Cloning of a cDNA for a T cell produced molecule with a putative immune regulatory role

The N termini of a-subunit isoforms are involved in signaling between vacuolar H+-ATPase (V-ATPase) and cytohesin-2

Previously, we reported an acidification-dependent interaction of the endosomal vacuolar H(+)-ATPase (V-ATPase) with cytohesin-2, a GDP/GTP exchange factor (GEF), suggesting that it functions as a pH-sensing receptor. Here, we have studied the molecular mechanism of signaling between the V-ATPase, cytohesin-2, and Arf GTP-binding proteins. We found that part of the N-terminal cytosolic tail of the V-ATPase a2-subunit (a2N), corresponding to its first 17 amino acids (a2N(1-17)), potently modulates the enzymatic GDP/GTP exchange activity of cytohesin-2. Moreover, this peptide strongly inhibits GEF activity via direct interaction with the Sec7 domain of cytohesin-2. The structure of a2N(1-17) and its amino acids Phe(5), Met(10), and Gln(14) involved in interaction with Sec7 domain were determined by NMR spectroscopy analysis. In silico docking experiments revealed that part of the V-ATPase formed by its a2N(1-17) epitope competes with the switch 2 region of Arf1 and Arf6 for binding to the Sec7 domain of cytohesin-2. The amino acid sequence alignment and GEF activity studies also uncovered the conserved character of signaling between all four (a1-a4) a-subunit isoforms of mammalian V-ATPase and cytohesin-2. Moreover, the conserved character of this phenomenon was also confirmed in experiments showing binding of mammalian cytohesin-2 to the intact yeast V-ATPase holo-complex. Thus, here we have uncovered an evolutionarily conserved function of the V-ATPase as a novel cytohesin-signaling receptor.

Abortion-prone mating influences alteration of systemic a2 vacuolar ATPase expression in spleen and blood immune cells

PROBLEM

a2 isoform of vacuolar ATPase (Atp6v0a2) is important for maintaining the delicate immunological balance required for successful pregnancy. The objective of this investigation is to study the dynamic changes in spleen and blood that appear during spontaneous abortion in mice.

METHOD OF STUDY

Atp6v0a2 was measured in multiple immune cell populations from spleen and blood recovered from non-abortion-prone and abortion-prone mating combinations.

RESULTS

Atp6v0a2 expression was significantly lower (P ≤ 0.01) in the spleen recovered from abortion-prone ♀CBA × ♂DBA mating on days 12 and 16 of pregnancy when compared to non-abortion-prone ♀BALB/c × ♂BALB/c and ♀CBA × ♂BALB/c matings. Flow cytometric studies showed that significantly decreased expression of Atp6v0a2 in splenic CD4(+), CD8(+), CD19(+), and CD14(+) cells directly correlated with the high percentages of fetal resorption observed in abortion-prone mating on days 12 and 16 of pregnancy. In blood, CD4(+), CD8(+), and CD19(+) cells had a significantly reduced expression of Atp6v0a2 in abortion-prone mating compared to the non-abortion-prone mating combinations only on day 12.

CONCLUSION

This deceased expression of Atp6v0a2 in the various immune cell populations of the spleen and blood suggests that the maternal environment is not supportive to fetus and leads to poor pregnancy outcome in the abortion-prone mating model.

A vacuolar-type proton (H+) translocating ATPase alpha subunit encoded by the Hc-vha-6 gene of Haemonchus contortus

In the present study, a full-length cDNA (designated Hc-vha-6) inferred to encode an alpha subunit of a vacuolar-type proton translocating adenosine triphosphatase (V-ATPase) was isolated from the parasitic nematode Haemonchus contortus, and characterized. The transcript for Hc-vha-6 was detected in all developmental stages and both sexes of H. contortus. Elements, including two TATA box (TATAA), two inverted CAAT box (ATTGG), five E box (CANNTG) and six GATA as well as five inverse GATA (TTATC) transcription factor motifs, were identified in the non-coding region upstream of Hc-vha-6. The open reading frame (ORF) of 2601 nucleotides encoded a protein (Hc-VHA-6) of 866 amino acids and a molecular weight of approximately 98.7 kDa. Comparison with a published protein sequence for a homologue (VPH1P) from yeast showed that Hc-VHA-6 had nine transmembrane domains and the 14 essential amino acid residues associated with enzyme activity, assembly, intracellular and/or membrane targeting. Phylogenetic analyses of selected amino acid sequence data revealed Hc-VHA-6 to be most closely related to VHA-6 of Caenorhabditis elegans. A predictive network analysis inferred that vha-6 interacts with at least seven other genes encoding V-ATPase subunits and a small Rab GTPase. This study provides the first insight into a V-ATPase of parasitic nematodes and a sound basis for future functional genomic work.

The a2 isoform of vacuolar ATPase is a modulator of implantation and feto-maternal immune tolerance in early pregnancy

In mammalian reproduction, two immunologically disparate entities, the mother and her fetus, co-exist in close proximity and mutually tolerate each other. The maternal immune system plays a major contributing role in the reproductive outcome. A coordinated set of immunological events takes place between the maternal and fetal cells to ensure fetal survival. Among these, cytokines secreted by proximal maternal immune cells as well as fetal trophoblast cells play a major role in feto-maternal tolerance. In this review, we describe the role of the vacuolar ATPase (and more specifically the a2 isoform, a2V-ATPase) in controlling the expression of these vital cytokines. a2V-ATPase is a key enzyme that controls the acidification of intracellular vesicles and the extracellular environment, processes that play a major role in cellular function. The localization of a2V-ATPase in tissues and immune cells of the reproductive tract which are essential for pregnancy will be described. Information will be provided on the role of a2V-ATPase on aspects of cell development in pregnancy, from fertilization to implantation and fetal growth. Particular emphasis will be placed on the role of a2V-ATPase in (a) regulating parts of the cytokine network at the implantation site and (b) attenuating the potentially harmful maternal immune response against trophoblast cells.

Novel role for the N-terminus domain of the a2 isoform of vacuolar ATPase in interleukin-1beta production

Interleukin-1beta (IL-1beta) is a mediator cytokine that is released by macrophages and epithelial cells in pregnancy and tumorigenesis before antigen recognition. a2V-ATPase is a protein expressed during pregnancy and tumorigenesis and has a novel role in immune regulation. It is expressed as a 70 kDa molecule in intracellular vesicles. Upon cell stimulation it migrates to the surface followed by the cleavage of a 20 kDa portion (a2 N-terminus domain, a2NTD). This study aimed to determine whether a2NTD could induce IL-1beta production in immune cells. Peripheral blood mononuclear cells (PMBC) were stimulated with a2NTD and analyzed for cytokine gene expression by gene arrays. Supernatants were analyzed for IL-1beta by enzyme-linked immunosorbent assay, and cells were analyzed for intracellular expression of IL-1alpha, IL-1beta, and TNF-alpha by flow cytometry. When PBMC were cultured with a2NTD, there was a 2.5-fold increase in IL1A and IL1B gene expression and no induction of TNF gene expression. There was a 72-fold increase in IL-1beta in supernatants of PBMC cultured with a2NTD. Finally, there was a 204-fold increase in intracellular expression of IL-1beta in monocytes incubated with a2NTD. These results indicate a regulatory role for a2NTD in IL-1 cytokine production and suggest a unique role for this molecule in inflammation.

Immune suppressor factor confers stromal cell line with enhanced supporting activity for hematopoietic stem cells

Immune suppressor factor (ISF) is a subunit of the vacuolar ATPase proton pump. We earlier identified a short form of ISF (ShIF) as a stroma-derived factor that supports cytokine-independent growth of mutant Ba/F3 cells. Here, we report that ISF/ShIF supports self-renewal and expansion of primary hematopoietic stem cells (HSCs). Co-culture of murine bone marrow cells with a stromal cell line overexpressing ISF or ShIF (MS10/ISF or MS10/ShIF) not only enhanced their colony-forming activity and the numbers of long-term culture initiating cells, but also maintained the competitive repopulating activity of HSC. This stem cell supporting activity depended on the proton-transfer function of ISF/ShIF. Gene expression analysis of ISF/ShIF-transfected cell lines revealed down-regulation of secreted frizzled-related protein-1 and tissue inhibitor of metalloproteinase-3, and the restoration of their expressions in MS10/ISF cells partially reversed its enhanced LTC-IC supporting activity to a normal level. These results suggest that ISF/ShIF confers stromal cells with enhanced supporting activities for HSCs by modulating Wnt-activity and the extracellular matrix.

Cloning, expression and functional characterization of the putative regeneration and tolerance factor (RTF/TJ6) as a functional vacuolar ATPase proton pump regulatory subunit with a conserved sequence of immunoreceptor tyrosine-based activation motif

In an attempt to identify new immunoreceptor tyrosine-based activation motif (ITAM)-containing human molecules that may regulate hitherto unknown immune cell functions, we BLAST searched the National Center for Biotechnology Information database for ITAM-containing sequences. A human expressed sequence tag showing partial homology to the murine TJ6 (mTJ6) gene and encoding a putative ITAM sequence has been identified and used to clone the human TJ6 (hTJ6) gene from an HL-60-derived cDNA library. hTJ6 was found to encode a protein of 856 residues with a calculated mass of 98 155 Da. Immunolocalization and sequence analysis revealed that hTJ6 is a membrane protein with predicted six transmembrane-spanning regions, typical of ion channels, and a single putative ITAM (residues 452-466) in a juxtamembrane or hydrophobic intramembrane region. hTJ6 is highly homologous to Bos taurus 116-kDa subunit of the vacuolar proton-translocating ATPase. Over-expression of hTJ6 in HEK 293 cells increased H+ uptake into intracellular organelles, an effect that was sensitive to inhibition by bafilomycin, a selective inhibitor of vacuolar H+ pump. Northern blot analysis demonstrated three different hybridizing mRNA transcripts corresponding to 3.2, 5.0 and 7.3 kb, indicating the presence of several splice variants. Significant differences in hTJ6 mRNA levels in human tissues of different origins point to possible tissue-specific function. Although hTJ6 was found to be a poor substrate for tyrosine-phosphorylating enzymes, suggesting that its ITAM sequence is non-functional in protein tyrosine kinase-mediated signaling pathways, its role in organellar H+ pumping suggests that hTJ6 function may participate in protein trafficking/processing.

The Placental Immunomodulatory Cytokine Regeneration and Tolerance Factor is also Expressed by Both Human Cycling and Early Pregnant Endometrium

PROBLEM

Regeneration and tolerance factor (RTF) has been recently suggested to contribute to the control of fetal-ablating immunity at the maternal-fetal interface through the induction of T helper 2 (Th2)-dominated response. The protein consists of a membrane-associated domain and an extracellular portion which is proteolitically cleaved to yield a soluble peptide. In humans, it has been shown to be expressed by invading cytotrophoblasts and decidual lymphoid cells, to be increased on peripheral blood B lymphocytes during a normal gestation and on circulating natural killer cells during unsuccessful pregnancies. However, the expression of RTF in other cell types and, specifically, in non-hematopoietic maternal cells of the human uterus has not been characterized in detail. Thus, we have specifically studied the expression and modulation of the cytokine in human endometrium obtained in different phases of the cycle and in early pregnancy.

METHODS

The 20 kDa extracellular domain of RTF has been localized by immunohistochemical method and Western blot analysis. Levels of RTF messenger RNA (mRNA) in basal and stimulated conditions have been evaluated by semiquantitative reverse transcription-polymerase chain reaction.

RESULTS

The extracellular domain of RTF could be detected in both the glandular epithelium and stroma with diffuse distribution in both cycling endometrium and first trimester decidua. Both cycling and pregnant endometrium expressed the gene for RTF but mRNA levels resulted significantly increased in secretory phase-endometrial stromal cells when compared to proliferative phase samples. Inflammatory cytokines, interleukin-1beta and tumour necrosis factor alpha were able to directly increase endometrial RTF mRNA expression.

CONCLUSION

These results indicate that RTF is constitutively expressed at endometrial and decidual level and its up-regulation during the secretory phase of the cycle may be relevant in mediating some immune-related aspects of uterine physiology.

Vacuolar H+ pumping ATPases in luminal acidic organelles and extracellular compartments: common rotational mechanism and diverse physiological roles

Cytoplasmic organelles with an acidic luminal pH include vacuoles, coated vesicles, lysosomes, the Golgi apparatus, and synaptic vesicles. Acidic compartments are also known outside specialized cells such as osteoclasts. The unique acidic pH is formed by V-ATPase (Vacuolar type ATPase), other ion transporters, and the buffering action of proteins inside the organelles. V-ATPase hydrolyzes ATP and transports protons inside an organelle or extracellular compartment. We have summarized recent progress on mouse V-ATPases and their varying localizations together with their mechanism emphasizing similarities with F-type ATPases.

PLIF induces IL-10 production in monocytes: a calmodulin-p38 mitogen-activated protein kinase-dependent pathway

Recently, we reported the cloning and preliminary characterization of a novel human immunomodulator named PLIF (placenta immunomodulatory ferritin). PLIF has a unique molecular structure, which is composed of a ferritin heavy chain-like domain and a novel cytokine-like domain called C48. Both intact molecule and C48 inhibit T cell proliferation following allogeneic or anti-CD3 stimuli. PLIF is localized at the fetal-maternal interface of human placenta and might play a role in down-modulating the maternal immune reaction toward the embryo. The inhibitory effect of PLIF on T cell activation can be direct, indirect through cytokine mediators, or both. In the present study we investigated the possible indirect effects of PLIF by using its bioactive domain C48. Measurement of various cytokines revealed that C48, predominantly, induce pronounced and rapid IL-10 production in monocytes, which is immune activation-independent. Further, we discovered that C48-induced IL-10 production is mediated through a calcium/calmodulin-p38 mitogen-activated protein (MAP) kinase signaling pathway. However, extracellular signal-related kinases1,2 (ERK1,2), also activated by C48 stimulation, exhibited a limiting effect on IL-10 production.

Inherited disorders of the H+-ATPase

PURPOSE OF REVIEW

The alpha-intercalated cell in the distal nephron shares a number of molecular features with the osteoclast, including site-limited proton pumps that are present at high density. These are multisubunit H -ATPases, which are essential for acid-base homeostasis and for the maintenance of normal bone turnover. In recent years it has become evident that some rare inherited human disorders are due to pump dysfunction in kidney or in bone; these are reviewed here.

RECENT FINDINGS

The present review provides an overview of acid secretion in both kidney and bone, and describes the recently identified diseases that are associated with mutations in tissue-specific subunits of these pumps.

SUMMARY

Elucidation of the molecular bases of a number of inherited renal acidopathies and bone disorders raises the possibility that additional tissue-specific subunits of these important pumps will be identified, gives hope for a better understanding of normal function at the molecular level, and may have implications for future therapeutic development.

Inhibition of human endothelial cell proliferation by ShIF, a vacuolar H(+)-ATPase-like protein

ShIF is a bone marrow stroma cell-derived factor originally identified to support proliferation of bone marrow cells in vitro. This protein shares high sequence homology to the yeast vacuolar H(+)-ATPase subunit, Vph1p, and the 116 kDa proton pump of the rat and bovine synaptic vesicle, Vpp1. We examined the function of ShIF in the proliferation of human umbilical vein endothelial cells (HUVEC). ShIF inhibited HUVEC proliferation in a dose-dependent manner. Recombinant ShIF added at 10 and 20 ng/ml inhibited HUVEC proliferation by 21.6 and 44.3%, respectively and increasing the concentration of ShIF to 100 ng/ml inhibited proliferation by as much as 55.5%. When HUVEC cells were cultured at various concentrations of ShIF in the presence of anti-ShIF antibody, the inhibitory effects of ShIF to HUVEC proliferation were abrogated by 89-91% indicating that the activity of ShIF to HUVEC was specific. HUVEC cultured in the presence of ShIF and bafilomycin, a specific inhibitor of ATPase, resulted to a 90% growth inhibition. Thus, ShIF may act as an antagonist to the ATPase complex by disrupting the production of cellular ATP thereby decreasing the ability of HUVEC to proliferate.

Molecular cloning and characterization of Atp6n1b: a novel fourth murine vacuolar H+-ATPase a-subunit gene

The 116-kDa a-subunit of the vacuolar proton pump (H(+)-ATPase) exists as several isoforms encoded by different genes and with different patterns of tissue expression. Its function within the multisubunit pump complex has yet to be elucidated. To date, three isoforms have been identified in mouse (designated a1-a3). We now report the cloning and characterization of Atp6n1b, encoding a novel fourth murine isoform (a4). Murine a4 has 833 residues and shows 85% amino acid identity to the human kidney-specific ATP6N1B protein in which loss-of-function alterations cause autosomal recessive distal renal tubular acidosis. The human and murine genes have similar genomic organization; furthermore, Atp6n1b maps to a region of mouse chromosome 6 that is syntenic with the segment of human 7q33-34 containing ATP6N1B. Together these findings establish the two genes as orthologs. The mouse a4 protein is 61, 52, and 47% identical to a1, a2, and a3, respectively. Phylogenetic analysis confirms that among vertebrates there are four a-subunit families, with a4 most resembling a1. Northern blot analysis of Atp6n1b reveals a 3.7-kilobase a4 transcript in kidney but not other major organs, and a reverse transcription polymerase chain reaction in 12 mouse tissues detects expression in kidney alone. Immunofluorescence studies in murine kidney demonstrate high intensity a4 staining at the surface of intercalated cells, with additional expression in the proximal tubule (not previously reported in human kidney). Similar apical a4 immunostaining is also present in male genital tissue. Identification of this novel murine kidney-enriched 116-kDa a-subunit provides a molecular tool for investigation of the currently unknown role of this protein, which is essential for proper function of the apical renal vacuolar H(+)-ATPase in man.

Expression of a novel protein by regenerating hepatocytes and peripheral blood lymphocytes

Regeneration and tolerance factor (RTF) is a protein with immunosuppressive activity and is normally present in the thymus and placenta. RTF was measured in the livers of patients with regenerating nodules due to alcoholic cirrhosis and hepatitis C. RTF was expressed in the regenerating nodules of 26 patients with alcoholic cirrhosis. All patients with chronic hepatitis C without cirrhosis failed to express RTF. Flow cytometry revealed upregulation of RTF on the lymphocytes from alcoholic cirrhosis and downregulation in hepatitis C disease.

a4, a unique kidney-specific isoform of mouse vacuolar H+-ATPase subunit a

The vacuolar-type H+ -ATPase (V-ATPase) translocates protons across membranes. Here, we have identified a mouse cDNA coding for a fourth isoform (a4) of the membrane sector subunit a of V-ATPase. This isoform was specifically expressed in kidney, but not in the heart, brain, spleen, lung, liver, muscle, or testis. Immunoprecipitation experiments, together with sequence similarities for other isoforms (a1, a2, and a3), indicate that the a4 isoform is a component of V-ATPase. Moreover, histochemical studies show that a4 is localized in the apical and basolateral plasma membranes of cortical alpha- and beta-intercalated cells, respectively. These results suggest that the V-ATPase, with the a4 isoform, is important for renal acid/base homeostasis.

Four subunit a isoforms of Caenorhabditis elegans vacuolar H+-ATPase. Cell-specific expression during development

We have identified four genes (vha-5, vha-6, vha-7, and unc-32) coding for vacuolar-type proton-translocating ATPase (V-ATPase) subunit a in Caenorhabditis elegans, the first example of four distinct isoforms in eukaryotes. Their products had nine putative transmembrane regions, exhibited 43-60% identity and 62-84% similarity with the bovine subunit a1 isoform, and retained 11 amino acid residues essential for yeast V-ATPase activity (Leng, X. H., Manolson, M. F., and Forgac, M. (1998) J. Biol. Chem. 273, 6717-6723). The similarities, together with the results of immunoprecipitation, suggest that these isoforms are components of V-ATPase. Transgenic and immunofluorescence analyses revealed that these genes were strongly expressed in distinct cells; vha-5 was strongly expressed in an H-shaped excretory cell, vha-6 was strongly expressed in intestine, vha-7 was strongly expressed in hypodermis, and unc-32 was strongly expressed in nerve cells. Furthermore, the vha-7 and unc-32 genes were also expressed in the uteri of hermaphrodites. RNA interference analysis showed that the double-stranded RNA for unc-32 caused embryonic lethality similar to that seen with other subunit genes (vha-1, vha-4, and vha-11) (Oka, T., and Futai, M. (2000) J. Biol. Chem. 275, 29556-29561). The progenies of worms injected with the vha-5 or vha-6 double-stranded RNA became died at a specific larval stage, whereas the vha-7 double-stranded RNA showed no effect on development. These results suggest that V-ATPases with these isoforms generate acidic compartments essential for worm development in a cell-specific manner.

A novel secreted form of immune suppressor factor with high homology to vacuolar ATPases identified by a forward genetic approach of functional screening based on cell proliferation

In the search for stromal-derived growth factors, we have identified a novel secreted short form of immune suppressor factor (ISF) using a combination of a genetic approach and retrovirus-mediated functional screening. This protein, which we termed ShIF, was isolated based on its ability to support proliferation of a mutant clone S21, which was established from Ba/F3 cells that are usually interleukin-3-dependent but became dependent on a stroma cell line ST2 after chemical mutagenesis. ISF, a membrane protein harboring six transmembrane domains, was reported to have immunosuppressive functions. The coding region of ShIF started from the third transmembrane domain of ISF. Biochemical analysis demonstrated that ShIF was expressed in both the secreted and membrane-bound forms of 27-kDa protein, which was supposed to have an internal ATG present in the third transmembrane domain of ISF as a start codon. In addition to the full-length form of ISF, a major protein with a molecular size of 27 kDa was also expressed through the proteolytic process of ISF. ShIF resembles this naturally occurring short form of ISF (sISF). Deletion analysis of the major domains of ISF cDNA revealed that ShIF is an active functional domain of ISF with a capability to support proliferation of S21 cells. Enforced expression of ShIF in MS10 cells, bone marrow stroma cells that do not express endogenous ShIF or ISF, conferred on the cells an ability to support the growth of S21 cells as well as bone marrow cells. Interestingly, ShIF shows a high sequence homology to the C-terminal part of a 95-kDa yeast vacuolar H (+)-ATPase subunit, Vph1p (39%), and a 116-kDa proton pump (VPP1) (54%) of the rat and bovine synaptic vesicle. Therefore, it is possible that ShIF also acts as a proton pump and somehow prevents the cells from undergoing apoptosis.

Regeneration and tolerance factor's potential role in T-cell activation and apoptosis

Regeneration and tolerance factor (RTF) is a novel membrane protein that has a diverse expression pattern and immunoregulatory properties. RTF is expressed in vivo on the surface of individuals with B cell chronic lymphocytic leukemia and on activated T lymphocytes of HIV infected individuals as determined by their coexpression with CD38 and HLA-DR. The unique expression patterns of this protein in vivo lead us to investigate its expression in vitro. The activation of human PBMCs through the TCR, using anti-CD3 antibody and PMA, upregulated cell surface expression of RTF from 2. 3% to 91.2% (mean channel fluorescence [MCF] increased threefold). The activation of Jurkat T cells through the TCR upregulated surface expression of RTF from 8.3% (MCF-1.3) to 58.7% (MCF-13.1). The Jurkat T-cell line was used as a model system to explore RTF's role in cellular activation. Using the Jurkat T-cell model, we found anti-RTF antibody induces apoptosis. The addition of anti-RTF antibody increased annexin V binding by threefold compared with the IgG1 kappa isotype control antibody (p < 0.00002) and activated caspase 3. These data indicate that RTF is expressed during T-cell activation and may be associated with apoptosis.

Properties of three isoforms of the 116-kDa subunit of vacuolar H+-ATPase from a single vertebrate species. Cloning, gene expression and protein characterization of functionally distinct isoforms in Gallus gallus

Vacuolar H+-ATPases (V-ATPases) are involved in a wide variety of essential cellular processes. An unresolved question is how the cell regulates the activity of these proton pumps and their targeting to distinct cellular compartments. There is growing evidence for the presence of subunit diversity amongst V-pumps, particularly regarding the 116-kDa subunit (called the a subunit). We have cloned and characterized three isoforms (a1, a2 and a3) of this subunit from chicken. The amino-acid sequences of these homologues are approximately 50% similar and their nucleotide differences indicate that they are products of distinct genes. The levels of mRNA expression of these isoforms was quantified by ribonuclease protection analysis. The a1 and a2 isoforms have a similar tissue distribution, with the highest level of mRNA expression in brain, an intermediate level in kidney and relatively low levels in liver and bone. In contrast, the highest level of expression of the a3 isoform is in bone and liver, with a moderate level in kidney, and the lowest level in brain. An antibody against the a1 isoform reacted with a 116 kDa protein in a brain V-ATPase preparation that was not detected in bone or liver V-ATPase preparations, whereas an antibody against the a3 isoform reacted with a 116-kDa peptide in bone and liver, but not brain V-ATPases preparations. The bone and brain V-ATPases showed differential sensitivity to the inhibitors bafilomycin and (2Z,4E)-5-(5,6-dichloro-2-indolyl)-2-methoxy-N-[4-(2, 2,6,6-tetramethyl)piperidinyl]-2,4-pentadienamide. Thus, this work demonstrates the presence of structurally and functionally distinct V-ATPases in a single vertebrate species.

Three subunit a isoforms of mouse vacuolar H(+)-ATPase. Preferential expression of the a3 isoform during osteoclast differentiation

Vacuolar H(+)-ATPase (V-ATPase) is a multi-subunit enzyme with a membrane peripheral catalytic (V(1)) and an intrinsic (V(o)) sector. We have identified three cDNA clones coding for isoforms of mouse V(o) subunit a (a1, a2, and a3). They exhibit 48-52% identity with each other and high similarity to subunit a of other species. The a1 isoform was mainly expressed in brain and liver. The a2 isoform was observed in heart and kidney in addition to brain and liver. Transcripts for the a3 isoform were strongly expressed in heart and liver. The a3 isoform was induced during osteoclast differentiation, and localized in the plasma membrane and cytoplasmic filamentous structures. In contrast to a3, the a1 isoform was constitutively expressed and localized in the cytoplasmic endomembrane compartments of the same cells. These findings suggest that the a3 isoform is a component of the plasma membrane V-ATPase essential for bone resorption.

Molecular cloning and expression of three isoforms of the 100-kDa a subunit of the mouse vacuolar proton-translocating ATPase

We have identified cDNAs encoding three isoforms (a1, a2, and a3) of the 100-kDa a subunit of the mouse vacuolar proton-translocating ATPase (V-ATPase). The predicted protein sequences of the three isoforms are 838, 856, and 834 amino acids, respectively, and they display approximately 50% identity between isoforms. Northern blot analysis demonstrated that all three isoforms are expressed in most tissues examined. However, the a1 isoform is expressed most heavily in brain and heart, a2 in liver and kidney, and a3 in liver, lung, heart, brain, spleen, and kidney. We also identified multiple alternatively spliced variants for each isoform. Reverse transcriptase-mediated polymerase chain reaction revealed that one splicing variant of the a1 isoform (a1-I) was expressed only in brain, whereas two other variants (a1-II and a1-III) were expressed in tissues other than brain. These alternatively spliced forms differ in the presence or absence of 6-7 amino acid residues near the amino and carboxyl termini of the proteins encoded. The a3 isoform is also encoded by three alternatively spliced variants, two of which are predicted to encode a protein that is truncated near the border of the amino- and carboxyl-terminal domains of the a subunit and therefore lacks the integral transmembrane-spanning helices thought to participate in proton translocation. Expression of each isoform (with the exception of a1-I) was detectable at all developmental stages investigated, with a1-I absent only in day 7 embryos. The results obtained suggest that isoforms of the 100-kDa a subunit may contribute to tissue-specific functions of the V-ATPase.

Genomic organization of the gene coding for TIRC7, a novel membrane protein essential for T cell activation

A novel human membrane protein, TIRC7, was recently identified and demonstrated to be essential in T cell activation. Here we report on the genomic organization of the TIRC7 gene, which is composed of 15 exons and spans 7.9 kb. The seven predicted transmembrane-spanning domains of the TIRC7 protein coincide well with exon-intron boundaries. TIRC7 and OC116, a recently described putative subunit of the vacuolar proton pump that was demonstrated to be expressed in an osteoclastoma tumor as well as in a human pancreatic adenocarcinoma cell line, are demonstrated to be alternative transcripts of the same gene. OC116 consists of 20 exons with the last 14 introns and exons being identical with those of TIRC7. The chromosomal locus for both transcripts was identified on chromosome 11q13.4-q13.5. In human alloactivated T lymphocytes, mRNA expression of TIRC7, but not OC116, is demonstrated, indicating that OC116 is not involved in regular T cell proliferation.

Expression of regeneration and tolerance factor on B cell chronic lymphocytic leukemias: a possible mechanism for escaping immune surveillance

Regeneration and tolerance factor (RTF) is a protein expressed on developing tissue such as the thymus and the placenta. RTF has been reported to down-regulate cell-mediated immune responses. To examine the potential role of tumor-derived RTF to suppressing antitumor responses, we analyzed a panel of seven B cell tumor lines for the membrane RTF using a fluorescein isothiocyanate (FITC) conjugated monoclonal antibody, which reacts with membrane RTF. All the B cell tumor lines we examined express RTF on the cell surface. We also tested conditioned media from these B cell lines for their ability to suppress IL-2R expression on activated cells. Conditioned media from each B cell line suppressed IL-2R expression on activated Jurkat T cells and activated peripheral blood mononuclear cells. A monoclonal antibody to the biologically active portion of RTF reversed this suppressive activity. Finally, the tumor cell population from patients with chronic lymphocytic leukemia was found to express cell surface RTF. Thus, RTF expression could be a new mechanism used by tumor cells to escape immune surveillance.

Increased expression of regeneration and tolerance factor in individuals with human immunodeficiency virus infection

Regeneration and tolerance factor (RTF) plays a pivotal role in successful pregnancy outcome and has potent immunomodulating properties. During pregnancy, it is abundantly expressed in the placenta and on peripheral B lymphocytes. Several lines of evidence suggest that both successful pregnancy outcome and progression from human immunodeficiency virus (HIV) infection to AIDS are associated with a Th2-type response. As a result, we hypothesized that the cellular expression of RTF may also be increased during infection with HIV. Using flow cytometric analysis, we showed a significantly (P < 0.01) increased expression of RTF on CD3(+) cells obtained from individuals with HIV over that for individuals without HIV. On average, 32.1% of the CD3(+) cells from individuals with HIV expressed high levels of RTF. In contrast, an average of only 6.7% of the CD3(+) cells from individuals without HIV expressed high levels of RTF. Similar results were obtained when CD19(+) cells from individuals with (mean, 44.1%) and without (mean, 25.8%) HIV were evaluated. Linear regression analysis suggested that high levels of RTF expression by CD3(+) cells correlated better with viral load (r value, 0.46) than with absolute CD4 count (r value, 0.09). While additional experiments are necessary to delineate the precise immunologic role of RTF, our current data suggest that RTF expression during HIV infection may be a useful marker of immune activation.

Identification and reconstitution of an isoform of the 116-kDa subunit of the vacuolar proton translocating ATPase

We have identified a cDNA encoding an isoform of the 116-kDa subunit of the bovine vacuolar proton translocating ATPase. The predicted protein sequence of the new isoform, designated a2, consists of 854 amino acids with a calculated molecular mass of 98,010 Da; it has approximately 50% identity to the original isoform (a1) we described (Peng, S.-B., Crider, B. P., Xie, X.-S., and Stone, D.K. (1994) J. Biol. Chem. 269, 17262-17266). Sequence comparison indicates that the a2 isoform is the bovine homologue of a 116-kDa polypeptide identified in mouse as an immune regulatory factor (Lee, C.-K., Ghoshal, K., and Beaman, K.D. (1990) Mol. Immunol. 27, 1137-1144). The bovine a1 and a2 isoforms share strikingly similar structures with hydrophilic amino-terminal halves that are composed of more than 30% charged residues and hydrophobic carboxyl-terminal halves that contain 6-8 transmembrane regions. Northern blot analysis demonstrates that isoform a2 is highly expressed in lung, kidney, and spleen. To determine the possible role of the a2 isoform in vacuolar proton pump function, we purified from bovine lung a vacuolar pump proton channel (VO) containing isoform a2. This VO conducts bafilomycin-sensitive proton flow after reconstitution and acid activation, and supports proton pumping activity after assembly with the catalytic sector (V1) of vacuolar-type proton translocating ATPase (V-ATPase) and sub-58-kDa doublet, a 50-57-kDa polypeptide heterodimer required for V-ATPase function. These data indicate that the a2 isoform of the 116-kDa polypeptide functions as part of the proton channel of V-ATPases.

Early pregnancy factor: an extracellular chaperonin 10 homologue

Early pregnancy factor (EPF) has been identified as a homologue of chaperonin 10 (cpn10) with immunosuppressive and growth factor properties. As a homologue of cpn10, it belongs to the heat shock family of proteins (hsp) but, unlike other members of this family, EPF is detected extracellularly. Early pregnancy factor was first discovered in pregnancy serum by the rosette inhibition test, and the novelty of its discovery was that its presence could diagnose pregnancy within 6-24 h of a fertile mating. As well as being a monitor of the presence of a viable embryo, it is necessary for embryonic survival. In this capacity it acts as both an immunosuppressant and growth factor. Early pregnancy factor is also a product of proliferating primary and neoplastic cells and functions as an autocrine growth factor both in vivo and in vitro. It has a modifying effect on the outcome of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. Early pregnancy factor is considered to be one of the major factors involved in the modification of multiple sclerosis observed during pregnancy.

Prevention of acute allograft rejection by antibody targeting of TIRC7, a novel T cell membrane protein

A novel 75 kDa membrane protein, TIRC7, is described that exhibits a central role in T cell activation in vitro and in vivo. Modulation of TIRC7-mediated signals with specific anti-TIRC7 antibodies in vitro efficiently prevents human T cell proliferation and IL-2 secretion. Moreover, anti-TIRC7 antibodies specifically inhibit type 1 subset specific IFN-gamma expression but spare the type 2 cytokine IL-4. Diminished proliferation but not IFN-gamma secretion is reversible by exogenous rIL-2. An anti-TIRC7 antibody that cross-reacts with the 75 kDa rat homolog exhibits inhibition of rat alloimmune response in vitro and significantly prolongs kidney allograft survival in vivo. Targeting of TIRC7 may provide a novel therapeutic approach for modulation of the immune response.

Expression of TJ6 during pregnancy

PROBLEM

TJ6 will be one of the molecules involved in fetal-specific immune suppression during pregnancy. In the mouse and human decidua, the regulation of uterine natural killer (uNK) cells is important during pregnancy.

METHOD OF STUDY

To further understand the possible functions of TJ6 during pregnancy, syngeneic, allogeneic, and mutant mice were examined for TJ6 expression.

RESULTS

Immunoblotting showed that TJ6 protein was expressed on most of the placenta-associated mononuclear cells, and the size was 70-72 kDa at all stages of pregnancy. The expression of TJ6 mRNA was studied by a ribonuclease protection assay in syngeneic and allogeneic matings, and in immune-deficient mice of genotypes scid/scid and scid/scid.bg/bg.

CONCLUSIONS

Genetic disparity, lack of T and B lymphocytes, and loss of NK lytic function had no significant effect on the expression of TJ6 mRNA.

Immunoactive products of placenta. VI. Induction of transient murine T cell anergy by a low-molecular-weight compound obtained from supernatants of human placental cultures

A low-molecular-weight material present in human placental supernatant (lymphocyte proliferation inhibiting factor, LPIF, or filtrate) can induce tolerance/hyporesponsiveness in vivo. We already knew from previous experiments that this material acted only on preactivated or malignant T cells, and even the malignant cells could be rescued from its action if cells were washed quickly after contact. To understand the mechanisms of its action, we have set up systems of specific stimulation. The material inhibits anti-Vbeta-specific stimulation. In a mixed lymphocyte reaction if responder cell populations from a first MLR performed in the presence of LPIF are harvested, extensively washed to discard suppressor molecules, and restimulated by related or third-party lymphocytes in an H2-incompatible combination, the response to a third-party stimulator (a primary one) is unaffected by prior exposure to the material, which nevertheless renders the population unresponsive to restimulation by the original MHC-stimulating haplotype. Cells triggered by anti-Vbeta6 antibodies in the presence of LPIF are unable to undergo restimulation by the very same anti-Vbeta6 MoAb, while they conserve their capacity to proliferate in a primary fashion in response to the unrelated anti-Vbeta8 MoAb. When analyzed by FACS using anti-Vbeta FITC-conjugated MoAbs, cells that are unresponsive or blocked in their proliferation by the action of the filtrate after anti-Vbeta stimulation are still live and unexpectedly transiently hyperexpress the TcR. These findings confirm the requirement for T cell stimulation for suppression to be enacted and demonstrate that such is exerted by anergy rather than by clonal deletion, at least in vitro.

Site-directed mutagenesis of the 100-kDa subunit (Vph1p) of the yeast vacuolar (H+)-ATPase

Vacuolar (H+)-ATPases (V-ATPases) are multisubunit complexes responsible for acidification of intracellular compartments in eukaryotic cells. V-ATPases possess a subunit of approximate molecular mass 100 kDa of unknown function that is composed of an amino-terminal hydrophilic domain and a carboxyl-terminal hydrophobic domain. To test whether the 100-kDa subunit plays a role in proton transport, site-directed mutagenesis of the VPH1 gene, which is one of two genes that encodes this subunit in yeast, has been carried out in a strain lacking both endogenous genes. Ten charged and twelve polar residues located in the seven putative transmembrane helices in the COOH-terminal domain of the molecule were individually changed, and the effects on proton transport, ATPase activity, and assembly of the yeast V-ATPase were measured. Two mutations (R735L and Q634L) in transmembrane helix 6 and at the border of transmembrane helix 5, respectively, showed greatly reduced levels of the 100-kDa subunit in the vacuolar membrane, suggesting that these mutations affected stability of the 100-kDa subunit. Two mutations, D425N and K538A, in transmembrane helix 1 and at the border of transmembrane helix 3, respectively, showed reduced assembly of the V-ATPase, with the D425N mutation also reducing the activity of V-ATPase complexes that did assemble. Two mutations, H743A and K593A, in transmembrane helix 6 and at the border of transmembrane helix 4, respectively, have significantly greater effects on activity than on assembly, with proton transport and ATPase activity inhibited 40-60%. One mutation, E789Q, in transmembrane helix 7, virtually completely abolished proton transport and ATPase activity while having no effect on assembly. These results suggest that the 100-kDa subunit may be required for activity as well as assembly of the V-ATPase complex and that several charged residues in the last four putative transmembrane helices of this subunit may play a role in proton transport.

TJ6: the pregnancy-associated cytokine

These studies have demonstrated that TJ6m protein can be measured in women prior to a spontaneous abortion based on expression of TJ6 on CD56-positive NK cells. This suggested to us a possible regulator function for TJ6 during pregnancy. We have shown that in T cells only crosslinking of the T-cell receptor can upregulate TJ6 expression and the other activators, such as mitogens, do not. A clear discrepancy in the pattern of expression of TJ6 on CD56 and CD19-positive cells was noted between successful and unsuccessful pregnancies. A successful pregnancy is denoted by TJ6 expression on B cells, whereas in a potential spontaneous abortion there is TJ6 expression on both NK and B cells.

Transforming growth factor-beta 2-related-decidual suppressor factor is not related to TJ6 protein

Transforming growth factor (TGF)-beta 2-related-decidual suppressor factor (DSF) and TJ6 protein are both immunosuppressive molecules present in murine and human pregnancy. Treatment of mice with either anti-TJ6 or anti-TGF-beta 2 neutralizing antibodies results in increased fetal loss. Western blots of supernatants from pregnant mouse decidua probed with anti-TJ6 (soluble form) showed a doublet at a similar molecular size as when the blot was probed with anti-TGF-beta 2 antibody. The problem is to determine whether TJ6 and DSF are the same protein. In order to determine if TJ6 and DSF are the same or different proteins, we used affinity column purified TGF-beta 2-DSF and stained Western blots with anti-TJ6. The TGF-beta 2-monoclonal antibody affinity column-purified DSF that stained with anti TGF-beta 2 was not reactive with anti-TJ6 antibody. TJ6 has only a 30% gene sequence homology and a 13% amino acid homology to TGF-beta 2. TJ6 and TGF-beta 2-related DSF appear to be different immunosuppressive proteins in decidua.

Expression of membrane form of the pregnancy associated protein TJ6 on decidual lymphocytes in the first trimester of pregnancy

TJ6, a newly described protein produced locally in the uterine decidua during pregnancy, may be involved in maintaining a unique immunological environment at the maternal-fetal interface. The aim of this study was to determine whether TJ6 is expressed as membrane form on decidual lymphocytes (DL), to define the phenotypes of TJ6m (membrane form TJ6) expressing cells and to analyze the fluorescence intensity of TJ6m expression. Peripheral blood lymphocytes (PBL) and DL were obtained from first trimester pregnancies undergoing elective termination and immunophenotyped for TJ6m and other cell surface antigens (CD3, CD8, CD19, CD56, CD16) by flow cytometry. This is the first study showing that TJ6 molecules are present on decidual lymphocytes in human pregnancy. TJ6m expression on PBL was not different from that of DL. However, a significantly higher percentage of double positive (TJ6m+CD3+, TJ6m+,CD8+,TJ6m+CD19+) cells were found in PBL when compared to DL. The average fluorescence intensity (AFI) for the TJ6m marker among cells with CD8+, CD19+ and CD56+ double positive was significantly higher in DL as compared with those of PBL. The AFI for granularity of double positive DL was significantly higher than observed in PBL.

Reciprocal alteration in circulating TJ6+ CD19+ and TJ6+ CD56+ leukocytes in early pregnancy predicts success or miscarriage

PROBLEM

TJ6 is a cytokine whose membrane form is regularly expressed on the B lymphocytes of women during pregnancy. In a previous study we have shown that pregnancies that end in a spontaneous abortion are characterized by an increase in natural killer (NK) cells and that NK cells in these pregnancies also expressed TJ6, whereas NK cells from pregnancies that terminate normally neither increase in number nor do they express significant amounts of the cytokine.

METHODS

To evaluate the ability of TJ6 to predict pregnancy outcome, 61 blood samples from pregnant women were studied. Blood samples were drawn between 5 and 12 weeks of gestation and analyzed for lymphocyte expression of TJ6 using Cytoron Absolute flow cytometry and two-color fluorescence. The percentage of CD19+ (B) cells and CD56+ (NK) cells that expressed TJ6 was calculated, and this percentage was correlated with subsequent pregnancy outcome classified as successful (viable birth) or unsuccessful (abortion, stillbirth). TJ6 CD19 and TJ6 CD56 was determined in 32 blood samples from women with successful pregnancy outcomes and 29 samples from women with unsuccessful pregnancy outcome.

RESULTS

The mean TJ6 CD19 expression for successful pregnancies was 10.6% and for unsuccessful pregnancies was 5.1% (P < 0.03). The mean TJ6 CD56+ percentage of circulating cells that express TJ6 expression for successful pregnancies was 3.3% and for unsuccessful pregnancies was 10.4% (P = 0.02). All unsuccessful pregnancies had less than 90% of circulating CD19 cells express TJ6 and/or greater than 50% of circulating CD56 cells express TJ6. Use of the expression of TJ6 on CD19 and CD56 cells during the first trimester predicts viable pregnancy with a sensitivity of 100%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 100%.

CONCLUSIONS

The work now being reported validates the hypothesis that expression of TJ6 on NK cells obtained from pregnant women predicts the outcome of pregnancy. In addition we show that this prognosticator can be reliably demonstrated early in the first trimester.

Purification and characterization of a pregnancy-associated protein: TJ6s

PROBLEM

Characterization of the soluble form of a novel protein, TJ6 (TJ6s) with immune suppressive activity from murine fetoplacental units.

METHOD

Preferential ammonium sulfate precipitation, gel filtration and ion-exchange chromatography were employed to purify the protein TJ6s from murine fetoplacental units using an anti-peptide antibody as a detection tool. Biological activity of the purified protein was studied in lymphocyte proliferation assays.

RESULTS

Purified TJ6s has a M(r) of approximately 18 kDa as evidenced by SDS-PAGE in both reducing and non reducing conditions. It exerted a strong anti-proliferative activity in both anti-CD3 and Con A proliferation lymphocyte proliferation assays but not in a PHA assay, suggesting that the anti-proliferative effects on T cells are exerted only on cells specifically activated directly through T cell receptor complex.

CONCLUSION

The results indicate that TJ6s is a novel anti-proliferative protein that has many of the characteristics that are considered necessary for survival of the fetal allograft.

The lack of direct effects of a monoclonal antibody against murine T-cell suppressor factor on murine embryo development in vitro

In previous studies, we reported that the injection of monoclonal antibody 14-30, specific for a T-cell suppressor factor (TSF), into mice during early stages of pregnancy could decrease the percentage of females that maintained pregnancy. In addition, further work has demonstrated the presence of an immunoreactive protein in fetal and maternal tissues with physiochemical properties similar to TSF. However, one alternate explanation for the antipregnancy effects of the injections of monoclonal antibody, not related to a specific role for TSF in early pregnancy, is the possibility of direct effects upon the embryo or embryonic antigens that prevent continued embryonic development. In the present studies, early preimplantation embryos were incubated with the monoclonal antibody 14-30 specific for TSF and the subsequent development of the embryos examined. The results of these studies demonstrate that monoclonal antibody, which has been shown to bind T-cell suppressor factor and has antipregnancy effects when injected in vivo, does not interfere with development of preimplantation or implantation stage mouse embryos in vitro.