Genes coding for sensitivity to interferon (IfRec) and soluble superoxide dismutase (SOD-1) are linked in mouse and man and map to mouse chromosome 16

Aspects of the structure, function, and applications of superoxide dismutase

The current status of superoxide dismutase (SOD) is that it is an enzyme with diverse ramifications. This review attempts an understanding of SOD as a structural, functional, and biological entity. Accordingly, the review is in three parts. The first part discusses SOD in terms of protein structure, proceeding from primary to secondary and three-dimensional structure for the three forms of SOD: copper/zinc SOD, manganese SOD, and iron SOD. This is the order of structural knowledge of the enzyme. Iron SOD is an enzyme of prokaryotes and some higher plants. Manganese SOD is an enzyme of prokaryotes and eukaryotes. Copper/zinc SOD is an enzyme of eukaryotes and certain prokaryotes. The evolutionary relationships of the three forms of SOD, the status of the copper/zinc SOD gene in prokaryotes, and the cloning and sequencing of SOD genes are discussed. The second part of the review deals with the catalytic mechanism of SOD in the three forms of the enzyme. Structural and mechanistic conclusions from various spectroscopic studies are critically considered. A detailed picture is given of the active site of copper/zinc SOD. The third part is a review of SOD in the general context of oxygen toxicity. After consideration of the question of superoxide toxicity and superoxide pathology, several areas in which SOD has been investigated or used as a tool in a biochemical, pharmacological, or clinical context are discussed, including population genetics; trisomy 21; development and senescence; the nutritional copper, zinc, and manganese status; hemolysis and anemia; oxygen toxicity in the lung and nervous system; inflammation, autoimmune disease and chromosome breakage, ischemia and degenerative changes; radiation damage; and malignancy. A comprehensive picture is given of measurements of SOD activity in disease states, and the question of superoxide-related disease is considered at several points.

Influence of mouse trisomy 16 on expression of specific genes

We examined developmental changes in the relative activities of three different isozyme systems: aldolase, enolase and phosphoglycerate mutase, in tissues of fetal mice with trisomy 16 and of fetal euploid littermates. We wanted to determine whether morphological abnormalities such as reduced weight and size, which are generally observed in murine trisomy, are reflected at the molecular level. Following electrophoretic separation and subsequent measurement of relative activities of enolase isozymes in brain and phosphoglycerate mutase isozymes in heart, we found no significant differences between trisomy 16 fetuses and their euploid littermates. Synthesis of liver-specific aldolase was, however, delayed in trisomy 16 fetuses.

Developmental genetics

Of particular concern to the human geneticist are the effects of genetic abnormalities on development. To gain an understanding of these effects it is necessary to engage in a reciprocal process of using knowledge of normal developmental events to elucidate the mechanisms operative in abnormal situations and then of using what is learned about these abnormal situations to expand our understanding of the normal. True developmental genes have not been described in man, although it is likely that they exist, but many developmental abnormalities are ascribable to mutations in genes coding for enzymes and structural proteins. Some of these even produce multiple malformation syndromes with dysmorphic features. These situations provide a precedent for asserting that not only monogenic developmental abnormalities, but also abnormalities resulting from chromosome imbalance must ultimately be explicable in molecular terms. However, the major problem confronted by the investigator interested in the pathogenesis of any of the chromosome anomaly syndromes is to understand how the presence of an extra set of normal genes or the loss of one of two sets of genes has an adverse effect on development. Several molecular mechanisms for which limited precedents exist may be considered on theoretical grounds. Because of the difficulties in studying developmental disorders in man, a variety of experimental systems have been employed. Particularly useful has been the mouse, which provides models for both monogenic and aneuploidy produced abnormalities of development. An example of the former is the mutation oligosyndactylism which in the heterozygous state causes oligosyndactyly and in the homozygous state causes early embryonic mitotic arrest. All whole arm trisomies and monosomies of the mouse can be produced experimentally, and of special interest is mouse trisomy 16 which has been developed as an animal model of human trisomy 21 (Down syndrome). In the long run, the most direct approach to elucidating the genetic problems of human development will involve not only the study of man himself but also of the appropriate experimental models in other species.

Interferon-regulated influenza virus resistance gene Mx is localized on mouse chromosome 16

Genomic Southern blots of mouse-hamster somatic cell hybrids were analyzed with a probe prepared from a cDNA encoding murine Mx protein, the product of the interferon-regulated influenza virus resistance allele Mx+. Results of this analysis indicate that the Mx gene is located on mouse chromosome 16. In appropriate backcross mice, no linkage was observed between Mx and md, a marker previously mapped close to the centromere of chromosome 16, suggesting a more distal localization of Mx.

Stem cell deficiencies and thymic abnormalities in fetal mouse trisomy 16

Mouse fetuses with trisomy 16 have severe abnormalities of several hematopoietic stem cell and precursor populations. The thymus is extremely hypoplastic, with a greater than or equal to 80% reduction in the number of thymocytes. This cellular deficiency appears to be the result of a deficiency in the number of precursor cells in the early thymus, since the rate of proliferation of thymocytes in explanted day-14 thymuses was normal. However, the functional maturation of thymocytes was delayed in vitro in day-17 organ explants, although the maximal response to the mitogenic and interleukin 2-stimulating effects of concanavalin A are quantitatively normal. B cells and pre-B cells in the fetal liver were moderately decreased, but the ability of fetal liver cells to be transformed by Abelson murine leukemia virus was nearly totally lost. There were also significant relative and absolute decreases in the number of spleen, culture, and erythroid colony-forming units (CFU-S, CFU-C, CFU-E) and of erythroid burst-forming units (BFU-E) in the trisomic liver, and the trisomic animals were anemic with small spleens and livers. However, unlike other genetically caused anemias, there was no reduction in the number of germ cells. The hematopoietic abnormalities in the trisomy 16 mouse, involving the lymphoid, myeloid, and erythroid cell lineages, are much more generalized than the abnormalities in any of the other described genetically caused immunodeficiencies or anemias in the mouse. They are also more severe than those in human trisomy 21 (Down syndrome), for which mouse trisomy 16 is a genetic model, but there does exist an interesting parallel between the thymic abnormalities in the two species.

Assignment of low-molecular-weight human (2', 5')A synthetase to chromosome 11

Human low-molecular-weight (2', 5')A synthetase is induced in certain human X mouse somatic hybrid cell lines when these cells are treated with mouse interferon. We have assigned the gene coding for this interferon-inducible antiviral enzyme to human chromosome 11 by somatic cell genetic techniques (1). Fluorescence-activated cell sorting for cells expressing or lacking 4F2 antigen in two independently derived, chromosome 11-containing hybrid cell lines separated the cells into subpopulations of cells that had retained or segregated chromosome 11, respectively (2). We used these subpopulations to confirm our gene assignment by demonstrating that retention of chromosome 11 was required for expression of human (2', 5')A synthetase.

Murine trisomy: developmental profiles of the embryo, and isolation of trisomic cellular systems

Many questions related to the development and the phenotypic expression of trisomy (Ts) are amenable to systematic investigation in a mouse model that allows the induction of Ts 1 to 19 by a breeding design of mice heterozygous for Robertsonian metacentric chromosomes. Some Ts do not survive the first critical phase of organogenesis on days 11 to 12 of fetal development; others as Ts 12, 14, 16, 18, and 19, have a life span until or beyond birth. Model type studies of the morphogenesis of developmental anomalies (e.g. craniocerebral, cardiovascular, or placental) are possible in Ts with a longer developmental span, and Ts 16 of the mouse is considered as a natural model of human trisomy 21. The eventual breakdown and death of the trisomic organism are inevitable. There is considerable interest to find ways for rescue and longer survival of Ts in competitive developmental systems, as e.g., in Ts in equilibrium with 2n blastocyst chimeras, or by isolation of trisomic cellular or tissue systems. Thus, the transfer of Ts hemopoietic stem cells of the fetal liver to irradiated adult recipients is a means of studying the functional capacities and maturation of trisomic hemopoiesis and lymphopoiesis. Both are almost completely restored by Ts 12, 14, 18, and 19 stem cell transplantation with survival periods of more than 6 months. But in other Ts, as of chromosomes 13 or 16, such capacity of reconstitution is impaired. The stepwise analysis of the effects of chromosome triplication on the cell level, in isolated functional systems and in the embryonic organism, is a promising way to understand the phenotypic expression of genome anomalies in complex developmental processes.

Characterization of superoxide dismutase (SOD-1 and SOD-2) activities in inbred mice: evidence for quantitative variability and possible nonallelic SOD-1 polymorphism

Liver Cu/Zn (SOD-1) and Mn (SOD-2) superoxide dismutase activities were determined in 12 inbred mouse lines. SOD-2 activity varied from 5 to 8 U/mg protein but was never more than 5% of the total. SOD-1 activity varied from 112 (SJL/J) to 155 (RF/J) U/mg protein, with the 12 strains falling into three activity classes. No correlation between SOD-1 activity and H-2 histocompatibility phenotype was observed, i.e., these two loci do not appear linked as previously suggested [Novak, R., Bosze, Z., Matkovics, B. and Fachet, J. (1980). Science 207:86]. Several tissues in all strains exhibited three SOD-1 charge electromorphs which did not differ in relative proportions between strains or tissues. The pI values of these three isozymes were 4.0, 4.5, and 5.0, respectively. The pI value of SOD-2 was 7.7. Both SOD-1 and SOD-2 were sensitive to CHCl3/EtOH extraction, but this sensitivity was not electromorph specific. Quantitation of the SOD-1 isozymic pattern indicated that the electromorphs were present at a ratio of 1:6:23 in order of increasing pI. Fitting of these data to a binomial distribution showed that they were consistent with the presence of two SOD-1 subunits (chains) of unequal pI. The mole fractions of the two chains were calculated to be 0.14 (lower-pI chain) and 0.86 (higher-pI chain). Since the mice used were highly inbred, this pattern could be due to unequal rates of transcription of linked, nonallelic SOD-1 loci, although other explanations are possible. The activity differences between SJL/J and RF/J appear large enough and the data precise enough to make genetic studies on the control of SOD-1 expression in the mouse practicable.

Insensitivity to interferon of two subclones of human endometrial carcinoma cell line, HEC-1

Two cloned cell lines, HEC-IC and HEC-ID, derived from the human endometrial adenocarcinoma cell line HEC-I, were found to be as resistant to the antiviral and anticellular activities of interferon (IFN) as were the parental cells, and 2'-5' oligoadenylate (2-5A) synthetase was not induced in these clones by IFN treatment. They were sensitive to the cytotoxicity of natural killer (NK) cells but their sensitivity was not changed by treatment of the cell lines with IFN. Binding of [3H]-leucine-labelled IFN-alpha to HEC-IC cells was examined, and Scatchard plot analysis showed that HEC-IC cells did not have any high-affinity binding sites for IFN-alpha. The cells had hyperploid chromosomes. HEC-IC had three copies of chromosome 21 while HEC-ID had only one copy of chromosome 21. The results suggest that these clones may have the structural gene for the IFN receptor but that functional receptor sites may be absent.

Mouse genes influence antiviral action of interferon in vivo

BALB/c mice are more sensitive to the antiviral effect of interferon than C57BL/6 mice, as demonstrated by experiments involving protection against lethal infection with encephalomyocarditis virus. This greater sensitivity of the BALB/c genotype to interferon action is in accord with previous observations that the bone marrow-derived erythroid precursors and macrophages of BALB/c mice are more sensitive to the anti-proliferative action of interferon than those of C57BL/6 mice. An analysis of the loci involved in the modulation of the activity of interferon against encephalomyocarditis virus infection was carried out in (BALB/c x C57BL/6)F1 progeny and in six recombinant inbred lines originally derived from a BALB/c x C57BL/6 cross. The antiviral effect of exogenous interferon in the F1 progeny was comparable to the effect in BALB/c mice, indicating dominance of the greater sensitivity to interferon action. The results obtained with the six recombinant inbred lines suggested a multifactorial influence. In vitro, interferon pretreatment of encephalomyocarditis virus-infected BALB/c and C57BL/6 fibroblast cultures did not reveal a difference in sensitivity between the two mouse genotypes. This finding demonstrates that it is not always possible to extrapolate from in vitro to in vivo when sensitivity to interferon action is studied.

Peptidase isozymes of the leopard frog Rana pipiens: properties and genetics

The substrate specificity of five peptidases in tissues of the leopard frog, Rana pipiens, corresponds to mammalian peptidases (Pep) A, B, C, D, and S. The inheritance of electrophoretic variants of Pep A, B, C, and D verifies the genetic basis of the variants and the control of the enzymes by separate genetic loci. Electrophoretic patterns of heterozygotes suggest that Pep A, B, and D are dimers, whereas Pep C has a monomer structure. The tissue distribution and developmental patterns suggest that frog peptidases are subject to cellular regulation. Tests of genetic linkage show independent assortment for Pep A and Pep C and for Pep C and Pep D. Pep C is closely linked to superoxide dismutase-1 (6.87% recombination), and Pep B is linked to mannose phosphate isomerase (30.4% recombination).

Trisomy 16 in the mouse fetus associated with generalized edema and cardiovascular and urinary tract anomalies

Murine trisomy (Ts) 16 occurs in the fetal and neonatal progeny of males doubly heterozygous for the Robertsonian metacentric chromosomes Rb(16.17)7Bnr/Rb(9.16)9Rma and "all acrocentric" females. The developmental aspects of this trisomy were studied between day 12 of gestation and birth. So far, postnatal survival longer than a few hours after birth has not been observed. The frequency of Ts 16 among all implants decreased from more than 20% on day 14 to values between 4% and 7% shortly before term. Main features of Ts 16 are moderate general hypoplasia, slight developmental retardation, and cardiovascular anomalies. These latter were found in 96% of the trisomies, the great majority belonging to the transposition type, i.e., riding aorta, double outlet right ventricle (DORV) and transposition of the great arteries (TGA). Association with common atrio ventricular (AV)-canal was frequent. Other anomalies as "open eyelid", hydronephrosis, and hydroureter seem to be attributable to the effects of retardation. Generalized transient edema was frequent in the later gestational stages of Ts 16. Severe cardiovascular malformation is possible one of the factors responsible for late fetal or neonatal death in some cases. Another factor probably contributing to Ts 16 fetal mortality is insufficiency of placental function due to hypoplasia of the fetal vasculature of this organ. The teratological study of Ts 16 demands interest since evidence has been forwarded to consider this trisomy as an animal model of human trisomy 21.

Assignment of the gene for beta 2-microglobulin (B2m) to mouse chromosome 2

We have assigned the gene (B2m) coding for murine beta 2-microglobulin (B2M) to mouse chromosome 2 by using a novel panel of Chinese hamster-mouse somatic cell hybrid clones. Because of 35 independent primary hybrids used in this study were derived from two types of feral mice, each with a different combination of Robertsonian translocation chromosomes, as well as from mice with a normal complement of acrocentric chromosomes, analysis of 16 selected mouse enzyme markers provided data on the segregation of all 20 mouse chromosomes in these hybrids. Mouse B2M was identified in cell hybrids by immunoprecipitation with a species-specific anti-mouse B2M antiserum followed by two-dimensional polyacrylamide gel electrophoresis of the immunoprecipitated polypeptides. Enzyme analysis of the segregant clones excluded all chromosomes for B2m assignment except mouse chromosome 2, and karyotype analysis of nine informative hybrid clones confirmed the assignment of B2m to this chromosome. These results demonstrate that, in the mouse, as in man, B2m is not linked to the major histocompatibility or immunoglobulin loci.

[Chromosome abnormalities, tumours and developmental disorders (author's transl)]

Clonal chromosome disorders occurring or acquired at any postnatal age are often closely related with the origin of tumours. In man the Ph1-chromosome (9; 22) anomaly in CML or the 8; 14 translocation in the African malignant Burkitt Non-Hodgkin lymphoma are, among other cases, prominent examples. On the other hand, constitutive, inherited or novel chromosome anomalies conveyed from the zygote to all tissues of the organism may cause a higher risk for the origin of tumours. Rarely, inheritable minor structural chromosome mutations are known to determine the occurrence of dysontogenetic tumours, as e.g., nephroblastoma, but it is assumed that more such cases will become elucidated in the future. As a special phenomenon, true hydatiform mole is a tumour of the placental tissue due to a disorder of intragenome regulation. Constitutive or numerical structural chromosome anomalies of man are a frequent cause of early or late abortion or of abnormal development and malformation. Despite the predominating principle of selective fetal elimination, a few anomalies such as Down's syndrome, may escape to longer survival due to the relatively mild effects of chromosome 21 triplication. Trisomies which represent in man the most frequent type of chromosome disorders, can be induced, and systematically studied in an experimental model of the mouse. This allows the elaboration of the developmental profiles of all trisomies (and monosomies) of the mouse. Also, the above mentioned principle of selective elimination of abnormal implants can be analysed experimentally. Although the developmental span of a trisomic zygote is limited, there is evidence that cells and tissues isolated from the chromosomally abnormal organism can survive much longer. Thus, haemopoietic stem cells, at least in Ts 12 and 19 of the mouse, can be rescued from trisomic fetuses by transferring them to lethally irradiated adult mice, whose blood forming organs may eventually become permanently repopulated by the trisomic cell lineage. This type of experiments is suited for closer analyses of potential functions vs. defects of chromosomally abnormal cellular systems, e.g., with regard to growth and development.

Establishment of the interferon-mediated antiviral state: possible role of superoxide dismutase

Superoxide dismutase (SOD; superoxide: superoxide oxidoreductase, EC 1.15.1.1) catalyzes the dismutation of O2- free radicals formed during various enzymatic reactions or by ionizing radiation. Genes coding for SOD and sensitivity to exogenous interferon (IF) are syntenic in both mouse and man. Diethyldithiocarbamate (DDC) has been shown to inhibit SOD activity by chelating Cu2+, the metal ion essential for the catalytic activity of the enzyme. Mouse cell lines L, L929, L1210 S6, and L1210 R3 and a human cell line (WISH) pretreated with homologous IF and different concentrations of DDC for various periods of time were tested for their ability to support virus multiplication. Treatment of cells with DDC resulted in dose- and time-dependent inhibition of SOD activity and, simultaneously, in the reduction of antiviral protection by exogenous IF. Cells pretreated for 4 hr with DDC and then washed thoroughly were also resistant to IF, but DDC was without effect if the IF effect was first "established" by a 4-hr exposure to IF before addition of DDC. Under the conditions employed, DDC treatment did not result in any detectable inhibition of DNA, RNA, or protein synthesis in these cells. The data suggest that SOD or a related Cu2+-requiring enzyme may be necessary for the establishment of the IF-induced antiviral state in both human and murine cells.

Antiproliferative action of interferon on murine bone-marrow derived macrophages is influence by the genotype of the marrow-donor

Mouse interferon inhibits proliferation of bone-marrow derived macrophages. The degree of inhibition of cell proliferation is significant influenced by the genotype of the bone marrow donor in that C57BL/6 cells are more resistant to the cell multiplication inhibitory effect of interferon than are BALB/c cells. These results thus confirm earlier observations using murine erythroid precursors as target cells and point to the existence of genes modulating the action of interferon.

Synthesis of interferon-induced polypeptides in normal and chromosome 21-aneuploid human fibroblasts: relationship to relative sensitivities in antiviral assays

Localization of the gene for the species specific response to interferon (IFRC) to human chromosome 21 has stimulated interest in the effect of aneuploidy for chromosome 21 on cell sensitivity to interferon. Previous reports have shown that the relative sensitivities of trisomy 21, diploid and monosomy 21 human fibroblasts as measured in an antiviral assay are greater than the ratio 0.67 : 1.0 : 2 predicted on the basis of gene dosage for IFRC. As an alternative test for sensitivity, we have investigated the synthesis of interferon-induced polypeptides visualized by 2-dimensional gel electrophoresis and autoradiography. Of 10 such polypeptides identified, 3 were measured quantitatively in 2 diploid, 2 trisomic, and one monosomic fibroblast strains. In contrast to the antiviral response, the relative responses in this test correspond closely to expected gene dosage relationships over a range of interferon concentrations from 0.5 to 5000 units/ml. These results are compatible with the conclusion that the number of IFRC gene products (presumed to be the interferon receptor) per cell is proportional to the number of IFRC genes. Thus, the amplified effect of aneuploidy as measured in the antiviral response appears to result from some step subsequent to synthesis of interferon receptors and formation of interferon-receptor complexes.