Stimulation of DNA polymerase alpha by a nuclear DNA/protein complex.

A nuclear DNA complex containing DNA polymerase and SV40 T-antigen was isolated from nuclei of SV40-transformed mouse fibroblasts. DNA polymerase could be separated from the complex. The remaining DNA/T-antigen-containing complex stimulated DNA polymerase alpha activity about 10-fold. The complex contained 4 major proteins with molecular weights of 46, 54, 76, and 94 kilo-dalton (KD). The stimulation activity was retained by protein A-Sepharose loaded with specific IgG from SV40-tumor bearer serum, or from antisera against the 94 KD and 76 KD components and was partially inhibited in the presence of these antisera. The stimulation activity was completely abolished by treatment of the complex with trypsin or DNase I.

Retrovirus-like particles in EBV-negative Burkitt's lymphoma cell line but not in EBV-DNA-positive lines from patients with ataxia telangiectasia and Down's syndrome.

Retrovirus-like particles can be recovered by arginine deprivation from the BJAB-1 Epstein-Barr virus (EBV) negative cell line derived from an African patient with typical Burkitt's lymphoma. These particles resemble retroviruses in their morphology and in their physicochemical properties. Particles with a similar morphology were obtained from derivative cell lines established by infecting BJAB-1 cells with EBV. On the other hand, retrovirus-like particles could not be induced in EBV-DNA-positive lymphoblastoid cell lines derived from non-leukaemic patients with ataxia telangiectasia and Down's syndrome and from a patient with infectious mononucleosis.

Cytotoxic activity of methylene bis-nucleotides.

New facts relating to the mechanism of cytotoxic and antitumor activity of formaldehyde-treated RNA and its hydrolysates have been revealed. Synthetic methylene bis-nucleotides and, in particular, methylene bis-nucleosides have a cytotoxic effect on cultured human adenocarcinoma cells (line HCCL). The cytotoxic effect of methylene bis-derivatives of the guanine series was most pronounced. In addition, methylene bis-nucleotides were depbosphorylated in the cell culture medium. Chromosome aberrations were induced by alkaline hydrolysate of dialyzed formaldehyde-treated RNA in which 39% of purine nucleotdies were modified to methylene bis-derivatives.

Effect of hydrolyzed formaldehyde-treated RNA on neoplastic and normal human cells.

Alkaline hydrolysate of dialyzed formaldehyde-treated RNA, in which 39% of purine nucleotides are modified to methylene bis derivatives (R-CH2-R'), displays cytotoxic activity toward cultured human tumor cells. The alkaline hydrolysate of dialyzed formaldehyde-treated RNA is substantially less toxic to normal human embryonic cells. There is a correlation between the cytotoxic effect and cell growth rate, which has been traced by quantitative tests.

Oncornavirus-like particles released from arginine-deprived human lymphoblastoid cell lines.

Type-C RNA tumor virus particles were released from three different human lymphoblastoid cell lines after incubation in arginine-deficient medium. The released virus-like particles were characterized by (a) their ability to band in sucrose gradients at a density of 1.16-1.18 g/ml; (b) the presence of an RNA-directed DNA polymerase activity resembling that of the oncornaviruses; and (c) isolation of cores that band at a density of 1.26-1.27 g/ml in sucrose gradients. Examination of the arginine-deprived human lymphoblastoid cell line strain P3HR-1 by electron microscopy revealed the presence of C-type particles in the intracellular spaces.

Transformation of cultured human embryonic fibroblasts by oncornavirus-like particles released from a human carcinoma cell line.

A fibroblast-like cell culture was established from a stomach biopsy of a patient with metastatic adenocarcinoma. One of the cultures, at the 6th passage level, left unattended for a month at 37 degrees, produced numerous foci of epithelioid cells. Upon subculturing, an epithelioid cell line, designated HCCL (human carcinoma cell line), was established. The HCCL cells released particles possessing the characteristics of oncornaviruses: density 1.175 g/ml, cores with a density of 1.22-1.26 g/ml, high-molecular-weight RNA (60-70S) and RNA-instructed DNA polymerase activity (deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7). Inoculation of particles released from HCCL cells into cultures of human embryo muscle fibroblasts resulted in the appearance of foci of transformed cells.