The high affinity state of inositol 1,4,5-trisphosphate receptor is a functional state

Inositol 1,4,5-trisphosphate (InsP3) is a second messenger responsible for the rapid and discontinuous release of Ca2+ from intracellular stores. In this study, the effects of the sulfhydryl reagent thimerosal were investigated on Ca2+ mobilization and on InsP3 binding. Thimerosal was shown to release Ca2+, in a dose-dependent manner, with an EC50 of 135.8 +/- 5.2 microM, from bovine adrenal cortex microsomes. Thimerosal-induced Ca2+ release was not prevented by heparin (250 micrograms/ml), ruling out a participation of InsP3 receptor in that effect. The slow rate of thimerosal-induced Ca2+ release rather suggested an inhibition of microsomal Ca2+ ATPase. At submaximal concentration, thimerosal (100 microM) was also shown to potentiate the release of Ca2+ induced by InsP3. Dose-response experiments revealed that thimerosal enhanced the apparent affinity of InsP3 by a factor 2.21 +/- 0.28, without modifying the maximal amount of Ca2+ released by InsP3. Thimerosal also enhanced, in a dose-dependent manner, [3H]InsP3 binding to adrenal cortex microsomes (EC50 = 43.3 +/- 7.6 microM). A similar effect was also observed on [3H]InsP3 binding to solubilized receptors, suggesting a direct modification of the receptor protein by thimerosal. The effects of thimerosal on Ca2+ release and [3H]InsP3 binding were abolished in the presence of the reducing agent dithiothreitol (1 mM), suggesting a modification by thimerosal of specific thiol groups on these microsomal proteins. Scatchard analysis revealed that thimerosal (100 microM) increased InsP3 receptor affinity by 1.87 +/- 0.26-fold. Kinetic analysis indicated that this increased affinity was due to an enhancement of InsP3 association rate constant. The concomitant increases of binding affinity and Ca2+ releasing potency suggest that the high affinity state of InsP3 receptor is a functional state.     

Acyclophostin: a ribose-modified analog of adenophostin A with high affinity for inositol 1,4,5-trisphosphate receptors and pH-dependent efficacy

The developing legs of Drosophila are subdivided into proximal and distal domains by the activity of the homeodomain proteins Homothorax (Hth) and Distal-less (Dll). The expression domains of Dll and Hth are initially reciprocal. Wingless and Dpp define both domains by activating Dll and by repressing Hth in the distal region of the disc. Wg and Dpp do not act through Dll to repress Hth. Hth functions to reduce the sensitivity of proximal cells to Wg and Dpp. This serves to limit the effective range of these signals in regulating later-acting genes such as Dac. We present evidence that proximal and distal cells tend to sort-out from one another. Cells forced to express Hth are unable to mix with distal cells. Likewise, cells forced to express Dll are unable to mix with proximal cells. Clones of cells unable to express Dll in the distal region sort-out from the disc. Clones of cells unable to express Hth lose the specialized population of cells at the interface between proximal and distal territories and cause fusion between body wall and leg segments. These observations suggest that sorting-out behavior of Hth- and Dll-expressing cells contributes to subdivision of the leg into proximal and distal domains.     

Blk, a BH3-containing mouse protein that interacts with Bcl-2 and Bcl-xL, is a potent death agonist

We identified and cloned a novel murine member of the pro-apoptotic Bcl-2 family. This protein, designated Blk, is structurally and functionally related to human Bik and localized to the mitochondrial membrane. Blk contains a conserved BH3 domain and can interact with the anti-apoptotic proteins Bcl-2 and Bcl-xL. Ectopic expression of Blk in mammalian cells induces apoptosis, which can be inhibited by mutations in the BH3 domain and by overexpression of Bcl-2 or Bcl-xL but not by CrmA. The apoptotic activity of Blk is also inhibited by a dominant negative caspase-9, suggesting that Blk induces apoptosis through activation of the cytochrome c-Apaf-1-caspase-9 pathway.     

Human anaphylatoxin C4a is a potent agonist of the guinea pig but not the human C3a receptor

A critical element of lutropin bioactivity in vivo is its rapid removal from the blood by a receptor, located in hepatic endothelial cells, that recognizes the terminal sulfated carbohydrate structure SO4-4-GalNAcbeta1,4GlcNAcbeta1,2Manalpha (S4GGnM). We have previously shown that the macrophage mannose (Man)-receptor cDNA directs the synthesis of a protein that binds oligosaccharides with either terminal S4GGnM or terminal Man, at independent sites. We now show that the cysteine-rich (Cys-Rich) domain at the N terminus of the Man/S4GGnM receptor accounts for binding of oligosaccharides with terminal GalNAc-4-SO4, whereas calcium-dependent carbohydrate recognition domains (CRDs) account for binding of ligands containing terminal Man. The Cys-Rich domain is thus a previously unrecognized carbohydrate binding motif. Cys-Rich domains have been described on the three other members of the endocytic C-type lectin family of receptors. The structural relationship of these receptors to the Man/S4GGnM receptor raises the possibility that their Cys-Rich domains also bind carbohydrate moieties and contribute to their function.     

Distribution of Na,K-ATPase is normal in the inner ear of a mouse with a null mutation of the glucocorticoid receptor

This study was performed in order to test the hypothesis that the glucocorticoid hormone stimulates the formation of Na,K-ATPase in the inner ear of the mouse. An immunohistochemical study with respect to the presence and distribution of glucocorticoid receptors (GR) and Na,K-ATPase in the vestibular and cochlear regions of the inner ear was performed on a C57BL mouse with a null mutation of the glucocorticoid receptor (GR mutant mouse). The wild type C57BL mouse and the CBA mouse served as normal controls. As expected, the homozygous GR mutant mouse showed no specific staining for GR in the inner ear. The heterozygous GR mutant mouse showed faint staining of GR in the spiral limbus, the spiral ganglion, the organ of Corti and the utricle. This staining was markedly less than in the wild type C57BL mouse. Antibody labelling of Na,K-ATPase in the inner ear showed no significant difference between the homozygous and the heterozygous GR mutant mouse as compared to the control wild type C57BL mouse or the CBA mouse. Although earlier studies have shown a positive correlation between levels of glucocorticoid hormone in serum and the concentration of Na,K-ATPase in the inner ear, the hypothesis that glucocorticoid hormones alone stimulate the formation of Na,K-ATPase in the inner ear could not be confirmed by this study. Thus other regulating substances must be considered.     

Pharmacologic evidence for involvement of phospholipase C in pemphigus IgG-induced inositol 1,4,5-trisphosphate generation, intracellular calcium increase, and plasminogen activator secretion in DJM-1 cells, a squamous cell carcinoma line

The precise mechanism for acantholysis after pemphigus IgG binds to the cell surface is as yet unknown, although involvement of proteinases such as plasminogen activator (PA) has been suggested. We previously reported that pemphigus IgG, but not normal nor bullous pemphigoid IgGs, caused a transient increase in intracellular calcium ([Ca++]i) and inositol 1,4,5-trisphosphate (IP3) concentration in cultured DJM-1 cells (a squamous cell carcinoma line). To clarify whether phospholipase C is involved in this process after the antibody binds to the cell surface, we examined the effects of a specific phospholipase C inhibitor (U73122) on the pemphigus IgG-induced increase in [Ca++]i, IP3, PA secretion, and cell-cell detachment in DJM-1 cells. [Ca+2]i and IP3 contents were determined with or without 30-min pre-incubation with U73122 or an inactive analogue (U73343) with fura-2 acetoxymethylester and a specific IP3 binding protein, respectively. PA activity in the culture medium was measured after various incubation periods with pemphigus IgG by two-step amidolytic assay. The detachment of cell-cell contacts was examined by detecting the retraction of keratin filament bundle from cell-cell contact points to the perinuclear region by immunofluorescence microscopy using anti-keratin antibody. Pemphigus IgG immediately increased [Ca++]i and IP3 content. PA activity in the culture medium has also been increased at 24 h after pemphigus IgG was added in association with cell-cell detachment. However, pre-incubation with U73122 (1-10 microM), but not with U73343 (10 microM), dramatically reduced the pemphigus IgG-induced increases in [Ca++]i, IP3, and PA activity and inhibited the pemphigus IgG-induced cell-cell detachment. Both U73122 and U73343 caused no effects on cell viability and IgG binding to the cell surface. These results suggest that phospholipase C plays an important role in transmembrane signaling leading to cell-cell detachment exerted by pemphigus IgG binding to the cell surface.     

The Golgi apparatus is an inositol 1,4,5-trisphosphate-sensitive Ca2+ store, with functional properties distinct from those of the endoplasmic reticulum

In the past few years, intracellular organelles, such as the endoplasmic reticulum, the nucleus and the mitochondria, have emerged as key determinants in the generation and transduction of Ca2+ signals of high spatio-temporal complexity. Little is known about the Golgi apparatus, despite the fact that Ca2+ within its lumen controls essential processes, such as protein processing and sorting. We report the direct monitoring of the [Ca2+] in the Golgi lumen ([Ca2+]Golgi) of living HeLa cells, using a specifically targeted Ca2+-sensitive photoprotein. With this probe, we show that, in resting cells, [Ca2+]Golgi is approximately 0.3 mM and that Ca2+ accumulation by the Golgi has properties distinct from those of the endoplasmic reticulum (as inferred by the sensitivity to specific inhibitors). Upon stimulation with histamine, an agonist coupled to the generation of inositol 1,4,5-trisphosphate (IP3), a large, rapid decrease in [Ca2+]Golgi is observed. The Golgi apparatus can thus be regarded as a bona fide IP3-sensitive intracellular Ca2+ store, a notion with major implications for the control of organelle function, as well as for the generation of local cytosolic Ca2+ signals.     

(R,S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors mediate a calcium-dependent inhibition of the metabotropic glutamate receptor-stimulated formation of inositol 1,4,5-trisphosphate

L-glutamate (3-1,000 microM) and (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD; 10-1,000 microM), a selective agonist for the metabotropic glutamate receptor, stimulated the formation of inositol 1,4,5-trisphosphate in a concentration-dependent manner. L-Glutamate was half as efficacious as 1S,3R-ACPD. N-methyl-D-aspartate (NMDA; 1 nM to 1 mM) did not significantly influence the response to a maximally effective concentration of 1S,3R-ACPD (100 microM). On the other hand, coapplication of (R,S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA; 1-300 nM) produced a concentration- and time-dependent inhibition of the 1S,3R-ACPD effect, with a maximal inhibition (97%) at 100 nM. Ten micromolar 6-cyano-7-nitroquinoxaline-2,3-dione, an antagonist of the AMPA receptor, blocked the inhibitory effect of AMPA. Reduced extracellular calcium concentration, as well as 10 microM nimodipine, an L-type calcium channel antagonist, inhibited the AMPA influence on the 1S,3R-ACPD response. W-7, a calcium/calmodulin antagonist, prevented the inhibition by AMPA, whereas H-7, an inhibitor of protein kinase C, had no effect. These data suggest that activation of AMPA receptors has an inhibitory influence on inositol 1,4,5-trisphosphate formation mediated by stimulation of the metabotropic glutamate receptor. The mechanism of action involves calcium influx through L-type type calcium channels and possible activation of calcium/calmodulin-dependent enzymes.     

Differences in partial agonist action at cholecystokinin receptors of mouse and rat are dependent on parameters extrinsic to receptor structure: molecular cloning, expression and functional characterization of the mouse type A cholecystokinin receptor

The mouse cholecystokinin (CCK) receptor is functionally distinct from the extensively studied rat receptor on the basis of differences in binding and biological activity of phenethyl ester analogs of CCK. These are partial agonists at the rat receptor and full agonists at the mouse pancreatic receptor. To explore this, we cloned the cDNA for the mouse type A CCK receptor, established a receptor-bearing Chinese hamster ovary (CHO) cell line and characterized its binding and biological characteristics. Despite 25 differences in amino acid sequence from the rat receptor, including a seven-amino acid insertion in the third intracellular loop, mouse and rat receptors were functionally indistinguishable when expressed in CHO cells. Of note, in the mouse pancreatic cell environment, a stable analog of guanosine triphosphate significantly inhibited binding of CCK-OPE, whereas it had no effect on binding to the same receptor on the CHO-CCKM cell line or to the rat receptor in either environment of the acinar cell. This likely reflects a difference in coupling of the mouse receptor to its G protein in the natural environment of the acinar cell. This may relate to differences extrinsic to the receptor, in the stoichiometry or character of G proteins or in the composition or organization of the lipid environment of the mouse acinar cell membrane. Although this may require complementation of the unique sequence of the mouse receptor, that structure alone is insufficient to explain this phenomenon. Receptor microenvironment makes an important, yet often ignored, contribution to receptor function.     

Ethical problems with the decision of refusal to a request for intra-conjugal in vitro fertilization

What is our knowledge of the couples who suffer refusal of access to IVF when information is available for only 52% of the pregnancies obtained by IVF? With a retrospective study on IVF refusal datas in a centre where they are available, and an investigation by questionnaire in twelve other centers, the authors tried to evaluate the incidence of these refusal. IVF refusal concern 6 to 30% of the couples addressed, varying on a plurifactorial preselection; but a register including refusal is available in only four of the twelve centers. The main reason for refusal is maternal age. Only three of the twelve centers inquired have a real multidisciplinary staff for access decision. Moreover, if the twelve centers knows the future for the obtained pregnancies, it's true sometimes for only seven centers when IVF is unsuccessful, and never for ten centers when refusal of IVF. Assessment of IVF is incomplete, and improvement is needed based on: a better diffusion of the actual knowledge and its applications; a vast application of "ethical committee procedure" when decision for access is taken; and a global approach of IVF, considering refusal as well as success.     

The dominant mutation Glazed is a gain-of-function allele of wingless that, similar to loss of APC, interferes with normal eye development

Dominant mutations have served as invaluable tools for Drosophila geneticists. Here we analyze the dominant eye mutation Glazed (Gla) that was described by T. H. Morgan more than 50 years ago. We show that Gla causes the loss of photoreceptor cells during pupal stages, in a process reminiscent of apoptosis, with a concomitant overproduction of eye pigment. This phenotype is very similar to that caused by the loss of D-APC, a negative regulator of Wingless (Wg) signal transduction. Genetic analyses reveal however that the Gla gain-of-function phenotype can be reverted to wild-type. By generating a P-element-induced revertant of Gla we demonstrate that Gla is allelic to wg. The molecular lesion in Gla indicates that the insertion of a roo retrotransposon leads to ectopic expression of wg during pupal stages. We show that the Gla phenotype is similar to that caused by ectopic expression of Wg driven by the sevenless (sev) enhancer. In both cases Wg exerts its effect, at least in part, by negatively regulating the expression of the Pax2 homolog sparkling (spa). Gla represents not only the first dominant allele of wg, but it may also be the first allele ever described for wg.     

Behavioral reversal of lithium effects by four inositol isomers correlates perfectly with biochemical effects on the PI cycle: depletion by chronic lithium of brain inositol is specific to hypothalamus, and inositol levels may be abnormal in postmortem brain from bipolar patients

The inositol depletion hypothesis of lithium (Li) action has been criticized, because depletion of inositol after chronic Li treatment has not been reproducible, effects of inositol to reverse Li-induced behaviors occurred also with epi-inositol, a unnatural isomer, and because inositol is ubiquitous in brain and hard to relate to the pathogenesis of affective disorder. Therefore, we review our studies showing that lithium depletion of brain inositol occurs chronically in the hypothalamus, a region not previously examined; that behavioral effects of four different inositol isomers including epi-inositol correlate perfectly with their biochemical effects; and that inositol in postmortem human brain is reduced by 25% in frontal cortex of bipolars and suicides as compared with controls. Because inositol in postmortem brain is reduced and not increased in bipolar patients, the relationship between inositol, lithium, and affective disorder is complex.     

Bgp2, a new member of the carcinoembryonic antigen-related gene family, encodes an alternative receptor for mouse hepatitis viruses

Murine coronaviruses such as mouse hepatitis virus (MHV) infect mouse cells via cellular receptors that are isoforms of biliary glycoprotein (Bgp) of the carcinoembryonic antigen gene family (G. S. Dveksler, C. W. Dieffenbach, C. B. Cardellichio, K. McCuaig, M. N. Pensiero, G.-S. Jiang, N. Beauchemin, and K. V. Holmes, J. Virol. 67:1-8, 1993). The Bgp isoforms are generated through alternative splicing of the mouse Bgp1 gene that has two allelic forms called MHVR (or mmCGM1), expressed in MHV-susceptible mouse strains, and mmCGM2, expressed in SJL/J mice, which are resistant to MHV. We here report the cloning and characterization of a new Bgp-related gene designated Bgp2. The Bgp2 cDNA allowed the prediction of a 271-amino-acid glycoprotein with two immunoglobulin domains, a transmembrane, and a putative cytoplasmic tail. There is considerable divergence in the amino acid sequences of the N-terminal domains of the proteins coded by the Bgp1 gene from that of the Bgp2-encoded protein. RNase protection assays and RNA PCR showed that Bgp2 was expressed in BALB/c kidney, colon, and brain tissue, in SJL/J colon and liver tissue, in BALB/c and CD1 spleen tissue, in C3H macrophages, and in mouse rectal carcinoma CMT-93 cells. When Bgp2-transfected hamster cells were challenged with MHV-A59, MHV-JHM, or MHV-3, the Bgp2-encoded protein served as a functional MHV receptor, although with a lower efficiency than that of the MHVR glycoprotein. The Bgp2-mediated virus infection could not be inhibited by monoclonal antibody CC1 that is specific for the N-terminal domain of MHVR. Although CMT-93 cells express both MHVR and Bgp2, infection with the three strains of MHV was blocked by pretreatment with monoclonal antibody CC1, suggesting that MHVR was the only functional receptor in these cells. Thus, a novel murine Bgp gene has been identified that can be coexpressed in inbred mice with the Bgp1 glycoproteins and that can serve as a receptor for MHV strains when expressed in transfected hamster cells.     

Ratio of pulmonary venous to mitral A velocity is a useful marker for predicting mean pulmonary capillary wedge pressure in patients with left ventricular systolic dysfunction

OBJECTIVE: To determine the effect of oral magnesium hydroxide [Mg(OH)2] on iron absorption after simulated iron overdose in human subjects. METHODS: A randomized, controlled crossover study was conducted in healthy adult male human volunteers taking no medications. Subjects received an average of 5.0 mg/kg elemental iron orally followed 1 hour later by either oral administration of 4.5 g of Mg(OH)2 per g ingested elemental iron or no treatment. Serial serum specimens were obtained over the 12 hours following iron ingestion and stored at -60 degrees C until standard serum iron assay was performed. After a 2-week washout period, the subjects were enrolled in the alternative trial arm. Individual baseline diurnal variation in serum iron levels was determined over a 12-hour period on the day prior to each trial. Area under time-concentration curves (AUCs) were calculated, and the AUC due to experimental iron ingestion (deltaAUC) was determined by subtracting the baseline diurnal AUC from the experimental AUC for each subject. RESULTS: Thirteen healthy adult male subjects were enrolled. Mean +/- SEM for deltaAUC due to experimental iron ingestion followed by treatment with Mg(OH)2, 78 +/- 23 micromol(hr)/L, was significantly less than that followed by no treatment, 144 +/- 33 micromol(hr)/L (p = 0.03 by signed rank test). CONCLUSIONS: Magnesium hydroxide, administered 1 hour post-iron ingestion at an oral dose of 4.5 g per g elemental iron ingested, significantly reduced iron absorption during a 12-hour period following simulated mild iron overdose in healthy adult human volunteers.     

The abnormal quinine drinking aversion in the Brattleboro rat with diabetes insipidus is reversed by the vasopressin agonist DDAVP: a possible role for vasopressin in the motivation to drink

The Brattleboro rat with hypothalamic diabetes insipidus (BDI) has an abnormal aversion to drinking quinine-adulterated water compared with normal rats of the parent Long Evans (LE) strain. This BDI animal tolerates marked hypovolemia and decreased body weight in preference to drinking the quinine-adulterated fluid, indicative of a reduced motivation to drink. Acute or chronic treatment of BDI rats with desamino-8D arginine vasopressin (DDAVP) restored to normal their drinking response to quinine solution. Partial restoration of fluid turnover in BDI rats with hydrochlorothiazide, which has an antidiuretic effect in diabetes insipidus (when vasopressin is absent), failed to abolish the abnormal drinking response to quinine-adulterated solution in 8 out of 12 animals. In contrast, induction of diabetes mellitus in LE rats, which resulted in a marked polydipsia and polyuria even though vasopressin was still present, did not impair the drinking response to quinine solutions. These results suggest that the abnormal drinking response to quinine-adulterated fluid in BDI rats is reversed by treatment with the vasopressin V2-receptor agonist DDAVP but is unlikely to be a consequence of the restoration of fluid turnover to normal levels by a renal action. A possible central action involving vasopressin and the motivation to drink is discussed.     

Exon 4, and in particular codon 152 of the LDL receptor gene, is a hot spot for point mutations

Chlorpromazine inhibited the hatching of eggs of the parasitic nematode Haemonchus contortus and the free-living nematode Caenorhabditis elegans. In both species, hatching occurred at a concentration of 100 microg/ml but was almost totally blocked at 400 microg/ml. In the case of C. elegans, the effect was shown to be reversible by removal of chlorpromazine after exposure of the eggs to the drug for 1 hr. Caenorhabditis elegans larvae that hatched in a chlorpromazine concentration of 100 microg/ml were killed, but those that hatched in a concentration of 6.25 microg/ml were not. Taken together with data published by others, these observations indicate that the first-stage larva of C. elegans is less sensitive to chlorpromazine than is the adult worm.     

APLP2, a member of the Alzheimer precursor protein family, is required for correct genomic segregation in dividing mouse cells

The mouse amyloid precursor-like protein 2 (APLP2) belongs to the Alzheimer peptide precursor family. A possible role in pre-implantation development had been suggested previously, and was investigated further by creating a large deletion in the genomic locus. While heterozygous mice developed normally, homozygous embryos were arrested before reaching the blastocyst stage. One-cell embryos which contained protein of maternal origin underwent a limited number of cleavages. The progressive disappearance of the protein at stages 4 and beyond correlated with the appearance of extensive cytopathological effects. Nuclear DNA contents of the arrested embryos departed widely from the normal 2-4C value, thus suggesting a role for the protein in replication and/or segregation of the embryonic genome. Embryonic mortality was not due to the untimely initiation of programmed cell death, and it occurred before the stage at which apoptotic cells normally appear. The same abnormal distribution of DNA contents was seen in primary cultures of Aplp2 +/- embryonic fibroblasts following transfection of an expression vector for Aplp2 antisense RNA with green fluorescent protein (GFP) expressed from a co-transfected construct. Daughter cells derived from a GFP-positive cell showed abnormal DNA contents both >4C and <2C, thus indicating a role for the protein in the mitotic segregation of the genome and establishment of the proper nuclear structure.     

CD4 is a critical component of the receptor for human herpesvirus 7: interference with human immunodeficiency virus

In this study, we demonstrate that the glycoprotein CD4, a member of the immunoglobulin superfamily, is a critical component of the receptor for human herpesvirus 7 (HHV-7), a recently discovered T-lymphotropic human herpesvirus. A selective and progressive downregulation of the surface membrane expression of CD4 was observed in human CD4+ T cells in the course of HHV-7 infection. Various murine monoclonal antibodies to CD4 and the recombinant soluble form of human CD4 caused a dose-dependent inhibition of HHV-7 infection in primary CD4+ T lymphocytes. Moreover, radiolabeled HHV-7 specifically bound to cervical carcinoma cells (HeLa) expressing human CD4. A marked carcinoma cells (HeLa) expressing human CD4. A marked reciprocal interference was observed between HHV-7 and human immunodeficiency virus (HIV), the retrovirus that causes the acquired immunodeficiency syndrome and also uses CD4 as a receptor. Previous exposure of CD4+ T cells to HHV-7 dramatically interfered with infection by both primary and in vitro-passaged HIV-1 isolates. Reciprocally, persistent infection with HIV-1 or treatment with the soluble form of gp120, the CD4-binding envelope glycoprotein of HIV-1, rendered CD4+ T cells resistant to HHV-7 infection. These data indicate that CD4 is critically involved in the receptor mechanism for HHV-7. The antagonistic effect between HHV-7 and HIV could be exploited to devise therapeutic approaches to AIDS.     

Echovirus 1 replication, not only virus binding to its receptor, VLA-2, is required for the induction of cellular immediate-early genes

Induction of immediate-early genes c-jun, junB, and c-fos was demonstrated during echovirus 1 infection in a human osteogenic sarcoma (HOS) cell line. Tenfold induction was seen at 10 h postinfection, corresponding approximately to the end of the first replication cycle of the virus. Echovirus 1 uses VLA-2 integrin as its cellular receptor, and ligand binding by integrin is known to trigger signal transduction pathways ultimately activating immediate-early genes. In the present study, however, VLA-2 binding alone was not sufficient to induce their expression; viral replication was needed. This conclusion was based on the observations that no stimulation of the immediate-early genes occurred in the MG-63 cell line where the virus attached only to VLA-2 but was not able to replicate and that induction of these genes was observed when the HOS cells were infected with echovirus type 7, known to use a different cellular receptor. Induction was not seen in the presence of the antiviral compound WIN 54954, which evidently inhibits the uncoating but not receptor binding of echovirus 1, suggesting that viral replication triggers the activation of the immediate-early genes. The induction of these genes may have a role in viral replication and in the pathogenesis of infection.     

2F1 antigen, the mouse homolog of the rat "mast cell function-associated antigen", is a lectin-like type II transmembrane receptor expressed by natural killer cells

Inhibitory lectin-like receptors expressed on the surface of hematopoietic cells are critically involved in regulation of their effector functions. Here we report that a novel mAb specific for mouse NK cells, 2F1, recognizes the mouse homolog of the mast cell function-associated antigen (MAFA), an inhibitory lectin-like transmembrane receptor expressed on rat mast cells. The 2F1 antigen (2F1-Ag) and rat MAFA are structurally highly conserved and contain a cytoplasmic motif similar to the immunoreceptor tyrosine-based inhibitory motif that is presumably utilized for inhibitory signaling. We also identified a human homolog that is closely related to the rodent MAFA/2F1-Ag proteins. Like rat MAFA, 2F1-Ag is probably encoded by a single gene, which exhibits relatively little polymorphism. Strikingly, while rat MAFA is considered a mast cell antigen, we have been unable to detect cell surface expression of 2F1-Ag by mouse mast cell lines, bone marrow-derived mast cells, or peritoneal mast cells. Furthermore, mouse bone marrow-derived mast cells were devoid of 2F1-Ag mRNA. Instead, we find that approximately 40% of mouse NK cells express 2F1-Ag. Thus, MAFA/2F1-Ag may modulate immunological responses on at least two different cell types bridging the specific and innate immune system.