The natural killer gene complex genetic locus Chok encodes Ly-49D, a target recognition receptor that activates natural killing

Previously, we established that natural killer (NK) cells from C57BL/6 (B6), but not BALB/c, mice lysed Chinese hamster ovary (CHO) cells, and we mapped the locus that determines this differential CHO-killing capacity to the NK gene complex on chromosome 6. The localization of Chok in the NK gene complex suggested that it may encode either an activating or an inhibitory receptor. Here, results from a lectin-facilitated lysis assay predicted that Chok is an activating B6 NK receptor. Therefore, we immunized BALB/c mice with NK cells from BALB.B6–Cmv1r congenic mice and generated a mAb, designated 4E4, that blocked B6-mediated CHO lysis. mAb 4E4 also redirected lysis of Daudi targets, indicating its reactivity with an activating NK cell receptor. Furthermore, only the 4E4+ B6 NK cell subset mediated CHO killing, and this lysis was abrogated by preincubation with mAb 4E4. Flow cytometric analysis indicated that mAb 4E4 specifically reacts with Ly-49D but not Ly-49A, B, C, E, G, H, or I transfectants. Finally, gene transfer of Ly-49DB6 into BALB/c NK cells conferred cytotoxic capacity against CHO cells, thus establishing that the Ly-49D receptor is sufficient to activate NK cells to lyse this target. Hence, Ly-49D is the Chok gene product and is a mouse NK cell receptor capable of directly triggering natural killing.

Transcriptional regulation by triiodothyronine of the UDP-glucuronosyltransferase family 1 gene complex in rat liver. Comparison with induction by 3-methylcholanthrene.

This study demonstrates that the expression of the phenol UDP-glucuronosyltransferase 1 gene (UGT1A1) is regulated at the transcriptional level by thyroid hormone in rat liver. Following 3,5, 3'-triiodo-L-thyronine (T3) stimulation in vivo, there is a gradual increase in the amount of UGT1A1 mRNA with maximum levels reached 24 h after treatment. In comparison, induction with the specific inducer, 3-methylcholanthrene (3-MC), results in maximal levels of UGT1A1 mRNA after 8 h of treatment. In primary hepatocyte cultures, the stimulatory effect of both T3 and 3-MC is also observed. This induction is suppressed by the RNA synthesis inhibitor actinomycin D, indicating that neither inducer acts at the level of mRNA stabilization. Indeed, nuclear run-on assays show a 3-fold increase in UGT1A1 transcription after T3 treatment and a 6-fold increase after 3-MC stimulation. This transcriptional induction by T3 is prevented by cycloheximide in primary hepatocyte cultures, while 3-MC stimulation is only partially affected after prolonged treatment with the protein synthesis inhibitor. Together, these data provide evidence for a transcriptional control of UGT1A1 synthesis and indicate that T3 and 3-MC use different activation mechanisms. Stimulation of the UGT1A1 gene by T3 requires de novo protein synthesis, while 3-MC-dependent activation is the result of a direct action of the compound, most likely via the aromatic hydrocarbon receptor complex.

First Staphylococcal Cassette Chromosome mec Containing a mecB-Carrying Gene Complex Independent of Transposon Tn6045 in a Macrococcus caseolyticus Isolate from a Canine Infection.

A methicillin-resistant mecB-positive Macrococcus caseolyticus (strain KM45013) was isolated from the nares of a dog with rhinitis. It contained a novel 39-kb transposon-defective complete mecB-carrying staphylococcal cassette chromosome mec element (SCCmecKM45013). SCCmecKM45013 contained 49 coding sequences (CDSs), was integrated at the 3' end of the chromosomal orfX gene, and was delimited at both ends by imperfect direct repeats functioning as integration site sequences (ISSs). SCCmecKM45013 presented two discontinuous regions of homology (SCCmec coverage of 35%) to the chromosomal and transposon Tn6045-associated SCCmec-like element of M. caseolyticus JCSC7096: (i) the mec gene complex (98.8% identity) and (ii) the ccr-carrying segment (91.8% identity). The mec gene complex, located at the right junction of the cassette, also carried the β-lactamase gene blaZm (mecRm-mecIm-mecB-blaZm). SCCmecKM45013 contained two cassette chromosome recombinase genes, ccrAm2 and ccrBm2, which shared 94.3% and 96.6% DNA identity with those of the SCCmec-like element of JCSC7096 but shared less than 52% DNA identity with the staphylococcal ccrAB and ccrC genes. Three distinct extrachromosomal circularized elements (the entire SCCmecKM45013, ΨSCCmecKM45013 lacking the ccr genes, and SCCKM45013 lacking mecB) flanked by one ISS copy, as well as the chromosomal regions remaining after excision, were detected. An unconventional circularized structure carrying the mecB gene complex was associated with two extensive direct repeat regions, which enclosed two open reading frames (ORFs) (ORF46 and ORF51) flanking the chromosomal mecB-carrying gene complex. This study revealed M. caseolyticus as a potential disease-associated bacterium in dogs and also unveiled an SCCmec element carrying mecB not associated with Tn6045 in the genus Macrococcus.

Expression of the Hox gene complex in the indirect development of a sea urchin

Hox complex genes control spatial patterning mechanisms in the development of arthropod and vertebrate body plans. Hox genes are all expressed during embryogenesis in these groups, which are all directly developing organisms in that embryogenesis leads at once to formation of major elements of the respective adult body plans. In the maximally indirect development of a large variety of invertebrates, the process of embryogenesis leads only to a free-living, bilaterally organized feeding larva. Maximal indirect development is exemplified in sea urchins. The 5-fold radially symmetric adult body plan of the sea urchin is generated long after embryogenesis is complete, by a separate process occurring within imaginal tissues set aside in the larva. The single Hox gene complex of Strongylocentrotus purpuratus contains 10 genes, and expression of eight of these genes was measured by quantitative methods during both embryonic and larval developmental stages and also in adult tissues. Only two of these genes are used significantly during the entire process of embryogenesis per se, although all are copiously expressed during the stages when the adult body plan is forming in the imaginal rudiment. They are also all expressed in various combinations in adult tissues. Thus, development of a microscopic, free-living organism of bilaterian grade, the larva, does not appear to require expression of the Hox gene cluster as such, whereas development of the adult body plan does. These observations reflect on mechanisms by which bilaterian metazoans might have arisen in Precambrian evolution.

Murine Nkg2d and Cd94 are clustered within the natural killer complex and are expressed independently in natural killer cells

Natural killer (NK) cells express C-type lectin-like receptors, encoded in the NK gene complex, that interact with major histocompatibility complex class I and either inhibit or activate functional activity. Human NK cells express heterodimers consisting of CD94 and NKG2 family molecules, whereas murine NK cells express homodimers belonging to the Ly-49 family. The corresponding orthologues for other species, however, have not been described. In this report, we used probes derived from the expressed sequence tag database to clone C57BL/6-derived cDNAs homologous to human NKG2-D and CD94. Among normal tissues, murine NKG2-D and CD94 transcripts are highly expressed only in activated NK cells, including both Ly-49A+ and Ly-49A− subpopulations. Additionally, mNKG2-D is expressed in murine NK cell clones KY-1 and KY-2, whereas mCD94 expression is observed only in KY-1 cells but not KY-2. Last, we have finely mapped the physical location of the Cd94 (centromeric) and Nkg2d (telomeric) genes between Cd69 and the Ly49 cluster in the NK complex. Thus, these data indicate the expanding complexity of the NK complex and the corresponding repertoire of C-type lectin-like receptors on murine NK cells.

Replication of association of IL1 gene complex members with ankylosing spondylitis in Taiwanese Chinese

Objective: To test the association of interleukin 1 ( IL1) gene family members with ankylosing spondylitis ( AS), previously reported in Europid subjects, in an ethnically remote population. Methods: 200 Taiwanese Chinese AS patients and 200 ethnically matched healthy controls were genotyped for five single nucleotide polymorphisms ( SNPs) and the IL1RN. VNTR, markers previously associated with AS. Allele, genotype, and haplotype frequencies were compared between cases and controls. Results: Association of alleles and genotypes of the markers IL1F10.3, IL1RN. 4, and IL1RN. VNTR was observed with AS ( p < 0.05). Haplotypes of pairs of these markers and of the markers IL1RN.6/1 and IL1RN.6/2 were also significantly associated with AS. The strongest associations observed were with the marker IL1RN. 4, and with the two-marker haplotype IL1RN.4-IL1RN.VNTR ( both p = 0.004). Strong linkage disequilibrium was observed between all marker pairs except those involving IL1B-511 ( D' 0.4 to 0.9, p < 0.01). Conclusions: The IL1 gene cluster is associated with AS in Taiwanese Chinese. This finding provides strong statistical support that the previously observed association of this gene cluster with AS is a true positive finding.

From sabotage to camouflage: viral evasion of cytotoxic T lymphocyte and natural killer cell-mediated immunity

The outcome of a virus infection is strongly influenced by interactions between host immune defences and virus 'anti-defence' mechanisms. For many viruses, their continued survival depends on, the speed of their attach: their capacity to replicate and transmit to uninfected hosts prior to their elimination by an effective immune response. In contrast, the success of persistent viruses lies in their capacity for immunological subterfuge: the evasion of host defence mechanisms by either mutation (covered elsewhere in this issue, by Gould and Bangham, pp. 321-328) or interference with the action of host cellular proteins that are important components of the immune response. This review will focus on the strategies employed by persistent viruses against two formidable host defences against virus infection: the CD8+ cytotoxic T lymphocyte (CTL) and natural killer (NK) cell responses.

Function of CMV-encoded MHC class I homologues

Homologues of MHC class I proteins have been identified in the genomes of human, murine and rat cytomegaloviruses (CMVs). Given the pivotal role of the MHC class I protein in cellular immunity, it has been postulated that the viral homologues subvert the normal antiviral immune response of the host, thus promoting virus replication and dissemination in an otherwise hostile environment. This review focuses on recent studies of the CMV MHC class I homologues at the molecular, cellular and whole animal level and presents current hypotheses for their roles in the CMV life cycle.

Inhibition of NK cells by murine CMV-encoded class I MHC homologue m144

Murine cytomegalovirus (CMV)-encoded protein m144 is homologous to class I MHC heavy-chain and is thought to regulate NK-cell-mediated immune responses in vivo. To examine the effects of m144 on Nh cytotoxicity in vitro, various cell lines were transfected with wild-type m144 or a chimeric construct in which the cytoplasmic domain of m144 was replaced with green fluorescence protein. Burkitt lymphoma line Raji expressed a significant level of m144 as determined by anti-m144 mAb binding or the green fluorescence of the fusion protein. The level of m144 expression was relatively low compared with that of transfected murine class I MHC Dd. However, m144 on Raji cells partially inhibited antibody-dependent cell-mediated cytotoxicity of IL-2-activated NK cells. NK cells from the CMV-susceptible BALB/c as well as those from the resistant C57BL/6 mice were inhibited by m144. Antibodies against the known murine NK inhibitory receptors Ly-49A, C, G, and I did not affect the inhibitory effect of m144. These results suggest that the murine CMV class I MHC homologue m144 partially inhibits MZ cells by interacting with a novel inhibitory receptor. (C) 1999 Academic Press.

A Role for the Substance P/NK-1 Receptor Complex in Cell Proliferation in Oral Squamous Cell Carcinoma

Objective: To investigate the presence and distribution of substance P (SP) and neurokinin I receptor (NK-IR) in oral squamous cell carcinoma (OSCC) and their relationship with proliferation. Patients and Methods: Ninety OSCCs from 73 patients were immunohistochemically analyzed using monoclonal antibodies against SP, NK-IR and Ki-67 in a case and control study. Results: Seventy-one percent (n=49) of cases expressed SP on tumour cell membrane, 81.3% (n=69) in cytoplasm, 39.4% (n=28) in nucleus, 81.6% (n=71) in infiltrating lymphocytes, and 58.1% (n=43) in peritumoural or intratumoural blood vessels; 14% (n=12) of cases expressed NK-1R on tumour cell membrane, 50% (n=43) in cytoplasm, 48.3% (n=42) in infiltrating lymphocytes and 22.5% (n=18) in tumour blood vessels. All cases expressed Ki-67, which was expressed in >25% of tumour cells in 79.8% of cases (n=63). Direct significant associations were observed in SP expression between different tissue levels (p<0.01), between SP and NK-IR tumour cell membrane expression (p<0.01), and between joint,SP and NK-IR expression in tumour cell cytoplasm and a higher expression of Ki-67 (p<0.05). Conclusion: The ubiquitous presence of SP strongly suggests a role for SP/NK-1R complex in tumour development and progression and possibly for NK-IR antagonists, such as L-773060, in the management of patients with oral cancer.

The E(NK) model: extending the NK model to incorporate gene-by-environment interactions and epistasis for diploid genomes

The haploid NK model developed by Kauffman can be extended to diploid genomes and to incorporate gene-by-environment interaction effects in combination with epistasis. To provide the flexibility to include a wide range of forms of gene-by-environment interactions, a target population of environment types (TPE) is defined. The TPE consists of a set of E different environment types, each with their own frequency of occurrence. Each environment type conditions a different NK gene network structure or series of gene effects for a given network structure, providing the framework for defining gene-by-environment interactions. Thus, different NK models can be partially or completely nested within the E environment types of a TPE, giving rise to the E(NK) model for a biological system. With this model it is possible to examine how populations of genotypes evolve in context with properties of the environment that influence the contributions of genes to the fitness values of genotypes. We are using the E(NK) model to investigate how both epistasis and gene-by-environment interactions influence the genetic improvement of quantitative traits by plant breeding strategies applied to agricultural systems. © 2002 Wiley Periodicals, Inc.

Dispersal of NK homeobox gene clusters in amphioxus and humans

The Drosophila melanogaster genome has six physically clustered NK-related homeobox genes in just 180 kb. Here we show that the NK homeobox gene cluster was an ancient feature of bilaterian animal genomes, but has been secondarily split in chordate ancestry. The NK homeobox gene clusters of amphioxus and vertebrates are each split and dispersed at two equivalent intergenic positions. From the ancestral NK gene cluster, only the Tlx-Lbx and NK3-NK4 linkages have been retained in chordates. This evolutionary pattern is in marked contrast to the Hox and ParaHox gene clusters, which are compact in amphioxus and vertebrates, but have been disrupted in Drosophila.

Human and murine cytomegalovirus evasion of cytotoxic T lymphocyte and natural killer cell-mediated immune responses

Herpesviruses, such as human and murine cytomegalovirus, possess an impressive array of genes believed to assist in virus survival against the host immune response. In this review, we cover the rapidly growing area of cytomegalovirus evasion of cellular immunity, specifically cytotoxic T lymphocytes and natural killer cells. The proposed mechanisms of action of viral proteins involved in blocking peptide presentation to CD8(+) T cells, namely, interference with peptide generation, inhibition of peptide assembly with class I MHC and retention/destabilization of class I MHC complexes, are described. In addition, recent evidence implicating the viral class I MHC-like proteins as inhibitors of natural killer cell-mediated clearance is reviewed, (C) 1998 Academic Press.

Cytomegalovirus MHC class I homologues and natural killer

Viruses that establish a persistent infection with their host have evolved numerous strategies to evade the immune system. Consequently, they are useful tools to dissect the complex cellular processes that comprise the immune response. Rapid progress has been made in recent years in defining the role of cellular MHC class I molecules in regulating the response of natural killer (NK) cells. Concomitantly, the roles of the MHC class I homologues encoded by human and mouse cytomegaloviruses in evading or subverting NK cell responses has received considerable interest. This review discusses the results from a number of studies that have pursued the biological function of the viral MHC class I homologues. Based on the evidence from these studies, hypotheses for the possible role of these intriguing molecules are presented. (C) 2000 Editions scientifiques et medicales Elsevier SAS.

Inhibition of natural killer cells by a cytomegalovirus MHC class I homologue in vivo

Herpesviruses, such as murine and human cytomegalovirus (MCMV and HCMV), can establish a persistent infection within the host and have diverse mechanisms as protection from host immune defences'. Several herpesvirus genes that are homologous to host immune modulators have been identified, and are implicated in viral evasion of the host immune response(2,3). The discovery of a viral major histocompatibility complex (MHC) class I homologue, encoded by HCMV(4), led to speculation that it might function as an immune modulator and disrupt presentation of peptides by MHC class I to cytotoxic T cells(5). However, there is no evidence concerning the biological significance of this gene during viral infection. Recent analysis of the MCMV genome has also demonstrated the presence of a MHC class I homologue(6). Here we show that a recombinant MCMV,in which. the gene encoding the class I homologue has been disrupted, has severely restricted replication during the acute stage of infection compared with wild-type MCMV, We demonstrate by in vivo depletion studies that natural killer (NK) cells are responsible for the attenuated phenotype of the mutant. Thus the viral MHC dass I homologue contributes to immune evasion through interference with NK cell-mediated clearance.