Lytic Expression Research Articles

Perforin and granzyme B lytic protein expression during chronic viral and autoimmune hepatitis.

Cytotoxic T lymphocytes and Kupffer cells are essential components of the immune response during liver diseases. Recent studies have highlighted the role of cytotoxic T lymphocytes using Fas and its ligand in induced hepatocyte death during acute and chronic hepatitis. In the present work, the main purpose was to investigate perforin and granzyme B expression in liver biopsies of patients with chronic hepatitis (10 HBV, 14 HCV and 10 autoimmune hepatitis) using immunohistochemistry. The liver biopsies of two normal individuals were also studied in the same conditions. Few intrahepatic T lymphocytes expressed perforin and granzyme B, while a large number of Kupffer cells were positive for both proteins in all the patients tested. The co-localization of perforin and granzyme B, and CD3 or CD68 antigens was visualized, respectively, in T cells and Kupffer cells, using confocal microscopy. In situ hybridization assays confirmed that perforin and granzyme B mRNAs were present in the liver during chronic hepatitis. The results were similar among the three groups of patients and whatever the activity of the disease. Perforin and granzyme B expression was lacking in liver samples from normal individuals. These data suggest a minor role for the T cell-mediated perforin/granzyme B death pathway, and a putative role for Kuppfer cells via lytic protein release, during chronic hepatitis.

A viral gene that activates lytic cycle expression of Kaposi's sarcoma-associated herpesvirus.

Herpesviruses exist in two states, latency and a lytic productive cycle. Here we identify an immediate-early gene encoded by Kaposi's sarcoma-associated herpesvirus (KSHV)/human herpesvirus eight (HHV8) that activates lytic cycle gene expression from the latent viral genome. The gene is a homologue of Rta, a transcriptional activator encoded by Epstein-Barr virus (EBV). KSHV/Rta activated KSHV early lytic genes, including virus-encoded interleukin 6 and polyadenylated nuclear RNA, and a late gene, small viral capsid antigen. In cells dually infected with Epstein-Barr virus and KSHV, each Rta activated only autologous lytic cycle genes. Expression of viral cytokines under control of the KSHV/Rta gene is likely to contribute to the pathogenesis of KSHV-associated diseases.

Alteration of a single serine in the basic domain of the Epstein-Barr virus ZEBRA protein separates its functions of transcriptional activation and disruption of latency.

The ZEBRA protein from Epstein-Barr virus (EBV) activates a switch from the latent to the lytic expression program of the virus. ZEBRA, a member of the bZIP family of DNA-binding proteins, is a transcriptional activator capable of inducing expression from viral lytic cycle promoters. It had previously been thought that ZEBRA's capacity to disrupt EBV latency resided primarily in its ability to activate transcription of genes that encode products required for lytic replication. We generated a point mutant of ZEBRA, Z(S186A), that was not impaired in its ability to activate transcription; however, this mutation abolished its ability to initiate the viral lytic cascade. The mutant, containing a serine-to-alanine substitution in the DNA-binding domain of the protein, bound to several known ZEBRA-binding sites and activated transcription from reporters bearing known ZEBRA-responsive promoters but did not disrupt latency in EBV-infected cell lines. Therefore, initiation of the EBV lytic cycle by the ZEBRA protein requires a function in addition to transcriptional activation; a change of serine 186 to alanine in the DNA-binding domain of ZEBRA abolished this additional function and uncovered a new role for the ZEBRA protein in disruption of EBV latency. The additional function that is required for initiation of the lytic viral life cycle is likely to require phosphorylation of serine 186 of the ZEBRA protein, which may influence either DNA recognition or transcriptional activation of lytic viral promoters in a chromatinized viral episome.

Synergistic interactions between overlapping binding sites for the serum response factor and ELK-1 proteins mediate both basal enhancement and phorbol ester responsiveness of primate cytomegalovirus major immediate-early promoters in monocyte and T-lymphocyte cell types.

Cytomegalovirus (CMV) infection is nonpermissive or persistent in many lymphoid and myeloid cell types but can be activated in differentiated macrophages. We have shown elsewhere that both the major immediate-early gene (MIE) and lytic cycle infectious progeny virus expression can be induced in otherwise nonpermissive monocyte-like U-937 cell cultures infected with either human CMV (HCMV) or simian CMV (SCMV) by treatment with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). Two multicopy basal enhancer motifs within the SCMV MIE enhancer, namely, 11 copies of the 16-bp cyclic AMP response element (CRE) and 3 copies of novel 17-bp serum response factor (SRF) binding sites referred to as the SNE (SRF/NFkappaB-like element), as well as four classical NFkappaB sites within the HCMV version, contribute to TPA responsiveness in transient assays in monocyte and T-cell types. The SCMV SNE sites contain potential overlapping core recognition binding motifs for SRF, Rel/NFkappaB, ETS, and YY1 class transcription factors but fail to respond to either serum or tumor necrosis factor alpha. Therefore, to evaluate the mechanism of TPA responsiveness of the SNE motifs and of a related 16-bp SEE (SRF/ETS element) motif found in the HCMV and chimpanzee CMV MIE enhancers, we have examined the functional responses and protein binding properties of multimerized wild-type and mutant elements added upstream to the SCMV MIE or simian virus 40 minimal promoter regions in the U-937, K-562, HL-60, THP-1, and Jurkat cell lines. Unlike classical NFkappaB sites, neither the SNE nor the SEE motif responded to phosphatase inhibition by okadaic acid. However, the TPA responsiveness of both CMV elements proved to involve synergistic interactions between the core SRF binding site (CCATATATGG) and the adjacent inverted ETS binding motifs (TTCC), which correlated directly with formation of a bound tripartite complex containing both the cellular SRF and ELK-1 proteins. This protein complex was more abundant in U-937, K-562, and HeLa cell extracts than in Raji, HF, BALB/c 3T3, or HL-60 cells, but the binding activity was altered only twofold after TPA treatment. A 40-fold stimulation of chloramphenicol acetyltransferase activity mediated by four tandem repeats of the SNE could be induced within 2 h (and up to 250-fold within 6 h) after addition of TPA in DNA-transfected U-937 cells, indicating that the stimulation appeared likely to be a true protein kinase C-mediated signal transduction event rather than a differentiation response. Slight differences in the sequence of the core SRF binding site compared with that of the classical c-Fos promoter serum response element, together with differences in the spacing between the SRF and ETS motifs, appear to account for the inability of the SCMV SNEs to respond to serum induction.

Regulation of the Fas lytic pathway in cloned CTL.

Cloned murine CTL activated via the TCR or by PMA and ionomycin up-regulate surface Fas ligand and show an increased ability to kill non-Ag-specific Fas+ target cells. This up-regulation starts after 45 to 60 min and has a t1/2 for reversal of about 90 min. Up-regulation of lytic function is accompanied by up-regulation of Fas ligand on the CTL surface, which can be blocked by protein synthesis inhibitors. When up-regulation of Fas lytic function was induced by PMA and ionomycin, EGTA blocked both activation of lytic function and expression of Fas ligand detected by FACS analysis. However, when up-regulation was induced by specific Ag, EGTA blocked activation of lytic function, but not up-regulation of Fas ligand. Moreover, EL-4 cells have very high levels of surface Fas ligand, although they are not cytotoxic. Thus, expression of surface Fas ligand may be required, but not sufficient, for Fas-mediated lysis.

Emission quantum efficiency and heating effects in YAG:Nd<sup>3+</sup> lasers

The intrinsic limitations of emission quantum efficiency of Nd 31 in YAG that lead to heating of active element are analyzed. The main factors characteristic of the system of active ions that lead to heat are the quantum defect and the emission quenching due to energy trans- fer by cross-relaxation and multisite structure (especially for laser or di- ode pumping). It is shown that for concentrations of interest for lasers, the reduction of emission quantum efficiency by energy transfer is due to two types of interactions between active ions. The high-resolution data are used to explain the global behavior of metastable level emission kinetics and the concentration reduction of quantum efficiency. An ana- lytic expression for the fractional thermal load is obtained, imposing a lower limit at each concentration. The estimated values of emission quantum efficiency and fractional load are in agreement with reported measured values. © 1996 Society of Photo-Optical Instrumentation Engineers. Subject terms: laser crystals; YAG:Nd; emission quantum efficiency; heating effects.

The lytic transition of Epstein-Barr virus is imitated by recombinant B-cells.

Lytic transition of Epstein-Barr virus (EBV) is initiated by distinct immediate early regulators of the viral cycle, in synchronization to temporary, permissive conditions during host cell differentiation. We developed eukaryotic vectors suitable to imitate the processes involved in lytic transition in cell culture systems. Two stable B cell lines were established: R59Z activator cells were used to induce lytic EBV expression in a constitutive manner by the production of the BZLF 1 trans-activator (Zta). R7-57 reporter cells, on the other hand, signaled induced activity of the lytic origin of EBV replication (ori Lyt). Different modes, like chemical induction, lytic superinfection with EBV and single gene trans-activation converted the recombinant ori Lyt element in R7-57 reporter cells. BZLF 1, transiently expressed in R7-57 reporter cells, was the only EBV trans-activator found, sufficient in inducing the viral lytic cycle. Basing on these experiments, trans-cellular activation of EBV was tested by cocultivation of BZLF 1-expressing R59Z activator cells with the R7-57 reporter line. No lytic effect on the reporter cells could be measured, neither by cocultivation of activator cells nor by coincubation of BZLF 1-containing cell lysates. Latency breaking activity, however, was transferred from activator to reporter cells when active, exogenous virus was added. The cell system described in these experiments provides a tool for the detection of EBV reactivation and demonstrates the potential of the lytic regulatory gene BZLF 1.

Hematopoietic origin of human natural killer (NK) cells: generation from immature progenitors.

Human natural killer (NK) cells originate from bone marrow, but little is known about NK cell progenitors and ontogeny. We studied the phenotype and functional activity of NK cells derived from highly purified human bone marrow CD34+ cells, which exhibited neither lytic activity nor expression of surface antigens characteristic of NK (CD56) or T (CD3) cells. However, when cultured with hematopoietic growth factors or feeder layers for up to 4 weeks, up to 86% functional CD56+ cells were seen in the absence of mature T cell development. CD56+ cells appeared in all cultures at 2 or 3 weeks, with the largest percentage in those exposed to IL-2. These studies demonstrated that NK cells arise 'in vitro' from immature bone marrow progenitors and also suggest a separate origin and differentiation pathway for NK and T cells.

Use of second-site homologous recombination to demonstrate that Epstein-Barr virus nuclear protein 3B is not important for lymphocyte infection or growth transformation in vitro.

Recombinant Epstein-Barr viruses with a stop codon inserted into the nuclear protein 3B (EBNA 3B) open reading frame were generated by second-site homologous recombination. These mutant viruses infected and growth transformed primary B lymphocytes, resulting in the establishment of lymphoblastoid cell lines (LCLs). Polymerase chain reaction analysis and Southern hybridizations with infected cell DNA demonstrated the presence of the mutant EBNA 3B and the absence of wild-type EBNA 3B. Immunoblot analysis of the LCLs with affinity-purified EBNA 3B antibodies confirmed the absence of EBNA 3B cross-reactive protein. Virus was reactivated from two of these infected LCLs and serially passaged through primary B lymphocytes. The newly infected cells contained only the mutant recombinant virus. No difference was noted between mutant and wild-type recombinants, derived in parallel, in latent (other than EBNA 3B) or lytic cycle-infected cell virus protein expression or in the growth of the latently infected transformed cell lines. These data indicate that the EBNA 3B protein is not critical for primary B-lymphocyte infection, growth transformation, or lytic virus infection in vitro.

Regulation of the Epstein-Barr virus DNA polymerase gene.

The gene (pol) encoding the Epstein-Barr virus (EBV) DNA polymerase is a member of the "early" class of viral genes which are expressed shortly after activation of latent virus infection. First, mRNA from the EBV-producing cell line, B95-8, treated with 12-O-tetradecanoylphorbol-13-acetate and sodium butyrate to induce lytic replication and expression of this gene was analyzed. Northern (RNA) analysis revealed a message of 3.7 kb found only in induced cells. 5' mapping of pol mRNA by S1 nuclease and primer extension analyses indicates that transcription initiates at tightly clustered sites within a G + C-rich region 126 bp upstream of the open reading frame. The same initiation region was identified in two other EBV-infected cell lines, P3HR1 and Raji, after induction. Second, a 1.29-kb genomic fragment containing this region, when cloned upstream of the chloramphenicol acetyltransferase reporter gene, demonstrated promoter activity in lymphoid cells cotransfected with pEBV-RZ, a genomic expression construct that includes genes for the EBV immediate-early transactivator proteins, BZLF-1 and BRLF-1. Within the upstream 1.29-kb sequence, two regions of 140 bp and 101 bp appear to be needed for promoter activity. These results demonstrate that unlike most EBV genes studied thus far, the pol gene contains multiple transcriptional start sites. The upstream regulatory region of the promoter for the pol gene does not contain canonical promoter elements such as TATA and CAAT boxes and, furthermore, is not constitutively active but requires transactivation by two or more viral proteins.

Cell phenotype (CD23)-dependent variation in EBV genome copy numbers within lymphoblastoid cell lines (LCL).

Three Epstein-Barr-virus-transformed lymphoblastoid cell lines (LCL) were analysed on the basis of their CD23 expression. Levels of EBV-DNA were compared in the positive and negative subpopulations. Two lines were further analysed with regard to EBNA, cytoplasmic immunoglobulin (cIg) and lytic (EA/VCA) protein expression. Both subpopulations had a similar MHC class-II transcription, but the CD23- subpopulation had a lower plating efficiency and a lower rate of DNA synthesis. In the B6, NAD50 and 0467.3 cell lines, CD23- cells contained 2 +/- 0.2 - 6.4 +/- 3.0 times less EBV DNA than the corresponding CD23+ population. EBNA was expressed in 81 +/- 4.2% - 93 +/- 3.8% of the CD23+ cells and in 0 - 46 +/- 8.0% of the CD23- cells. No CD23+ cells in B6 or NAD50 contained any EA/VCA, while 19 +/- 2.8% - 24 +/- 4.2% of the CD23- cells were positive for the lytic-cycle-associated antigens. Of the CD23- cells, 70 +/- 8.6% - 86 +/- 6.0% were positive for cytoplasmic immunoglobulin compared to 14.7 +/- 2.7% - 14.9 +/- 1.8% in the corresponding CD23+ population. We have previously shown that only 18% of the cIg-positive cells were EBNA-positive in the B6 line compared to 94% in the cIg- population. This was open to 2 alternative interpretations: loss of EBV genomes from a fraction of the cells with subsequent differentiation to secretory immunoglobulin production, or down-regulation of EBNA expression in differentiating, EBV-genome-positive cells. Our present findings speak for the first alternative, indicating that a certain proportion of the cells may lose their EBV genomes in both long-established and freshly transformed LCLs. This is accompanied by a reduced percentage of EBNA-positive cells, the disappearance of at least one activation marker (CD23) associated with the virally induced blast transformation, and an increased synthesis of cIg.

Expression of heterologous sequences in adenoviral vectors.

Adenoviruses (Ad) have served as outstanding agents in contributing to an understanding of transformation and regulation of gene expression in cultured cells (reviewed in Tooze 1981; Doerfler 1983, 1984; Ginsberg 1984). Three decades after their original isolation (Rowe et al. 1953) 41 serotypes of Ad which cause infections in over a dozen species have been identified. Initial classification was based on immunological criteria and on turmorigenicity in immunocompetent rodents, which ranges from highly oncogenic (e.g., Ad 12) to generally nononcogenic (e.g., Ad2 and Ad5). More recently DNA homology has also been included as a criterion. Because they provided the first example of a human virus capable of inducing tumors in experimental animals and because Ad is capable of transformation in vitro, there was obvious, immediate interest in them. Subsequent revelation that the Ad heavily employs much of the cellular machinery during its life cycle made the adenovirus family an excellent probe for dissecting macromolecular biosynthesis and expanded this interest. Adaptation of Ad as a vector for various applications was thus a natural consequence of the considerable wealth of information accrued about this virus. Establishing cell lines by transformation with Ad recombinants that contain heterologous genes was one obvious application. Another was its development as a vector for producing high level expression of heterologous genes, stimulated by the extremely efficient lytic expression of this virus.

Construction of a recombinant adenovirus containing the den V gene from bacteriophage T4 which can partially restore the DNA repair deficiency in xeroderma pigmentosum fibroblasts

The denV gene from bacteriophage T4 encodes a pyrimidine dimer-specific endonuclease that has the capacity to initiate excision repair of DNA. Cells from excision repair-deficient xeroderma pigmentosum (XP) patients are able to carry out excision repair initiated by the denV gene product and introduction of the denV gene into XP cells results in the partial restoration of colony-forming ability after irradiation with UV light. In this work we have constructed a helper-independent recombinant human adenovirus, Ad5denV, which contains the denV gene. A 1.9 kb cartridge consisting of the denV gene flanked by the long terminal repeat (LTR) promoter from Rous sarcoma virus (RSV) and the simian virus 40 (SV40) polyadenylation (poly A) splice signals, was inserted into the E3 region of an E3 deletion mutant (Ad5d1E3) of adenovirus type 5. Infection of human fibroblasts and other permissive human cells with Ad5denV resulted in lytic infection and expression of the denV gene was confirmed by primer extension of infected cell RNA. The ability of the denV gene to restore the DNA repair deficiency in XP fibroblasts was examined using host cell reactivation of viral structural antigen formation for UV-irradiated adenovirus. The control virus, Ad5VSV, was also a recombinant which contained the gene for vesicular stomatitis virus glycoprotein G inserted into the E3 region of Ad5d1E3. UV survival of Ad5denV was similar to that of Ad5VSV following infection of two normal fibroblast strains and a Cockayne syndrome fibroblast strain, CS7SE, from complementation group B. In contrast, UV survival of Ad5denV was significantly greater than that for Ad5VSV after infection of three unrelated XP fibroblast strains from complementation groups A, C and E. However, UV survival of Ad5denV in the XP fibroblasts did not reach levels obtained in normal fibroblasts, indicating that restoration of the XP defect was partial.

Use of early baculovirus promoters for continuous expression and efficient processing of foreign gene products in stably transformed lepidopteran cells.

Baculoviruses are currently used as vectors for the transient high-level expression of foreign gene products in insect cells. In this study, we demonstrate that baculoviruses can also be made to continuously express a foreign gene product by using the promoter from IE1, an immediate early viral gene, to produce stably-transformed insect cells. This approach gave levels of foreign gene expression lower than those usually obtained with the lytic baculovirus expression vector system. Expression, however, was continuous and stable, and a complex human glycoprotein (tissue plasminogen activator) was processed more efficiently. We conclude that stable transformation is a feasible approach for baculovirus-mediated foreign gene expression in lepidopteran cells, particularly for products that are relatively poorly-expressed and/or processed in lytically infected cells.

Human tumor infiltrating lymphocytes. Analysis of lymphokine mRNA expression and relevance to cancer immunotherapy.

Tumor infiltrating lymphocytes (TIL) isolated from 12 patients with metastatic malignant melanoma, renal cell carcinoma, or breast adenocarcinoma were expanded in rIL-2 for 22 to 45 days (median 33 days) and analyzed for lymphokine mRNA expression and patterns of TCR gene rearrangement. All TIL cultures were significantly enriched for T cells, with CD3+ CD8+ cells predominant in 8 of 10 cases tested, and demonstrated an oligoclonal (rather than polyclonal) pattern of TCR gene rearrangement. Nine of 12 cultures could effectively lyse the autologous targets in short term chromium release assays. IL-2 expanded-TIL expressed mRNA for TNF-alpha and TNF-beta (lymphotoxin) and, in 5 of 9 (41%) cases, granulocyte/macrophage-colony stimulating factor mRNA but not IL-1 beta or IL-2 transcripts. Cultured TIL deprived of rIL-2 for 4 days did not constitutively express mRNA for any of the lymphokines tested. One long term TIL line in culture was followed and periodically tested for lytic activity and TNF-mRNA expression. Loss of the specific cytolytic but not proliferative activity at day 85 was associated with disappearance of TNF mRNA. Profiles of lymphokine secretion may provide a useful marker for functionally characterizing different T cell subsets and may provide correlates of the in vivo anti-tumor effects of these cells when TIL are adoptively transferred into cancer-bearing patients.

Differential protein synthesis by murine peritoneal macrophages elicited by various stimuli.

Protein synthetic patterns of murine peritoneal macrophages were analyzed by two-dimensional polyacrylamide gel electrophoresis (2D PAGE) of 35S methionine-labeled proteins. While the protein synthetic patterns exhibited by resident, inflammatory, and activated macrophages had numerous common features that distinguished them from the other normal non-macrophage cell types examined, unique proteins also characterized each macrophage population from the others. The accumulation by resident macrophages of proteins 23, 25, and 37 distinguished them from elicited cells, as did the former's more abundant synthesis of proteins 54 and 52. The protein synthetic patterns of inflammatory thioglycollate- and proteose peptone-elicited macrophages were strikingly similar, save for the former's greater levels of accumulation of proteins 14 and 28, and the latter's more pronounced expression of p23.5. Peritoneal macrophages elicited by treatment with heat-killed Propionibacterium acnes, the live, attenuated Mycobacterium bovis strain BCG, Listeria monocytogenes, and the protozoan flagellate Trypanosoma rhodesiense, all exhibited tumoricidal activity in 16-h or 72-h functional assays. They shared a common protein synthetic profile that differentiated them from the synthetic patterns characteristic of the non-tumoricidal resident and inflammatory macrophages. These tumoricidal macrophages were unique in synthesizing a protein(s) of approximate molecular weight 26,000 daltons. A time-course study employing P. acnes-activated peritoneal macrophages indicated that p26 accumulation decayed with tumoricidal capacity as a function of time in culture, although no direct correlation between lytic activity and p26 expression could be definitively established. Peritoneal macrophages elicited with proteose peptone were not directly tumoricidal but were rendered so upon in vitro treatment with nanogram amounts of bacterial lipopolysaccharide. The accumulation of low levels of p26 by the newly explanted proteose peptone-elicited macrophages suggests the possibility that this protein characterizes macrophage populations primed as well as triggered for tumoricidal activity.

Mechanism of cell-mediated cytotoxicity at the single cell level. VI. Direct assessment of the cytotoxic potential of human peripheral blood non-lytic effector-target cell conjugates.

Single cell cytotoxicity assays reveal that a large percentage of lymphocytes are unable to kill attached targets in a 4- to 18-hr assay. Additional signals (in the form of lectin or anti-target antibody) delivered to target-bound lymphocytes enable these previously non-lytic lymphocytes to kill attached target cells. This finding was obtained by using a modification of the single cell assay, in which lectin or target cell antibody is incorporated into agarose with preformed lymphocyte-target conjugates. Human peripheral blood lymphocytes (PBL) or Percoll density gradient-enriched large granular lymphocytes (LGL) were used as effector cells in natural killer (NK), antibody-dependent cellular cytotoxicity (LDCC) assay systems. The targets used were NK-sensitive K562 and Molt-4 and NK-insensitive Raji. Several findings were made in the modified single cell assay, namely a) the frequency of cytotoxic NK or ADCC effector cells was not augmented, suggesting that the initial trigger was sufficient for lytic expression in these instances. Furthermore, these results showed that the NK-sensitive targets used do not bind nonspecifically to the LDCC effector cells. K562 coated with Con A, however, serve as LDCC targets. b) The frequency of two target conjugate lysis by NK/K effectors was not augmented by Con A. These results suggest that Con A does not potentiate the killing of multiple targets bound to a single cytotoxic lymphocyte. c) Although conjugates formed between LGL or PBL and NK-insensitive Raji are non-lethal, significant lysis was observed when these conjugates were suspended in Con A or antibody agarose. These results demonstrate that Raji bind to cytotoxic NK, K, and LDCC effector cells, but are lysed only when the appropriate trigger is provided. d) The cytotoxic potential of non-lytic conjugates appears to lie within the low density Percoll fraction, although the high density lymphocytes are able to nonlethally bind to targets. Altogether the results demonstrate that target recognition and/or binding by the effector cells is a distinct event from the trigger or lytic process. The implications of these findings are discussed.

Augmentation of natural killer cells involves both enhancement of lytic machinery and expression of new receptors

A good correlation was found between the sensitivity of six hematopoetic cell lines to natural killing by both unstimulated and Interferon (IFN)-stimulated effector cells and the ability of these cell lines to induce interferon among human leukocytes. Two cell lines (HL 60 and P3HR1) were not sensitive to natural killing by unstimulated effectors (<10 lytic units) and did not induce IFN. Augmentation of natural killing by preincubation of effector cells with IFN was found to alter the binding of lymphocytes to HL 60 cells but not K 562 cells. This indicates that the augmentation of natural killer cells by IFN involves both enhancement of the lytic machinery and development of new receptors.

A physiological study of functional expression in Escherichia coli of the cloned yeast imidazoleglycerolphosphate dehydratase gene

Functional expression in Escherichia coli of bacteriophage λ and plasmid hybrids containing the Saccharomyces cerevisiae (yeast) gene for imidazoleglycerolphosphate (IGP) dehydratase ( his3) has been characterized in growing E. coli cells lacking the bacterial IGP dehydratase activity and during lytic infection of these cells. his3 expression of an integrated bacteriophage λhis3 hybrid requires transcriptional initiation from a “promoter” in the yeast DNA. A deletion mutant lacking this promoter, but containing the his3 structural gene has been isolated. Fusion of a DNA segment containing this promoter to a segment containing the intact structural gene for tetracycline resistance ( tet r ) but lacking an intact promoter results in expression of the tet r gene. Using four physiological criteria, the level of his3 expression in growing E. coli cells is affected by gene dosage. By these criteria, cells containing multiple copies of the his3 gene produce nearly wild-type E. coli activity levels of yeast IGP dehydratase. There is no evidence for regulation of his3 expression at the gene level as a function of histidine starvation. Expression of the his3 gene during lytic infection by bacteriophage λ hybrids has been assessed by the ability of such hybrids to grow in histidine-starved E. coli cells lacking IGP dehydratase. Phage containing a functional his3 gene grow with a single burst of five under these conditions and also form “plaques without lawns” on the starved cells. Lytic expression depends on transcription from the λ promoter P L; the level depends on the distance from P L to the his3 gene. The results indicate that expression in E. coli of a eukaryotic gene obeys prokaryotic rules of gene expression and that it can occur at a significantly high level. This suggests that the basic gene recognition signals of eukaryotes and prokaryotes may not be so different.

The Requirement for Macrophages in the Augmentation of Natural Killer Cell Activity by BCG

Abstract Intraperitoneal injection of BCG gives rise to a rapid augmentation of peritoneal natural killer (NK) cell activity in mice. Depletion of macrophages in vivo by injection of silica particles markedly diminished BCG-induced NK cell augmentation. In contrast, short-term in vitro treatment of BCG-induced peritoneal exudate cells (BCG-PEC) with silica did not affect NK cell activity, despite considerable toxicity to macrophages. The mechanism of BCG-induced enhancement of NK cell activity was evaluated with an in vivo inductive transfer system. Intraperitoneal transfer of BCG-PEC, but not normal peritoneal cells, induced cytotoxic activity in recipient PEC as measured 1 to 10 days later. That this cytotoxic activity was due to NK cells was shown by their lability at 37°C and by their adherence properties. Macrophages were required for the induction of NK cell augmentation, as it was shown that 3-day BCG-PEC depleted of phagocytic cells, adherent cells, or Fc receptor-bearing cells failed to induce NK activity. Furthermore, cell-free supernatants of 24-hr cultures of 3-day BCG-PEC were also active in inducing NK cell enhancement in vivo. These results suggest that the augmentation of NK cell activity by BCG involves cell-derived soluble factors and it requires macrophages during the induction phase, but not for the lytic expression of NK cells.