Biomedical subjects
Publications and source records attributed to M Stroun.
About one third of patients with various malignant diseases were found to have extractable amounts of DNA in their plasma whereas no DNA could be detected in normal controls. Using the test established by one of us (M.B.), which is based on decreased strand stability of cancer cell DNA, we have found that several plasma DNA originate from cancer cells.
Human blood lymphocytes carrying different allotypes were divided into B and T subpopulations and cultured in presence or in absence of ultraviolet inactivated Herpes Simplex Virus. Isolated B or T cells did not produce any antiherpetic activity. The B lymphocytes cultured in presence of 1 or 50% of the supernatant collected from virus exposed T cells synthesized on antiherpetic antibody with some allotypic markers of the T cell donor.
Lymphocytes carrying different allotypes were separated into B and T subpopulations and cultured in presence or in absence of U.V. inactivated Herpes simplex virus. The B lymphocytes cultured in presence of 1% of the supernatant collected from virus exposed T cells, synthesized an anti-herpetic antibody with some allotypic markers of the T cell donor.
Both antigen-stimulated and non-stimulated human blood lymphocytes release in vitro a DNA-containing complex which is not the product of dying or disintegrating cells. Lymphocytes obtained from different PPD or HBs positive or negative donors were incubated with one of these antigens and the DNA released in the culture medium was tested for its information content using, successively, two cell-free systems. The ability of the resulting protein product to bind specifically to the stimulating antigen was examined by immunoadsorption chromatography. Results show that DNA excreted by stimulated lymphocytes was transcribed into an RNA which coded for an antigen-binding protein, whereas DNA released by unstimulated lymphocytes did not. The protein produced in this system, using as template the DNA released after cell stimulation, bound specifically to PPD or HBs Sepharose 4B coated columns, depending on the stimulating antigen and on the cell response to this antigen. After elution from the column the protein sedimented at 19S in a linear sucrose gradient.
Cell systems as different as normal human blood lymphocytes and frog auricles release spontaneously a nucleoprotein complex in their culture medium. This release seems to be an active mechanism that is unrelated to cell death. The presence of RNA in this complex is demonstrated. The amount of extracellular RNA is regulated by the same homeostatic mechanism that has previously been shown to govern DNA release in the same cell systems. This extracellular RNA is linked by hydrogen bonds to the extracellular DNA and cannot be extracted by a usual phenol procedure, due perhaps to the presence of a glycoprotein. Further purifications by chloroform, sodium perchlorate, and hydroxyapatite are necessary to obtain an RNA molecule that is acid precipitable, RNase and KOH sensitive, and orcinol positive. The extracellular RNA sediments between 2.5 and 4S and is not a transfer RNA. It is more highly methylated than the 28S, 18S, and 4 to 5S cellular RNA. It activates DNA synthesis in vitro.
Unstimulated human blood lymphocytes have been shown to release in vitro a complex containing DNA and RNA. These nucleic acids are composed of newly synthesized material and appear to be released according to a homeostatic mechanism. Extracellular synthesis of the released DNA has been demonstrated by using a nearest neighbor analysis technique. The characteristics of the extracellular nucleic acids have been investigated biochemically and by electron microscopy.
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Human lymphocytes were shown to release, in vitro and in the absence of any stimulation, a complex containing DNA. It has also been reported that the release process is unrelated to cell death and is regulated by a homeostatic mechanism. Some properties of the extracellular DNA were investigated. When a phosphorylated precursor was added to the cell-free supernatant, the DNA recovered from the medium was labeled. Evidence that DNA lebeling represented true precursor incorporation and not simple attachment was obtained from nearest neighbor analysis data. When [alpha-32P]thymidine triphosphate was added to the supernatant and the labeled DNA was completely hydrolyzed to 3'-deoxyribonucleotides, radioactivity was found in all four nucleotides. Although the exact kind of synthesis cannot be determined at this stage, the possibility of a terminal transferase system in which the enzyme would merely add a nucleotide at the end of the chain was eliminated since comparative digestion with DNase and venom phosphodiesterase showed that labeling was located along the whole length of the chain. Precursor incorporation into the DNA was inhibited by DNase, RNase, Pronase, and actinomycin D. This extracellular synthesis was not affected by cell death rate. The renaturation curve of the extracellular [3H]DNA synthesized in the cell-free medium showed a lack of gene reiteration suggesting a preferential synthesis of unique sequences.
Human blood lymphocytes released DNA in vitro in the absence of any stimulation. Once purified from the complex appearing in the supernatant, this DNA exhibited typical characteristics as shown by its UV absorption curve, its deoxyribose coloration, and its sensitivity to DNase. Elution patterns on hydroxyapatite columns indicated that the excreted DNA is double stranded. The released DNA was smaller than the cellular DNA; its molecular weight ranged from 3.5 x 10(5) to 3.7 x 10(6) daltons. The DNA appearing in the supernatant does not seem to be due to dead or dying cells since: (a) the same amount of DNA was found in the medium whether the incubation lasted 2 hr or as long as 16 hr; (b) cell death rate had no effect on the amount of extracellular DNA; (c) when the lymphocytes were centrifuged and placed in a new medium several times in a row, a similar amount of extracellular DNA was isolated from each of the successive supernatants, whereas if, after centrifugation, the lymphocytes were put back in their original medium, no increase in the amount of extracellular DNA was observed, suggesting an active regulatory mechanism independent of a mechanical effect; (d) it took more than 1 hr for extracellular DNA to reach its maximum concentration, a fact that also argues against a mechanical effect; (e) the specific activity of the released DNA was different from that of the cellular DNA, depending on the time of labeling; and (f) the cells that had excreted DNA kept their functional integrity, as shown by their fully maintained capacity to increase DNA synthesis after stimulation. The extracellular DNA hybridized specifically with cellular DNA. The hybridization curves indicate that the DNA excreted is highly complex, and they suggest that it is composed of part of the newly synthesized DNA. The higher specific activity of the released DNA, compared with that of the cellular DNA after a long labeling period, can be explained only by a preferential release of the newly synthesized DNA.