Novel source of 1,2-diacylglycerol elevated in cells transformed by Ha-ras oncogene

Genes involved in the transduction of signals required for normal cell proliferation commonly appear to be subverted in the neoplastic process. One such group is the highly conserved family of ras genes, which have been detected as transforming genes in a wide variety of naturally occurring tumours. By analogy with other known G proteins, the p21 proteins encoded by ras genes may act as regulatory proteins in the transduction of signals that lead to DNA synthesis. A major pathway involved in the DNA synthesis induced by growth factors is mediated by phosphatidylinositol turnover: cleavage of phosphoinositides by phospholipase C produces 1,2-diacylglycerol, and inositol phosphates. The former acts as an essential cofactor for protein kinase C (ref. 4), and inositol-(1,4,5)-triphosphate mobilizes Ca2+ from non-mitochondrial intracellular stores. We demonstrate a reproducible increase in 1,2-diacylglycerol, in the absence of a detectable increase in inositol phosphates, in transformed cells containing Ha-ras oncogenes and with different membrane targeting signals for the ras p21 protein. These findings suggest that a source other than phosphoinositides exists for the generation of 1,2-diacylglycerol and that the Ha-ras oncogene specifically activates this novel pathway for 1,2-diacylglycerol production.     

AIDS virus-specific cytotoxic T lymphocytes in lung disorders

Human immunodeficiency virus (HIV) is implicated in the development of AIDS (acquired immune deficiency syndrome). HIV infection leads to the generation of HIV-specific thymus-derived (T) lymphocytes in humans and apes. We describe an experimental system permitting the quantitative and systematic analysis of HIV-specific cytotoxic T lymphocytes (CTL). Functional, HIV-specific CTL are obtained by broncho-alveolar lavage (BAL) from the lungs of seropositive patients with lymphocytic alveolitis. These alveolar CTL: (1) recognize and kill HIV-infected alveolar macrophages in vitro under autologous, but not heterologous, conditions; (2) correspond to standard CTL as they express the CD3 and CD8 surface markers, but not the CD4 marker; and (3) are restricted by class I HLA transplantation antigens in their cytotoxic activities. We propose the hypothesis that interactions between HIV-specific CTL and infected macrophages induce major inflammatory reactions in seropositive patients.     

Ligand binding to the beta-adrenergic receptor involves its rhodopsin-like core

Recently the genes for several hormone receptors that interact with guanine nucleotide binding proteins (G proteins) have been cloned, including the hamster beta 2-adrenergic receptor (beta 2AR), a human beta AR, the turkey erythrocyte beta AR and the porcine muscarinic acetylcholine receptor (MAR). All these receptors share some amino-acid homology with rhodopsin, particularly in 7 hydrophobic stretches of residues that are believed to represent transmembrane helices. To determine whether differences in ligand specificity result from the divergence in the sequences of the hydrophilic regions of these receptors, we have expressed in mammalian cells genes for the wild-type hamster and human beta AR proteins, and a series of deletion mutant genes of the hamster beta 2AR. The pharmacology of the expressed receptors indicates that most of the hydrophilic residues are not directly involved in the binding of agonists or antagonists to the receptor. In addition, we have identified a mutant receptor that has high agonist affinity but does not couple to adenylate cyclase.     

The role of clonal selection and somatic mutation in autoimmunity

Polyclonal activation has been proposed as the reason that autoantibodies are produced during autoimmune disease. This model denies a role for specific antigen selection of B cells and predicts instead a multiclonal population of unmutated or randomly mutated autoantibodies. We have found that the genetic features and clonal composition of spontaneously derived immunoglobulin G (IgG) antiself-IgG (rheumatoid factor (RF] autoantibodies derived from the autoimmune MRL/lpr mouse strain are inconsistent with both the predictions of this model and the actual outcome of experimental polyclonal activation. Instead we have found that MRL/lpr RFs are oligoclonal or even monoclonal in origin. They harbour numerous somatic mutations which are distributed in a way that suggests immunoglobulin-receptor-dependent selection of these mutations. In this sense, the MRL/lpr RFs resemble antibodies elicited by exogenous antigens after secondary immunization. The parallels suggest that, like secondary immune responses, antigen stimulation is important in the generation of MRL/lpr RFs.     

The X-linked chronic granulomatous disease gene codes for the beta-chain of cytochrome b-245

Chronic granulomatous disease (CGD) is a rare inherited disorder associated with a profound predisposition to infection due to the lack of a microbicidal oxidase system in the phagocytes of these patients. This syndrome is most commonly inherited through a defect on the X chromosome and the only clearly defined component of the oxidase system, the very unusual cytochrome b (b-245), has been shown to be missing from the cells of these patients. This cytochrome is a heterodimer composed of an alpha-chain of relative molecular mass (Mr) 23,000 (23K) and a 76-92K beta-chain; neither are detectable in neutrophils from X-linked CGD subjects. The defective X-CGD gene has recently been cloned by 'reverse genetics' but the protein predicted from the proposed complementary DNA sequence was not identified. We have purified the beta-chain of the cytochrome and sequenced 43 amino acids from the N terminus. Almost complete homology was obtained between this sequence and that of the complementary nucleotides 19-147 of the sequence of the X-CGD gene, originally designated as a non-coding region.     

Failure of familial Alzheimer's disease to segregate with the A4-amyloid gene in several European families

The gene coding for the amyloid protein, a component of neuritic plaques found in brain tissue from patients with Alzheimer's disease, has been localized to chromosome 21, and neighbouring polymorphic DNA markers segregate with Alzheimer's disease in several large families. These data, and the association of Alzheimer's disease with Down's syndrome, suggest that overproduction of the amyloid protein, or production of an abnormal variant of the protein, may be the underlying pathological change causing Alzheimer's disease. We have identified a restriction fragment length polymorphism of the A4-amyloid gene, and find recombinants in two Alzheimer's disease families between Alzheimer's disease and the A4-amyloid locus. This demonstrates that the gene for plaque core A4-amyloid cannot be the locus of a defect causing Alzheimer's disease in these families. These data indicate that alterations in the plaque core amyloid gene cannot explain the molecular pathology for all cases of Alzheimer's disease.     

Demographic study of a wild house sparrow population by DNA fingerprinting

Over the past twenty years, several techniques from biochemical and molecular genetics, such as enzyme electrophoresis and isoelectric focusing, have been widely and successfully applied to the study of population differentiation and evolution. However, they have been less applicable to demographic problems such as assigning parentage to individuals within a population. This stems from a general weakness of data derived from enzyme loci: allele frequencies at polymorphic loci are sufficiently skewed that the majority of individuals are of one or two genotypes. Many enzyme systems can only be examined post mortem, so that the loci are of little use if the animals are to be studied in the wild. The search for new and more sensitive techniques for detecting genetic variation has continued, and recently a major discovery has come from molecular biology. Jeffreys et al. have reported the detection of a type of hypervariable 'minisatellite' DNA that is extraordinarily polymorphic in human populations. We have applied their technique to several bird species and particularly to a population of house sparrows (Passer domesticus) near Nottingham. We report here that one of the human minisatellite clones is a suitable probe for sparrow DNA and that it reveals variation as extensive as that found in man. These results suggest that analysis of minisatellite DNA will be a powerful tool in the study of demographic population genetics.     

Genomic imprinting determines methylation of parental alleles in transgenic mice

Mouse embryogenesis relies on the presence of both the maternal and the paternal genome for development to term. It has been proposed that specific modifications are imprinted onto the chromosomes during gametogenesis; these modifications are stably propagated, and their expression results in distinct and complementary contributions of the two parental genomes to the development of the embryo and the extraembryonic membranes. Genetic data further suggest that a substantial proportion of the genome could be subject to chromosomal imprinting, the molecular nature of which is unknown. We used random DNA insertions in transgenic mice to probe the genome for modified regions. The DNA methylation patterns of transgenic alleles were compared after transmission from mother or father in seven mouse strains carrying autosomal insertions of the same transgenic marker. One of these loci showed a clear difference in DNA methylation specific for its parental origin, with the paternally inherited copy being relatively undermethylated. This difference was observed in embryos on day 10 of gestation, but not in their extraembryonic membranes. Moreover, the methylation pattern was faithfully reversed upon each germline transmission to the opposite sex. Our findings provide evidence for heritable molecular differences between maternally and paternally derived alleles on mouse chromosomes.     

Kinetics of smooth and skeletal muscle activation by laser pulse photolysis of caged inositol 1,4,5-trisphosphate

Inositol 1,4,5-trisphosphate (InsP3) can stimulate skinned smooth and skeletal muscle to contract by initiating Ca2+ release from the sarcoplasmic reticulum. Whether this process is an integral component of the in vivo muscle activation mechanism was tested by releasing InsP3 rapidly within skinned muscle fibers of rabbit main pulmonary artery and frog semitendinosus. InsP3 was liberated on laser pulse photolysis of a photolabile but biologically inactive precursor of InsP3 termed caged InsP3. Caged InsP3 is a mixture of compounds in which InsP3 is esterified with 1(2-nitrophenyl)diazoethane (probably at the P4- or P5-position). Photochemical release of InsP3 induced a full contraction in both muscles at physiological free Mg2+ concentrations, but only in the smooth muscle were the InsP3 concentration (0.5 microM) and the activation rate compatible with the in vivo physiological response. Endogenous InsP3-specific phosphatase activity was present in smooth muscle and had about 35-fold greater activity than that in the skeletal-muscle preparation. Caged InsP3 was not susceptible to phosphatases in either preparation.