Diversity of cellular receptors and functions for the lysophospholipid growth factors lysophosphatidic acid and sphingosine 1-phosphate

The lysophospholipid (LPL) mediators lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) are generated by enzymatic cleavage of stores of glycerophospholipids and sphingomyelin, respectively, in membranes of stimulated cells. LPLs are albumin bound, distributed widely in mammalian tissues, and increased in concentration by physiological activation of platelets and some other cells, tissue injury, inflammation, and neoplasia. The principal effects of LPA and S1P are growth related, including induction of cellular proliferation, alterations in differentiation and survival, and suppression of apoptosis. LPA and S1P also evoke cellular effector functions, which are dependent on cytoskeletal responses such as contraction, secretion, adhesion, and chemotaxis. The extracellular mediator activities of LPLs are transduced by subfamilies of G-protein-coupled receptors (GPCRs), of which the most completely characterized are those encoded by the endothelial differentiation genes (edgs). One homology cluster composed of Edg-1, -3, and -5 recognizes and responds to S1P, and the other cluster of Edg-2 and -4 is dedicated to LPA. Edg proteins are developmentally regulated and differ in tissue distribution, but couple similarly to multiple types of G-proteins to signal through ras and mitogen-activated protein kinase, rho, phospholipase C, and several protein tyrosine kinases. Numerous interactions between glycerophospholipids and sphingolipids are observed in their biosynthetic and signaling pathways. Many of the cellular effects of LPA and S1P are attributable to modifications in the content and/or activity of a major functional protein. Examples are increases in nuclear levels of transcription factors that regulate the serum response element, suppression of death caspase activities in apoptosis, and elevation of membrane content of heparin binding-epidermal growth factor-like growth factor, which serves as an autocrine and juxtacrine stimulus of proliferation. These ubiquitous LPL mediators of cellular growth, differentiation, and activities thus act directly through complex subfamilies of GPCRs and by regulating expression of biologically critical proteins.

Recombinant human G protein-coupled lysophosphatidic acid receptors mediate intracellular calcium mobilization

Mobilization of intracellular Ca2+ is a critical cellular response to lysophosphatidic acid (LPA) in many cell types. Recent identification of endothelial differentiation gene (Edg) 2 and Edg4 as subtypes of G protein-coupled receptors for LPA allowed examination of the Ca2+ mobilization mediated specifically by each subtype. To reduce endogenous background levels while enhancing recombinant receptor-specific signals, the aequorin luminescence method was used to quantify cytoplasmic Ca2+ levels. In TAg-Jurkat T cells transiently co-transfected with apoaequorin and human Edg2 or Edg4 cDNA, LPA dose-dependently increased light emission triggered by increased Ca2+ bound to aequorin. N-Palmitoyl-L-serine-phosphoric acid and N-palmitoyl-L-tyrosine-phosphoric acid, which had been previously shown to be antagonists for Xenopus laevis LPA receptors, did not antagonize the Ca2+-mobilizing effects of Edg2 and Edg4. Surprisingly, they acted as agonists or partial agonists for Edg2 and Edg4. The Ca2+ mobilization by Edg2 and Edg4 was further characterized in stable transfectants of rat HTC4 hepatoma cells. By using the fura-2 fluorescence method, a difference in the kinetics of Ca2+ flux with Edg2 and Edg4 was observed. With Edg2, but not Edg4, the initial increase in the Ca2+ concentration was followed by a sustained influx of extracellular Ca2+. The coincident production of inositol phosphates and the inhibition of Ca2+ mobilization by the phospholipase C inhibitor U73122 strongly suggested that Edg2 and Edg4 mobilize Ca2+ through inositol trisphosphate generated by phospholipase C activation. Pertussis toxin almost completely blocked LPA-induced Ca2+ mobilization by Edg2 but only partially blocked that by Edg4, which suggests that Edg2 transduces Ca2+ mobilization largely through pertussis toxin-sensitive Gi proteins, whereas Edg4 requires both Gi and Gq.

EP4/EP2 receptor-specific prostaglandin E2 regulation of interleukin-6 generation by human HSB.2 early T cells

Human leukemic early T cells of the HSB.2 line coexpress the EP2, EP3 and EP4 subtypes of prostaglandin E2 (PGE2) receptors (Rs). EP3 Rs have previously been demonstrated to transduce PGE2 stimulation of secretion of matrix metalloproteinase (MMP)-9 by HSB.2 T cells through Ca++-dependent enhancement of MMP-9 mRNA transcription. We now show that PGE2 and the EP4/EP2/EP3 R-selective agonist misoprostol, but not the EP3 R-directed agonists sulprostone and M&B28767, induced increases in HSB.2 T cell interleukin-6 (IL-6) mRNA and secretion. Pharmacological agents that increase intracellular concentration of cyclic AMP ([cAMP]i) mimicked and synergistically enhanced induction of IL-6 secretion by PGE2, whereas inhibitors of protein kinase A (PKA) but not protein kinase C suppressed PGE2-evoked increases in IL-6 secretion, suggesting that cAMP and PKA are the intracellular messengers of the PGE2 effect. Exposure of HSB.2 T cells to the mitogenic lectin concanavalin A (Con A) increased basal IL-6 secretion, without a change in IL-6 mRNA level. Con A-stimulated HSB.2 T cells responded to PGE2 with greater increases in IL-6 mRNA and secretion of IL-6. Con A also down-regulated mRNA encoding both EP3 Rs and EP2 Rs, and concurrently up-regulated mRNA encoding EP4 Rs of HSB.2 T cells. Therefore, EP4 and EP2 Rs mediate PGE2-induced increases in IL-6 secretion by HSB.2 T cells through a transcriptional and cAMP dependent-mechanism. The increased ratio of EP4 Rs/EP3 Rs may contribute to Con A enhancement of PGE2-elicited increases in IL-6 secretion by HSB.2 T cells.

Selectivity of effects of vasoactive intestinal peptide on macrophages and lymphocytes in compartmental immune responses

The major immunoregulatory effects of vasoactive intestinal peptide (VIP) are mediated by structurally distinct type I (VIPR1) and II (VIPR2) G protein-associated receptors on many different types of immune cells. VIP is released in functionally relevant concentrations during many immunologic and inflammatory responses. Mast cells (VIPR1), macrophages (VIPR1 and VIPR2), B cells, and T cells (VIPR1, VIPR2, or VIPR1 and VIPR2) recognize and respond to VIP in patterns that are controlled by the relative levels of expression of VIPR1 and VIPR2. VIPR2 transduces human T-cell chemotaxis, expression of matrix metalloproteinases (MMPs) 2 and 9 and consequently basement membrane and connective tissue transmigration, while signaling suppression of proliferation and cytokine production. In contrast, VIPR1 fails to transduce T-cell chemotaxis but mediates suppression of chemotaxis and MMP expression elicited by some cytokines and chemokines. The relative representation of each type of VIPR, which is presumed to be under cytokine control, thus may determine T-cell responses to VIP and other immune mediators in tissue compartments innervated by VIPergic nerves.

Characterization of a novel subtype of human G protein-coupled receptor for lysophosphatidic acid

The recent identification of the Vzg-1/Edg2 protein as a functional G protein-coupled receptor for lysophosphatidic acid (LPA) has allowed a sequence-based search for new genes that may encode novel subtypes of LPA receptors. A human cDNA encoding a G protein-coupled receptor, designated Edg4, was identified by searching the GenBankTM for homologs of the human Edg2 LPA receptor. The Edg4 protein is 46% identical and 72% similar in amino acid sequence to human Edg2. When overexpressed in Jurkat T cells, the Edg4 protein mediated LPA-induced activation of a serum response element reporter gene with LPA concentration dependence (EC50 of 10 nM) and specificity. This LPA-induced reporter gene activation could be partially inhibited by pretreatment with pertussis toxin or C3 exoenzyme, suggesting requirements for both a Gi protein and Rho GTPase. Overexpression of Edg4 in Jurkat cells also led to increases in specific binding sites for [3H]LPA. Northern blots revealed that two edg4 mRNA transcripts of 1.8 and 8 kilobases are distributed very differently from edg2 mRNAs in adult human tissues and several cancer cell lines. The existence and distinctive tissue expression of structurally different subtypes of LPA receptors may provide one basis for tissue-specific functions and permit independent regulation of each subtype of LPA receptor.

Vasoactive intestinal peptide enhancement of antigen-induced differentiation of a cultured line of mouse thymocytes

The prominence of vasoactive intestinal peptide (VIP) in rodent thymic neurons suggested that this potent mediator of T cell functions may alter developmental responses of thymocytes to T cell receptor (TCR) -dependent stimulation. CD4+8+ DPK cells derived from a thymic lymphoma of a TCR transgenic mouse respond to pigeon cytochrome C (PCC) antigen in association with distinct I-E MHC II haplotypes on antigen-presenting cells (APCs) by differentiating into CD4+8- T cells. The specific recognition of VIP by two types of homologous G-protein-coupled receptors (VIPR1 and VIPR2) on DPK cells was attributable predominantly to VIPR1 before and to VIPR2 after exposure to APCs and PCC, as assessed by quantification of the respective mRNAs. PCC-evoked differentiation of DPK cells was enhanced significantly by 1 to 100 nM VIP after 3 to 4 days. The effects of VIP analogs with VIPR type selectivity implied that VIP enhancement of differentiation of DPK cells was mediated principally by VIPR2. Differential reduction in the expression of each type of VIPR by transfection of DPK cells with plasmids encoding the respective antisense mRNAs confirmed the central role of VIPR2 in VIP-enhanced conversion to CD4+8- T cells. The suppression of DPK cell differentiation by inhibitors of adenylyl cyclase and protein kinase A suggested a transductional role for VIP-elicited increases in [cAMP]i. That the changes in frequency of CD4+8+ and CD4+8- DPK cells reflected principally differentiation was supported by the lack of consistent differences between the two subsets in the effects of VIP and VIPR2 agonist on cell number, viability, apoptosis, and proliferation. VIP may be one endogenous mediator that explains the unique thymic microenvironment for topographically specific development of T cells.

Identification of cDNAs encoding two G protein-coupled receptors for lysosphingolipids

The structural similarity of lysosphingolipids to lysophosphatidic acid (LPA) prompted a sequence-based search for lysosphingolipid receptors using cDNA sequence of the Edg2 human LPA receptor. Two closely related G protein-coupled receptors, rat H218 and human Edg3, are highly similar to Edg2. When overexpressed in Jurkat cells, H218 and Edg3 activated serum response element-driven transcriptional reporter gene in response to sphingosine 1-phosphate (S1P), dihydro-S1P and sphingosylphosphorylcholine, but not to LPA. H218 and Edg3 expressed in Xenopus oocytes conferred responsiveness to S1P and dihydro-S1P in agonist-triggered 45Ca2+ efflux. Therefore, H218 and Edg3 are functional receptors for S1P and perhaps other closely related lysosphingolipids.

Novel cyclic peptide agonist of high potency and selectivity for the type II vasoactive intestinal peptide receptor

Ro 25-1392 [Ac-Glu8,OCH3-Tyr10,Lys12,Nle17,Ala19,A sp25,Leu26,-Lys27,28-vasoactive intestinal peptide(cyclo 21-25)] is a cyclic peptide analog of vasoactive intestinal peptide (VIP) that potently exerts cellular effects typical of VIP. The selectivity of Ro 25-1392 for type I (VIPR1) and type II (VIPR2) VIP receptors was investigated first in competitive binding studies using Chinese hamster ovary cell transfectants stably expressing recombinant human VIPR1 and VIPR2. Nonradioactive Ro 25-1392 was as potent a competitive inhibitor as VIP for the binding of 125I-VIP to VIPR2 transfectants (Ki = 9.6 +/- 1.0 and 16 +/- 1.7 nM, respectively; mean +/- S.E.M., n = 4). In contrast, Ro 25-1392 had a very low affinity for VIPR1, compared with VIP, and attained a maximum of only 40% mean inhibition of binding of 125I-VIP at 1 microM. The affinity of VIP (Ki = 3.4 +/- 1.5 nM, mean +/- S.E.M., n = 4) for binding to VIPR1 was 1000-fold greater than that of Ro 25-1392. Ro 25-1392 evoked concurrent and concentration-dependent increases in intracellular levels of calcium and cyclic AMP (EC50 = 3.0 +/- 0.4 nM, mean +/- S.E.M., n = 4) in VIPR2 transfectants, but not in VIPR1 transfectants. The VIP receptor specificity of Ro 25-1392 was confirmed by preincubation of Chinese hamster ovary transfectants with 0.1 microM Ro 25-1392 for 18 hr at 37 degrees C, to down-regulate each type of VIP receptor. Pretreatment of VIPR2 transfectants with Ro 25-1392 decreased Bmax by a mean of 58% and VIP-induced increases in the intracellular concentration of cyclic AMP by a mean of 65%. In contrast, there was no significant change in VIPR1 transfectants after pretreatment with Ro 25-1392. Ro 25-1392 thus is selectively recognized by VIPR2, with consequent initiation of cyclic AMP and Ca+2 signals and down-regulation of VIPR2. This potent analog of VIP may prove useful for investigations of VIPR2-mediated physiological effects of VIP and exploration of the roles of VIPR2 in diseases.

Molecular cloning of the human Edg2 protein and its identification as a functional cellular receptor for lysophosphatidic acid

A cDNA homologous to that encoding sheep Edg2 protein was cloned from a human lung cDNA library. The full-length sequence encodes a 364-amino acid protein which belongs to the superfamily of guanine nucleotide-binding (G) protein-coupled receptors. Human Edg2 mRNA is widely distributed in human tissues with the highest abundance in brain. HEK293 cells expressing the human Edg2 protein showed an elevated response to lysophosphatidic acid (LPA) in a serum response element reporter gene assay, which was LPA concentration-dependent and specific to LPA compared to other lysophospholipids. Over-expression of human Edg2 in CHO cells correlated with increases in specific binding of [3H]-LPA. Recently, the mouse counterpart of Edg2 protein also was identified as a receptor for LPA (Hecht et al., 1996, J. Cell Biol. 135, 1071). Therefore, it is concluded that the human Edg2 protein functions as a cellular receptor for LPA.

Upregulation of neuropeptides and neuropeptide receptors in a murine model of immune inflammation in lung parenchyma

The lung is richly supplied with peptidergic nerves that store and secrete substance P (SP), vasoactive intestinal peptide (VIP), and other neuropeptides known to potently modulate leukocyte function in vitro and airway inflammation in vivo. To investigate and characterize neuromodulation of immune responses compartmentalized in lung parenchyma, neuropeptide release and expression of neuropeptide receptors were studied in lungs of antigen-primed C57BL/6 mice after intratracheal challenge with sheep erythrocytes. The concentrations of cytokines in bronchoalveolar lavage (BAL) fluid rose early and peaked on day 1 for interleukin (IL)-2, interferon gamma, and IL-10; days 1 to 2 for IL-6; and day 3 for IL-4, whereas the total number and different types of leukocytes in BAL fluid peaked subsequently on days 4 to 6 after i.t. antigen challenge. Immunoreactive SP and VIP in BAL fluid increased maximally to nanomolar concentrations on days 1 to 3 and 2 to 7, respectively in lungs undergoing immune responses. The high-affinity SP receptor (NK-1 R), and VIP types I (VIPR1) and II (VIPR2) receptors were localized by immunohistochemistry to surface membranes of mononuclear leukocytes and granulocytes in perivascular, peribronchiolar, and alveolar inflammatory infiltrates during immune responses. As quantified by reverse transcription-polymerase chain reaction, significant increases were observed in levels of BAL lymphocyte mRNA encoding NK-1 R (days 2 to 4), VIPR1 (days 2 to 4), and VIPR2 (days 4 to 6), and in alveolar macrophage mRNA encoding NK-1 R (days 2 to 6) and VIPR1 (days 2 to 4), but not VIPR2. Systemic treatment of mice with a selective, nonpeptide NK-1 R antagonist reduced significantly the total numbers of leukocytes, lymphocytes, and granulocytes retrieved by BAL on day 5 of the pulmonary immune response. The results indicate that SP and VIP are secreted locally during pulmonary immune responses, and are recognized by leukocytes infiltrating lung tissue, and thus their interaction may regulate the recruitment and functions of immune cells in lung parenchyma.

Changes in adhesion molecule expression during distinct patterns of immune cell migration in the inflamed lung

In response to antigen inhalation, immune cells including alveolar macrophages expressing a VIP1 receptor subtype (VIP1R), lymphocytes and leukocytes participate in the inflammatory event, migrating into and from vascular regions in lung tissue of sensitized mice. To analyze these migratory mechanisms of immune cells, we immunohistochemically examined the expression of the following: cellular adhesion molecules, lymphocyte function-associated antigen-1 (LFA-1) very late activation antigen-4 (VLA-4), and the alpha V (alpha v) subunit and their respective ligands, intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and fibronectine; the examination was carried out in pulmonary tissue from days 0, 2, 6 and 12 following intratracheal administration of sheep red blood cells (SRBC) as an antigen to previously sensitized mice. Two days following the antigen challenge, VIP1R-positive macrophages strongly expressing the alpha v integrin subunit were found clustered on the endothelial surface and among the aggregates of perivascularly infiltrated leukocytes. On the endothelium of arteries, veins and capillaries, alpha v immunoreactivity was prominently reduced, whereas staining for fibronectin was enhanced more than the prechallenge control level. The blood vessel endothelium was also stained positive for VCAM-1 and ICAM-1, while many of the infiltrating lymphocytes were positive for VLA-4 and LFA-1 immunolabelings. By post-challenge, day 6, delta v integrin subunit immunoreactivity was re-expressed on the blood vessel endothelium and only weakly expressed on VIP1R-positive macrophages, which were in retreat from the leukocyte-aggregating perivascular region and located in the alveoli. VLA-4 bearing lymphocytes conspicuously increased in number among the perivascular leukocytes, while immunoreactivity for LFA-1, VCAM-1, ICAM-1 and fibronectin was unchanged from that for post-challenge day 2. The results indicate that the expression of the alpha v-bearing integrin and its ligand fibronectin drastically changes as pulmonary inflammatory responses. These changes in expression of adhesion molecules during immune response may play an important role in the dynamic regulation of VIP1R-positive macrophage migration in the lung parenchymal compartment.

Regulation of expression of matrix metalloproteinase-9 in early human T cells of the HSB.2 cultured line by the EP3 subtype of prostaglandin E2 receptor

The expression by T lymphocytes (T cells) of more than one of the functionally distinct subtypes of prostaglandin E2 (PGE2) receptors (Rs), designated EP1, EP2, EP3, and EP4 Rs, is a principal determinant of specificity and diversity of the immune effects of PGE2. The cultured line of human leukemic T cells, termed HSB.2, co-expresses a total of 7282 +/- 1805 EP3, EP4, and EP2 Rs per cell with a Kd of 3.7 +/- 1.4 nM (mean +/- S.E., n = 9). The EP3/EP1 R-selective agonist sulprostone, EP3/EP2/EP4 R-selective agonists M&B 28767 and misoprostol, and EP2 R-selective agonist butaprost but not the EP1 R-selective antagonist SC-19220 competitively inhibited the binding of [3H]PGE2 to HSB.2 cells. Stimulation of increases in the intracellular concentration of cyclic AMP ([cAMP]i) by PGE2, misoprostol, and butaprost and of increases in the intracellular concentration of calcium ([Ca2+]i) by PGE2 and sulprostone demonstrated the respective involvement of EP2/EP4 Rs and EP3 Rs in transduction of biochemical signals. Matrix metalloproteinase (MMP)-9 was identified by zymography and Western blots as the principal MMP secreted by HSB.2 cells. The cytosolic level and secretion of MMP-9 were increased maximally after 24 h of incubation of HSB.2 cells with 10(-8)-10(-6) M PGE2, sulprostone, M&B 28767, and misoprostol but not with 10(-6) M PGF2alpha, PGD2, PGI2, or butaprost, suggesting a principal dependence on EP3 Rs. That stimulation of MMP-9 secretion by PGE2 was not diminished in Ca2+-free medium but was suppressed significantly and dose-dependently by thapsigargin, an inhibitor of endomembrane Ca2+-ATPase, suggested that MMP-9 expression by HSB.2 cells is mediated by increases in [Ca2+]i attributable to release of Ca2+ from intracellular stores. The lack of effect of dibutyryl cAMP, forskolin, and SQ 22536, an adenylyl cyclase inhibitor, on MMP-9 secretion by HSB.2 cells argued against any role for cAMP-dependent mechanisms linked to EP2/EP4 Rs. Cycloheximide and actinomycin D, which respectively inhibited protein and RNA synthesis, suppressed basal and PGE2 induction of MMP-9 production by HSB.2 cells. Northern analysis indicated that PGE2 and sulprostone time-dependently increased expression of MMP-9 mRNA. Thus, stimulation of MMP-9 in HSB.2 T cells by PGE2 is attributable to [Ca2+]i-dependent EP3 R-mediation of increases in message transcription.

Transduction of specific inhibition of HuT 78 human T cell chemotaxis by type I vasoactive intestinal peptide receptors

The major immunoregulatory effects of vasoactive intestinal peptide (VIP) are mediated by structurally distinct types I (VIPR1) and II (VIPR2) G protein-associated receptors on some T cells, B cells, and macrophages. Identification of the separate immunologic activities of each type of VIPR has been complicated by the usual expression of only VIPR2 or of VIPR1 and VIPR2 together by most human T cells obtainable in sufficient number for functional analyses. The results of reverse-transcription PCR, Western blot, and [125I]VIP-binding studies have established that HuT 78 cultured human lymphoma T cells bear a mean of 75,000 VIPR1s per cell with a mean Kd of 3.3 nM, which transduce mean maximal increases in intracellular concentration of cAMP of 2.1-fold (ED50 = 72 nM), but no VIPR2s. HuT 78 T cells, in contrast to T cells that express VIPR2, did not respond to VIP by chemotaxis through micropore filters without or with a top layer of basement membrane-like Matrigel. Matrix metalloproteinase (MMP)-dependent in situ cleavage of [3H]type IV human collagen in the layer of Matrigel by HuT 78 T cells also was not stimulated by VIP. In contrast, IL-4 and TNF-alpha both stimulated HuT 78 T cell chemotaxis and in situ MMP activity at respective optimal concentrations ranging from 3 x 10(-10) M to 3 x 10(-9) M and 10(-10) M to 3 x 10(-10) M. VIP inhibited significantly HuT 78 T cell chemotaxis through Matrigel in response to both IL-4 and TNF-alpha, as a result of suppression of both chemotactic mobility, assessed by migration through micropore filters without Matrigel, and in situ MMP activity. The transduction of opposite effects of VIP on T cell migration through a model basement membrane by VIPR1 and VIPR2 suggests that the net chemotactic response of most T cells to VIP is determined by the VIPR2/VIPR1 ratio and that the predominant expression of VIPR1 would stabilize T cell populations in lymphoid follicles and tissue infiltrates.

Transduction of specific inhibition of HuT 78 human T cell chemotaxis by type I vasoactive intestinal peptide receptors

The major immunoregulatory effects of vasoactive intestinal peptide (VIP) are mediated by structurally distinct types I (VIPR1) and II (VIPR2) G protein-associated receptors on some T cells, B cells, and macrophages. Identification of the separate immunologic activities of each type of VIPR has been complicated by the usual expression of only VIPR2 or of VIPR1 and VIPR2 together by most human T cells obtainable in sufficient number for functional analyses. The results of reverse-transcription PCR, Western blot, and [125I]VIP-binding studies have established that HuT 78 cultured human lymphoma T cells bear a mean of 75,000 VIPR1s per cell with a mean Kd of 3.3 nM, which transduce mean maximal increases in intracellular concentration of cAMP of 2.1-fold (ED50 = 72 nM), but no VIPR2s. HuT 78 T cells, in contrast to T cells that express VIPR2, did not respond to VIP by chemotaxis through micropore filters without or with a top layer of basement membrane-like Matrigel. Matrix metalloproteinase (MMP)-dependent in situ cleavage of [3H]type IV human collagen in the layer of Matrigel by HuT 78 T cells also was not stimulated by VIP. In contrast, IL-4 and TNF-alpha both stimulated HuT 78 T cell chemotaxis and in situ MMP activity at respective optimal concentrations ranging from 3 x 10(-10) M to 3 x 10(-9) M and 10(-10) M to 3 x 10(-10) M. VIP inhibited significantly HuT 78 T cell chemotaxis through Matrigel in response to both IL-4 and TNF-alpha, as a result of suppression of both chemotactic mobility, assessed by migration through micropore filters without Matrigel, and in situ MMP activity. The transduction of opposite effects of VIP on T cell migration through a model basement membrane by VIPR1 and VIPR2 suggests that the net chemotactic response of most T cells to VIP is determined by the VIPR2/VIPR1 ratio and that the predominant expression of VIPR1 would stabilize T cell populations in lymphoid follicles and tissue infiltrates.

Selective regulation of RNK-16 cell matrix metalloproteinases by the EP4 subtype of prostaglandin E2 receptor

Cell surface expression of multiple structurally and functionally distinct prostaglandin E2 (PGE2) receptors (Rs), designated the EP1, EP2, EP3, and EP4 Rs, is a principal determinant of the diverse cellular effects of PGE2. The RNK-16 line of rat large granular lymphocytes, which has served as a model for natural killer cells, coexpresses a mean of 1092 EP3 Rs and EP4 Rs per cell with a mean Kd of 2.7 nM. The presence of the EP3 and EP4 Rs and the absence of the EP1 and EP2 Rs were revealed by inhibition of [3H]PGE2 binding by the EP3/EP1R agonist sulprostone, the EP3/EP2/EP4R agonist M&B 28767, and the EP2/EP4/EP3R agonist misoprostol but not by the EP1R antagonist SC-19220 or the EP2R agonist butaprost. Functional EP4 R expression was confirmed by finding that PGE2 and misoprostol, but not butaprost or sulprostone, evoked increases in the intracellular concentration of cyclic AMP ([cAMP]) in RNK-16 cells. Matrix metalloproteinase (MMP)-1 and -3 were identified by zymography and Western blots as the principal MMPs secreted by RNK-16 cells. Secretion of both MMPs by RNK-16 cells attained a maximal level after 24 h of incubation and was enhanced significantly by 10(-9) to 10(-7) M PGE2, 10(-6) M misoprostol, and 10(-4) M dibutyryl cyclic AMP, but not by the EP3R agonist sulprostone. Thus, the effect of PGE2 on RNK-16 cell MMP secretion is mediated by an EP4 R-dependent mechanism involving increases in [cAMP]i. The migration of RNK-16 cells across micropore filters, without or with a layer of Matrigel, was stimulated chemokinetically by PGE2 and misoprostol. PGE2-elicited chemokinesis of RNK-16 cells across a Matrigel model basement membrane, but not across a microfilter alone, was suppressed by the GM 6001 inhibitor of MMP activities. Stimulation of MMP activities in RNK-16 cells by the EP4R thus facilitates migration of the NK cells across vascular basement membranes.

Integrin-dependent role of human T cell matrix metalloproteinase activity in chemotaxis through a model basement membrane

Human T lymphoblastoma cells of the CD4+ 8+ Tsup-1 line, that express alpha 4 and alpha 5 but not alpha 6 integrins of the beta 1 family, and CD4+ human blood T cells bind vasoactive intestinal peptide (VIP) with high affinity, leading to increased adherence, secretion of matrix metalloproteinases (MMPs), and chemotaxis. VIP-enhanced adherence of T cells to fibronectin was inhibited significantly by neutralizing monoclonal antibodies to beta 1 > alpha 4 > > alpha 5, but not to alpha 6. Antibodies to beta 1 and alpha 4 suppressed to a similarly significant extent VIP stimulation of both MMP-dependent T cell chemotaxis through fibronectin-enriched Matrigel and T cell degradation of 3H-type IV collagen in the Matrigel, without affecting VIP-evoked secretion of MMP by suspensions of T cells. The lesser inhibition of VIP-enhanced adherence of T cells to fibronectin by anti-alpha 5 antibody, than antibodies to beta 1 or alpha 4 chains, was associated with lesser or no suppression of MMP-dependent T cell chemotaxis through Matrigel and T cell degradation of type IV collagen in the Matrigel in response to VIP. Specific beta 1 integrins thus mediate interactions of stimulated T cells with basement membranes, including adherence, localized digestion by MMPs, and chemotactic passage, that promote entry of T cells into extravascular tissues.

Matrix metalloproteinases in immunity

Matrix metalloproteinases (MMPs) are a family of zinc-containing endo-proteinases that share structural domains but differ in substrate specificity, cellular sources, and inducibility. Macrophage production and secretion of large quantities of many MMPs, after contact with matrix proteins, is enhanced by surface determinants on activated T cells and suppressed by cytokines from Th1 and Th2 cells. T cells secrete predominantly the gelatinases MMP-2 and -9, after beta 1, integrin- or vascular cell adhesion molecule (VCAM)-1-dependent stimulation by cytokines and inflammatory mediators. MMPs of both T cells and macrophages facilitate secretion of TNF-alpha, by cleavage of the membrane-bound form. T cell MMPs prepare connective tissue matrices for T cell chemotaxis across basement membranes and through tissues. The greater amounts of diverse MMPs from macrophages are capable of degrading connective tissues, which may release stored growth factors. In limited studies of animal models of autoimmunity, specific MMP inhibitors have significantly decreased edema and inflammatory tissue damage, suggesting possible therapeutic benefits.

Predominant expression of type II vasoactive intestinal peptide receptors by human T lymphoblastoma cells: transduction of both Ca2+ and cyclic AMP signals

An immunoregulatory role for vasoactive intestinal peptide (VIP) is suggested by the high concentrations in subsets of neurons supplying lymphoid organs and by the capacity of VIP to affect T lymphocyte functions. The Tsup-1 line of human T lymphoblastoma cells expresses both type I and type II G protein-coupled VIP receptors (Rs), as shown by detection of the encoding mRNAs with reverse transcription-polymerase chain reaction analyses. Northern blot quantification of the relative amounts of mRNA encoding the two VIPRs in Tsup-1 cells indicated that type II predominates over type I, as it does in human blood CD4+ T cells. Tsup-1 cells bound 125I-VIP to 8.95 x 10(4) high-affinity sites/cell (Kd = 6.0 nM) and 7.45 x 10(5) low-affinity sites/cell (Kd = 210 nM). VIP increased [cAMP]i in Tsup-1 cells (EC50 = 14.4 nM) and stimulated a rapid and transient increase in [Ca2+]i (EC50 = 30 nM). Functional coupling of G proteins to type II VIPRs was suggested by the change in binding of 125I-VIP to Tsup-1 cell membranes from two sites with Kd values of 3.8 and 109 nM to one site of Kd 30 nM by GTP-gamma-S and the suppression by pertussis toxin of increases in [Ca2+]i evoked by VIP. The VIP antagonists, VIP4-28 and (4-Cl-D-Phe6-Leu17) VIP, inhibited 125I-VIP binding by type II VIPRs, as well as VIP-elicited increases in [Ca2+]i and [cAMP]i. Type II VIPRs thus are the major transducers of VIP signals to a subset of human T cells.

Matrix metalloproteinases in immunity

Matrix metalloproteinases (MMPs) are a family of zinc-containing endo-proteinases that share structural domains but differ in substrate specificity, cellular sources, and inducibility. Macrophage production and secretion of large quantities of many MMPs, after contact with matrix proteins, is enhanced by surface determinants on activated T cells and suppressed by cytokines from Th1 and Th2 cells. T cells secrete predominantly the gelatinases MMP-2 and -9, after beta 1, integrin- or vascular cell adhesion molecule (VCAM)-1-dependent stimulation by cytokines and inflammatory mediators. MMPs of both T cells and macrophages facilitate secretion of TNF-alpha, by cleavage of the membrane-bound form. T cell MMPs prepare connective tissue matrices for T cell chemotaxis across basement membranes and through tissues. The greater amounts of diverse MMPs from macrophages are capable of degrading connective tissues, which may release stored growth factors. In limited studies of animal models of autoimmunity, specific MMP inhibitors have significantly decreased edema and inflammatory tissue damage, suggesting possible therapeutic benefits.

Stimulus specificity of matrix metalloproteinase dependence of human T cell migration through a model basement membrane

Chemotaxis of human T lymphoblastoma cells of the Tsup-1 line, which migrate similarly to blood T cells, through a layer of basement membrane-like Matrigel on a polycarbonate micropore filter was evoked by vasoactive intestinal peptide (VIP; concentration for a maximal response, 10(-7)M), IL-2 (10(-9)M), and the chemokines RANTES (10(-10)M) and macrophage inflammatory protein-1 alpha (10(-10)M). Chemotactic concentrations of each factor increased Tsup-1 cell secretion of matrix metalloproteinase-9 (MMP-9), with significant responses by 4 h for VIP, IL-2, and IL-4, but only after 24 h for macrophage inflammatory protein-1 alpha and RANTES, as quantified by Western blots and zymography. 3H-Labeled type IV human collagen incorporated in the Matrigel layer was degraded by migrating Tsup-1 cells, as assessed by release of radioactive fragments of the collagen. The in situ degradation of type IV collagen in Matrigel by migrating Tsup-1 cells was enhanced most significantly by VIP, IL-2, and IL-4 after 4 h at concentrations that increased the secretion of MMP-9 optimally, but only after 24 h by macrophage inflammatory protein-1 alpha and RANTES. The specific MMP inhibitor GM6001 suppressed Tsup-1 cell MMP activity evoked by all stimuli, as determined by zymography and in situ degradation of 3H-Labeled type IV human collagen. The chemotactic migration of Tsup-1 cells through Matrigel, but not through a filter alone, in response to optimal concentrations of VIP, IL-2, and IL-4, but not the chemokines, was inhibited by GM6001, with a concentration dependence similar to that for suppression of MMP activity. Thus elicitation of T cell chemotactic migration through a model basement membrane by stimuli that increase MMP activity early in the response depends on degradation of matrix proteins by MMP, whereas stimuli that recruit MMP late may rely on early activation of other proteases.

Stimulus specificity of matrix metalloproteinase dependence of human T cell migration through a model basement membrane

Chemotaxis of human T lymphoblastoma cells of the Tsup-1 line, which migrate similarly to blood T cells, through a layer of basement membrane-like Matrigel on a polycarbonate micropore filter was evoked by vasoactive intestinal peptide (VIP; concentration for a maximal response, 10(-7)M), IL-2 (10(-9)M), and the chemokines RANTES (10(-10)M) and macrophage inflammatory protein-1 alpha (10(-10)M). Chemotactic concentrations of each factor increased Tsup-1 cell secretion of matrix metalloproteinase-9 (MMP-9), with significant responses by 4 h for VIP, IL-2, and IL-4, but only after 24 h for macrophage inflammatory protein-1 alpha and RANTES, as quantified by Western blots and zymography. 3H-Labeled type IV human collagen incorporated in the Matrigel layer was degraded by migrating Tsup-1 cells, as assessed by release of radioactive fragments of the collagen. The in situ degradation of type IV collagen in Matrigel by migrating Tsup-1 cells was enhanced most significantly by VIP, IL-2, and IL-4 after 4 h at concentrations that increased the secretion of MMP-9 optimally, but only after 24 h by macrophage inflammatory protein-1 alpha and RANTES. The specific MMP inhibitor GM6001 suppressed Tsup-1 cell MMP activity evoked by all stimuli, as determined by zymography and in situ degradation of 3H-Labeled type IV human collagen. The chemotactic migration of Tsup-1 cells through Matrigel, but not through a filter alone, in response to optimal concentrations of VIP, IL-2, and IL-4, but not the chemokines, was inhibited by GM6001, with a concentration dependence similar to that for suppression of MMP activity. Thus elicitation of T cell chemotactic migration through a model basement membrane by stimuli that increase MMP activity early in the response depends on degradation of matrix proteins by MMP, whereas stimuli that recruit MMP late may rely on early activation of other proteases.

Independent down-regulation of EP2 and EP3 subtypes of the prostaglandin E2 receptors on U937 human monocytic cells

Co-expression of EP2 and EP3 subtypes of prostaglandin E2 (PGE2) receptors (R) by U937 human monocytic cells permitted comparative studies of desensitization of each subtype. Specific binding of [3H]PGE2 to membranes of U937 cells showed a Kd of 2.9 +/- 0.3 nM (mean +/- SEM) and a Bmax of 40.5 +/- 1.0 fmol/mg protein, and was competitively inhibited by PGE2 > or = PGE1 > PGF2 alpha > PGD2 > PGI2. EP2 R and EP3 R mRNA were detected by reverse transcription-polymerase chain reaction and Northern blots. EP3 R expression was demonstrated by inhibition of [3H]PGE2 binding with the EP1/EP3 agonist sulprostone [50% inhibitory concentration (IC50 = 3.3 +/- 0.6 nM)] and the EP3/EP2 agonist M&B 28767 (IC50 = 2.1 +/- 0.3 nM), but not with the EP1 antagonist SC-19220. EP2 R protein was identified by Western blot analysis using specific rabbit IgG antibodies to an amino-terminal peptide of the EP2 R. EP2 R transduced PGE2 stimulation of significant increases in cellular [cAMP]i [50% effective concentration (EC50 = 20 +/- 2.5 nM)], and EP3 R mediated sulprostone inhibition of forskolin elevation of [cAMP]i (IC50 = 1.3 +/- 0.4 nM). Pretreatment of U937 cells with phorbol 12-myristate 13-acetate (PMA), which activates protein kinase C (PKC), for 1 hr reduced the total number, but not the affinity, of PGE2 R by down-regulating principally EP2 R. In contrast, a 24-hr exposure to PMA, which is known to down-regulate PKC, suppressed both the total number and affinity of PGE2 R on U937 cells with concurrent reductions in EP2 R and EP3 R. The down-regulation of EP2 R by PMA at 1 hr was blocked by staurosporine, an inhibitor of PKC, whereas the down-regulation of EP3 R by PMA at 24 hr was blocked by indomethacin. Pretreatment of U937 cells with PGE2 for 1 and 24 hr reduced both the binding affinity and the total number of PGE2 R, by co-ordinate suppression of the EP2 R and EP3 R. Desensitization of EP2 R and EP3 R for 1 hr with PGE2 suppressed subsequent PGE2-evoked chemokinetic responses to PGE2, whereas selective down-regulation of EP2 R alone by PMA for 1 hr had no effects on U937 cell migration. Thus expression of each subtype of PGE2 R is regulated independently and EP3 R, but not EP2 R, transduces PGE2 effects on migration of mononuclear phagocytes.

Cloning, sequencing and tissue distribution of two related G protein-coupled receptor candidates expressed prominently in human lung tissue

A novel G protein-coupled receptor, named GPR12A, was cloned by a PCR strategy using degenerate primers designed from sequences conserved among receptors for inflammatory mediators. Screening of a human lung cDNA library with GPR12A as a probe also identified a closely-related cDNA (GPR6C.1) that has been previously reported as GPR4 [13]. GPR12A and GPR6C.1 are 46.1% identical in amino acid sequence, but are less than 33% identical to any other known receptors. Northern analysis revealed that they are expressed prominently in the lung. Although the ligands for GPR12A and GPR6C.1 are unknown, their similarity suggests that they are receptors for ligands of similar or identical chemical nature.

Stimulation of matrix metalloproteinase-dependent migration of T cells by eicosanoids

Prostaglandin E2 (PGE2) and leukotriene B4 (LTB4), at nanomolar to micromolar concentrations, elicited migration of human blood T cells and cultured T lymphoblastoma cells of the Tsup-1 line through a layer of Matrigel basement membrane matrix. The density of Tsup-1 cell high-affinity receptors was low for PGE2 and high for LTB4, resulting in respectively predominant chemokinetic and chemotactic stimulation of migration. Migration-enhancing concentrations of PGE2 and LTB4 also increased Tsup-1 cell content and secretion of matrix metalloproteinases (MMPs) 2, 3, and 9, which were quantified by Western blots and zymography, and augmented Tsup-1 cell-surface expression of the MMPs, as shown by flow cytometry. That a specific MMP inhibitor suppressed migration of blood T cells and Tsup-1 cells through Matrigel, but did not affect PGE2- and LTB4-initiated T cell migration through micropore filters without Matrigel, suggests dual requirements for MMP expression and enhanced motility in T cell passage through basement membranes.

Specificity of expression and effects of eicosanoid mediators in normal physiology and human diseases

The eicosanoids are a family of oxygenated arachidonic acid derivatives that potently mediate diverse physiological and pathophysiological processes. Recent research on eicosanoids has revealed novel pathways of synthesis, a family of related cell membrane receptors, and distinctive roles in cellular functions. There are two cyclooxygenases that convert arachidonic acid to thromboxane and prostaglandins, one of which is localized in the endoplasmic reticulum and the other in the nuclear envelope. The cyclooxygenases differ in their susceptibility to inhibition by nonsteroidal antiinflammatory drugs. The leukotriene-generating pathway consists of a cytosolic perinuclear 5-lipoxygenase, two integral nuclear envelope proteins, termed 5-lipoxygenase-activating protein and LTC4 synthase, and a cytosolic LTA4 hydrolase. Each protein of the leukotriene synthetic pathway is a target for specific pharmacological intervention. Cellular recognition and effects of eicosanoids are mediated by at least 12 different G protein-associated primary receptors, which differ in tissue distribution, signaling mechanisms, and cellular behavior, as well as binding specificity. Transient localized increases in tissue concentrations of eicosanoids and the concurrent upregulation of complementary receptors influence differentiation, migration, and specific activities of cells in immunity and other integrated physiological responses.

Neuropeptide signaling of lymphocytes in immunological responses

Peptidergic nerves in immune organs and lymphoid tissues of the lungs and gastrointestinal tract end on or in close proximity to lymphocytes, mast cells and macrophages. Vasoactive intestinal peptide, substance P and some other neuropeptides, that are recognized by distinct sets of cell surface receptors, regulate aspects of T cell differentiation in the thymus, such as negative selection, and contribute to mediating compartmental immune responses. The latter effects include stimulating expression of adhesive proteins by lymphocytes, enhancement of lymphocyte and macrophage migration in vascular and connective tissues, and modulation of proliferative and synthetic responses of lymphocytes to diverse antigens.

Immunochemical localization of type I VIP receptor and NK-1-type substance P receptor in rat lung

Peptidergic nerves in the respiratory tract release vasoactive intestinal peptide (VIP) and substance P (SP), which mediate physiological and immune functions. Antipeptide antibodies to type I VIP receptor (VIPR) and NK-1-type SP receptor (SPR) were used to identify these receptors in normal rat lungs. VIPRs and SPRs were detected on airway epithelium from the trachea to the respiratory bronchioles but not in alveoli, submucosal glands, or pulmonary smooth muscle, except for that of some pulmonary veins. VIPRs also were expressed on macrophages around capillaries, in tracheal and bronchial connective tissue, in alveolar walls, and in the subintima of pulmonary veins and some arterioles. The absence of receptors from airway smooth muscle and submucosal glands implies that mediation of some known effects of SP and VIP may be epithelial or macrophage dependent. Other types of VIPRs and SPRs on airway glands and smooth muscle may transduce direct effects. The similar localization of VIPRs and SPRs in rat lung suggests that VIP and SP may coordinately regulate some pulmonary functions.

Structure, expression, and chromosomal localization of the type I human vasoactive intestinal peptide receptor gene

Vasoactive intestinal peptide (VIP) and other members of the pituitary adenylyl cyclase-activating peptide (PACAP) and secretin neuroendocrine peptide family are recognized with specificity by related G protein-coupled receptors. We report here the cloning, characterization, and chromosomal location of the gene encoding the human type I VIP receptor (HVR1), also termed the type II PACAP receptor. The gene spans approximately 22 kb and is composed of 13 exons ranging from 42 to 1400 bp and 12 introns ranging from 0.3 to 6.1 kb. Primer extension analysis with poly(A)+ RNA from human HT29 colonic adenocarcinoma cells indicated that the transcription initiation site is located at position -110 upstream of the first nucleotide (+1) of the translation start codon, and 75 nt downstream of a consensus CCAAT-box motif. The G+C-rich 5' flanking region contains potential binding sites for several nuclear factors, including Sp1, AP2, ATF, interferon regulatory factor 1, NF-IL6, acute-phase response factor, and NF-kappa B. The HVR1 gene is expressed selectively in human tissues with a relative prevalence of lung > prostate > peripheral blood leukocytes, liver, brain, small intestine > colon, heart, spleen > placenta, kidney, thymus, testis. Fluorescence in situ hybridization localized the HVR1 gene to the short arm of human chromosome 3 (3p22), in a region associated with small-cell lung cancer.

Specific suppression by prostaglandin E2 of activation-induced apoptosis of human CD4+CD8+ T lymphoblasts

Receptors (Rs) for prostaglandin E2 (PGE2) of the EP2 subtype are expressed at high levels in rodent and human thymuses, with preferential localization on immature thymocytes. Human cultured lymphoblasts of the Tsup-1 line express CD4 and CD8 but only a low level of CD3, typical of immature thymocytes, and bear EP2-type Rs for PGE2 that were identified by binding of [3H]PGE2 and Ab to recombinant EP2Rs, and by cAMP responses to PGE2. PGE2 protected Tsup-1 cells from apoptosis initiated by diverse stimuli, including mitogenic lectins and anti-Fas or anti-CD3 plus anti-CD28 Abs, but not ionomycin, as assessed by suppression of both fragmentation of [3H]thymidine-labeled DNA and appearance of free 3'-OH ends of cleaved DNA. An EP2R-selective synthetic agonist also significantly suppressed lectin-induced apoptosis of Tsup-1 cells. Phosphodiesterase inhibition synergistically enhanced PGE2-induced increases in cAMP and decreases in apoptosis in parallel, which suggests that the EP2R-specific protective effect of PGE2 is mediated predominantly by cAMP suppression of apoptosis. Dibutyrylcyclic AMP alone protected Tsup-1 cells against lectin-induced apoptosis, but the maximal effect was less than that for PGE2. The thromboxane A2 mimetic U46619 initiated apoptosis of Tsup-1 cells that was suppressed significantly by PGE2. Immune negative selection of immature thymocytes thus may be regulated by opposing effects of endogenous eicosanoids that include destruction by thromboxane A2 and protection by PGE2.

Specific suppression by prostaglandin E2 of activation-induced apoptosis of human CD4+CD8+ T lymphoblasts

Receptors (Rs) for prostaglandin E2 (PGE2) of the EP2 subtype are expressed at high levels in rodent and human thymuses, with preferential localization on immature thymocytes. Human cultured lymphoblasts of the Tsup-1 line express CD4 and CD8 but only a low level of CD3, typical of immature thymocytes, and bear EP2-type Rs for PGE2 that were identified by binding of [3H]PGE2 and Ab to recombinant EP2Rs, and by cAMP responses to PGE2. PGE2 protected Tsup-1 cells from apoptosis initiated by diverse stimuli, including mitogenic lectins and anti-Fas or anti-CD3 plus anti-CD28 Abs, but not ionomycin, as assessed by suppression of both fragmentation of [3H]thymidine-labeled DNA and appearance of free 3'-OH ends of cleaved DNA. An EP2R-selective synthetic agonist also significantly suppressed lectin-induced apoptosis of Tsup-1 cells. Phosphodiesterase inhibition synergistically enhanced PGE2-induced increases in cAMP and decreases in apoptosis in parallel, which suggests that the EP2R-specific protective effect of PGE2 is mediated predominantly by cAMP suppression of apoptosis. Dibutyrylcyclic AMP alone protected Tsup-1 cells against lectin-induced apoptosis, but the maximal effect was less than that for PGE2. The thromboxane A2 mimetic U46619 initiated apoptosis of Tsup-1 cells that was suppressed significantly by PGE2. Immune negative selection of immature thymocytes thus may be regulated by opposing effects of endogenous eicosanoids that include destruction by thromboxane A2 and protection by PGE2.

Immunohistochemical localization of peptidergic nerve fibers and neuropeptide receptors in Peyer's patches of the cat ileum

This study examined the distribution of peptidergic nerve fibers in Peyer's patches to determine whether appropriate receptors were present. Vasoactive intestinal peptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP) and receptors for VIP and SP were localized in lymphoid follicles of the cat ileum using a combined indirect horseradish peroxidase and streptavidin-biotin method. The margins of follicles were innervated by nerve fibers containing VIP, SP and CGRP. Nerve fibers were predominantly around lymphatics and high endothelial venules at the edges of follicles. Specific receptors for VIP and SP were present at the margins of follicles and in the lamina propria around crypts. VIP receptors were numerous on T cells within and around high endothelial venules and lymphatic vessels and at the margins of follicles. SP receptors were identified on a small number of T and B cells, granulocytes and macrophages, restricted to the margins of follicles. The defined distribution in ileal lymphoid tissue of nerve fibers containing VIP and SP and the corresponding localization of their appropriate receptors support immunoregulatory roles for neuropeptides in mucosal immunity.

Isoforms of the EP3 subtype of human prostaglandin E2 receptor transduce both intracellular calcium and cAMP signals

The EP3 subtype of prostaglandin E2 receptor transduces diverse physiological responses in mammalian tissues through signaling pathways coupled to heterotrimeric G proteins. Distinct cDNA clones encoding five isoforms of the EP3 receptor were isolated from a human uterus cDNA library. The human EP3 receptor isoforms designated hEP3-I, I', II, III, and IV are derived from alternative RNA splicing and differ only in the distal sequences of their carboxyl-terminal cytoplasmic tails. The unique cytoplasmic tails consist of 31 amino acids for isoforms I and I', 29 for II, 6 for III, and 15 for IV. When stably expressed in CHO cell transfectants, all isoforms exhibited similar EP3-specific binding of [3H]-PGE2 and PGE2 analogs. The EP3-selective agonist M&B 28767 both decreased the intracellular cAMP concentration ([cAMP]i) and increased the intracellular concentration of calcium ([Ca2+]i) with quantitative differences among different isoforms, but none mediated an increase in [cAMP]i. Pertussis toxin treatment completely blocked the decrease in [cAMP]i, but not the increase in [Ca2+]i evoked by M&B 28767. PGE2-induced desensitization of [3H]PGE2 binding by isoforms III and IV was rapid and transient, whereas that by isoform II was slow and persistent. Reverse transcription-PCR amplification of EP3 receptor messages in human kidney and uterine tissue RNA detected expression of all isoforms with different abundancies. The dual signal transduction pathways and distinctive tissue distribution of isoforms of the EP3 receptor are consistent with its mediation of diverse functions of PGE2.

Human vasoactive intestinal peptide1 receptors expressed by stable transfectants couple to two distinct signaling pathways

Vasoactive intestinal peptide (VIP) is a potent neuropeptide mediator of central and peripheral nervous system function. A human VIP1 receptor (HVR) cDNA clone was previously obtained from HT29 intestinal epithelial cells and lung tissue. Stably-transfected human embryonic kidney 293 cells and chinese hamster ovary (CHO) cells expressing about 10(6) HVRs per cell that bind [125I]VIP with a Kd of 0.2-0.8 nM, and specifically recognized by anti-HVR antibodies, were established and characterized. VIP induced increases in intracellular cAMP levels ([cAMP]i) dose-dependently with an EC50 of 0.2 nM in 293 and CHO stable transfectants and concurrently evoked dose-dependent increases in intracellular calcium concentrations ([Ca2+]i), as determined by fluorescence-dye spectroscopy. Untransfected 293 and CHO cells showed minimal binding or intracellular effects of VIP; however, native VIP1 receptors of HT29 cells also increased [cAMP]i and [Ca2+]i in dose-dependent responses to VIP. Thus recombinant and native human VIP1 receptors both couple to two distinct signal transduction pathways within a single cell type.

Specific recognition of the human neuroendocrine receptor for vasoactive intestinal peptide by anti-peptide antibodies

Rabbit polyclonal IgG antibodies were generated to three distinct synthetic peptide substituents of the human neuroendocrine-type 7 transmembrane-domain receptor for vasoactive intestinal peptide (VIP), including a portion of the amino-terminus, first extracellular loop, and carboxyl-terminus. Immunofluorescent staining of both human K293 cell transfectants, expressing recombinant VIP receptors, and HT-29 human intestinal epithelial cells, bearing native VIP receptors, was observed with each of the antibodies and was eliminated specifically after absorption of antibodies with the respective peptide immunogen. Each of the antibodies recognized the same approximately 70-kDa membrane proteins, extracted from both K293 cell transfectants and HT-29 cells, in sodium dodecyl sulfate-polyacrylamide gel electrophoresis blots. Neither IgG nor Fab preparations of the antibodies inhibited VIP binding to cellular receptors at a concentration of 1 microgram/ml, that yielded optimal immunofluorescence, or at 5-300 micrograms/ml. In contrast, 5-200 micrograms/ml of anti-peptide antibodies as IgG, but not Fab, significantly inhibited the increase in concentration of cyclic AMP in HT-29 cells elicited by 1 nM VIP, without affecting the greater increase evoked by 100 nM VIP or alone altering the level of cyclic AMP. Antibodies to several peptide substituents thus bind specifically to VIP receptors in immunoblots and permeabilized cells, and may affect the cellular functions of VIP receptors with sufficient selectivity to reduce transduction of signals, without altering the binding of VIP.

Cloning and expression of the EP3-subtype of human receptors for prostaglandin E2

Prostaglandin E2 (PGE2) is a potent mediator in many human tissues that is recognized by three distinct subtypes of receptors (Rs), designated EP1, EP2 and EP3. A cDNA from a human kidney library encodes a 367 amino acid protein, of 85% homology with the mouse EP3R, that is expressed predominantly in kidney tissue. Human EP3Rs of transfectants bound [3H]-PGE2 with a mean Kd of 2.6 nM and native specificity. In contrast to the reliance of EP2Rs on increases in the intracellular concentration of cyclic AMP ([cAMP]i) for cellular signaling, EP3Rs transduce both decreases in [cAMP]i and modest increases in [Ca++]i.

Inhibition of human HL-60 cell responses to chemotactic factors by antisense messenger RNA depletion of G proteins

Chemotactic factors bound to receptors of the seven-transmembrane domain family signal leukocytes through associated guanine nucleotide-binding (G) proteins. Human leukocytes of the HL-60 line, which express G protein-coupled receptors for leukotriene B4 (LTB4) and N-formyl-methionyl-leucyl-phenylalanine (fMLP) after differentiation with vitamin D3 and transforming growth factor-beta, were transfected with expression plasmids containing antisense-oriented cDNAs encoding the alpha-chains of Go, Gi1, Gi2, and Gi3. Antisense mRNA for Go and Gi2 alpha-chains suppressed by over 80% the level of the respective G protein. Go-deficient HL-60 cells had depressed functional and intracellular calcium responses to LTB4 and fMLP, but no alterations in the responses of cyclic adenosine 3',5'-monophosphate (cAMP). In contrast, HL-60 cells deficient in Gi2 lost only responses of the intracellular concentration of cAMP. Antisense mRNA suppression of distinct G proteins thus may delineate some transductional requirements for cellular responses.

Isotype-specific regulation of human lymphocyte production of immunoglobulins by sustained exposure to vasoactive intestinal peptide

Exposure of lymphocytes to nanomolar to micromolar concentrations of vasoactive intestinal peptide (VIP) for 1 to 3 days only modestly suppressed or enhanced the production of IgA and IgM, but not IgG. The effects of twice daily additions of 10(-12) to 10(-7) mol/L VIP for up to 18 days on pokeweed mitogen-stimulated peripheral blood mononuclear cells (PBMCs) from normal human subjects was examined by quantifying the production of IgG, IgM, and IgA. The maximum suppression of IgG by 10(-9) mol/L VIP was 79% +/- 33% (mean +/- SD) (range, 41% to 97%; p < 0.015) on day 9 and 84% +/- 1% (range, 74% to 96%; p < 0.0001) on day 14 and was significant at 6 x 10(-10) to 4 x 10(-9) mol/L VIP. Suppression of IgM production by 10(-9) mol/L VIP was significant and was observed first on day 5 and persisted through day 14. VIP did not alter IgA production or affect the proliferation or viability of PBMCs. The production of IgE by interleukin-4 stimulated PBMCs was enhanced consistently in two subjects but not in two other subjects. The duration of exposure to nanomolar concentrations of VIP is thus a critical determinant of its immunoregulatory effect, as manifested by late suppression of production of IgG and IgM and concurrent enhancement of production of IgE in some subjects.

Cloning and expression of the EP2 subtype of human receptors for prostaglandin E2

Prostaglandin E2 (PGE2) is a potent mediator in many human tissues, that is recognized by three distinct subtypes of receptors, designated EP1, EP2 and EP3. A cDNA from a human lung library encodes a 53 kDa protein of 88% homology with the mouse EP2 receptor. Human EP2 receptors in COS-7 cell transfectants bound [3H]-PGE2 with a mean Kd of 2.2 nM and native specificity, and transduced increases in the intra-cellular concentration of cyclic AMP, but not of Ca++. That most EP2 receptor mRNA is in lung, kidney, intestinal, glandular and immune tissues, is consistent with functional responses.

Variants of vasoactive intestinal peptide in mouse mast cells and rat basophilic leukemia cells

Radioimmunoassays for neuroendocrine vasoactive intestinal peptide (VIP1-28) detected 30-120 fmol of structurally related peptides in extracts of 10(7) mouse peritoneal mast cells, bone marrow-derived mast cells, cultured PT-18 and C1.MC/C57.1 lines of mast cells, and rat basophilic leukemia (RBL) cells. No VIP was found in peritoneal cells of mast cell-deficient WBB6F1-W/Wv mice, whereas the amounts extracted from peritoneal cells of the congenic normal (WBB6F1-+/+) mice were similar to those from cultured mouse mast cells. Sephadex G-25 gel filtration resolved two different-sized variants of VIP from mouse mast cells and RBL cells. Amino acid sequence analyses showed that the smaller variant is VIP10-28. The principal amino-terminally larger variant of VIP from C1.MC/C57.1 mouse mast cells and RBL cells exhibited amino acid sequence homology with VIP(-6)-28, and this sequence was established for the corresponding larger VIP from PT-18 mast cells. Polymerase chain reaction amplification of two different substituent sequences of prepro VIP in RBL cell RNA identified the VIP message. VIP10-28 was released from mouse mast cells concurrently with histamine by IgE-dependent stimulation. Rodent mast cell-derived VIP thus consists of both the truncated VIP10-28 and amino-terminally larger forms that appear to be generated by peptidolysis of a preproVIP similar to that found in neural cells.

Induction of aggregation of Raji human B-lymphoblastic cells by vasoactive intestinal peptide

Subsets of neurons in the thymic cortex, Peyer's patches and lymphoid tissues of the respiratory system deliver vasoactive intestinal peptide (VIP) at nanomolar concentrations. The possible effects of VIP on B-cell adhesiveness in these tissues were examined in studies of the homotypic aggregation (HA) of human B-lymphoblastoid cells of the Raji line, which express a mean of 27,950 VIP receptors/cell with a mean Kd of 0.8 nM. Mean HA, assessed microscopically, attained a maximum of 54% after 8 hr with 0.1 microgram/ml of phorbol 12-myristate 13-acetate (PMA) (P < 0.01) and 31% after 24 hr with 10(-8) M VIP (P < 0.05), as contrasted with 13% and 20% at the respective times in medium alone, and both stimuli also increased the mean size of aggregates. The presence of the phosphodiesterase inhibitor Ro 20-1724 permitted 10(-9) M VIP, which had no effect alone, to raise the mean cyclic AMP content of Raji cells by more than 10-fold and concurrently to elevate mean HA from 55% in medium alone at 48 hr to 70% and from 55% at 72 hr to 68% (P < 0.05 for both). Monoclonal antibodies to lymphocyte function-associated (LFA-1) adhesive protein and to intercellular adherence molecule-1 (ICAM-1) suppressed significantly the HA of Raji cells induced by VIP and PMA. The effects of VIP on compartmental immunity in the lungs and intestines thus may be mediated in part by increases in lymphocyte adhesiveness, which could contribute to the regional accumulation of specifically immunocompetent cells.

Cloning and functional expression of a human neuroendocrine vasoactive intestinal peptide receptor

Vasoactive intestinal peptide (VIP) is a potent mediator of gastrointestinal, nervous, pulmonary, vascular and immune functions. A cDNA was obtained from human HT29 intestinal epithelial cells and found to encode a 457 amino acid, 52 kDa VIP receptor. Transfection of the cDNA into COS-7 cells and 293 cells resulted in expression of specific saturable binding of VIP with a Kd of 0.8 nM, and induction of increases in intracellular cAMP by VIP with an EC50 of 1 nM. The human VIP receptor is homologous to other G protein-coupled receptors of the secretin-parathyroid hormone receptor family. A 2.8 kb transcript was detected in human lung, HT29 cells and Raji B-lymphoblasts with weaker expression in human brain, heart, kidney, liver and placenta.

Activation of human neutrophil LFA-1 (CD11a) by leukotriene B4

Homotypic aggregation (HA) of human neutrophils by the potent leukotactic factor, leukotriene B4 (LTB4), and phorbol myristate acetate (PMA) was evaluated by recording the net decrease in absorbency at 650 nm of suspensions of 10(7) neutrophils/ml in a microtiter plate reader, which was found to correlate with microscopic evidence of aggregation. LTB4-elicited HA was increased maximally by approximately one third above HA in buffer at 30 min, whereas PMA-induced HA reached a maximal level more than 2 1/2-fold higher than buffer control at 60 min. The involvement of LFA-1 in LTB4-induced HA of neutrophils was suggested initially by the inhibitory effect of monoclonal anti-CD18 and anti-CD11a antibodies. The binding to neutrophils of a monoclonal anti-LFA-1 antibody (NK1-L16) specific for an activation epitope of CD11a was increased a maximum of 28-fold and sixfold, respectively, after 1 and 5 min of preincubation with 10 nM LTB4 and fivefold after 5 min with PMA. Thus, both LTB4 and PMA induce an activating conformational change in the CD11a adherence receptor of human neutrophils.

The SKW 6.4 line of human B lymphocytes specifically binds and responds to vasoactive intestinal peptide

Vasoactive intestinal peptide (VIP1-28) is a neuromediator recognized by high-affinity receptors on human lymphocytes, which inhibits T-cell proliferation and cytokine secretion, and suppresses immunoglobulin production by mitogen-stimulated mixed mononuclear leucocytes. The direct interactions of VIP1-28 with B cells were studied in the SKW 6.4 line of EBV-transformed human B cells, that express a mean (+/- SD) of 6116 +/- 969 receptors for [125I]VIP1-28 with a mean Kd of 59 nM, that decreases to 12 nM after exposure to phorbol 12-myristate 13-acetate (PMA). The secretion of IgM by SKW 6.4 B cells stimulated optimally with 100 ng/ml of PMA, but not unstimulated secretion of IgM, was suppressed significantly by 10(-12) M to 10(-9) M VIP1-28 and up to a mean maximum (+/- SD) of 40 +/- 2% by 10(-10) M VIP1-28. VIP1-28 elicited concomitant increases in intracellular cyclic AMP up to a mean maximum of 163% at 10(-10) M VIP1-28. The requirement for specific signal transduction by the occupied VIP receptors to inhibit IgM secretion was demonstrated by the lack of effect of VIP4-28 on both cyclic AMP concentration and IgM secretion, despite the equal affinity of binding of VIP4-28 and VIP1-28. The effects of VIP on immunoglobulin secretion by stimulated mixed mononuclear leucocytes thus may be due in part to a direct action on B cells.

Neuropeptides in pulmonary edema fluid of adult respiratory distress syndrome

A role for peptidergic nerves in the adult respiratory distress syndrome (ARDS) was examined by radioimmunochemically quantifying neuropeptides in pulmonary edema (PE) fluids from seven patients with ARDS and six patients with PE from congestive heart failure (CHF). The PE fluid mean concentrations of substance P (SP) and gastrin-releasing peptide (GRP) were significantly higher in ARDS (0.59 +/- 0.29 SD and 0.10 +/- 0.03 nM, respectively, P < 0.001 for both) than in CHF (0.19 +/- 0.08 and 0.04 +/- 0.01), whereas no difference was detected between the mean levels of vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP) in the two forms of PE. Mean alveolar fluid concentration of SP was 8.7 nM (range 2.1-20.5 nM, N = 4) in sheep with acute lung injury from intravenous Pseudomonas aeruginosa, but was undetectable in sheep with balloon-induced high left atrial pressure simulating CHF (N = 2) or control sheep (N = 2). Pulmonary lymphatic clearance of SP, which reflected the rate of generation of SP in the lungs, attained a maximum of 25-95 pmol/h in sheep given P. aeruginosa intravenously, but was detected in only one of four control sheep at a lower level. Some pulmonary neuropeptides thus are released locally by acute lung injury and may contribute to endothelial and/or epithelial abnormalities underlying the altered capillary-alveolar permeability in ARDS.