Inhibition of DNA synthesis and oncogene expression in tumor cells by the biological factor DIF.

A regulatory factor isolated from the maternal part of bovine placentas (decidua inhibitory factor, DIF) inhibits the incorporation of thymidine into the DNA of a variety of animal and human tumors. The degree of inhibition is dependent on the concentration of the factor. Results indicate that signal transduction occurs via a Ca2+ mobilizing pathway after specific binding of the inhibitor to tumor cell surface receptors.

Inhibition of tumor cell proliferation by a novel growth regulator from placenta: modulation of membrane phosphorylation and oncogene expression.

The tumor specific inhibition of thymidine uptake by a negative growth regulator isolated from the maternal part of the bovine placenta is in concert with an inhibited expression of ras oncogenes. The results indicate that primary processing is blocked in case of Ha-ras, while a lower transcription rate or a stimulated degradation of mRNA is more likely for N-ras. These reactions are preceded by a specific binding of the inhibitor to tumor cell surface membranes.

Tumor-specific inhibition of DNA synthesis and cell proliferation by a factor from bovine placenta--possible mechanism.

A polypeptide isolated from the maternal part of bovine placentas inhibits significantly the incorporation of thymidine into the DNA of tumor cells. When normal cells are used, this effect is found only to a very limited degree. Surface membrane components have been identified which are enriched on tumor cells and which are responsible for a better binding of the inhibitor to tumor cells than to normal cells.

The evaluation of an average nucleotide composition from melting curves.

A new formula has been derived for the calculation of the average G + C content - X of DNAs from different origins using thermal melting data. As compared to existing formulas the new method gives highly accurate results, although being much easier to use than similar equations.

Changes in chromatin structure during rat liver regeneration as demonstrated by thermal melting analyses.

Chromatin was isolated from regenerating rat livers at different times after 2/3 hepatectomy and enriched with respect to active sequences. Thermal melting analyses of the material resulted in profiles reflecting the specific structural organization of the chromatin during different phases of the regeneration process: The high transcriptional activity of the chromatin 1, 16, and 36 hours after hepatectomy is demonstrated by a high proportion of DNA-protein complexes melting between 80 degrees C and 85 degrees C, while the period of active DNA synthesis 24 hours after hepatectomy is reflected by high amounts of components with Tm around 90 degrees C.

Early alterations in rat liver chromatin structure after a single dose of diethylnitrosamine.

In the chromatin of 24-h regenerating rat livers, derivative melting profiles are characterized by a high proportion of transitions above 90 degrees C. After the injection of diethylnitrosamine there is a rapid shift to lower melting temperatures. This is due to a rearrangement of the chromatin to higher amounts of nucleosomal components but possibly also a consequence of chemical modifications and conformational alterations of the DNA.

Inhibition of thymidine incorporation into the DNA of normal and neoplastic cells by a factor from bovine maternal placenta: interaction of the inhibitor with cell membranes.

An inhibitor was isolated from the maternal part of bovine placentas which inhibits the incorporation of [3H]thymidine into the DNA of a variety of tumor cells to a significantly higher degree as compared to normal cells. This protein-type component was labeled by reaction with N-succinimidyl[2,3-3H]propionate, and interactions with receptors on cell membranes were investigated. Results indicated that receptors on tumor cell surfaces have higher binding capacities versus the inhibitor than those of normal cells.

Isolation and characterization of the growth-stimulating factor in supernatants of herpes simplex virus type 2 infected cells.

Lytic infection of CV1 cells with herpes simplex virus type 2 does not stimulate ornithine decarboxylase activity and there is no correlation between polyamines and a growth-stimulating factor (GSF) which is present in the supernatant of the cultures. The factor was partially purified by gel filtration on Sephadex G-50 and polyacrylamide gel electrophoresis. Gel filtration as well as dialysis through membranes with different pore diameters indicated a molecular weight between 3,500 and 10,000 daltons.

[Attempts to characterize a tumor specific inhibitor extracted from the maternal part of the bovine placenta].

A fraction was isolated from the maternal part of bovine placenta, which significantly inhibits the incorporation of thymidine into the DNA of tumour cells. This factor has, however, only a limited effect on the same reaction in bone marrow cells or in fibroblasts. It is suggested that the factor enters the cell by an active transport mechanism and that the active part thereof is a protein.

The phosphorylation of histones in herpes virus infected Vervet-monkey kidney cells (CV-1).

The phosphorylation of histones of the F1 group and of fraction F2a2 is stimulated in monkey kidney cells (CV-1) to almost two times the control values 14 hours after their infection with herpes virus, type 2. At the same time high amounts of viral DNA are produced. It seems very likely that the stimulated phosphorylation of these histone fractions is a prerequisite for the enhanced synthesis of DNA and possibly also RNA.

The phosphorylation of histones in rat liver undergoing malignant transformation.

The incorporation of inorganic phosphate into H1-histones of rat liver was stimulated after the repeated s.c. administration of diethylnitrosamine.

The tumor enhancing property of herpes simplex virus type-2 (HSV-2).

The s.c. infection of DBF-1 mice with HSV-2 has a tumor enhancing effect on simultaneously i.

The phosphorylation of nuclear proteins in the regenerating and premalignant rat liver and its significance for cell proliferation.

In liver regeneration or neoplastic transformation, phosphorylation of nuclear proteins is stimulated. In the regenerating liver all main histone fractions are involved in this process. The type of histone phosphorylated seems to be dependent on the position of the partially synchronized cells within the generation cycle.