Interaction of polynucleotides with cultured mammalian cells. 3. Initial binding at cell surfaces

Nucleic acid interaction with VERO cells. A temperature barrier in the interaction pattern

The interaction of VERO cell monolayers with spin (nitroxide)-(labeled polynucleotides (1(N)n) was examined by electron spin resonance (ESR) spectroscopy at various temperatures. Nitroxide labels covalently linked to (A)n, (dUfl)n, (U)n and (A)n . (U)n were used to monitor the interaction. The VERO cells were grown on small quartz plates with a cell viability of 95% or better and then used directly for the ESR studies. The ESR results indicated that the interaction between VERO cells and spin-labeled nucleic acids is temperature dependent. No temperature dependence was found when VERO cells were in contact with nitroxide radicals which were free in solution or covalently bound to Sepharose 4B. The temperature dependence established with nitroxide-labeled nucleic acids indicates that a temperature barrier must exist between 20 and 26 degrees C for the interaction between nucleic acids and VERO cells; namely, at 26 degrees C or above spin-labeled nucleic acids interact significantly with a VERO cell surface; whereas, at 20 degrees C the ESR signal reports no interaction. It is concluded that a temperature-dependent phase transition of membrane components or cell surface products active at 26 degrees C or above play a key role in the nucleic acid cell surface interaction process.

Interaction of normal and unusually modified microbial DNA with cultured mammalian cells. Breakdown and reincorporation vs. uptake of polymerized DNA

The uptake of radioactively labeled bacterial and phage DNA and the incorporation of acid-soluble DNAase I digests of these DNAs by cultures of human foreskin and 3T3 cells were studied. The presence of large amounts of unusually modified pyrimidine residues in donor phage DNAs allowed radioactive donor DNA in the nuclei of DNA-treated cells to be distinguished from host DNA labeled with breakdown products derived from donor DNA. This distinction could be made because it was found that radioactively labeled 5-methylcytosine residues in predigested XP-12 DNA and glucosylated 5-hydroxymethylcytosine residues in predigested T4 DNA could not be incorporated in an unaltered form into animal cell DNA. The results obtained from the study of uptake of these DNAs suggest that approx. 4--40 ng of phage DNA per 10(6) cells was transported to the nuclei of DEAE-dextran-pretreated cells during 3 days of incubation in medium after treatment with the DNA. However, interpretation of the results is complicated by the finding of considerable amounts of donor DNA binding to and persisting at the cell surface, which might attach to nuclei during subcellular fractionation.

Interaction of microbial DNA with cultured mammalian cells. Binding of the donor DNA to the cell surface

Cultured fibroblasts grown in monolayer were incubated for a short time with radioactively labeled microbial DNA and diethylaminoethyl-dextran (DEAE-dextran), poly-L-lysine, or calcium phosphate, agents previously demonstrated by others to markedly enhance transfection. Immediately after such treatment of 1 by 10(-6)-1.5 by 10(6) cells with DNA, approx. 0.05-0.15 mug of donor DNA representing 10-30% of the input DNA became cell associated. In contrast, when the cells are similarly treated with only a DNA solution approx. 0.5-5% of the donor DNA was retained by the cells. More than 95% of the cell-associated donor DNA was shown to be bound to the surface of cells treated with polycation. It was also shown that in the absence of polycation treatment, most of the cell-associated donor DNA was bound to the cell surface.

Kinetics of monocyte receptor activity for immunoproteins in patients with sarcoidosis

Peripheral blood monocytes from patients with active sarcoidosis have increased ability to bind IgG-antibody-coated and C3-coated erythrocytes. Binding of monocytes from sarcoid patients is inhibited less than for normals with IgG1 and IgG3 in the fluid phase. Following phagocytosis of latex particles, monocytes from sarcoides patients retain the capacity to bind IgG-coated erythrocytes, whereas monocytes from normal individuals show disappearance of IgG receptors followed by recovery during a 6-8 hr period. Preliminary studies (8 patients) of monocytes from patients with Crohn's disease show some increase in binding of IgG-coated erythrocytes as compared with normals; this increase, however, is less than for sarcoidosis patients. Preliminary experiments with multistranded polynucleotides (poly I:C:U) show increased activity for normal monocytes and no detectable effect on IgG receptor activity for sarcoid monocytes. Thus peripheral blood monocytes of patients with sarcoidosis have increased IgG and C3 receptors sites, suggesting activation of monocytes in this disease and perhaps in other granulomatous disorders.

The fluid double polar-nonpolar-polar leaflet model for biological membranes

A model for biological membranes is proposed according to which the plasma membrane consists of two functionally different polar-nonpolar-polar leaflets separated by a polar space. The binding of water-soluble proteins, integral lipoproteins and spanning proteins to a biological membrane as well as possible conformations of interphase peptides partitioned between polar and nonpolar layers are discussed. A model for the diffusion of water soluble proteins across nonpolar layers of a membrane is described. Three complete biological membranes containing two leaflets and an inter-leaflet space are defined. These are: 1: The inner nuclear membrane + the perinuclear space and the endoplasmatic cisternae + the outer nuclear membrane and the endoplasmatic reticulum, 2: the innner mitochondrial membrane + the mitochondrial intermembraneous space + the outer mitochondrial membrane and 3: the cytoplasmic leaflet of the plasma membrane + an intramembraneous space in the plasma membrane + the outer leaflet of the plasma membrane.

Optimal conditions for uptake of exogenous DNA by Chinese hamster lung cells deficient in hypoxanthine-guanine phosphoribosyltransferase

Conditions were characterized for maximizing the uptake of exogenous mammalian cell DNA by hypoxanthine-guanine phosphoribosyltransferase-deficient Chinese hamster lung cells. Recipient cell cultures in an exponential growth phase were found to be more competent in taking up DNA than stationary cultures. Polyornithine enhanced the uptake of exogenous DNA more reproducibly and to a greater extent than did any of the other facilitators tested (DEAE-dextran, CaCl2, latex spheres, spermine, polylysine and polyarginine). Maximal DNA incorporation occurred when polyornithine and DNA were mixed together prior to inoculation. About 25-30% of the DNA inoculum became deoxyribonuclease-resistant in a typical experiment utilizing polyornithine as the facilitator. Both homologous and heterologous exogenous DNAs rapidly became associated with recipient cell nuclei: approximately 95% of the deoxyribonuclease-resistant donor DNA was nuclear-associated 15 min after inoculation.