A maternally inherited superantigen encoded by a mammary tumour virus.

A collection of superantigens, molecules which in combination with class II major histocompatibility complex (MHC) engage T cells bearing particular V beta chains as part of their alpha beta receptors, have recently been described. The mouse self superantigen, Mls-1a, for example, in conjunction with many MHC class II proteins, engages mouse T cells bearing V beta 6, 7, 8.1 and 9, almost regardless of the sequences of the other variable components of the receptors on the T cells. Two types of superantigen have been identified so far: first, superantigens encoded in the mouse genome, such as Mls-1a; second, superantigens produced by bacteria, such as the staphylococcal enterotoxins. Although the latter type of superantigens are in many cases known to be proteins of about 220 amino acids, nothing is known about the structures of any of the superantigens encoded in mouse. Here we describe the properties of a new mouse superantigen. The antigen is maternally transmitted in milk and is probably encoded by a mammary tumour virus (MTV). Given the known genetic linkage between at least one of the mouse genomic superantigens and endogenous MTV integration sites, it is tempting to speculate that the superantigen described here and some of the endogenous mouse superantigens are encoded by MTVs.     

MTV的时尚特点

音乐电视（MTV）这种独具特色的综合艺术形式，在中国迅速发展，已成为各家电视台重要的音乐节目之一。音乐电视作品被大众所喜爱，接受，传唱，产生一定的影响，从音乐电视的产生，音乐电视作品的创作，音乐电视节目主持人的特殊作用等方面，对音乐电视传播中的求新，求变及时尚性特点进行了探讨。     

RANK ligand mediates progestin-induced mammary epithelial proliferation and carcinogenesis

RANK ligand (RANKL), a TNF-related molecule, is essential for osteoclast formation, function and survival through interaction with its receptor RANK. Mammary glands of RANK- and RANKL-deficient mice develop normally during sexual maturation, but fail to form lobuloalveolar structures during pregnancy because of defective proliferation and increased apoptosis of mammary epithelium. It has been shown that RANKL is responsible for the major proliferative response of mouse mammary epithelium to progesterone during mammary lactational morphogenesis, and in mouse models, manipulated to induce activation of the RANK/RANKL pathway in the absence of strict hormonal control, inappropriate mammary proliferation is observed. However, there is no evidence so far of a functional contribution of RANKL to tumorigenesis. Here we show that RANK and RANKL are expressed within normal, pre-malignant and neoplastic mammary epithelium, and using complementary gain-of-function (mouse mammary tumour virus (MMTV)-RANK transgenic mice) and loss-of function (pharmacological inhibition of RANKL) approaches, define a direct contribution of this pathway in mammary tumorigenesis. Accelerated pre-neoplasias and increased mammary tumour formation were observed in MMTV-RANK transgenic mice after multiparity or treatment with carcinogen and hormone (progesterone). Reciprocally, selective pharmacological inhibition of RANKL attenuated mammary tumour development not only in hormone- and carcinogen-treated MMTV-RANK and wild-type mice, but also in the MMTV-neu transgenic spontaneous tumour model. The reduction in tumorigenesis upon RANKL inhibition was preceded by a reduction in pre-neoplasias as well as rapid and sustained reductions in hormone- and carcinogen-induced mammary epithelial proliferation and cyclin D1 levels. Collectively, our results indicate that RANKL inhibition is acting directly on hormone-induced mammary epithelium at early stages in tumorigenesis, and the permissive contribution of progesterone to increased mammary cancer incidence is due to RANKL-dependent proliferative changes in the mammary epithelium. The current study highlights a potential role for RANKL inhibition in the management of proliferative breast disease.     

Linkage of Mls genes to endogenous mammary tumour viruses of inbred mice.

T cells that recognize self antigen are clonally deleted in the thymus--a maturation process that occurs in the context of histocompatibility molecules and the T-cell receptor. The minor lymphocyte stimulation antigens (Mls) effect these deletions through interactions with the V beta portion of the T-cell receptor, thus mimicking bacterial 'superantigens'. Intrigued by the fact that each known Mls gene maps to the same chromosomal region as an endogenous mouse mammary tumour virus (Mtv), we reevaluated the linkage relationships between the two gene families. Here we report perfect concordance in inbred and recombinant inbred mice between the presence of four Mtv proviruses with the expression of Mls gene products. These data suggest a general model in which mammary tumour virus gene products themselves are the ligands that shape a considerable portion of the immunological repertoire of common laboratory mice.     

Glucocorticoids regulate expression of dihydrofolate reductase cDNA in mouse mammary tumour virus chimaeric plasmids

Fusions between the mouse mammary tumour virus long terminal repeat and a mouse dihydrofolate reductase cDNA have been constructed in a SV40 vector. When these plasmids are transferred into recipient cells, the production of dihydrofolate reductase is regulated by glucocorticoid hormones. These results define a hormonally responsive region of the viral genome.     

Restoration of normal function in genetically defective myotubes by spontaneous fusion with fibroblasts

Muscular dysgenesis in mice is a genetic disease of skeletal muscle caused by the recessive mutation mdg. Muscle fibres in affected mice are paralysed because of the failure of excitation-contraction coupling. Unlike normal myotubes in primary culture, dysgenic myotubes do not contract, either spontaneously or in response to electrical stimulation. The deficiency results from mutation of the gene for the skeletal muscle dihydropyridine receptor, an essential sarcolemmal component both of excitation-contraction coupling and of the slow calcium-ion channel. It has recently been shown that the addition of fibroblasts from normal (but not dysgenic) mice to cultures of dysgenic myotubes can restore spontaneous contractions in a small fraction of these myotubes, but the mechanism for this 'rescue' was not determined. In principle, if fibroblast nuclei were able to incorporate into myotubes, such nuclei could then supply the missing muscle-specific gene product. We have now investigated this possibility using nuclear, cytoplasmic and plasmalemmal markers. We report that the rescue to contractile ability in genetically paralysed dysgenic muscle is mediated by the previously unrecognized ability of fibroblasts to fuse spontaneously with developing myotubes.     

Androgen regulation of cell proliferation and expression of viral sequences in mouse mammary tumour cells

The role of steroids in promoting cell proliferation is well established but the molecular mechanisms are not clear. The S115 mouse mammary tumour cell line provides a model system for molecular studies in vitro in that it exhibits in tissue culture both a positive proliferative response to androgens and a change from a transformed phenotype in the presence of androgen to a normal phenotype when androgen is removed. We have considered here the possible involvement of mouse mammary tumour virus (MMTV) in these processes. We have demonstrated the presence in S115 cells of MMTV-related sequences which are transcribed into RNA only in the long-term presence of androgen. Prolonged culture in the absence of androgen, which results in loss of proliferative response to androgen, is accompanied by loss of MMTV-related RNA and increased methylation of MMTV-related sequences.     

A superantigen encoded in the open reading frame of the 3' long terminal repeat of mouse mammary tumour virus.

Mice express a collection of superantigens, which bind to class II major histocompatibility proteins and interact with T cells bearing particular V beta chains as part of their alpha beta receptors. These superantigens have been suggested to be encoded by exogenous or endogenous mouse mammary tumour viruses. One such superantigen is now shown to be encoded in the open reading frame of the long terminal repeat of a mammary tumour virus, a gene of previously unknown function.     

Activation of two signal-transduction systems in hepatocytes by glucagon

The ability of glucagon to stimulate glycogen breakdown in liver played a key part in the classic identification of cyclic AMP and hormonally stimulated adenylate cyclase. But several observations indicate that glucagon can exert effects independent of elevating intracellular cAMP concentrations. These effects are probably mediated by an elevation of the intracellular concentration of free Ca2+ although the mechanism by which this occurs is unknown. We show here that glucagon, at the low concentrations found physiologically, causes both a breakdown of inositol phospholipids and the production of inositol phosphates. Indeed, we show that the glucagon analogue, (1-N-alpha-trinitrophenylhistidine,12-homoarginine)glucagon (TH-glucagon), which does not activate adenylate cyclase or cause any increase in cAMP in hepatocytes yet can fully stimulate glycogenolysis, gluconeogenesis and urea synthesis, stimulates the production of inositol phosphates. This stimulation of inositol phospholipid metabolism by low concentrations of glucagon provides a mechanism whereby glucagon can exert cAMP-independent actions on target cells. We suggest that hepatocytes possess two distinct receptors for glucagon, a GR-1 receptor coupled to stimulate inositol phospholipid breakdown and a GR-2 receptor coupled to stimulate adenylate cyclase activity.     

Thy-1-mediated T-cell activation requires co-expression of CD3/Ti complex

In addition to monoclonal antibodies against the CD3 (T3)-T-cell antigen receptor (CD3/Ti) complex, several other monoclonals directed towards distinct cell surface structures on human (CD2 (T11) and Tp44) and murine (Thy-1, TAP, and Ly-6) T lymphocytes are capable of activating T cells. It has been proposed that such structures may function as alternative pathways of stimulation. To examine directly whether any relationship exists between Thy-1-dependent activation phenomena and T-cell activation mediated through the CD3/Ti complex, we have transfected several CD3/Ti- variants of the human T-cell line Jurkat with the murine Thy-1.2 gene. Our data indicate that in CD3/Ti-, Thy-1.2+ transfectants, monoclonal antibodies against Thy-1.2 can induce a rise in cytoplasmic free calcium ([Ca2+]i), but fail to stimulate interleukin-2 (IL-2) production. The only defect in these variant cell lines responsible for the inability to produce IL-2 in response to Thy-1 stimulation was in the expression of the CD3/Ti complex, because replacement of defective Ti alpha- or beta-chain genes reconstributed both surface expression of CD3/Ti and responsiveness to Thy-1 in the IL-2 production assay.     

Stimulation of the Na/H exchanger of sea urchin eggs by phorbol ester

On fertilization of a sea urchin egg, marked changes occur in the cytoplasmic concentration of calcium and hydrogen ions. These ionic signals represent the necessary and sufficient stimuli for the increased metabolism, protein synthesis and DNA synthesis that constitute egg activation. Cytoplasmic alkalinization, the major immediate cause of the increased rate of protein synthesis which occurs at fertilization, arises because the sperm-induced intracellular calcium transient activates a coupled flux of sodium ions and hydrogen ions across the oolemma. The experiments reported here suggest that the second messenger which links the activation of the Na/H exchange to the calcium transient may be a substance which stimulates protein kinase C8, as 12-O-tetradecanoyl phorbol acetate (TPA), a known activator of protein kinase C9, appears to stimulate protein synthesis by turning on the Na/H exchanger and causing a cytoplasmic alkalinization. Our data indicate that one consequence of treating other tissues with TPA, a tumour promoter, may be an increase in intracellular pH.     

Deleted in colorectal carcinoma suppresses metastasis in p53-deficient mammary tumours

Since its discovery in the early 1990s the deleted in colorectal cancer (DCC) gene, located on chromosome 18q21, has been proposed as a tumour suppressor gene as its loss is implicated in the majority of advanced colorectal and many other cancers. DCC belongs to the family of netrin 1 receptors, which function as dependence receptors as they control survival or apoptosis depending on ligand binding. However, the role of DCC as a tumour suppressor remains controversial because of the rarity of DCC-specific mutations and the presence of other tumour suppressor genes in the same chromosomal region. Here we show that in a mouse model of mammary carcinoma based on somatic inactivation of p53, additional loss of DCC promotes metastasis formation without affecting the primary tumour phenotype. Furthermore, we demonstrate that in cell cultures derived from p53-deficient mouse mammary tumours DCC expression controls netrin-1-dependent cell survival, providing a mechanistic basis for the enhanced metastatic capacity of tumour cells lacking DCC. Consistent with this idea, in vivo tumour-cell survival is enhanced by DCC loss. Together, our data support the function of DCC as a context-dependent tumour suppressor that limits survival of disseminated tumour cells.     

Phorbol ester and diacylglycerol mimic growth factors in raising cytoplasmic pH

There is now good evidence that cytoplasmic pH (pHi) may have an important role in the metabolic activation of quiescent cells. In particular, growth stimulation of mammalian fibroblasts leads to a rapid increase in pHi (refs 3-6), due to activation of a Na+/H+ exchanger in the plasma membrane, and this alkalinization is necessary for the initiation of DNA synthesis. However, the mechanism by which mitogens activate the Na+/H+ exchanger to raise pHi is not known, although an increase in cytoplasmic free Ca2+ ([Ca2+]i) has been postulated as the primary trigger. We now present data suggesting that the Na+/H+ exchanger is set in motion through protein kinase C, a phospholipid- and Ca2+-dependent enzyme normally activated by diacylglycerol produced from inositol phospholipids in response to external stimuli. Using newly developed pH microelectrodes and fluorimetric techniques, we show that a tumour promoting phorbol ester and synthetic diacylglycerol, both potent activators of kinase C (refs 12-15), mimic the action of mitogens in rapidly elevating pHi in different cell types. Furthermore, we demonstrate that, contrary to previous views, an early rise in [Ca2+]i is not essential for the activation of Na+/H+ exchange and the resultant increase in pHi. Finally, we suggest that an alkaline pHi shift, mediated by Na+/H+ exchange, may be a common signal in the action of those hormones which elicit the breakdown of inositol phospholipids.     

Tumour evolution inferred by single-cell sequencing

Genomic analysis provides insights into the role of copy number variation in disease, but most methods are not designed to resolve mixed populations of cells. In tumours, where genetic heterogeneity is common, very important information may be lost that would be useful for reconstructing evolutionary history. Here we show that with flow-sorted nuclei, whole genome amplification and next generation sequencing we can accurately quantify genomic copy number within an individual nucleus. We apply single-nucleus sequencing to investigate tumour population structure and evolution in two human breast cancer cases. Analysis of 100 single cells from a polygenomic tumour revealed three distinct clonal subpopulations that probably represent sequential clonal expansions. Additional analysis of 100 single cells from a monogenomic primary tumour and its liver metastasis indicated that a single clonal expansion formed the primary tumour and seeded the metastasis. In both primary tumours, we also identified an unexpectedly abundant subpopulation of genetically diverse 'pseudodiploid' cells that do not travel to the metastatic site. In contrast to gradual models of tumour progression, our data indicate that tumours grow by punctuated clonal expansions with few persistent intermediates.