Detection of receptor-mediated membrane effects of dexamethasone in B16 murine melanoma cell lines by cell partitioning in aqueous two-polymer systems

Four metastatic variant sublines of the B16 murine melanoma were assayed for glucocorticoid receptors and examined for effects of dexamethasone on surface charge-related partition behaviour in aqueous two-polymer systems, expression of membrane external proteins, and adhesion to growth substratum. BL6 and F10 cells possessed cytosolic glucocorticoid receptors and, on exposure to dexamethasone, showed increased partition in the charged aqueous two-polymer system with high phosphate, but not in non-charged PO4/NaCl buffer system. This suggests that the charged two-polymer system may detect membrane changes that may be receptor-mediated effects of dexamethasone. An increase in expression of certain proteins (p250) was detected in glucocorticoid receptor-positive BL6 and F10 cells but not in the receptor-negative lines. However, other proteins, such as p220, showed an increase in all four cell lines, presumably not receptor-mediated. Dexamethasone produced no detectable changes in the ability of the cells to adhere to plastic substratum.     

The cell surface sulphydryl content of metastatic variants of B16 murine melanoma

The cell surface sulphydryl content of three metastatic variants of the B16 murine melanoma has been determined using isoelectric equilibrium techniques. The F1 variant, which has no ability for natural metastasis, and the F10 variant with moderate metastatic ability appeared to have no detectable surface thiol groups. The variant BL6, which shows a high degree of natural metastasis, possessed surface thiol groups. The variants were found to be heterogeneous in isoelectric distribution. Three subpopulations were identified based on isoelectric criteria. The size of the pI 5.0 subpopulation appeared to increase with metastatic ability. A proportion of this subpopulation, approximately 4% in the F10 and 10% in the BL6, was found to possess surface thiol groups. In the BL6 line, 10-20% of the pI 4.6 subpopulation possessed surface thiol groups. The surface negative charge density of the cell types showed no correlation with their natural metastatic ability.     

Isoelectric characteristics and the secondary structure of some nucleic acids

The isoelectric characteristics of some nucleic acid preparations from rat liver have been examined. 10S and 4S RNA species and SV-DNA were found to have isoelectric points of 5.2, 6.0-6.7, and 4.35 respectively. The molecular charge ratios (net negative charge/nucleotide) were calculated. Using SV-DNA as a standard, these isoelectric characteristics and charge ratios have been interpreted as indicating that the 10S and 4S RNAs have 35 and 56% of the molecules involved in secondary structure.     

Membrane surface properties of normal and malignant cells: partition in aqueous two-polymer phase systems

The partition of normal and malignantly transformed fibroblast lines and cell lines initiated from malignant human astrocytomas and a benign ganglioneuroma has been examined in aqueous dextran-polyethylene glycol phase system containing phosphate buffer with a low phosphate/sodium chloride ratio. The malignant astrocytomas showed a significantly lower partition coefficient as compared with the benign ganglioneuroma. Treatment of astrocytoma cells with dexamethasone caused an increase in the partitioning of the cell population. No differences were found in the partition behaviour of normal BHK-21 cells and their malignant transformants, the TRES fibrosarcoma cells. Polyoma and simian virus-transformed 3T3 fibroblasts showed partition ratios similar to the untransformed cells. Dexamethasone pre-treatment had no effect on the partition behaviour of these cells. The significance of these observations has been discussed in relation to the surface hydrophobicity and the neoplastic state.     

The morphogenetic action of follicle-stimulating hormone on post-nodal fragments of early chick blastoderms

Summary The morphogenetic action of ovine follicle-stimulating hormone has been studied. The hormone is incorporated in known concentrations in agar-albumen-compton base and post-nodal fragments of primitivestreak stage chick blastoderms 0.7 mm behind theHensen's node are cultured on the base for 35–45 hours. The hormone is found to induce the formation of neural tissue, notochord-like tissue and mesodermal aggregations resembling somites.