Effect of a mammary-derived growth inhibitor on the expression of the oncogenes c-fos, c-myc and c-ras.

A mammary-derived growth inhibitor (MDGI) inhibits the resumption of growth of stationary Ehrlich ascites carcinoma (EAC) cells in vitro. The present study shows that the resumption of growth is accompanied by a rapid increase of the steady state mRNA level of the proto-oncogenes c-fos, c-myc and c-ras, which is reduced by MDGI. EAC cells from the exponential growth phase insensitive to MDGI did not show a reduced RNA expression.

Altered growth control by natural growth inhibitors in the mutant HD33 substrain of the Ehrlich-Lettré ascites mammary carcinoma.

The mutant substrain HD33 of the Ehrlich-Lettré ascites mammary carcinoma (EAC) was found to be altered in its ability to respond to and to produce natural growth inhibitors. Cells of this substrain did not respond to (1) a highly purified growth inhibitor from bovine mammary gland, inhibiting the proliferation of two strains of the original EAC already at concentrations of 0.5-2.

Ribonucleotide reductase in ascites tumour cells detected by electron paramagnetic resonance spectroscopy.

Tyrosine radicals localized in the M2 subunits of ribonucleotide reductase have been detected by electron paramagnetic resonance (EPR) in ordinary ascites tumour cells. The intensity of its doublet EPR spectrum is higher in rapidly proliferating cells. Hydroxyurea, a specific inhibitor of this enzyme, decreases the concentration of the tyrosine radical.

Is ribonucleotide reductase in Ehrlich ascites mammary tumour cells the target of a growth inhibitor purified from bovine mammary gland?

2'-deoxycytidine (dCyd), 2'-deoxyuridine (dUrd) and cytidine (Cyd) were found to relieve the inhibitory action by a factor, highly purified from bovine mammary gland, on the resumption of growth in vitro of stationary Ehrlich ascites mammary tumour cells. As described earlier, this effect is also achieved by insulin, proinsulin and epidermal growth factor and fetal calf serum. The effect of purine-2'-deoxyribonucleosides could not be properly assessed, because they were inhibitory themselves.

Fetal calf serum and epidermal growth factor prevent the inhibitory action of a chalone-like growth inhibitor for Ehrlich ascites mammary carcinoma cells in vitro.

A growth inhibitor for the Ehrlich ascites mammary carcinoma, purified from bovine mammary gland, is antagonized by very low concentrations of epidermal growth factor (2-16 X 10(-10) M) or fetal calf serum (0.001-0.1%).

Aspects of chalone action.

The following aspects of action of a chalone-like factor for the Ehrlich ascites mammary carcinoma and of the granulocytic chalone are discussed: 1) Dependence on the state of proliferation. Rapidly growing cells respond poorly or not at all. 2) Antagonism with growth factors.

Purification of a chalone-like inhibitor for Ehrlich ascites mammary carcinoma cells from bovine mammary gland.

A factor which inhibits the resumption of proliferation of stationary Ehrlich ascites mammary carcinoma (EAC) cells in vitro was isolated from the normal, lactating bovine mammary gland. After fractionation of the 50,000 g supernatant of the tissue homogenate by ammonium sulfate precipitation and gel filtration, it was further purified 2600-fold by ultrafiltration and lectin affinity chromatography. Polyacrylamide electrophoresis revealed one band containing all the activity.

[Mathematical methods in flow cytometry: the problem of evaluating DNA histograms of partially synchronous cell populations].

There is presented a procedure for determining the phase fractions in a cell population (i.e. the fractions of the G1-, S- and G2 + M-cells) from the corresponding DNA histogram obtained by flow cytometry.

On a "chalone"-like factor for Ehrlich ascites mammary carcinoma.

In an aqueous ultrafiltrate (10 000--50 000) prepared from Ehrlich ascites mammary carcinoma (EAC) cells, ascites fluid and bovine mammary gland, a new factor was obtained which is involved in the growth regulating system of EAC cells as shown by the following facts: 1) It reversibly inhibits the proliferation of EAC cells in a 24 h suspension culture, depending on their proliferative state. Thus, stationary cells from the plateau phase of growth in vivo are prevented from resuming growth in vitro, while cells taken from the active phase of in vivo growth are not inhibited under the same conditions. Likewise, stationary cells do not respond when incubated in serum before the addition of the factor (depending on serum concentrations and time).

Chalone-like inhibition of Ehrlich ascites cell proliferation in vitro by an ultrafiltrate obtained from the ascitic fluid.

An aqueous ultrafiltrate (10 000-50 000 dalton) prepared from the cell-free ascitic fluid of mice bearing Ehrlich ascites tumour (EAT) in the plateau phase of growth (12-16 days after transplantation) was investigated with regard to its inhibitory effects on the proliferation of EAT cells in a 24-hr suspension culture. The following results were obtained: (1) The in vitro proliferation of cells obtained from the plateau phase of in vivo growth was reversibly inhibited. (2) The dose-response curves show a plateau with a maximum inhibition of about 50%, which suggests that not all cells can be affected.