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PubMed1994

Cellular epigenetics: topochronology of progressive "spontaneous" transformation of cells under growth constraint.

Early passages of NIH 3T3 cells yield about 10 transformed foci for every 10(5) cells seeded after the cells multiply to confluence in a standardized 2-week assay. The question arose whether more cells would give rise to foci if given more time for their development. This question could not be answered simply by extending the incubation period, since the original foci spread to cover much of the area of the culture dish. Transformed cells can also detach into the medium from the original foci to initiate new foci by reattaching at a distance. These problems were averted by growing cells in multiwell plates which in effect simulated partitioned culture dishes. All the wells in a given plate were assayed for focus formation at successive intervals up to 14 weeks. The results indicated the spatial pattern and sequence of transformation on different parts of the "partitioned" dish. The number of multiwells containing focus-forming cells increased steadily with time, indicating that all parts of a dish eventually undergo transformation. Also, most of the transformations were recorded long after confluence in the multiwells was reached. Hence such a transformation is much more likely to occur in the nondividing state rather than in the dividing state of the cells and is thus inconsistent with a mutational basis. The results suggest that "spontaneous" transformation is a population-wide, epigenetic phenomenon. This agrees with the results from clonal analysis and other studies and is well described by the concept of progressive state selection, in which "spontaneous" transformation represents a heterogeneous, adaptive response of competent cells to moderate constraints on cell growth.

3T3 Cells↗
PubMed1996

Selective pressure of a quinoxaline nonnucleoside inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) on HIV-1 replication results in the emergence of nucleoside RT-inhibitor-specific (RT Leu-74-->Val or Ile and Val-75-->Leu or Ile) HIV-1 mutants.

The quinoxaline nonnucleoside RT inhibitor (NNRTI) (S)-4-isopropoxycarbonyl-6-methoxy-3-(methylthiomethyl)-3,4- dihydroquinoxaline-2(1H)-thione (HBY 097) was used to select for drug-resistant HIV-1 variants in vitro. The viruses first developed mutations affecting the NNRTI-binding pocket, and five of six strains displayed the RT G190-->E substitution, which is characteristic for HIV-1 resistance against quinoxalines. In one variant, a new mutant (G190-->Q) most likely evolved from preexisting G190-->E mutants. The negative charge introduced by the G190-->E substitution was maintained at that site of the pocket by simultaneous selection for V179-->D together with G190-->Q. After continued exposure to the drug, mutations at positions so far known to be specific for resistance against nucleoside RT inhibitors (NRTIs) (L74-->V/I and V75-->L/I) were consistently detected in all cultures. The inhibitory activities of the cellular conversion product of 2',3'-dideoxyinosine (ddI, didanosine), 2',3'-dideoxyadenosine (ddA) and of 2',3'-didehydro-3'-deoxythymidine (d4T, stavudine) against these late-passage viruses were shown to be enhanced with the L74-->V/I RT mutant virus as compared with the wild-type (wt) HIV-1MN isolate. Clonal analysis proved linkage of the codon 74 and codon 75 mutations to the NNRTI-specific mutations in all RT gene fragments. The nonnucleoside- and nucleoside-resistance mutation sites are separated by approximately 35 A. We propose that the two sites "communicate" through the template-primer which is situated in the DNA-binding cleft between these two sites. Quinoxalines cause high selective pressure on HIV-1 replication in vitro; however, the implication of these findings for the treatment of HIV-1 infection has yet to be determined.

Antiviral Agents↗
PubMed2002

Peripheral T-cell lymphoma with eosinophilia presenting as monoarthritis: a case study.

Direct involvement of the joints is unusual in patients with non-Hodgkin's lymphoma (NHL). This may pose a diagnostic problem for pathologists, especially since synovial localization can disclose NHL. In the following case of T-cell NHL with eosinophilia, we point out the essential importance of clonality analysis on frozen tissue to distinguish between synovial NHL and specific inflammatory damage.

Adolescent↗
PubMed1991

Activation of the simian virus 40 (SV40) genome abrogates sensitivity to AVP in a rabbit collecting tubule cell line by repressing membrane expression of AVP receptors.

To analyze the role of SV40 genome in the phenotypic alterations previously observed in SV40-transformed cell lines, we infected rabbit renal cortical cells with a temperature-sensitive SV40 mutant strain (tsA58) and compared the cell phenotypes at temperatures permissive (33 degrees C) and restrictive (39.5 degrees C) for SV40 genome expression. At both temperatures, the resulting cell line (RC.SVtsA58) expresses cytokeratin and uvomorulin, but epithelial differentiation is more elaborate at 39.5 degrees C as shown by the formation of a well-organized cuboidal monolayer with numerous tight junctions and desmosomes. Functional characteristics are also markedly influenced by the culture temperature: cells grown at 33 degrees C respond only to isoproterenol (ISO, 10(-6) M) by a sevenfold increase in cAMP cell content above basal values; in contrast, when transferred to 39.5 degrees C, they exhibit increased sensitivity to ISO (ISO/basal: 19.1) and a dramatic response to 10(-7) M dDarginine vasopressin (dDAVP/basal: 18.2, apparent Ka: 5 X 10(-9) M) which peaks 48 h after the temperature shift. The latter is associated with membrane expression of V2-type AVP receptors (approximately 50 fmol/10(6) cells) which are undetectable when SV40 genome is activated (33 degrees C). Clonal analysis, additivity studies, and desensitization experiments argue for the presence of a single cell type responsive to both AVP and ISO. The characteristics of the RC. SVtsA58 cell line at 39.5 degrees C (effector-stimulated cAMP profile, lack of expression of brush-border hydrolases and Tamm-Horsfall protein) suggest that it originates from the cortical collecting tubule, and probably from principal cells.

Animals↗
PubMed1999

Skeletal myogenic progenitors originating from embryonic dorsal aorta coexpress endothelial and myogenic markers and contribute to postnatal muscle growth and regeneration.

Skeletal muscle in vertebrates is derived from somites, epithelial structures of the paraxial mesoderm, yet many unrelated reports describe the occasional appearance of myogenic cells from tissues of nonsomite origin, suggesting either transdifferentiation or the persistence of a multipotent progenitor. Here, we show that clonable skeletal myogenic cells are present in the embryonic dorsal aorta of mouse embryos. This finding is based on a detailed clonal analysis of different tissue anlagen at various developmental stages. In vitro, these myogenic cells show the same morphology as satellite cells derived from adult skeletal muscle, and express a number of myogenic and endothelial markers. Surprisingly, the latter are also expressed by adult satellite cells. Furthermore, it is possible to clone myogenic cells from limbs of mutant c-Met-/- embryos, which lack appendicular muscles, but have a normal vascular system. Upon transplantation, aorta-derived myogenic cells participate in postnatal muscle growth and regeneration, and fuse with resident satellite cells.The potential of the vascular system to generate skeletal muscle cells may explain observations of nonsomite skeletal myogenesis and raises the possibility that a subset of satellite cells may derive from the vascular system.

Aging↗
PubMed2002

Myogenic cell proliferation and generation of a reversible tumorigenic phenotype are triggered by preirradiation of the recipient site.

Environmental influences have profound yet reversible effects on the behavior of resident cells. Earlier data have indicated that the amount of muscle formed from implanted myogenic cells is greatly augmented by prior irradiation (18 Gy) of the host mouse muscle. Here we confirm this phenomenon, showing that it varies between host mouse strains. However, it is unclear whether it is due to secretion of proliferative factors or reduction of antiproliferative agents. To investigate this further, we have exploited the observation that the immortal myogenic C2 C12 cell line forms tumors far more rapidly in irradiated than in nonirradiated host muscle. We show that the effect of preirradiation on tumor formation is persistent and dose dependent. However, C2 C12 cells are not irreversibly compelled to form undifferentiated tumor cells by the irradiated muscle environment and are still capable of forming large amounts of muscle when reimplanted into a nonirradiated muscle. In a clonal analysis of this effect, we discovered that C2 C12 cells have a bimodal propensity to form tumors; some clones form no tumors even after extensive periods in irradiated graft sites, whereas others rapidly form extensive tumors. This illustrates the subtle interplay between the phenotype of implanted cells and the factors in the muscle environment.

Animals↗
PubMed1978

Isolation of a heterogeneous population of temperature-sensitive mutants of measles virus from persistently infected human lymphoblastoid cell lines.

Two human lymphoblastoid B-cell lines, WI-L2 and 8866, were infected with the Edmonston strain of measles virus at a multiplicity of infection of 10(-6), and stable persistent infections were established. By immunofluorescence and electron microscopy, the vast majority of cells from both cell lines were expressing viral antigens and releasing virion-like particles. However, very little infectious virus could be detected at 37 degrees C, either by an infectious centers assay or by titration of supernates from persistently infected cultures. When cultures were shifted to 31 degrees C, the cells released a population of virus that was temperature-sensitive. Clonal analysis of supernatant virus at 31 degrees C revealed a highly heterogeneous population of temperature-sensitive mutants, differing in plating efficiency ratios, thermolability, and antigen production at the nonpermissive temperature. Factors such as interferon, defective interfering particles, and extracellular virus do not appear to be important in maintaining the persistent carrier state. These studies have important implications for persistent infections of lymphoid cells in vivo, and the slow neurological diseases associated with measles, subacute sclerosing panencephalitis, and multiple sclerosis.

Antibodies, Viral↗
PubMed1981

Expression of the macrophage-specific antigen F4/80 during differentiation of mouse bone marrow cells in culture.

We have defined the expression of the macrophages (m phi)-specific antigen (Ag) F4/80 during differentiation in culture. The progenitor cells-the colony-forming unit in culture and cluster-forming cell-lacked Ag F4/80 but gave rise to colonies of F4/80-positive adherent m phi, as shown by fluorescence-activated cell sorting and clonal assays with L cell-conditioned medium as the source of growth factor. Ag F4/80 first appeared on a nonadherent precursor found in mass liquid BM cultures after 3 d. Once adherent, m phi expressed high levels of Ag F4/80 and other markers. The role of L cell-conditioned medium and of adherence on expression of Ag F4/80 was also examined. Clonal analysis of F4/80 and other Ag, Mac-1, and 2.4G2 (FcR) showed that all cells in all independent colonies come to express these markers. These studies establish that F4/80 is a marker for the more mature stages of m phi development and that Ag expression increases progressively during maturation in vitro. Heterogeneity of Ag expression can be ascribed to variation in development and not to independent subsets of the m phi.

Animals↗
PubMed1985

Trans-acting element(s) operating across species barriers positively regulate expression of major histocompatibility complex class II genes.

Raji, a human B lymphoma line, expresses high levels of major histocompatibility complex (MHC) class II antigens. Conversely, none of the detectable human Ia antigens is present in RJ 2.2.5, an immunoselected Raji variant. Clonal analysis, biochemical characterization, and nucleic acid hybridization studies of hybrids between mouse spleen cells and RJ 2.2.5 show that MHC class II gene expression is regulated in trans by a factor which, as judged by dominance studies, has the characteristics of an activator. Such a positive trans acting factor is expressed in mouse spleen cells, and is able to implement MHC class II gene expression across species boundaries. Expression of this factor in spleen cells strongly suggests that it plays a role in in vivo regulation of Ia expression. Additional data suggest that different subsets of class II genes such as DR and DQ may, in part, be regulated by different mechanisms. It has also been possible to show that the amount of In chain-specific mRNA, present at reduced levels in RJ 2.2.5 cells compared to the parental Raji cells, drastically increased in human X mouse cells hybrids reexpressing human Ia antigens, suggesting that the In chain gene and the class II genes, although located on different chromosomes, are regulated in a concerted fashion, either directly through the same implementing factor, or indirectly through a cascade mechanism.

Animals↗
PubMed1993

Cytokine mRNA expression during an in vitro response of human B lymphocytes: kinetics of B cell tumor necrosis factor alpha, interleukin (IL)6, IL-10, and transforming growth factor beta 1 mRNAs.

Expression of mRNA for eight cytokines was analyzed in an in vitro response-proliferation and Ig-secretion--of normal human B lymphocytes. This was made possible by the use of murine thymoma cells as helper cells in conjunction with human T cell supernatant, and the design of human DNA sequence-specific primers for RT-polymerase chain reaction. mRNAs for interleukin (IL)2 and IL-4, but also for IL-1 alpha and IL-1 beta remained undetectable during the whole culture period in highly purified B cells prepared by a three-step purification protocol. However, tumor necrosis factor alpha and IL-6 mRNAs peaked during days 1-3 after culture start and became undetectable after 5-6 d, shortly before bulk B cell proliferation started to decline. In contrast, transforming growth factor beta 1 mRNA, after a progressive increase during the first few days, and IL-10 mRNA, after a peak on days 1-3, remained detectable in immunoglobulin (Ig)-secreting cultures throughout the observation period of 22 d. Clonal analysis on 8-d cultures that had been seeded with single B cells by autocloning with the cell sorter, revealed that 85% of 77 B cell clones studied, expressed TGF-beta 1 mRNA, and only 19% IL-10 mRNA. These findings show a differentiation stage-related cytokine program during a B cell response, whereby (a) B cells can become activated without IL-1 alpha or IL-1 beta expression; (b) mRNA for positive (IL-10) and negative (TGF-beta 1) autoregulatory factors coexists in cell populations during the later phase of the response, although not necessarily in all B cell clones; and (c) normal Ig-secreting cells cease IL-6 expression in contrast to their malignant counterparts, myeloma cells.

Antigens, CD↗
PubMed1993

Different HLA-B27 subtypes present the same immunodominant Epstein-Barr virus peptide.

An immunological basis has been postulated for the strong association between at least five subtypes of the HLA-B27 allele (B27.01, .02, .04, .05, and .06) and ankylosing spondylitis, namely that cytotoxic T lymphocyte (CTL) responses are induced against an "arthritogenic" peptide that these different subtypes can all present. This requires a degree of overlap between the peptide binding repertoires of different B27 molecules. The present work, using CTL responses to Epstein-Barr virus (EBV) as a model system in which to identify B27-restricted epitopes, provides the first direct evidence that different disease-related alleles can present the same immunodominant peptide. We first noted that EBV-specific CTL clones, whether from B27.05-, B27.02-, or B27.04-positive donors, were largely subtype-specific in their restriction, recognizing only EBV-transformed B cell lines of the relevant B27 subtype. However, when tested against targets expressing individual EBV proteins from recombinant vaccinia virus vectors, all B27.05-restricted, all B27.02-restricted, and a proportion of B27.04-restricted clones were reactive to the same viral nuclear antigen, Epstein-Barr nuclear antigen (EBNA)3C. In subsequent peptide sensitization assays, all the EBNA3C-specific clones tested and also the EBNA3C-specific component within polyclonal CTL preparations from B27.05-, B27.02-, or B27.04-positive donors recognized the same immunodominant viral peptide RRIYDLIEL (EBNA3C residues 258-266). This sequence accords well with the proposed B27.05 peptide motif and clearly must be accommodated within the different peptide binding grooves of B27.05, B27.02, and B27.04 molecules. Clonal analysis revealed a second component of the B27.04-restricted response that was not shared with other subtypes. This was directed against an EBV latent membrane protein LMP2 epitope whose sequence RRRWRRLTV satisfies some but not all requirements of the B27.05 peptide motif. We conclude that there is indeed a degree of functional overlap between different B27 subtypes in their selection and presentation of CTL epitopes.

Amino Acid Sequence↗
PubMed1997

Immediate early and early lytic cycle proteins are frequent targets of the Epstein-Barr virus-induced cytotoxic T cell response.

Epstein-Barr virus (EBV), a human gamma-herpesvirus, can establish both nonproductive (latent) and productive (lytic) infections. Although the CD8+ cytotoxic T lymphocyte (CTL) response to latently infected cells is well characterized, very little is known about T cell controls over lytic infection; this imbalance in our understanding belies the importance of virus-replicative lesions in several aspects of EBV disease pathogenesis. The present work shows that the primary CD8+ CTL response to EBV in infectious mononucleosis patients contains multiple lytic antigen-specific reactivities at levels at least as high as those seen against latent antigens; similar reactivities are also detectable in CTL memory. Clonal analysis revealed individual responses to the two immediate early proteins BZLF1 and BRLF1, and to three (BMLF1, BMRF1, and BALF2) of the six early proteins tested. In several cases, the peptide epitope and HLA-restricting determinant recognized by these CTLs has been defined, one unusual feature being the number of responses restricted through HLA-C alleles. The work strongly suggests that EBV-replicative lesions are subject to direct CTL control in vivo and that immediate early and early proteins are frequently the immunodominant targets. This contrasts with findings in alpha- and beta-herpesvirus systems (herpes simplex, cytomegalovirus) where viral interference with the antigen-processing pathway during lytic infection renders immediate early and early proteins much less immunogenic. The unique capacity of gamma-herpesvirus to amplify the viral load in vivo through a latent growth-transforming infection may have rendered these agents less dependent upon viral replication as a means of successfully colonizing their hosts.

Amino Acid Sequence↗
PubMed1998

Distinct methylation of the interferon gamma (IFN-gamma) and interleukin 3 (IL-3) genes in newly activated primary CD8+ T lymphocytes: regional IFN-gamma promoter demethylation and mRNA expression are heritable in CD44(high)CD8+ T cells.

Differential genomic DNA methylation has the potential to influence the development of T cell cytokine production profiles. Therefore, we have conducted a clonal analysis of interferon (IFN)-gamma and interleukin (IL)-3 gene methylation and messenger (m)RNA expression in primary CD8+ T cells during the early stages of activation, growth, and cytokine expression. Despite similar distributions and densities of CpG methylation sites, the IFN-gamma and IL-3 promoters exhibited differential demethylation in the same T cell clone, and heterogeneity between clones. Methylation patterns and mRNA levels were correlated for both genes, but demethylation of the IFN-gamma promoter was widespread across >300 basepairs in clones expressing high levels of IFN-gamma mRNA, whereas demethylation of the IL-3 promoter was confined to specific CpG sites in the same clones. Conversely, the majority of clones expressing low or undetectable levels of IFN-gamma mRNA exhibited symmetrical methylation of four to six of the IFN-gamma promoter CpG sites. Genomic DNA methylation also has the potential to influence the maintenance or stability of T cell cytokine production profiles. Therefore, we also tested the heritability of IFN-gamma gene methylation and mRNA expression in families of clones derived from resting CD44(low)CD8+ T cells or from previously activated CD44(high)CD8+ T cells. The patterns of IFN-gamma gene demethylation and mRNA expression were faithfully inherited in all clones derived from CD44(high) cells, but variable in clones derived from CD44(low) cells. Overall, these findings suggest that differential genomic DNA methylation, including differences among cytokine genes, among individual T cells, and among T cells with different activation histories, is an important feature of cytokine gene expression in primary T cells.

Animals↗
PubMed2006

Yersinia pseudotuberculosis disseminates directly from a replicating bacterial pool in the intestine.

Dissemination of Yersinia pseudotuberculosis within mice after oral inoculation was analyzed. Y. pseudotuberculosis translocated to organs such as the liver and spleen shortly after oral inoculation, but was quickly cleared. In contrast, a second temporally distinct bacterial translocation event resulted in successful hepatosplenic replication of the bacteria. Replicating pools of bacteria could be established in these organs in mouse mutants that lacked Peyer's patches. These animals frequently had sterile mesenteric lymph nodes, a finding consistent with translocation taking place independently of regional lymph node colonization. In further contradiction to accepted models for dissemination of enteropathogens, clonal analysis revealed that bacteria causing disease in the spleen and liver of C57BL/6J mice were derived from populations located outside the intestinal lymph nodes. Replication of bacteria in the intestine before translocation appeared critical for dissemination, as transient selective suppression by streptomycin of bacterial growth in the intestine delayed dissemination of Y. pseudotuberculosis. These results collectively indicate that hepatosplenic colonization appears intimately connected with the ability of Y. pseudotuberculosis to successfully establish replication in the intestinal lumen and does not result from ordered spread leading from the intestine to regional lymph nodes before dissemination.

Animals↗
PubMed2002

Evolution of human immunodeficiency virus type 1 populations after resumption of therapy following treatment interruption and shift in resistance genotype.

Conventional genotyping of human immunodeficiency virus type 1 often reveals a shift from a drug-resistant genotype to a wild-type genotype after treatment interruption. A real-time polymerase chain reaction-based technique was used to detect minority resistant populations in 13 patients who showed genotype reversion after interruption of treatment for 3 months. Sixty-two percent of patients in whom the V82A and L90M protease mutations were no longer detectable by conventional genotyping still harbored minority resistant variants, in proportions ranging from 0.1% to 21%. None of the patients with these minority resistant variants who received a protease-inhibitor regimen on resumption of therapy had a response to treatment. However, population sequencing and clonal analysis of plasma samples obtained 1-2 months after resumption of treatment revealed the presence of wild-type virus during the initial decline in plasma virus load, which indicates that minority resistant variants were not rapidly selected.

Amino Acid Sequence↗
PubMed2004

Detection of drug-resistant minority variants of HIV-1 during virologic failure of indinavir, lamivudine, and zidovudine.

We evaluated zidovudine-experienced patients for whom treatment with indinavir, lamivudine, and zidovudine failed, for indinavir-resistant minority variants. Of 10 patients with plasma human immunodeficiency virus type 1 RNA suppression and subsequent rebound, 6 without primary indinavir-resistance mutations underwent clonal analysis. One had evidence of V82A in 9 of 30 clones at week 24, with no increase at week 40. The dominant week-40 82V-M184V clones had changes at protease codons 62-64, compared with all clones at week 24 and minority clones at week 40. Resistance to indinavir can emerge during treatment failure in nucleoside-experienced patients but may be missed by routine sequence analysis. Selection for indinavir-resistant variants on treatment with indinavir, lamivudine, and zidovudine may occur slowly, depending on the genetic context in which they arise.

Acquired Immunodeficiency Syndrome↗
PubMed2003

Identification of a transmission chain of HIV type 1 containing drug resistance-associated mutations.

We have investigated a potential transmission chain of HIV-1 with drug resistance-associated mutations between three individuals over a period of 5 years by use of cloning and sequencing of viral genes, and phenotypic characterization. Viruses containing reverse transcriptase drug resistance-associated mutations were transmitted sequentially between three homosexual men (A, B, and C), and persisted in one individual for at least 4 years, despite intermittent therapy and reduced viral replicative capacity compared with wild-type strains. Clonal analysis of the envelope gene from semen and blood virus showed that the virus transmitted to patient C was more closely related to virus from the semen than the blood of patient B. Our data suggest that HIV variants with drug resistance-associated mutations can persist following primary infection, despite intervening antiretroviral therapy, and subsequently sexually transmitted. We provide "proof of principle" that such mutations can therefore become "fixed" within the circulating virus pool.

Anti-HIV Agents↗
PubMed2003

Comparison of three retroviral vector systems for transduction of nonobese diabetic/severe combined immunodeficiency mice repopulating human CD34+ cord blood cells.

The use of recombinant vectors based on wild-type viruses that are absent in humans and are not associated with any disease in their natural animal hosts or in accidentally infected humans would add an additional level of safety for human somatic gene therapy approaches. These criteria are fulfilled by foamy viruses (FVs), a family of complex retroviruses whose members are widely found among mammals and are apathogenic in all hosts. Here, we show by comparison of identically designed vector constructs that recombinant retroviral vectors based on FVs were as efficient as lentiviral vectors in transducing nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice repopulating human CD34(+) cord blood (CB) cells. The FV vector was able to achieve gene transfer levels up to 84% of engrafted human cells in a short overnight transduction protocol. In contrast, without prestimulation of the target cells, a human immunodeficiency virus type 1 (HIV-1)-based lentiviral vector pseudotyped with gibbon ape leukemia virus envelope (GALV Env) was nearly as inefficient as murine leukemia virus (MLV)-based oncoretroviral vectors in transducing NOD/SCID repopulating cells. The same HIV vector pseudotyped with the vesicular stomatitis virus glycoprotein G (VSV-G) achieved high marking efficiency. Clonality analysis of bone marrow samples showed oligoclonal hematopoiesis with single to multiple insertions per cell, both for FV and HIV vectors. These data demonstrate that vectors based on FVs warrant further investigation and development for medical use.

Animals↗