WITHDRAWN: Plant Cell Hybrids

Ringertz, Nils R.; Savage, Robert E.

doi:10.1016/b978-0-12-589150-9.50020-0

Cited by 35 publications

(48 citation statements)

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“…Our findings are in agreement with the fact that rRNA synthesis decreases in differentiated cells (44) and that the nucleolus actually disappears in terminally differentiated cells. The chick erythrocyte nucleus is the best example of nucleolar involution in differentiated cells (45). Finally, rRNA synthesis is much lower in 32D IGF-IR cells that do not express IRS-1 than in 32D IGF-IR/IRS-1 cells, where IRS-1 is in the nucleus.…”

Section: Discussionmentioning

confidence: 99%

Nuclear Translocation of Insulin Receptor Substrate-1 by Oncogenes And Igf-I

Batta

Innocent

et al. 2002

Journal of Biological Chemistry

174

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The insulin receptor substrate-1 (IRS-1) is one of the major substrates of both the insulin and IGF-I receptors and is generally localized in the cytosol/membrane fraction of the cell. We show here that a substantial fraction of IRS-1 is translocated to the nucleus in mouse embryo fibroblasts (MEF) expressing the simian virus 40 T antigen. Nuclear translocation of IRS-1 occurs also in MEF stimulated with IGF-I or in MEF expressing the oncogene v-src. Nuclear translocation of IRS-1 can be demonstrated by confocal microscopy, immunohistochemistry, or subcellular fractionation. An antibody to IRS-1 immunoprecipitates from nuclear fractions (but not from cytosolic fractions) the upstream binding factor, which is a key regulator of RNA polymerase I activity and ribosomal RNA (rRNA) synthesis. In agreement with this finding, in 32D murine hemopoietic cells, nuclear translocation of IRS-1 correlates with a markedly increased rRNA synthesis. Our experiments suggest that nuclear IRS-1 may play a specialized role in rRNA synthesis and/or processing.The insulin receptor substrate (IRS) 1 proteins are a family of docking proteins, which include IRS-1-4, Gab-1, and p62 dok (1). IRS-1 was the first to be identified as a docking protein for both the insulin and the IGF-I receptors. It transmits a signal from both receptors by interacting with a number of partners, including phosphatidylinositol 3-kinase, SHP2, Grb2, Crk, and others (2, 3). Tyrosine kinase activity of the receptors and phosphorylation of IRS-1 are essential steps in signal transduction. Of the downstream signals generated by IRS-1, the best studied is the phosphatidylinositol 3-kinase signaling pathway, which plays a major role in a number of biological responses to growth factors (1, 4). IRS-1 interacts directly with both the insulin and the IGF-I receptors, and the domains required for their interaction have also been identified (5). Because of its direct interaction with the receptors, its size, and its downstream signaling, it has been generally assumed that IRS-1 is an exclusively cytosolic (or plasma membrane) protein (6, 7). However, IRS-1 is known to interact with the SV40 T antigen (8, 9) and nucleolin (10). T antigen and nucleolin are predominantly nuclear proteins, although minor fractions of either protein can be found in the cytosol (11-13). It has been therefore tacitly assumed that IRS-1, anchored to the receptor, was interacting with the minor cytosolic fractions of T antigen and nucleolin. There is evidence, however, that signal-transduction molecules can translocate to the nucleus. They include mitogen-activated protein kinase (14), p70 S6K /TOR (15, 16), the STAT proteins (17, 18), Akt (19), ␤-catenin (20), the epidermal growth factor receptor (21), phosphatases (22), IRS-3 (23), and a cleaved ErbB-4 receptor (24). Indeed, Jans and Hassan (25) have summarized in a review the evidence that growth factors and their receptors can accumulate in the nuclei of cells. IGF-I, IGF-IR, and IRS-1 are not mentioned in that review, but insulin is (26).T...

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Section: Discussionmentioning

confidence: 99%

Nuclear Translocation of Insulin Receptor Substrate-1 by Oncogenes And Igf-I

Batta

Innocent

et al. 2002

Journal of Biological Chemistry

174

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“…What might these interactions be? It has been shown that, in heterokaryons formed between nondividing cells (erythrocytes, macrophages) and cells of permanent lines (A9, HeLa, melanoma cells), DNA synthesis is induced in the dormant nucleus (28)(29)(30); such is probably also the case in hepatocyte-A9 heterokaryons. Indeed, hybrids derived from these fusions (with the exception of erythrocyte hybrids) have a normal chromosome constitution (7,27).…”

Section: Discussionmentioning

confidence: 99%

Control of serum protein production in hepatocyte hybridomas: immortalization and expression of normal hepatocyte genes.

Szpirer¹,

Szpirer²,

Wanson³

1980

Proc. Natl. Acad. Sci. U.S.A.

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ABSTRACT"Hepatocyte hybridomas" have been isolated after fusion of adult hepatocytes and a-fetoprotein (AFP-producing mouse hepatoma cells. The yield of viable hybrid clones was low but could be increased by culturing the cells in the presence of insulin. On the basis of their chromosome constitution, the hybrids were classified into two groups characterized by either a single or a double set of mouse (hepatoma) chromosomes. The hybrids segregated rat chromosomes and thus constitute an excellent material for gene mapping studies in the rat.Most of the hepatocyte hybridomas retained the production of one or more rat serum proteins, indicating that the corresponding structural genes, contributed by the normal hepatocyte parent, have been immortalized and maintained in the active state after fusion. However, these hybrids do not produce rat AFP, although mouse AFP synthesis is maintained. This result strongly suggests that silent rat (hepatocyte) AFP genes coexist in hepatocyte hybridoma nuclei with active mouse (hepatoma) AFP genes. Finally, on the basis of certain proerties of these hepatocyte-hepatoma hybrids, we suggest that the nondividing state of the hepatocytes is actively controlled by a regulatory mechanism which prevents DNA synthesis or entry into mitosis or both. Hybrids formed between normal diploid cells and tumor cells of the same tissue origin (hybridomas) have proved useful for immortalizing certain functions expressed by normal differentiated cells, as shown by the numerous studies on the now classical "lymphocyte hybridomas" (1, 2). We have explored the possibility that differentiated liver functions could be immortalized by hybridization of normal hepatocytes with mouse hepatoma cells. In this communication, we report the successful isolation of interspecies "hepatocyte hybridomas" and show that these hybrids provide a tool for immortalizing normal liver functions.Hybridomas could also be valuable for analyzing the expression of differentiated functions subjected to developmental controls or to alterations associated with a malignant phenotype. This possibility has not yet been subjected to much investigation. Production of a-fetoprotein (AFP) is modulated during hepatic differentiation: AFP is produced actively by the fetal hepatocytes but only in trace amounts by the adult liver; and, in addition, it is synthesized by most hepatomas (3, 4). By fusing liver cells which differ in the expression of the AFP gene, it should be possible to explore the mechanisms controlling the expression of this gene. In previous studies, we have shown that hybrids formed between AFP-producing mouse hepatoma cells and non-AFP-producing rat hepatoma cells retain the capacity to secrete mouse AFP (5), unlike hybrids generated between AFP-producing mouse hepatoma cells and fibroblasts (6, 7). By fusing AFP-producing mouse hepatoma cells with adult ratThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U....

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“…This process of cell fusion has been known for a long time and it has been recognized as a spontaneous occurrence in multicellular organisms (Ringertz and Savage 1976). Induced cell fusion was then developed to study the expression of traits of two differentiated states in new hybrids: a typical example is the reactivation of the inactive X chromosome when thymocytes were fused with teratocarcinoma cells (Takagi et al 1983).…”

Section: The Problem Of Cell 'Plasticity'mentioning

confidence: 99%