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S Gordon

Publications and source records attributed to S Gordon.

At least 595 records · Page 33Linked to original sources
PubMed1971

The preparation and properties of macrophage-L cell hybrids.

The plasma membrane of the mouse peritoneal macrophage has specific receptors which enable the cell to bind IgG or complement-coated sheep red cells and is also rich in a divalent cation-dependent adenosine triphosphatase (ATPase) activity. L cells lack these macrophage membrane markers. The question of macrophage membrane receptor expression was investigated in DBA/2 mouse macrophage x mouse LMTK(-) cell hybrids produced with the aid of Sendai virus. Three independent clones and one mass culture were isolated by their ability to grow in hypoxanthine, aminopterin, and thymidine (HAT) selection medium. These hybrids retained 85-100% of the sum of two parent cells' chromosomes and expressed several genes derived from both parents, including glucose phosphate isomerase isozymes and H-2 antigens. The hybrids displayed ATPase activity which was intermediate between that of the macrophage and L cell. The macrophage specific receptors for antibody or complement-coated red cells could not be demonstrated on hybrid cells. The selective absence of these receptors is probably because of a failure in gene expression rather than to loss of genes.

Adenosine Triphosphatases↗
PubMed1971

Macrophage-melanoma cell heterokaryons. 3. The activation of macrophage DNA synthesis. Studies with inhibitors of protein synthesis and with synchronized melanoma cells.

Dormant macrophage nuclei initiate DNA synthesis 2-3 hr after fusion of macrophages with exponentially growing melanoma cells. Cycloheximide treatment (1-5 microg/ml) of heterokaryons during the preceding lag period inhibits the initiation of macrophage DNA synthesis, in a reversible fashion. Each type of cell was also treated with streptovitacin A, an irreversible inhibitor of protein synthesis. Pretreatment of the melanoma cells (0.5-2 microg/ml), 1 hr before fusion, inhibited the induction of macrophage DNA synthesis in heterokaryons, whereas pretreatment of macrophages (1-20 microg/ml) had no effect. Melanoma cell pretreatment reduced the incorporation of leucine-(3)H into the cytoplasm and nuclei of heterokaryons, whereas macrophage pretreatment had no effect. These experiments suggested that melanoma proteins played an important role in the initiation of macrophage DNA synthesis. The relationship between the melanoma cell cycle and macrophage DNA synthesis was studied with synchronous melanoma cells. If the melanoma cells were in S phase at the time of fusion, macrophage DNA synthesis occurred 2 hr later. However, the fusion of melanoma cells in G(1) delayed macrophage DNA synthesis until the melanoma nuclei had entered S. Experiments with actinomycin and cycloheximide showed that RNA and protein, essential to achieve DNA synthesis in the macrophage nucleus, were made during late G(1) as well as S. Melanoma cells and macrophages differ in their radiolabeled acid-soluble products after incubation in thymidine-(3)H. Thymidine taken up by the macrophage remained unphosphorylated, whereas it was recovered mainly as thymidine triphosphate from melanoma cells. These findings, as well as those reported previously, suggest that the melanoma cell provides the RNA, protein, and precursors which initiate macrophage DNA synthesis. In the absence of a requirement for new macrophage RNA and protein synthesis, other changes must be responsible for the 2 hr delay in DNA synthesis. These may involve physical changes in DNA, associated with swelling, as well as the transport of melanoma products into the macrophage nucleus.

Animals↗
PubMed1971

Macrophage-melanoma cell heterokaryons. IV. Unmasking the macrophage-specific membrane receptor.

Mouse peritoneal macrophages possess a specific plasma membrane receptor for antibody-coated particles. Sheep red cells coated with rabbit 7S antibody attach readily to the macrophage surface and are subsequently interiorized. The fusion of macrophage with nonphagocytic mouse melanoma cells produces heterokaryons in which the macrophage receptor is drastically altered. The receptor is present shortly after fusion and heterokaryons are actively phagocytic. The ability to bind and ingest red cells is, however, progressively lost over the next 12-24 hr and does not reappear thereafter. Exposure of heterokaryons to trypsin (1-100 microg/ml for 30 min at 37 degrees C) results in the reappearance of initial receptor activity and the unmasking of the surface receptor. This property is again lost upon subsequent cultivation. The masking process takes place when cells are cultivated in the absence of IgG so that the adsorption of antibody from the medium is not responsible for this phenomenon. Inhibition of heterokaryon protein synthesis preserves phagocytic activity in a reversible fashion and prevents the masking of macrophage receptors. Inhibition of melanoma RNA synthesis before fusion is also able to block subsequent masking, but is ineffective if delayed until after fusion. Ultraviolet irradiation of the melanoma cell before fusion prevents subsequent masking, whereas similar treatment of the macrophage has no effect. Cells differ markedly in their ability to mask the macrophage phagocytic receptor after fusion. Ehrlich ascites tumor cells mask the receptor rapidly, primary chick fibroblasts minimally, and embryonic chick erythrocytes not at all.

Animals↗
PubMed1971

Macrophage-melanocyte heterokaryons. II. The activation of macrophage DNA synthesis. Studies with inhibitors of RNA synthesis.

Mouse peritoneal macrophages, which do not synthesize DNA in vitro, were fused with melanocytes, a mouse cell strain which proliferates rapidly in vitro. DNA synthesis was induced in macrophage nuclei 2-3 hr after fusion and occurred irrespective of the number of macrophage nuclei present per melanocyte nucleus in each heterokaryon. 50-80% of macrophage nuclei initiated DNA synthesis in the 3-7 hr period after fusion. The activation of most 11-12-day chick red cell nuclei in melanocyte cytoplasm took longer than 10 hr. The lag before DNA synthesis may reflect the heterochromatin content of each nucleus. Studies with actinomycin showed that heterokaryon RNA synthesis was essential for subsequent macrophage DNA synthesis. This RNA was synthesized 1-4 hr before the DNA and was unlikely to be ribosomal RNA, since it was insensitive to <0.1 microg/ml actinomycin. Melanocytes and macrophages were treated before fusion with actinomycin and bromotubercidin to bring about a more selective inhibition of RNA synthesis. Macrophages pretreated for 1 hr with 5 microg/ml of actinomycin showed less than 20% of control RNA synthesis in the first 4 hr after fusion, but a normal activation of macrophage DNA synthesis. Pretreatment of melanocytes for 3-7 hr with 5 microg/ml bromotubercidin, a reversible inhibitor of RNA synthesis, prevented macrophage DNA synthesis without affecting macrophage RNA synthesis in the heterokaryons (81% of control). These studies showed that only melanocyte RNA synthesis was essential for the production of macrophage DNA. The exposure of one cell partner to actinomycin before fusion caused cross-toxicity of the untreated nucleus after fusion. Bromotubercidin, an adenosine analogue which is incorporated into RNA, did not give rise to such cross-toxicity after fusion. Once the macrophage nucleus becomes activated in the heterokaryon it becomes less sensitive to the action of actinomycin.

Autoradiography↗