an agonist-mediated association of the receptor with a guanine nucleotide-binding protein, presumably the stimulatory guanine nucleotide-binding protein (Ns) of adenylate cyclase. Results obtained in studies with membranes prepared from wild-type S49 lymphoma cells and the adenylate cyclase-deficient variant (cyc-) were similar to those obtained in experiments carried out with membranes prepared from L6 myoblasts. Thus, the high affinity binding of (-)-[3H]HBI to membranes prepared from wild-type and cyc- S49 lymphoma cells was stereoselectively inhibited by the active isomers of isoproterenol and propranolol, and was inhibited by GTP. Moreover, the density of sites determined with (-)-[3H]HBI was less than that determined with [125I]IPIN. These results suggest either that cyc- cells contain a partially functional Ns, or alternatively, that the inhibitory guanine nucleotide-binding protein (Ni) is capable of interacting with beta-adrenergic receptors.     

Cellular requirements for induction of human primary proliferative responses to trinitrophenyl-modified cells

Cellular requirements for induction of primary proliferative responses by human T cells to trinitrophenylated autologous stimulators have been characterized. Substantial proliferative responses were observed with each of the Ia+ stimulator populations tested. Nevertheless, major differences in the hapten specificity of such responses were observed. Thus purified macrophages/monocytes (M phi) when TNP-modified induced responses that were relatively modest in absolute magnitude, but were highly hapten specific. This reflected the very limited capacity of purified M phi to induce proliferation when unmodified, i.e., an autologous mixed leukocyte response (AMLR). In contrast, unmodified M phi-depleted B plus null cells were potent stimulators of AMLR, but hapten modification did not significantly enhance the responses induced by these cells. Moreover, when M phi were added to B plus null cell stimulators AMLR responses were reduced and, with TNP-modified stimulators, hapten-specific responses were restored. The data thus suggest that M phi may have important roles in induction of primary T cell responses to conventional antigens but function largely as regulators rather than stimulators of AMLR. Finally, we have introduced a novel antigen-presenting cell population, the irradiated Ia+ TNP-specific cloned T cell. The possibility that such cells may utilize autostimulatory positive feedback circuits for activation of naive T cells and in interactions between subpopulations of hapten-reactive T cells is discussed.