Elevated ribonuclease activity in the thymus and white blood cells of genetically cancer prone mice.

Ribonuclease activity in cell-free thymus homogenates was elevated for five strains of mice genetically predisposed toward leukemia or reticulum cell neoplasms (AKR, C58, PL, RF, and SJL). Such increased activity was directed against polyuridylic acid and was observed in 8-wk old mice, well before the onset of neoplastic transformation. Similarly, white blood cell ribonuclease activity was elevated in mice of the strains AKR, C2H/He, PL and RF. Statistical analysis indicated that such elevated activity in these strains related to their high incidence of spontaneous neoplastic disease. Elevated ribonuclease activity thus represents a new biochemical marker relating to the genetic propensity of some strains of mice to die prematurely of spontaneous neoplasia.

Influence of renal insufficiency on levels of serum ribonuclease in patients with multiple myeloma.

Serum RNase levels were measured in 34 patients with multiple myeloma and compared with 51 normal controls and 28 non-myeloma patients on chronic hemodialysis. Nineteen of the myeloma patinets with creatinine clearance (CCr) greater than 50 ml/minute had mean serum RNase levels that were statistically indistinguishable from those of the normal controls. The 15 myeloma patinets with CCr less than 50 ml/minute had mean RNase levels much higher than normal controls or myeloma patients with normal renal function. Patients without myeloma but on hemodialysis for chronic renal failure of varied etiologies had markedly elevated serum RNase levels. A strong correlation between RNase levels and renal insufficiency, as measured by CCr, has thus been demonstrated. In addition, case histories of 5 representative myeloma patients were analyzed in greater detail; they illustrated the rise and fall of RNase levels as a function of the status of their renal insufficiency, regardless of the extent of the underlying myeloma. We concluded that the serum RNase level was an indicator of renal function, and was not a biomarker either for the presence or extent of the plasma cell tumor.

A white blood cell RNase assay for the possible monitoring of malignancy.

The RNase activity observed in the sera of leukemic guinea pigs was compared to that observed in white blood cell (WBC) lysates of the same animals. The WBC-associated RNase activity directed against polyuridylic acid decreased with the progression of neoplastic disease, though serum RNase activity remained unchanged. With certain forms of cancer, therefore, variations in cell RNase may be more sensitive markers than changes in serum RNase for the evaluation of the progression or regression of disease.

Alterations in ribonuclease activities in the plasma, spleen, and thymus of tumor-bearing mice.

Six transplantable murine tumor models were evaluated for changes in RNase activity. This study was conducted with spleen and thymus homogenates, as well as with plasma collected from tumor-bearing mice. Nuclease activity directed against the synthetic substrates, polyadenylic acid, polyuridylic acid, and polycytidylic acid, was measured and the data obtained for tumor-bearing animals were compared to their normal counterparts. Elevated activity against polyuridylic acid was observed in the plasma of all tumor-bearing mice. Although not as all inclusive, RNase levels in both the spleen and thymus were generally altered as well. The observance of unilateral changes in nuclease activity directed against the synthetic substrates demonstrated that, in most cases, two or more enzymes were being detected. The assay may have some eventual value in the monitoring of cancer

Possible sites of origin of human plasma ribonucleases as evidenced by isolation and partial characterization of ribonucleases from several human tissues.

The ribonucleases (RNases) present in a number of human tissues, including heart, brain, lung, and kidney, were purified, partially characterized, and compared in their properties to the previously described RNases from human liver, spleen, pancreas, and serum. The enzymes appeared to fall into two major classes: liver-spleen type RNase and plasma-type RNase. These two types of enzymes were present in varying proportions in all tissues examined. The extent to which the tissues studied possibly contribute to serum RNase levels is discussed.

Anomalous behavior or ribonuclease A on Sephadex G-100.

Ribonuclease A was found to behave in an unusual fashion on a Sephadex gel column. Though ribonuclease A produces a single, well-defined protein peak on elution, enzyme activity can be detected several void volumes after the protein peak. A second unrelated protein added to the column will displace further activity as will 0.5 M phosphate buffer. This additional activity, apparently due to ribonuclease A or an active fragment of the enzyme, would appear to make this enzyme unsuitable for use as a standard in molecular weight determinations of other nucleases.

A DNA topoisomerase activity copurifies with the DNA polymerase induced by herpes simplex virus.

A DNA-relaxing enzyme was found to copurify along with herpes simplex virus type I (HSV-1)-induced DNA polymerase throughout a multistep purification scheme. Both the enzymes had similar sedimentation velocity, required high ionic strength for optimal enzymatic activities and showed time dependence of reaction. The DNA-relaxing enzyme however, differed from the HSV-1 DNA polymerase in its requirement for higher Mg2+ concentration, rATP and much broader pH dependence. Furthermore, phosphonoacetic acid, a potent inhibitor of HSV-1 DNA polymerase did not influence the DNA-relaxing activity even at a much higher concentration. On the other hand, the DNA-relaxing enzyme associated with the DNA polymerase may be specified by HSV-1 since IgG fraction of rabbit antisera against the virus-infected cells but not against the mock-infected cells strongly inhibited both the enzymatic activities. Thus, HSV-1-induced DNA polymerase which is known to be associated with a 3' to 5' exonuclease may also be associated with yet another enzymatic activity involved in DNA metabolism.

Peptides isolated from Enterobacter nuclease as potential polyamine binding sites.

The Enterobacter nuclease, which cleaves RNA between the 3'-phosphate group of cytidylic acid and the 5'-hydroxyl group of adenylic acid, has been shown to be affected by the polyamines, spermidine, spermine and putrescine. These substances enhance the hydrolytic activity of the enzyme against both poly(C) and yeast RNA. Sperimidine and spermine also reverse the inhibition of the enzyme by the ordered polynucleotides, apparently by removing them from the surface of the enzyme. Treatment of poly(G)-bound peptides (obtained from tryptic digests of poly(G)-bound nuclease) with an excess of spermidine resulted in the isolation of spermidine-bound peptides. Purification of these peptides through ion-exchange chromatography resulted in the isolation of three spermidine-bound peptides which consisted of 17 residues (6 amino acids), 19 residues (10 amino acids), and 12 residues (9 amino acids). The binding ratio of spermidine to peptides varied from 1:1 to 3:1.