DNA polymerase activity in phytohemagglutinin-stimulated and non-stimulated human lymphocytes

Concentration of nucleotides and deoxynucleotides in peripheral and phytohemagglutinin-stimulated mammalian lymphocytes. Effects of adenosine and deoxyadenosine

Concentrations of purine and pyrimidine ribonucleotides were measured with HPLC in lymphocytes of man, horse, pig and sheep and in rat thymocytes. The ATP concentration was highest in lymphocytes of all species and about 850 pmol/10(6) cells in human and equine lymphocytes, higher in porcine and lower in ovine lymphocytes and rat thymocytes. The GTP concentration was comparable in human, equine and porcine lymphocytes, but lower in ovine lymphocytes. ATP concentration was also measured in lymphocytes of man, horse and pig with a luciferin-luciferase assay. During culturing with or without phytohemagglutinin the ATP concentrations decreased in these lymphocytes. The concentrations of TTP and dATP were measured with a DNA polymerase assay. Phytohemagglutinin-stimulation increased the TTP concentration in lymphocytes of all three species, the dATP concentration only in human lymphocytes. ATP, TTP and dATP concentrations and thymidine incorporation were measured in phytohemagglutinin-stimulated lymphocytes after 24 and 48 h culturing in the presence of adenosine or deoxyadenosine. Adenosine increased the ATP concentration in porcine and equine, but not in human lymphocytes. Deoxyadenosine and adenosine did not affect the TTP concentration. Deoxyadenosine decreased the ATP concentration only in the presence of EHNA in human lymphocytes, but increased it in other conditions and in equine and porcine lymphocytes. Deoxyadenosine in the presence of EHNA increased the dATP concentration in human, equine and porcine lymphocytes 3-, 10-, and 9-fold, respectively, and decreased considerably thymidine incorporation. Deoxyadenosine without EHNA increased the dATP concentration 2-5-fold, decreased the thymidine incorporation in lymphocytes of man and horse, but stimulated incorporation in porcine lymphocytes about 5-fold. The latter results indicate that accumulation of dATP is not always associated with inhibition of cell proliferation.

Effect of hydroxyurea and 5-fluorodeoxyuridine on deoxyribonucleoside triphosphate pools early in phytohemagglutinin-stimulated human lymphocytes

The induction of deoxyribonucleoside triphosphate pools was studied in phytohemagglutinin-stimulated human lymphocytes in the presence of metabolic inhibitors. The dATP pool was completely inhibited in cells treated with hydroxyurea, in contrast to the dTTP pool. However, 1-formyl-isoquinoline thiosemicarbazone inhibited the formation of these pools equally. During approximately 3 hr of treatment of stimulated cells with hydroxyurea, the dATP, dGTP and dCTP pools were depleted to the base levels observed in the cells before the pools were induced. The base level of the dTTP pool was achieved only in the presence of 5-fluorodeoxyuridine, but the inhibition was completely prevented by addition of thymidine. It is suggested that, when resting lymphocytes were stimulated to enter the growth cycle, the formation of deoxyribonucleoside triphosphates in the early transformation was due to the de novo pathway.

Ultraviolet-induced DNA excision repair in human B and T lymphocytes. II. Effect of inhibitors and DNA precursors

Despite their great sensitivity to ultraviolet light purified human B and T lymphocytes are capable of complete repair provided that the ultraviolet dose does not exceed 0.5 Jm-2. Their capacity to repair, as measured by the restoration of DNA supercoiling in preparations of nucleoids, and their survival are significantly increased in the presence of deoxyribonucleosides. Certain agents which inhibit semi-conservative DNA synthesis (hydroxyurea, 1-beta-D-arabinofuranosylcytosine (arafCyt) either stop or delay the repair process in lymphocytes. The effect of hydroxyurea is eventually overcome spontaneously, but changes in the sedimentation behaviour of ultraviolet-irradiated nucleoids caused by arafCyt can only be neutralized by addition of deoxycytidine. The effective inhibition of repair by arafCyt permits the detection of extremely small amounts of ultraviolet damage and also the estimation of when repair is complete.

Suppression of phytohemagglutinin-induction of thymidine uptake in guinea pig lymphocytes by methylglyoxal bis(guanylhydrazone) treatment

Treatment with methylglyoxal bis(guanylhydrazone), a specific inhibitor of S-adenosylmethionine decarboxylase (EC 4.1.1.50), suppressed the phytohemagglutinin-induction of [3H]thymidine uptake by guinea pig lymphocytes. The kinetics of [3H]thymidine uptake revealed that the Km value for thymidine was not changed, but the V value was markedly lowered by the methylglyoxal bis(guanylhydrazone) treatment. The induction of ATP: thymidine 5'-phosphotransferase (EC 2.7.1.75) (thymidine kinase) activity by phytohemagglutinin was suppressed to about the same extent as the induction of thymidine uptake. These suppressions were dependent on the methylglyoxal bis(guanylhydrazone) doses and on duration of the methylglyoxal bis(guanylhydrazone) treatment. Analysis of [3H]thymidine labelled compounds of the acid-soluble fraction showed that conversion of thymidine to thymidine 5'-triphosphate was inhibited by the methylglyoxal bis(guanylhydrazone) treatment. DNA polymerase activity was less inhibited by the methylglyoxal bis(guanylhydrazone) treatment in comparison with the methylglyoxal bis(guanylhydrazone) inhibition of thymidine uptake by whole cells. These results strongly suggested that blocking of polyamine accumulation by the methylglyoxal bis(guanylhydrazone) treatment influenced phytohemagglutinin induction of thymidine phosphorylation, resulting in a decrease of thymidine incorporation into DNA.

Induction of thymidine kinases in phytohaemagglutinin-stimulated human lymphocytes

Thymidine kinase (ATP:thymidine 5'-phosphotransferase, EC 2.7.1.21) activity increased approx. 200-fold during transformation of human lymphocytes with phytohaemagglutinin. Two peaks of thymidine kinase (peak IS and peak IIS) were separated from stimulated lymphocytes on DEAE-Sephadex. The activity in peak IS was 20-fold the activity in peak IIS. Only one peak was obtained from normal lymphocytes (peak IIN). The elution volume of this peak was identical to that of peak IIS. The Km values for ATP were 1 mM for peak IS, 0.2 mM for peak IIS and 0.3 mM for peak IIN. 90 micronM dTTP gave 50% inhibition of the activity in peak IS, while the same inhibition of the activities in peak IIS and peak IIN was obtained with only 15 micronM dTTP. Km for thymidine was about 6 micronM for peak IS. The kinetic relation between thymidine and the activity in peak IIS was complex but very similar to that of peak IIN. It is suggested, that a new form of thymidine kinase appears in the lymphocytes due to phytohaemagglutinin stimulation.

Early effects of phytohemagglutinin on induction of DNA polymerase, thymidine kinase, deoxyribonucleoside triphosphate pools and DNA synthesis in human lymphocytes

In phytohemagglutinin stimulated human lymphocytes the time relationship was determined between induction of the parameters mentioned. The results indicate that the induction occurred in a specific sequence. Thus, a simultaneous increase in the activity of DNA polymerase and thymidinekinase occurred after 15 h of incubation with Phytohemagglutinin. Furthermore, this enhancement occurred 2 h before the expansion of the TTP and dCTP pools and 4 h before the expansion of the dATP and dGTP pools. The rate of [3H] deoxyguanosine incorporation into DNA increased simultaneously with the expansion of the TTP and dCTP pools.

Thymidine kinase, DNA synthesis and cancer

A resume has been presented of some recent investigations which show that DNA synthesis can be initiated in many types of quiescent animal cells by external stimuli, by introducing a quiescent nucleus into the cytoplasm of a proliferating cell, or by a virus infection. The components of the DNA replication apparatus are described. It is shown that deoxyribonucleoside triphosphate pools increase substantially in animal cells at the time DNA synthesis is initiated due to the enhanced activities of enzymes functioning in nucleotide synthesis. Especially striking is the increase of thymidine kinase activity, indicating that this enzyme may be a useful marker of the shift from the quiescent to the replicative state. The thymidine kinase isozymes of vertebrate cells have been characterized. Thymidine kinase F, which is found principally in the cytosol, is the isozyme that increases when G1 (Go) phase cells are stimulated or infected with oncogenic viruses. Chick cytosol thymidine kinase F can also be reactivated by introducing differentiated chick erythrocyte nuclei into the cytoplasm of enzyme-deficient LM (TK-) mouse cells. Furthermore, herpesviruses code for distinctive, virus-specific thymidine kinase isozymes, so that another way to transform thymidine kinase-deficient LM TK-) cells to kinase-positive cells is by infecting them with UV-irradiated herpes simplex viruses. The experiments on the activation of DNA synthesis and thymidine kinase F activity have been discussed in the context of the proliferative activity in vivo and the immortalization in culture of neoplastic cells. These experiments suggest that genes determining cell cycle proteins are readily accessible to transcription and translation in essentially all nucleated cells. The tendency of transformed cells to become multinucleated after cytochaliasin B treatment also suggests that one important difference between malignant cells and most normal cells may be the ability of malignant cells to 'stockpile' the proteins (and/or their messenger RNAs) of the DNA replicative apparatus and to maintain the 'stockpiles' in progeny cells.

Cumulative indices of DNA synthesizing myocytes in different compartments of the working myocardium and conductive system of the rat's heart muscle following extensive left ventricle infarction

Ten successive 3H-thymidine injections at 12 h intervals (which is a little shorter than the adult heart myocyte S phase) were performed for labeling of the majority of cardiac myocytes synthesizing DNA at any moment of such a 5 days experiment. In the hearts of control unoperated rats ten-fold repeated 3H-thymidine administration results in labeling of 2-3% myocyte nuclei in both atria, ca. 1% of the specialized muscle cell nuclei in the atrioventricular conductive system, only occasional muscle cells being labeled in the working ventricular myocardium. When ten successive 3H-thymidine injections were made between the 5th and 10th days following extended left ventricle infarction, the percentage of labeled myocytes in left and right atria reaches, respectively, 51.4 +/- 4.4% and 34.7 +/- 3.6%. In the left ventricle labeled muscle nuclei are accumulated predominantly (9.3 +/- 2.1%) within the thin subepicardial layer of the surviving myofibers, while myofibers located in other perinecrotic areas contained only 1.3 +/- 0.5% labeled muscle nuclei. The number of these nuclei in the atrioventricular system remains at the level observed in control hearts (up to 2%), approaching closely the zero level in the working myocardium of both the ventricles and interventricular septum, located at the considerable distance from the infarcted region. When similar experiments with ten-fold repeated 3H-thymidine injections were performed between 15th and 20th post-infarction days the number of labeled myocyte nuclei was found to be reduced 4-6 times in atria, being changed rather a little in the perinecrotic ventricular myocardium and in the specialized myocardium of the atrioventricular system. Some possible reasons of the observed differences in the proliferative behaviour of cardiac myocytes in terms of their topology and/or specialization are discussed.

Variations of DNA polymerase-alpha and -beta during prolonged stimulation of human lymphocytes

Stimulation of human lymphocytes with phytohemagglutinin is known to induce an increase in overall DNA polymerase activity (DNA nucleotidyltransferase; deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7). Previous work [Pedrali Noy, G., Dalprà, L. Pedrini, A. M., Ciarrocchi, G., Giulotto, E., Nuzzo, F. & Falaschi, A. (1974) Nucleic Acids Res. 1, 1183] has shown that two subsequent waves of induction of DNA polymerase can be observed in this system; a first wave occurs in parallel with the increase in DNA replication rate; a second one occurs when the DNA synthesis rate is returned to minimal levels; the second peak is parallel to a maximum in DNA ligase and DNase levels. In the present work we have measured the levels of the DNA polymerases-alpha and -beta in phytohemagglutinin-stimulated lymphocytes during a 12-day period; both enzymes are present at detectable levels at time zero; in correspondence to the peak of DNA synthesis rate (between the fourth and fifth day) a peak of DNA polymerase-alpha is observed, increasing by a factor of approximately 20-fold over the zero time value; subsequently, the level of DNA polymerase-alpha decreases in parallel with DNA synthesis rate. The DNA polymerase-beta is also increased in correspondence to the peak in DNA synthesis rate, but reaches its maximum at later times, between the eighth and tenth day of incubation. The capacity of stimulated lymphocytes to perform repair synthesis following UV damage was measured in the same cells used for the enzyme activity determinations; this capacity also shows two maxima: a first one correlated with the peak in DNA replication rate, and a second one correlated with the peak of DNA polymerase-beta. These data suggest a certain tendency to the specialization of functions in human cell DNA polymerases; the alpha-enzyme seems mainly correlated with DNA replication, whereas the beta-enzyme seems more correlated with the ability of the cell to perform repair type synthesis.

Lymphocyte stimualtion by a mammary carcinoma assoicated glycoprotein

A glycoprotein was isolated from 3M KCl extracts of mammary carcinoma. Addition of an optimal amount of the carcinoma associated glycoprotein induces proliferation of both peripheral blood lymphocytes from normal donors and from patients with mammary carcinoma. RNA-dependent DNA-polymerase levels were found to be markedly increased in glycoprotein-untreated lymphocytes from patients with mammary carcinoma and in glycoprotein-treated lymphocytes of both normal donors and tumor-bearing patients. A factor ("Blocking Factor") was eluted at pH 3.1 from the cell membrane of the mammary carcinoma cells. Addition of an optimal amount of this factor inhibits the glycoprotein induced stimulation of the RNA-dependent DNA-polymerase activity in glycoprotein-treated lymphocytes of both normal donors and tumor-bearing patients.

Evidence for two waves of induction of DNA enzymes in stimulated human lymphocytes

The stimulation of human lymphocytes with phytohaemoagglutinin induces the appearance or increase of several enzymes of DNA metabolism [Pedrini etal., Biochem. Biophys. Res. Comm., 47:1221(1972)]. With long times of stimulation, two phenomena are observed; an increase in the levels of DNA polymerase, of a DNase acting on single-stranded DNA, and of an endonuclease, occurring between the third and fourth day, in parallel with a wave of DNA synthesis;a second wave of increase of the same enzymes and of DNA ligase,occurring between the fifth and eight day when the DNA replication rate, as measured by thymidine-pulses, has decreased to values close to the background.

Synthesis of DNA in human lymphocytes: possible control mechanism

Partially purified, isolated nuclei from lymphocytes either stimulated or not stimulated by phytohemagglutinin can equally well synthesize DNA when [(3)H]dTTP is used as precursor. Studies of DNA polymerase activity in nuclei and cytoplasm from these cells showed that the enzyme can be detected in either stimulated or nonstimulated lymphocytes. In nonstimulated lymphocytes the uptake of thymidine is very low. The use of inhibitors such as cycloheximide, arbinosylcytosine, and actinomycin D showed that a parallel existed between thymidine uptake and DNA synthesis. All the conditions in which DNA synthesis was inhibited resulted also in an inhibition of thymidine uptake.