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Biomedical subjects

L Raptis

Publications and source records attributed to L Raptis.

47 records · Page 3Linked to original sources
PubMed1986

Phosphatidylinositol metabolism and polyoma-mediated transformation.

The effect of polyoma middle-sized tumor antigen (MTAg) on phosphatidylinositol metabolism has been characterized in vivo and in vitro using polyoma-transformed and polyoma-infected cells. Cells infected with transformation-competent polyoma virus exhibit increased levels of inositol phospholipids and the second messenger inositol trisphosphate. MTAg or pp60c-src immunoprecipitates from MTAg-transformed cells contain an activity that phosphorylates phosphatidylinositol and phosphatidylinositol 4-phosphate. This activity is induced in parallel with MTAg when the MTAg synthesis is regulated by hormonal or heavy metal inducers. Immunoprecipitates from one class of polyoma mutants defective in transformation have a reduced level of associated phosphatidylinositol kinase activity in vitro yet are capable of tyrosine phosphorylation on exogenous protein substrates at rates comparable to wild-type virus. Thus, for these mutants, phosphatidylinositol kinase activity is more tightly correlated with transformation than is protein kinase activity. These results suggest that alterations in phosphatidylinositol metabolism by MTAg play a role in transformation by polyoma virus.

Animals↗
PubMed1985

Effects of pre-feeding on food-approach latency and food consumption speed in food deprived rats.

Deprived rats were trained to receive a major portion of their daily food ration in meal segments of five 45 mg food pellets, presented for 36 sec each at 72 sec intervals. Latency to make oral contact with first pellets did not change over 18 meal segments, while the time to complete the eating of meal segments increased progressively. Pre-feeding with 45 or 90 pellets had little effect on latencies except in the last few trials in the 90-pellet condition. Pre-feeding had a marked effect on time to complete segments, increasing it in proportion to the number of pellets consumed. Thus satiation caused a progressive change in speed of eating, while it caused an all-or-none change in initiation of eating. That is, animals responded to new food pellets with normal latency up to the point when they stopped responding completely. With repeated testing the effects of prefeeding on both speed and latency measures was reduced; the animals ate more steadily, and came to eat every pellet, as familiarity with the situation increased.

Animals↗
PubMed1985

Regulation of cellular phenotype and expression of polyomavirus middle T antigen in rat fibroblasts.

Polyoma middle T antigen (mT) was expressed in rat F-111 cells under control of the dexamethasone-regulatable mouse mammary tumor virus promoter. Graded phenotypic responses to levels of mT induction by the hormone were seen, with morphological transformation, focus formation, and anchorage-independent growth requiring increasing levels of mT expression. The ability of different clones to form tumors reflected their maximum level of induction of mT-associated kinase and their ability to grow in soft agar. Expression of transformation parameters and tumorigenicity correlates with the level of mT phosphorylated by pp60c-src in immune complexes and not with the total amount of mT determined by metabolic labeling. We suggest that cellular factors regulate mT activity by forming a kinase-active fraction of mT molecules that controls the transformed state.

Animals↗
PubMed1982

Stable integration of adenovirus DNA is not required for the induction of mutations in the hypoxanthine phosphoribosyltransferase gene in Chinese hamster cells.

Adenovirus type 2 induces EMS-like mutations at the hpt13 locus coding for hypoxanthine phosphoribosyl transferase (HPRT) in Chinese hamster cells (J. Virol., 38, 184--190, 1981). In this report we show that: (a) the hpt- 13 mutation is in the structural gene of HPRT, (b) adenovirus induces intracistronic reversion mutations which suppress the hpt- 13 phenotype, and (c) the stable integration of adenovirus DNA is not required for the induction of these mutations.

Adenoviruses, Human↗
PubMed1981

Immunological cross-reactivity between simian virus 40 large T antigen and D2 hybrid T antigen.

A specific antiserum was raised in rabbits against D2 hybrid T antigen that had been purified from HeLa cells infected with the adenovirus/simian virus 40 hybrid, Ad2(+)D2. The specificity of this serum was compared with that of a conventional hamster antiserum against simian virus 40-induced tumors by immunoprecipitation and by a new radioimmune assay that can detect nanogram quantities of D2 hybrid T antigen.

Adenoviruses, Human↗
PubMed1980

Quantitation and characterization of plasma DNA in normals and patients with systemic lupus erythematosus.

Using the in vitro DNA labeling technique of nick translation on purified plasma DNA, we have estimated the plasma DNA concentration in three normal individuals to be 266 +/- 57 ng/ml (mean +/- SD). This was not significantly different in three patients with a chronic inflammatory disease (209 +/- 14 ng/ml) or in five patients with steroid-inactivated systemic lupus erythematosus (SLE) (293 +/- 57 ng/ml). In two untreated, newly diagnosed, active SLE patients, however, the plasma DNA concentration was considerably higher (4,024 and 2,437 ng/ml, respectively). Characterization of these in vitro labeled DNA preparations by neutral sucrose-gradient sedimentation analysis showed a sedimentation coefficient of 6-8S, corresponding to a molecular weight of similar to or approximately 0.2-0.45 x 10(6). No difference was observed between normal subjects or patients. In addition, the relative size uniformity of these DNA molecules might suggest some form of specific protection of the DNA from blood DNAases. Further characterization in terms of buoyant density in cesium chloride did not reveal a difference between normal or SLE plasma and the human (HEp-2 cell) DNA used as marker. Taking into account the limitations of the method, no indication of a possible exogenous origin of the DNA circulating in SLE patients could be found. The physiological or pathophysiological role of this plasma DNA remains to be determined.

Arthritis, Rheumatoid↗
PubMedDate not supplied

Ras modulates commitment and maturation of 10T1/2 fibroblasts to adipocytes.

The positive association of the ras oncogene with human cancer and the recognition that malignancy may, in part, represent the imbalance between cell proliferation and differentiation have generated intense interest in the potential role of ras in cell differentiation. We investigated this possibility utilizing as a model system the differentiation of the mesenchymal cell line C3H 10T1/2 (10T1/2) to adipocytes, and a series of transfectants of 10T1/2 cells in which the level of the ras gene product (p21ras; Ras) can be effectively up- or down-modulated. In agreement with previous reports, we found that 10T1/2 cultures, propagated in the resting state for several weeks, spontaneously convert to fat cells at a very low frequency. Downmodulation of endogenous p21ras levels, as a consequence of expression of antisense ras, markedly increased the rapidity and frequency of adipose conversion (6- to 10-fold), which was equivalent in magnitude to that effected by the potent differentiating agent 5-azacytidine. Conversely, overexpression of ras completely inhibited cell differentiation. In addition, adipocytes derived from antisense-ras expressing lines were characterized by a decrease in hormone responsiveness, as well as an apparent deficiency in attaining the terminally differentiated state. These findings suggest that Ras may be a negative regulator of the decision-making step of fibroblast differentiation to adipocytes. In addition, Ras may play an essential positive role in the transduction of hormonal signals necessary for full adipocyte maturation during later progression along the differentiation pathway.

Adipose Tissue↗