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S Efrat

Publications and source records attributed to S Efrat.

46 records · Page 3Linked to original sources
PubMed1990

Proglucagon processing similar to normal islets in pancreatic alpha-like cell line derived from transgenic mouse tumor.

A pancreatic alpha-like cell line has been established from a glucagonoma arising in transgenic mice expressing a hybrid gene consisting of the rat glucagon-promoter sequence fused to the sequence encoding the SV40 T-antigen oncoprotein. The alpha-tumor cell 1 (alpha TC1) line maintained many characteristics of differentiated alpha-cells for greater than 40 passages in culture and expressed levels of glucagon mRNA 5- to 10-fold higher than those reported previously in rat and hamster islet cell lines. By radioimmunoassay, the cells synthesized considerable amounts of glucagon, glucagonlike peptide I (GLP-I), the major proglucagon fragment, and small amounts of unprocessed proglucagon but no free GLP-II. This distribution of peptides is similar to that found in extracts of rodent pancreases and is distinct from that seen with other islet cell lines, which process proglucagon in patterns more characteristic of intestinal cells. The GLP-I peptide in the alpha TC1 cell line was in the form of GLP-I-(1-37), which is inactive as a stimulator of insulin secretion, and not GLP-I-7-37) or -(7-36)-amide peptides, both of which are potent insulin secretagogues. The alpha TC1 cell line produced glucagon-related peptides in a relatively uniform pattern by immunocytochemistry, and electron microscopy revealed typical alpha-type (glucagon) secretory granules. Although the cell line was derived from an islet tumor producing only glucagon, the alpha TC1 cell line also produced insulin in addition to the glucagon peptides.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenoma, Islet Cell↗
PubMed1988

Glucagon gene regulatory region directs oncoprotein expression to neurons and pancreatic alpha cells.

The regulatory region of the rat preproglucagon gene targets expression of the SV40 large T oncoprotein to two cell types in transgenic mice, the pancreatic alpha cells and a set of neurons localized in the hindbrain, both of which normally produce preproglucagon. Additional neurons in the forebrain and midbrain stain for T antigen but do not express the endogenous glucagon gene. Synthesis of T antigen in endocrine alpha cells results in the heritable development of pancreatic glucagonomas. In brains of transgenic mice from three independent lineages, expression of the hybrid gene begins at embryonic day 12 in neuroblasts of the hindbrain, where it continues throughout adult life, most notably in the medulla. Remarkably, oncoprotein expression in both proliferating neuroblasts and mature neurons has no apparent consequences, either phenotypic or tumorigenic. Expression of the hybrid glucagon gene in both neurons and islet cells supports a possible interrelationship between these cell types.

Animals↗
PubMed1988

Beta-cell lines derived from transgenic mice expressing a hybrid insulin gene-oncogene.

Three pancreatic beta-cell lines have been established from insulinomas derived from transgenic mice carrying a hybrid insulin-promoted simian virus 40 tumor antigen gene. The beta tumor cell (beta TC) lines maintain the features of differentiated beta cells for about 50 passages in culture. The cells produce both proinsulin I and II and efficiently process each into mature insulin, in a manner comparable to normal beta cells in isolated islets. Electron microscopy reveals typical beta-cell type secretory granules, in which insulin is stored. Insulin secretion is inducible up to 30-fold by glucose, although with a lower threshold for maximal stimulation than that for normal beta cells. beta TC lines can be repeatedly derived from primary beta-cell tumors that heritably arise in the transgenic mice. Thus, targeted expression of an oncogene with a cell-specific regulatory element can be used both to immortalize a rare cell type and to provide a selection for the maintenance of its differentiated phenotype.

Adenoma, Islet Cell↗
PubMed1987

Coordinate expression of the endogenous p53 gene in beta cells of transgenic mice expressing hybrid insulin-SV40 T antigen genes.

The expression of p53 has been evaluated during oncogenesis of the pancreatic beta cells in transgenic mice harboring hybrid insulin-SV40 T antigen genes. Significant levels of p53 are detected in all cells expressing large T antigen. In contrast, the protein is undetectable in normal beta cells. There is a complete correspondence between the onset of expression of T antigen and the appearance of the endogenous p53 protein. In tumors, the two proteins are found in a complex. In addition, free uncomplexed T antigen is detected in every cell which expresses the transgene. These results are consistent with the participation of p53 in T antigen-induced tumorigenesis in vivo. The early appearance of p53 in all beta cells expressing large T cannot readily explain the progression of a small fraction of these cells into solid tumors.

Animals↗
PubMed1987

Bidirectional activity of the rat insulin II 5'-flanking region in transgenic mice.

We have identified a new transcription initiation site in the 5'-flanking regulatory region of the rat insulin II gene. This site is located on the opposite strand with respect to the insulin gene promoter, upstream of the insulin gene transcriptional enhancer. The cell-specific activity of this reverse promoter element is demonstrated in two lineages of transgenic mice, in which it directs expression of simian virus 40 T antigen specifically to the beta cells of the endocrine pancreas, resulting in development of pancreatic tumors. Analysis of RNA from the tumor cells demonstrates bidirectional transcription from the insulin regulatory region of the transgene. These data raise the possibility that bidirectional activity is a quality of the regulatory region of the insulin gene in its natural genomic context.

Animals↗
PubMed1984

A qualitative difference in the interleukin 2 (IL-2) requirement of helper and cytotoxic T lymphocytes.

A qualitative difference in the requirement of mouse helper and cytotoxic T lymphocytes for interleukin 2 (IL-2) was revealed by offering such cells IL-2 synthesized in Xenopus laevis oocytes that had been microinjected with messenger RNA (mRNA) encoding human IL-2. While both helper and cytotoxic mouse T-cell lines proliferate in response to the IL-2 present in medium conditioned by stimulated human lymphocytes, only helper-T-cell lines respond to human IL-2 secreted from oocytes. This result demonstrates a difference between helper and cytotoxic T lymphocytes in their response to IL-2. The growth response of murine cells shows that IL-2 secreted from human cells has properties not found in the IL-2 secreted from oocytes, even though a monoclonal antibody directed against the human IL-2 receptor blocks the activity of both types of IL-2. Quite possibly, this difference results from a post-translational modification.

Animals↗
PubMed1984

Superinduction of human interleukin-2 messenger RNA by inhibitors of translation.

Stimulation of human lymphocytes with phytohemagglutinin results in the induction of messenger RNA encoding interleukin-2 (IL-2), a lymphokine possessing immuno-regulatory properties. We have previously demonstrated a dramatic superinduction of the formation of IL-2 and of biologically active IL-2 mRNA in the presence of cycloheximide, an inhibitor of translation. These findings suggested the involvement of a labile protein repressor in the regulation of human IL-2 gene expression. Here, we show a commensurate superinduction of IL-2 mRNA sequences by three additional inhibitors of protein synthesis with distinct modes of action: T-2 toxin, pactamycin, and sparsomycin. These results strengthen the concept that a labile protein controls the formation of mature IL-2 mRNA. They tend to eliminate the possibility that the superinduction phenomenon observed in the presence of cycloheximide is due to its action on a process other than translation.

Cells, Cultured↗
PubMed1984

Control of biologically active interleukin 2 messenger RNA formation in induced human lymphocytes.

The regulation of human interleukin 2 (IL-2) mRNA production in induced normal lymphocytes was studied by following the expression of isolated mRNA in microinjected oocytes of Xenopus laevis. Mitogenic stimulation results in the appearance of greatly increased levels of IL-2 mRNA activity. This process requires de novo transcription. Induction is followed promptly by a shutoff of active IL-2 mRNA formation. This shutoff requires the synthesis of a protein repressor and can be prevented by cycloheximide, an inhibitor of translation. The presence of cycloheximide leads to extensive superinduction of IL-2, concomitant with an increase in active IL-2 mRNA formation up to 30-fold over normal levels. The repressor appears to be short-lived, as the addition of cycloheximide after shutoff leads to an immediate resumption of active IL-2 mRNA formation. The shutoff mechanism is restored rapidly upon removal of cycloheximide. The repressed state is readily reversed also by reinduction of the cells, even soon after shutoff has occurred, without a refractory period. The accumulated active IL-2 mRNA decays with a half-life of about 20 hr. The net result is the generation of a relatively short wave of IL-2 mRNA activity, demonstrating the tight control of IL-2 gene expression.

Cells, Cultured↗