Genomic structure of NKG5, a human NK and T cell-specific activation gene

A NK-lysin from Cynoglossus semilaevis enhances antimicrobial defense against bacterial and viral pathogens

NK-lysin is an effector protein of cytotoxic T lymphocytes and natural killer cells. Mammalian NK-lysin is known to possess antibacterial property and antitumor activity. Homologues of NK-lysin have been identified in several teleost species, but the natural function of fish NK-lysin remains essentially unknown. In this study, we identified a NK-lysin, CsNKL1, from half-smooth tongue sole (Cynoglossus semilaevis) and analyzed its expression, genetic organization, and biological effect on pathogen infection. CsNKL1 is composed of 135 residues and shares 33.1-56.5% overall sequence identities with other teleost NK-lysin. CsNKL1 possesses a Saposin B domain and six conserved cysteine residues that in mammals are known to form three intrachain disulfide bonds essential to antimicrobial activity. The genomic sequence of the ORF region of CsNKL1 is 1240bp in length and, like human NK-lysin, contains five exons and four introns. Expression of CsNKL1 occurred in multiple tissues and was upregulated by bacterial and viral infection in a time dependent manner. When CsNKL1 was overexpressed in tongue sole, significant upregulation of interleukin-1 and chemokines was observed in spleen and head kidney. Following bacterial and viral infection, the pathogen loads in the tissues of CsNKL1-overexpressing fish were significantly lower than those in control fish. These results indicate that CsNKL1 possesses the novel capacities of immunomodulation and enhancing antimicrobial defense against pathogens of both bacterial and viral nature.

Interleukin-21 and cellular activation concurrently induce potent cytotoxic function and promote antiviral activity in human CD8 T cells

Infection with human immunodeficiency virus (HIV)-1 induces a progressive deterioration of the immune system that ultimately leads to acquired immune deficiency syndrome (AIDS). Murine models indicate that the common γ-chain (γ(c))-sharing cytokine interleukin (IL)-21 and its receptor (IL-21R) play a crucial role in maintaining polyfunctional T cell responses during chronic viral infections. Therefore, we analyzed the ability of this cytokine to modulate the properties of human CD8 T cells in comparison with other γ(c)-sharing cytokines (IL-2, IL-7, and IL-15). CD8 T cells from healthy volunteers were stimulated in vitro via T cell receptor signals to mimic the heightened status of immune activation of HIV-infected patients. The administration of IL-21 upregulated cytotoxic effector function and the expression of the costimulatory molecule CD28. Notably, this outcome was not accompanied by increased cellular proliferation or activation. Moreover, IL-21 promoted antiviral activity while not inducing HIV-1 replication in vitro. Thus, IL-21 may be a favorable molecule for immunotherapy and a suitable vaccine adjuvant in HIV-infected individuals.

Induction of granulysin in CD8+ T cells by IL-21 and IL-15 is suppressed by human immunodeficiency virus-1

Immunosuppression following infection with HIV-1 predisposes patients to a myriad of opportunistic pathogens, one of the most important of which is Mtb. Granulysin, expressed by NK cells and CTL, exhibits potent antimicrobial activity against Mtb and several other opportunistic pathogens associated with HIV-1 infection. The immune signals that promote granulysin expression in human CTL are not fully understood. Using primary human CD8+ T cells, in this study, we identify IL-21 as a strong inducer of granulysin, demonstrate that IL-21 and IL-15 activate granulysin expression within CD8+ CD45RO+ T cells, and establish a role for Jak/STAT signaling in the regulation of granulysin within CD8+ T cells. We show that infection of PBMC from healthy donors in vitro with HIV-1 suppresses granulysin expression by CD8+ T cells, concomitant with reduced p-STAT3 and p-STAT5, following activation with IL-15 and IL-21. Of note, simultaneous signaling through IL-15 and IL-21 could partially overcome the immunosuppressive effects of HIV-1 on granulysin expression by CD8+ T cells. These results suggest that HIV-1 infection of PBMC may reduce the antimicrobial profile of activated CD8+ T cells by disrupting signaling events that are critical for the induction of granulysin. Understanding the effects of HIV-1 on CD8+ T cell activation is essential to understanding the physiological basis for inadequate cytotoxic lymphocyte activity in HIV+ patients and for informed guidance of cytokine-based therapy to restore T cell function.

Comparative antimicrobial activity of granulysin against bacterial biothreat agents

Granulysin is a cationic protein produced by human T cells and natural killer cells that can kill bacterial pathogens through disruption of microbial membrane integrity. Herein we demonstrate antimicrobial activity of the granulysin peptide derived from the active site against Bacillus anthracis, Yersinia pestis, Francisella tularensis, and Burkholderia mallei, and show pathogen-specific differences in granulysin peptide effects. The susceptibility of Y. pestis to granulysin is temperature dependent, being less susceptible when grown at the flea arthropod vector temperature (26°C) than when grown at human body temperature. These studies suggest that augmentation of granulysin expression by cytotoxic lymphocytes, or therapeutic application of granulysin peptides, could constitute important strategies for protection against select agent bacterial pathogens. Investigations of the microbial surface molecules that determine susceptibility to granulysin may identify important mechanisms that contribute to pathogenesis.

NK-lysin of channel catfish: Gene triplication, sequence variation, and expression analysis

Antimicrobial peptides (AMPs) are important components of the host innate immune response against microbial invasion. In addition to the previously known four classes of antimicrobial peptides, a fifth class of antimicrobial peptides has been recently identified to include NK-lysins that have a globular three-dimensional structure and are larger with 74-78 amino acid residues. NK-lysin has been shown to harbor antimicrobial activities against a wide spectrum of microorganisms including bacteria, fungi, protozoa, and parasites. To date, NK-lysin genes have been reported from only a limited number of organisms. We previously identified a NK-lysin cDNA in channel catfish. Here we report the identification of two novel types of NK-lysin transcripts in channel catfish. Altogether, three distinct NK-lysin transcripts exist in channel catfish. In this work, their encoding genes were identified, sequenced, and characterized. We provide strong evidence that the catfish NK-lysin gene is tripled in the same genomic neighborhood. All three catfish NK-lysin genes are present in the same genomic region and are tightly linked on the same chromosome, as the same BAC clones harbor all three copies of the NK-lysin genes. All three NK-lysin genes are expressed, but exhibit distinct expression profiles in various tissues. In spite of the existence of a single copy of NK-lysin gene in the human genome, and only a single hit from the pufferfish genome, there are two tripled clusters of NK-lysin genes on chromosome 17 of zebrafish in addition to one more copy on its chromosome 5. The similarity in the genomic arrangement of the tripled NK-lysin genes in channel catfish and zebrafish suggest similar evolution of NK-lysin genes.

[Granulysin: antimicrobial molecule of innate and acquired immunity in human tuberculosis]

The recent global increase in cases of tuberculosis and the emergence of multidrug-resistant strains of tuberculosis have focused attention on the molecular mechanisms of human antimycobacterial immunity. The macrophage is not only the primary site for Mycobacterium tuberculosis growth but also ordinarily provides the primary lines of host defense against invading pathogens in its role as an effector of innate immunity. The ability of M. tuberculosis to survive and replicate in the host macrophage is critical to its pathogenesis, emphasizing a need for a clearer understanding of its interactions with the host macrophage. Macrophages use varied strategies to kill and destroy invading organisms, including production of reactive nitrogen and oxygen intermediates, phagosome maturation and acidification, fusion with lysosomes, exposure to defensins and host cell apoptosis. In human, granulysin is a recently identified antimicrobial protein expressed on cytotoxic T cells, natural killer (NK) cells and NKT cells. It has been shown that granulysin contributes to the defense mechanisms against mycobacterial infection. We hypothesized that human macrophages may possess antimicrobial substances, such as granulysin, and play a role in the defense mechanism.

Opposing roles of activator protein-1 and CCAAT/enhancer binding protein beta in the regulation of inducible granulysin gene expression in a human monocytic cell line, THP-1

We previously reported that inducible granulysin gene expression in a human monocytic cell line, THP-1 is dominantly dependent on transcription factor activator protein-1 (AP-1). Here, we further examined the precise regulatory mechanisms underlying granulysin gene expression using THP-1 cells treated with Acholeplasma laidlawii. Transfection of reporter gene constructs into THP-1 cells indicated that the presence of a positive regulatory element(s) is located from -329 to -85 base pairs, containing two distinct AP-1 binding sites and one nuclear factor-kappaB (NF-kappaB) binding site. Deletion or mutation of the NF-kappaB binding site failed to affect inducible promoter activity, whereas deletion or mutation of both the AP-1 binding sites abrogated the promoter activity. Interestingly, deletion of the putative CCAAT/enhancer binding protein beta (C/EBPbeta) binding site upstream of the positive regulatory element induced the augmentation of granulysin promoter activity. Electrophoretic mobility shift assays demonstrated that nuclear extract prepared from A. laidlawii-treated THP-1 cells generated a specific binding to oligonucleotides, including AP-1, C/EBPbeta, and NF-kappaB element. Furthermore, over-expression of liver-enriched transcriptional activator protein, a subunit of C/EBPbeta, augmented A. laidlawii-induced granulysin promoter activity, whereas over-expression of liver-enriched transcriptional inhibitory protein inhibited the promoter activity. NF-kappaB p50 homodimer had no transactivation property, although it bound to the NF-kappaB site. These results indicate that AP-1 and C/EBPbeta, but not NF-kappaB participate in the regulation of inducible granulysin gene expression in THP-1 cells. Moreover, the Toll-like receptor 2-dependent signalling pathway may be involved in A. laidlawii-induced transactivation of the granulysin promoter. Thus, these results suggest that the gene expression of granulysin in macrophages would be exquisitely regulated by positive and negative transcription factors when microbial invasion occurs.

Adenovirus vector-mediated transfer of 9 kDa granulysin induces DNA fragmentation in HuD antigen-expressing small cell lung cancer murine model cells

OBJECTIVE

Granulysin is a tumoricidal molecule secreted by cytotoxic T cells (CTL) and natural killer (NK) cells, that induces apoptotic cell death in tumour cells. It has been demonstrated that small cell lung cancer (SCLC) cell lines are susceptible to NK cells and lymphokine activated killer (LAK) cells, and HuD antigen is assumed to be a target molecule on SCLC cells for host cellular immunity.

METHODOLOGY

In order to understand the mechanism of sensitivity of SCLC to cellular immunity, we evaluated granulysin-induced apoptosis using mouse adenocarcinoma Colon 26 (Colon 26/HuD) cells transfected with the 9 kDa active form of granulysin using an adenovirus vector as a murine model of SCLC cells.

RESULTS

Adenovirus vector-mediated transfer of 9 kDa granulysin increased DNA fragmentation in Colon 26/HuD cells 2.5-fold and suppressed Colon 26/HuD proliferation by 21% on day 3 (P < 0.05 for each value) compared with the control adenovirus vector transfer. In contrast, adenovirus vector-mediated transfer of 9 kDa granulysin did not increase DNA fragmentation nor suppress the proliferation of Colon 26 parent cells.

CONCLUSIONS

The sensitivity of HuD-expressing tumour cells to granulysin is likely to partially explain the susceptibility of SCLC to cell-mediated immunity.

Acholeplasma laidlawii up-regulates granulysin gene expression via transcription factor activator protein-1 in a human monocytic cell line, THP-1

An antimicrobial protein granulysin is constitutively expressed in cytotoxic T lymphocytes (CTL) and natural killer (NK) cells. However, little is known about the precise regulatory mechanisms underlying granulysin gene expression. In this study, we examined the regulatory mechanisms underlying granulysin gene expression using a human monocytic cell line, THP-1, treated with Acholeplasma laidlawii. The level of granulysin mRNA expression in THP-1 cells was significantly augmented in response to stimulation with A. laidlawii. The transfection of reporter gene constructs into THP-1 cells indicated that DNA sequences between residues -329 and -239, relative to the transcriptional start site of the granulysin gene, are responsible for mediating gene induction. In addition, mutagenesis of a putative activator protein-1 (AP-1)-binding site between residues -277 and -271 in the granulysin promoter resulted in the reduction of granulysin promoter activity. Electrophoretic mobility shift assays (EMSA) demonstrated that nuclear extract prepared from A. laidlawii-treated THP-1 cells can generate specific binding to DNA oligonucleotides encompassing the AP-1-binding site, whereas unstimulated nuclear extract from the cells failed to do so. Furthermore, competition and supershift assays confirmed that A. laidlawii can induce the activation of AP-1. These results indicate that AP-1 dominantly participates in the regulation of inducible granulysin gene expression in THP-1 cells. Therefore, the finding of inducible granulysin gene expression by A. laidlawii suggests that inducible granulysin in macrophages may function as a protective weapon when microbial invasion occurs.

MER53, a non-autonomous DNA transposon associated with a variety of functionally related defense genes in the human genome

We report a new medium reiteration frequency repeat MER53 present in human and mammalian genomes. A 189 bp MER53 consensus sequence has been reconstructed based on the computer analysis of GenBank sequences. TA target site duplication and terminal inverted repeats indicate that the MER53 repeat is a non-autonomous DNA transposon related to the mariner family. Two MER53 repeats were found integrated within different mobile elements. We have found that most of the genes harboring the MER53 repeat are involved in the host defense system. The reasons for this non-random distribution of the repeat are discussed.

An expressed sequence tag database of T-cell-enriched activated chicken splenocytes: sequence analysis of 5251 clones

The cDNA and gene sequences of many mammalian cytokines and their receptors are known. However, corresponding information on avian cytokines is limited due to the lack of cross-species activity at the functional level or strong homology at the molecular level. To improve the efficiency of identifying cytokines and novel chicken genes, a directionally cloned cDNA library from T-cell-enriched activated chicken splenocytes was constructed, and the partial sequence of 5251 clones was obtained. Sequence clustering indicates that 2357 (42%) of the clones are present as a single copy, and 2961 are distinct clones, demonstrating the high level of complexity of this library. Comparisons of the sequence data with known DNA sequences in GenBank indicate that approximately 25% of the clones match known chicken genes, 39% have similarity to known genes in other species, and 11% had no match to any sequence in the database. Several previously uncharacterized chicken cytokines and their receptors were present in our library. This collection provides a useful database for cataloging genes expressed in T cells and a valuable resource for future investigations of gene expression in avian immunology. A chicken EST Web site (http://udgenome. ags.udel. edu/chickest/chick.htm) has been created to provide access to the data, and a set of unique sequences has been deposited with GenBank (Accession Nos. AI979741-AI982511). Our new Web site (http://www. chickest.udel.edu) will be active as of March 3, 2000, and will also provide keyword-searching capabilities for BLASTX and BLASTN hits of all our clones.

Novel hyperactive mitogen to endothelial cells: human decidual NKG5

PROBLEM

The purpose of this study was the isolation and characterization of decidual extract proteins that exhibit mitogenicity on endothelial cells.

METHOD OF STUDY

A partially purified extract (F1 fraction) was obtained from human decidua of the first trimester of pregnancy. F1 was separated by heparin-sepharose column and showed significant mitogenicity on bovine brain capillary endothelial (BBCE) cells in vitro, using methylene blue stain nuclear assay. Sodium-dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) revealed four fractions with MW less than 30 KDa.

RESULTS

Mitogenic fraction, E11-12 (eluted at 1.5 M NaCl) was identified as basic fibroblast growth factor (bFGF). Vascular endothelial growth factor (VEGF) and acidic (a)FGF were not identified as one of the mitogenic fractions. However, fractions E5-6, and E7-8 induced statistically significant mitogenicity at concentration of 1 pg/mL, which is 10(3) times lower than bFGF. Sequencing of E5-6 fraction identified NKG5 protein, a putative secreted polypeptide derived from human natural killer (NK) cells and activated T cells of unknown function.

CONCLUSION

This work demonstrates that NKG5 stimulates mitogenicity of endothelial cells and may be involved in angiogenesis.

Amoebapore homologs of Caenorhabditis elegans

It is shown that the Caenorhabditis elegans genome contains several distantly related members of the gene family of saposin-like proteins. The putative products of genes T07C4.4, T08A9.7A, T08A9.7B, T08A9.8, T08A9.9, T08A9.10 are similar to the amoebapores of Entamoeba histolytica, granulysin of cytotoxic T lymphocytes and a putative amoebapore-related protein of the liver fluke Fasciola hepatica inasmuch as they consist of only a single saposin-like domain and a secretory signal peptide. The saposin-like domain of protein T07C4.4, which is most closely related to NK-lysin and granulysin, has been expressed in Escherichia coli and the recombinant protein was shown to have a circular dichroism spectrum consistent with the helix bundle structure characteristic of saposin-like domains. Recombinant T07C4.4 protein was found to have antibacterial activity, suggesting that these amoebapore homologs may play a role in antibacterial mechanisms of C. elegans.

Cytokine-induced cytotoxic function expressed by lymphocytes of the innate immune system: distinguishing characteristics of NK and LAK based on functional and molecular markers

Several molecular events are now identifiable during the activation, recognition, and killing by natural killer (NK) cells that are distinct from those differentiated in response to cytokines during the generation of lymphokine-activated killer (LAK) cells or during lymphocyte proliferation. Because LAK and MHC-unrestricted killing activities also include the prototypic NK targets as part of their broad recognition spectra, accurate identification of the complete function being studied is critical. In many publications, past and present, only NK-sensitive target cells were used (K562, Molt-4, others), and, therefore, the results do not necessarily indicate whether the effectors are NK or have differentiated into LAK cells. Such a consideration becomes critical when the effectors are grown in interleukin-2 (IL-2), and an attempt is made to define receptor recognition, signal transduction pathways, and specificity at the molecular level. In some instances, effector cells are likely to have stopped, therefore merely expressing NK activity, and have also acquired LAK function. The identified receptors may not have been unique to NK cells or NK function. Not until the targets employed are also confirmed to be NK sensitive, and the effectors do not kill NK-resistant targets can the results of molecular studies be proposed to represent aspects unique to NK. Reports of the use of IL-2-expanded NK clones are most likely providing data concerning the biology of LAK and not of classic NK. The classic NK activity surveying our blood apparently performs an important function, including the ability to respond rapidly to certain cytokines and to acquire additional functions and receptors for use in destroying a vast array of target cells. It is critical for scientists to appreciate the functional distinctions and to identify the molecules and pathways unique to each of these curious cytolytic systems.

Animal membrane receptors and adhesive molecules

This review summarizes some important data, principles, opinions, commentaries, and modern methodology concerning the receptor structure, interactions, signaling and receptor-mediated cell functions. Three sections give a brief overview of the signaling synergy, multivariant signaling, and some reactions in phosphorylation networks. A concise report about the cytotoxic reaction of NK cells represents an example of multistage recognition reaction, involving differently acting receptors, changes in affinities of cell-cell interactions, and secretion of regulatory and cytotoxic molecules. Some interesting trends in receptor engineering, including antibody molecules as a special receptor phenomenon are mentioned in the final section.

Cloning and characterization of a novel NK cell-specific serine protease gene and its functional 5'-flanking sequences

Rat natural killer cell Met-ase-1 (RNK-Met-1) is a 30,000 M(r) serine protease (granzyme) found in the cytolytic granules of CD3- large granular lymphocytes (LGL) with natural killer (NK) activity. To characterize the genomic sequences responsible for the CD3- LGL-restricted expression of this gene, we screened a rat genomic library with RNK-Met-1 cDNA, and obtained bacteriophage clones that contained the RNK-Met-1 gene. The RNK-Met-1 gene comprises 5 exons and spans approximately 5.2 kilobases (kb), exhibiting a similar structural organization to a class of CTL-serine proteases with protease catalytic residues encoded near the borders of exons 2, 3, and 5. The 5'-flanking region of the RNK-Met-1 gene contains a number of putative promoter and enhancer regulatory elements and shares several regions of homology with the 5'-flanking region of the mouse perforin gene. We have prepared nested deletions from approximately 3.3 kb of the 5'-flanking region of the RNK-Met-1 gene, and inserted these upstream of the chloramphenicol acetyltransferase (CAT) reporter gene. These 5'-flanking RNK-Met-1-CAT constructs were transiently transfected into rat LGL leukemia, T-lymphoma, and basophilic leukemia cell lines. The transcriptional activity of the RNK-Met-1 5'-flanking region was strong, restricted to the RNK-16 LGL leukemia and controlled by several positive cis-acting regions spread over at least 3.3 kb. The longest and most active 5'-flanking region (-3341 to -33) was also used to drive specific expression of beta-galactosidase in RNK-16. These data are consistent with the NK cell-specific expression of RNK-Met-1 and suggest the potential utility of this gene promoter in the development of transgene models of NK cell biology in vivo.