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Biomedical subjects

R E Scott

Publications and source records attributed to R E Scott.

At least 109 records · Page 6Linked to original sources
PubMed1982

Topography of the predifferentiation GD growth arrest state relative to other growth arrest states in the G1 phase of the cell cycle.

The differentiation of 3T3 T proadipocytes is preceded by growth arrest at a state in the G1 phase of the cell cycle (GD) which is distinct from other G1 growth arrest states including those induced by serum deprivation (GS) or nutrient deprivation (GN) (Scott et al., 1982). We now report that the GD, GS, and GN arrest states are also distinct in their topography in G1. This conclusion was derived from kinetic studies which measured the time required for cells arrested at various G1 states to synthesize DNA and from studies on the ability of GD-, GS-, or GN-arrested cells to be converted from one arrest state to another in the absence of DNA synthesis. The results suggest that relative to the start of the G1 phase of the cell cycle, the following arrest state topography exists: GD, GS, GN.

Adipose Tissue↗
PubMed1982

Growth arrest of proadipocytes at a distinct predifferentiation G1 state associated with cytotoxic responsiveness to 8-bromo cyclic AMP.

The control of cell proliferation can result from the coupling of growth arrest and differentiation. In this regard, we recently demonstrated that growth arrest which precedes the differentiation of 3T3 T proadipocytes must occur at a distinct state in the G1 phase of the cell cycle (GD). Cells arrested at GD differ in several biological parameters from cells arrested in G1 at other states induced by either serum deprivation (GS) or nutrient deficiency (GN). Specifically, GD-arrested cells can differentiate in the absence of DNA synthesis and GD-arrested cells can be induced to proliferate when stimulated with 1-methyl-3-isobutylxanthine; GS- and GN-arrested cells cannot. In addition, GD-, GS- and GN-arrested cells reside at topographically distinct states in G1. We now report that GD-arrested proadipocytes are also distinct in that they are highly sensitive to a cytotoxic effect of 8-bromocyclic AMP, whereas GS- and GN-arrested cells are not.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1982

Coupling of growth arrest and differentiation at a distinct state in the G1 phase of the cell cycle: GD.

The differentiation of most mammalian cells is preceded by growth arrest in the G1 phase of the cell cycle, but the characteristics of this state have not been established. We now report that the growth arrest that precedes the differentiation of BALB/c 3T3 T mouse proadipocytes must occur at a distinct state in G1 designated GD. GD-arrested cells are characterized by their ability to differentiate in the absence of DNA synthesis and by their unique sensitivity to the mitogenic effect of isobutylmethylxanthine. Proadipocytes induced to become G1 growth arrested at other states by culture in medium deficient in growth factor or nutrients, by contrast, are unable to differentiate in the absence of DNA synthesis and are not stimulated to proliferate by isobutylmethylxanthine even when they are exposed to differentiation-promoting medium prior to arrest. These data support the conclusion that, prior to the expression of a differentiated phenotype, proadipocytes must arrest their growth at a distinct state in the G1 phase of the cell cycle, GD. These data also provide the basis for the hypothesis that carcinogenesis is associated with defects in the coupling of growth arrest and differentiation at the GD state.

1-Methyl-3-isobutylxanthine↗
PubMed1982

Coupling of proadipocyte growth arrest and differentiation. I. Induction by heparinized medium containing human plasma.

The differentiation of proadipocytes in vitro typically required prolonged culture of cells as a high density in high concentrations of serum and added hormones. With such culture conditions it is difficult to design experiments to determine the mechanisms that control the differentiation process. We now describe the rapid and parasynchronous growth arrest and differentiation of low density murine proadipocytes in heparinized medium containing only human plasma. When low density cells are cultured under these conditions, growth arrest at a distinct state in the G1 phase of the cell cycle occurs within 2 d and the differentiation of 80-100% of the cell population occurs within 4 d thereafter. The factors in human plasma which promote growth arrest and differentiation are heat labile and can be separated by barium adsorption. In the following paper we have used these methods to show that there are five separate phases which regulate the coupling of proadipocyte growth arrest and differentiation. The data reported in this paper establish that: (a) high cell density and extensive cell-to-cell contact are not required for adipocyte differentiation, (b) prolonged culture is not required for adipocyte differentiation, and (c) high concentrations of serum and/or added hormones are not required for adipocyte differentiation.

Adipose Tissue↗
PubMed1982

Coupling of proadipocyte growth arrest and differentiation. II. A cell cycle model for the physiological control of cell proliferation.

Experimental evidence is presented that supports a cell cycle model showing that there are five distinct biological processes involved in proadipocyte differentiation. These include: (a) growth arrest at a distinct state in the G1 phase of the cell cycle; (b) nonterminal differentiation; (c) terminal differentiation; (d) loss of the differentiated phenotype; and (e) reinitiation of cell proliferation. Each of these events is shown to be regulated by specific human plasma components or other physiological factors. At two states designated GD and GD', coupling of growth arrest and differentiation is shown to occur. We propose that these mechanisms for the coupling of growth arrest and differentiation are physiologically significant and mimic the regulatory processes that control stem cell proliferation in vivo.

Adipose Tissue↗
PubMed1982

Neoplastic transformation and defective control of cell proliferation and differentiation.

The control of proliferation of nontransformed 3T3 t-proadipocytes in vitro can be mediated at three states in the G1 phase of the cell cycle. These states are induced by the commitment of cells to differentiate (GD); by growth factor deprivation at low density or "contact inhibition" at high density (Gs); and by nutrient deprivation (GN). To determine if neoplastic transformation of proadipocytes is associated with a selective defect in one or more of these G1 growth arrest processes, we developed and studied eight cloned and several noncloned tumorigenic proadipocyte cell lines. We report that all transformed proadipocyte cell lines are tumorigenic and all lack the ability to arrest at GD and differentiate. By contrast, or approximately 90% of transformed proadipocyte cell lines retain their ability to growth arrest at Gs at low density when deprived of growth factors, and or approximately 90% growth arrest at GN when deprived of nutrients. These observations suggest that neoplastic transformation of proadipocytes is primarily associated with abrogation of growth control mediated at GD. However, whereas most transformed proadipocytes arrest at Gs at low density when deprived of serum, all transformed proadipocyte cell lines do not efficiently arrest at Gs at high density due to "contact inhibition." This suggests that neoplastic transformation of proadipocytes results from a primary defect in growth control mediated at GD and from an additional defect at Gs. These results are discussed with respect to their possible significance for the biological mechanisms of the initiation and promotion of carcinogenesis.

Adipose Tissue↗
PubMed1982

Cell cycle models for the aberrant coupling of growth arrest and differentiation in hyperplasia, metaplasia, and neoplasia.

The control of cell proliferation can be regulated by the coupling of growth arrest and differentiation. Since this process has been demonstrated both in vivo and in vitro, it is thought to be of considerable physiologic significance. The mechanisms that serve to couple growth arrest and differentiation were, however, poorly defined prior to our recent studies. We established that the coupling of growth arrest and differentiation of proadipocytes occurs at a distinct state in the G1 phase of the cell cycle, GD, and that it consists of at least five phases. These include: 1) growth arrest at GD; 2) nonterminal differentiation; 3) terminal differentiation; 4) loss of the differentiated phenotype, and 5) reinitiation of cell proliferation. On the basis of these observations we developed a cell cycle model to explain the biologic mechanisms of the coupling process. This model is now used to predict where defects in the coupling of growth arrest and differentiation may occur in hyperplastic, metaplastic, and neoplastic cells.

Adipose Tissue↗
PubMed1981

Freeze-fracture electronmicroscopic analysis of plasma membranes of cultured muscle cells in Duchenne dystrophy.

Depletion of intramembranous particles has been reported in the muscle fiber plasma membrane in Duchenne dystrophy. We searched for a similar abnormality in plasma membranes of cultured muscle cells obtained from six patients with Duchenne dystrophy and six controls. A precise method for phase microscopic to freeze-fracture electronmicroscopic correlation was devised to identify the cell of origin of each replicated membrane face. For both control and patient cells, P-face particle density was higher in myotubes than in mononuclear cells. However, there were no significant differences between control and dystrophic cells when comparing P faces of myotubes, E faces of myotubes, P faces of single cells, or E faces of single cells. The frequency distribution of particle diameters was similar in P faces of control and Duchenne myotubes. Other structural features of the freeze-fractured plasma membrane also were similar.

Adolescent↗
PubMed1981

PRomotion of smooth surface tumorigenicity by phorbol myristate acetate in Balb/3T3 cells and Balb/3T3 T proadipocytes.

In vitro exposure of Balb/3T3 cells to phorbol and phorbol myristate acetate significantly increased their tumorigenic potential when implanted sc on smooth surface plates into syngeneic mice. This finding supports the hypothesis that many so-called normal cell lines may actually represent initiated cells that can be induced to become tumorigenic following exposure to promoting agents. Since the tumorigenic potential of many tissues in vivo is inversely proportional to the state of differentiation of the stem cell populations undergoing transformation, we assayed the relative tumorigenicity of Balb/3T3 T proadipocytes, which can differentiate in culture, and Balb/3T3 cells, which cannot differentiate in culture. The effects of tumor-promoting agents on these cells were also tested. Plate-implanted Balb/3T3 T proadipocytes were markedly less tumorigenic than Balb/3T3 cells, and Balb/3T3 T proadipocytes were not sensitive to the promotional effects of phorbol myristate acetate.

Animals↗
PubMed1981

Differentiation of fibroblast-like cells into macrophages.

Differentiated cells with the morphological, enzymatic, antigenic, and functional characteristics of macrophages formed when a variety of nontransformed and transformed fibroblast-like mouse embryo cell lines were grown in a medium supplemented only with human plasma. Differentiated cells contained numerous lysosomes and phagosomes, nonspecific esterase and acid phosphatase activities, and cell surface la antigens and were capable of phagocytosis of iron particles. Differentiated cells were also growth arrested in the G1 phase of the cell cycle, but both growth arrest and differentiation were reversible processes. These observations suggest that cells with the morphology of fibroblasts have the capacity to undergo nonterminal differentiation into macrophages.

Animals↗
PubMed1980

Plate-induced tumors of BALB/3T3 cells exhibiting foci of differentiation into pericytes, chondrocytes, and fibroblasts.

The BALB/3T3 clone A31 mouse embryo cell line has been used by many investigators as a model "normal" "fibroblast" line for a variety in vitro studies. It has been shown, however, that these cells are not "normal" because they will produce tumors within 2-4 months if 3 x 10(4) cells are implanted subcutaneously in BALB/c mice attached to 0.2 x 5 x 10-mm plastic plates. Previous studies also suggested that these cells were not fibroblasts because they gave rise tumors with the characteristics of vascular endothelium not fibroblasts. We now report that BALB/3T3 (clone A31), BALB/3T3-T, a proadipocyte subclone of clone A31 cells, and six recent subclones of BALB/3T3-T cells show additional differentiation patterns were tumors derived by implantation of these cells attached to plastic plates are examined. Differentiation into pericytes, chondrocytes, and fibroblasts was observed. We conclude that the BALB/3T3 clone A31 cell line and related lines are multipotent mesenchymal cells which are capable of differentiation into a variety of cell types.

Adipose Tissue↗
PubMed1980

Cyclic adenosine 3',5'-monophosphate-independent phosphorylation of externally oriented plasma membrane proteins in transformed and nontransformed mouse embryo cell lines.

Thirty transformed and nontransformed mouse embryo cell lines were analyzed to determine if increased plasma membrane phosphorylation is a characteristic of all transformed cell lines. Nontransformed, virally and chemically transformed, and smooth surface-transformed cell lines derived from Swiss, BALB/c, AKR, or C3H mice were studied. Cyclic AMP-independent phosphorylation of plasma membrane proteins was comparable in nontransformed and simian virus 40 (SV40)-transformed Balb/3T3 cells, in nontransformed and 3-methylcholanthrene (MCA)-transformed C3H/10T 1/2 cells, and in nontransformed and MCA-transformed AKR-2B cells. In contrast, increased plasma membrane phosphorylation was observed in MCA- and smoooth surface-transformed Balb/3T3 cells and in SV40-transformed Swiss 3T3 cells compared to the respective nontransformed parent cell lines. These observations suggest that increased cyclic AMP-independent phosphorylation of externally oriented plasma membrane proteins is not a universal marker for the transformed phenotype.

Animals↗
PubMed1980

Differences in the cyclic AMP-dependent phosphorylation of plasma membrane proteins of differentiated and undifferentiated L6 myogenic cells.

Differences in the cyclic AMP-dependent plasma membrane phosphorylation system of undifferentiated and differentiated L6 myogenic cells have been detected. Endogenous plasma membrane protein phosphorylation in undifferentiated L6 myoblasts was stimulated more than three fold by 5 x 10(-5) M cyclic AMP, whereas no statistically significant cyclic AMP-dependent phosphorylation of endogenous plasma membrane proteins was observed in differentiated L6 cells. In undifferentiated cells cyclic AMP promoted the phosphorylation of several proteins, the most prominent of which had a molecular weight of 110,000. In differentiated cells cyclic AMP did not selectively promote the phosphorylation of specific plasma membrane proteins. Both differentiated and undifferentiated L6 cells, however, contain a cyclic AMP-dependent protein kinase capable of catalyzing the phosphorylation of exogenous substrates, such as histone f2b. Therefore, the data show that differentiation in L6 cells is associated with a selective change in the activity of a plasma membrane cyclic AMP-dependent protein kinase which employs endogenous membrane proteins as substrate.

Animals↗
PubMed1980

Carcinoid tumor of the thymus: a clinicopathologic report of seven cases with a review of the literature.

Carcinoid tumor of the thymus is a rare neoplasm. Formerly confused with thymoma, a tumor of thymic epithelial cells, carcinoid tumor of the thymus has recently been shown to arise from cells of neuroendocrine origin that are normally present in the thymus. About half of the tumors are either functionally active (usually producing Cushing's syndrome) or are found in association with other endocrine tumors, as part of a multiple endocrine neoplasia syndrome. The remainder occur as symptomatic or asymptomatic anterior mediastinal masses, clinically indistinguishable from thymoma. At least 30% of thymic carcinoids are malignant on the basis of local invasion or metastasis or both. A protracted course, with late recurrence of tumor, is not uncommon. Aggressive surgical extirpation, followed by radiotherapy, offers the best hope for cure.

Adult↗
PubMed1980

Defective cyclic adenosine 3'-5'-monophosphate-dependent phosphorylation of plasma membrane proteins in chemically and virally transformed cells.

Cyclic adenosine 3':5'-monophosphate (cyclic AMP)-dependent phosphorylation of endogenous plasma membrane proteins catalyzed by an endogenous plasma membrane protein kinase was assayed in purified plasma membrane preparations derived from nontransformed, methylcholanthrene-transformed, and simian virus 40 (SV40)-transformed BALB/3T3 cells. In nontransformed cells, cyclic AMP stimulated the phosphorylation of two proteins with molecular weights of 24,000 and 14,000. The labeling of these proteins could be inhibited by rabbit skeletal muscle protein kinase inhibitor. In methylcholanthrene-transformed cells, no cyclic AMP-dependent phosphorylation of endogenous plasma membrane proteins was observed. SV40-transformed cells also showed markedly decreased cyclic AMP-dependent phosphorylation of both endogenous plasma membrane substrates. Addition of exogenous cyclic AMP-dependent protein kinase from bovine kidney to plasma membrane preparations isolated from methylcholanthrene or SV40-transformed isolated from methylcholanthrene or SV40-transformed cells, however, catalyzed the cyclic AMP-dependent phosphorylation of both the M.W. 24,000 and M.W. 14,000 substrates. These data show that the plasma membranes of transformed cells have a defect in an endogenous cyclic AMP-dependent phosphorylation system and that this defect can be corrected by addition of an exogenous cyclic AMP-dependent protein kinase.

Animals↗
PubMed1980

Effect of dithiothreitol on plasma membrane intramembranous particle topography in BALB/c 3T3 and simian virus-transformed 3T3 cells and plasma membrane vesicles.

A statistical analysis of plasma membrane intramembranous particle topography was performed on purified 3T3 and simian virus (SV)-transformed 3T3 plasma membrane vesicles and on intact 3T3 and SV3T3 cells. The results show that intramembranous particles were more aggregated in intact 3T3 cells than in intact SV3T3 cells. By contrast, in purified plasma membrane vesicles intramembranous particles were significantly more aggregated in SV3T3 than in 3T3 preparations. These unexpected results suggest that intramembranous particle topography is selectively altered in SV3T3 plasma membranes during the membrane vesicle isolation procedure. Inasmuch as the disulfide-reducing agent dithothreitol (DTT) was used to isolate membranes, tests were done to determine if DTT would preferentially affect particle topography in intact SV3T3 cells. Exposure of intact SV3T3 cells to 10 or 50 mM DTT induced intramembranous particle aggregation but had no effect on intact 3T3 cells. Preliminary studies also showed that other sulfhydrylreactive compounds preferentially induced particle aggregation in SV3T3 specimens. These observations suggest that the state of cross-linking of membrane-associated proteins by disulfide bonding influences intramembranous particle topography and that differences exist in plasma membrane-associated sulfhydryl proteins in nontransformed and transformed cells.

Animals↗