Probe for polyanionic regions on the cell surface

The influence of urea and cell-surface protein on the behavior of nontumorigenic and chemically transformed cells

Alterations in cell-cell interactions induced by urea and urea-isolated cell-surface protein (CSP) were examined using the nontumorigenic mouse fibroblast 10T1/2 cell line and the malignantly transformed MCA daughter cell line as a model system. Both cell lines were exposed to urea and CSP, and contact inhibition was quantitated based on nuclear overlaps. The Abercrombie Overlap index was found to be dependent on cell density, and a new method of overlap analysis was developed based on the regression of the number of overlaps per microscope field on the number of cells per field. Urea had a differential effect on both protein and deoxyribonucleic acid synthesis and a differential effect on the overlap regression in the two cell lines. Urea increased the regression coefficient in the normal (10T1/2) cell line while decreasing it in the transformed (MCA) cell line to approximately equal levels of overlap. Added CSP had no effects on overlaps in the MCA line but increased overlaps in the 10T1/2 line to the level of the MCA control, suggesting that the CSP interactions were more specific than the urea interactions. Trypsin-derived cell-surface glycopeptide profiles of the two cell lines showed a difference consistent with previously reported differences between normal and transformed cell lines. However, the glycopeptide profile of the urea-isolated CSP from the normal 10T1/2 cell line and the trypsin-derived glycopeptides of the transformed MCA cell line were not significantly different in the high-molecular-weight region, suggesting that the relative abundance of CSP may be higher in the MCA line, and the fact that the addition of CSP to the 10T1/2 line increased overlap tendency to the level of the MCA line suggested that CSP is an important factor in the modulation of overlap tendency. Urea and CSP may exert their effects on overlap tendency by affecting the integrity or order of the cell-surface components. The increased overlap tendency of the 10T1/2 line in the presence of CSP was not associated with increased cell density. Density dependence of cell growth was apparently not directly related to density dependence of overlap tendency. Many xenobiotics have surface-active properties and are known to inhibit protein synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Increased cotransformation of distant markers and altered patterns of DNA-cell interactions following the exposure of transforming DNA to two carcinogenic and mutagenic alkylating agents, diethyl and dimethyl sulfate

Transforming DNA exposed to either diethyl sulfate (diES) or dimethyl sulfate (diMS) is inactivated. The rate of inactivation depends on the marker tested and on the chemical used: diMS is more active than diES. Cotransformation of linked markers is similarly depressed. In contrast, there is a transient increase in the cotransformation of distant, unlinked markers. These observations indicate that some of the intermolecular complexes of transforming DNA created in the test tube by the treatment with diES and diMS are biologically active. Radioactively labeled DNA treated with diES or diMS changes its patterns of interaction with cellular surfaces that are characteristic of untreated DNA. A possibility is considered that such alterations in DNA-protein interactions as well as the ability of these alkylating agents to transpose fragments of chromosomal material may play an important role in the processes of mutagenesis and, especially, carcinogenesis.

Interaction of purified DNA with plant protoplasts of different cell cycle stage: The concept of a competent phase for plant cell transformation

The polycation mediated attachment of purified tritiated DNA to plant protoplasts has been measured by quantitative microautoradiography. The automated grain counting technique used, also provides information on the cell cycle stage of individual protoplasts, which circumvents the need to synchronize the plant cell population before preparation of protoplasts. With protoplasts from asynchronously dividing suspension cultures of Nicotiana syhestris (NS-1), S-phase protoplasts appear to be inefficient binders of (3)H-DNA, as compared with G1 or G2 protoplasts. Protoplasts derived from a tumour line of Crepis capillaris (CAPT) exhibit (3)H-DNA binding at all cell cycle phases, but Sphase protoplasts appear to be preferential binders. These differences are discussed with reference to cell cycle kinetics, membrane charge variation and the possibility of increasing the efficiency of genetic transformation of higher plant cells in culture.