PubMed Health⌕ Search

Biomedical subjects

J E Martner

Publications and source records attributed to J E Martner.

6 recordsLinked to original sources
PubMed1986

Enhanced protein phosphorylation of carcinogen-initiated 10T1/2 cells accompanies their neoplastic transformation.

Retinyl acetate (RAC) prevents neoplastic transformation of carcinogen-exposed C3H/10T1/2 C18 cells, and has allowed the isolation of cells having the properties expected of initiated cells. After removal of RAC from logarithmically growing initiated cells, cultures first become confluent and growth arrested, as occurs with their normal counterparts. This is followed by an increase in thymidine labelling index and finally by morphological transformation on days 15 and 23, respectively, after seeding and drug removal. The increase in labelling index is the earliest indication yet seen of transformation taking place in these cultures. Phosphorylation of three nonionic detergent-soluble proteins was observed to be correlated with the increase in labelling index. Using two-dimensional gel electrophoresis, a protein of 35 kd (pp35(1)) and one of 38 kd (pp38) were seen to become more heavily phosphorylated in association with the increase in labelling index. A second protein of 35 kd (pp35(2)) was only detected in isolated transformed cells and is phosphorylated in an alkali-resistant manner consistent with phosphorylation of tyrosine residues. Alkali-resistant phosphorylation of pp35(2)) could be eliminated in transformed cells by treatment with RAC. Phosphorylation of pp35(1)) appears to be a permanently acquired characteristic of these cells, and cannot be made to revert. Phosphorylation of pp38, as indicated by isoelectric point, is reduced by RAC treatment. These studies implicate changes in protein phosphorylation in loss of growth control, and suggest that the cancer chemopreventive action of retinoids may also be mediated at this level.

Animals↗
PubMed1985

Inhibition by retinoids of neoplastic transformation in vitro: cellular and biochemical mechanisms.

We have demonstrated that non-toxic concentrations of retinoids can cause a dose-dependent inhibition of 3-methylcholanthrene-induced transformation of C3H/10T1/2 cells. On removal of the retinoid, transformed foci appear after a latent period of about four weeks at the same frequency as observed in controls treated with carcinogen only. Reasoning that this activity is compatible with the stabilization of the carcinogen-initiated state, we have succeeded in isolating from carcinogen-treated cultures a cell line which in the presence of retinyl acetate is similar to the parental 10T1/2 cells, but without retinyl acetate transforms at a high frequency after a latent period of about four weeks. Retinyl acetate treatment of this cell line (INIT/10T1/2) and the parental 10T1/2 cells induces an ultra-normal phenotype. In retinoid-deprived INIT/10T1/2 cells, the first sign of transformation (an increased thymidine-labelling index) occurs 16 days after retinyl acetate removal. We have detected by two-dimensional electrophoresis that concomitant with this there is an increase in phosphorylation of a protein of Mr 34 000 (34K) which may be associated with the cytoskeleton. This phosphoprotein has been found in all transformed lines examined. A second phosphoprotein, of about 38K, has also been detected in transformed cells. Retinyl acetate treatment of transformed cells alters the isoelectric point of this protein, a change compatible with decreased phosphorylation. Alkali-resistant phosphorylation, presumably on tyrosine, has been found on a second 34K protein of transformed cells. Retinyl acetate treatment specifically decreases this phosphorylation. Mechanisms for the altered tyrosine phosphorylation induced by retinyl acetate are as yet unresolved, but the decrease could be due to altered levels of substrate, kinase or phosphorylase. In view of the apparent role of tyrosine kinases as mediators of growth factors and as oncogene products, we consider the activity of retinoids as modulators of tyrosine phosphorylation to be of great potential significance.

Animals↗
PubMed1983

Quantitative neoplastic transformation of C3H/10T1/2 fibroblasts: dependence upon the size of the initiated cell colony at confluence.

The efficiency of transformation of C3H/10T1/2 fibroblasts by chemical or physical carcinogens varies inversely with the seeding density of the cells. Colony size at confluence, accumulated cell generations, and epigenetic events independent of seeding density have been proposed to explain this variability. By controlling the total number and colony size (i.e., cells/colony) of initiated cells at confluence and their accumulated cell generations, we have determined that (a) the colony size of the initiated cells at confluence is directly related to the expression of the transformed phenotype, (b) the probability that an initiated cell will form a colony of transforming cells does not vary with the accumulation of large numbers of cell generations, and (c) the total number of initiated cells in a confluent culture does not determine the number of transformed foci formed. We have developed a mathematical representation which, when applied to our results and the published results from other laboratories, clearly describes the relationship between the size of the initiated cell colony at confluence and the expression of the transformed phenotype. These results have significant implications in the quantification of the transformation of C3H/10T1/2 cells by chemical and physical carcinogens.

Animals↗