ABSTRACT
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. The effect of MDGI represents a novel activity at the level of gene expression and suggests a link to exist between growth inhibition and the reduction of c-fos, c-myc and c-ras expression.
Subject(s)
Gene Expression Regulation , Growth Inhibitors/pharmacology , Mammary Glands, Animal/analysis , Proto-Oncogenes , Animals , Carcinoma, Ehrlich Tumor/metabolism , Carcinoma, Ehrlich Tumor/pathology , Cattle , Cell Division , Kinetics , Mice , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins c-fos , Proto-Oncogene Proteins c-myc , Proto-Oncogene Proteins p21(ras) , RNA, Messenger/metabolism , Tumor Cells, CulturedABSTRACT
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 0.5-2.0 ng/ml, (2) inhibitory activities found in the ascites fluid of these sensitive strains and partially purified. However, from the ascites fluid of the mutant substrain an inhibitory activity was partially purified, which was inhibitory towards this substrain. It also inhibited the cells from an original strain, although less effectively. This new inhibitory activity is similar in its properties to that of the others investigated in that its mol. wt is between 10,000 and 50,000 D, it is heat labile and its activity can be overcome by insulin, epidermal growth factor and 2'-deoxycytidine, the dose-response curve levels off at 35-45% inhibition. The results demonstrate that the regulation of cell proliferation by endogenous (autocrine) inhibitors can be altered by mutagen treatment.
Subject(s)
Carcinoma, Ehrlich Tumor/metabolism , Growth Inhibitors/metabolism , Mammary Neoplasms, Experimental/metabolism , Animals , Ascitic Fluid/metabolism , Cell Line , Proteins/metabolismABSTRACT
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. Whereas in different ascites tumours the doublet EPR spectrum dominates at g = 2.004, in solid tumours another more intense EPR spectrum from nitrosyl-hemoproteins appears. In conclusion, EPR spectroscopy can be used to monitor the content and variations of active M2 subunits of ribonucleotide reductase in intact ascites tumour cells.
