Colon tumor: enzymology of the neoplastic program

The biochemical strategy of colon tumor was investigated by comparing the enzymic programs of glycolysis, pentose phosphate production and purine and pyrimidine biosynthesis and degradation in liver, normal colon mucosa and transplantable colon adenocarcinoma in the mouse. In normal colon mucosa the carbohydrate and pentose phosphate enzymes were 2- to 9-fold higher in specific activity than those in liver. Among the enzymes of CTP synthesis, CTP synthetase was the rate-limiting one in both liver and colon. In colon tumor CTP synthetase, OMP decarboxylase, uracil phosphoribosyltransferase and thymidine kinase activities increased to 927, 863, 597 and 514% of activities of normal colon. In contrast, the activity of the catabolic enzymes, dihydrothymine dehydrogenase and uridine phosphorylase, decreased to 51 and 25%. The ratios of activities of uridine kinase/uridine phosphorylase and thymidine kinase/dihydrothymine dehydrogenase were elevated 6- and 10-fold. The activity of the key purine synthetic enzyme, glutamine PRPP amidotransferase, increased 7-fold and the opposing rate-limiting enzyme of purine catabolism, xanthine oxidase, decreased to 7%. The ratio of amidotransferase/xanthine oxidase was elevated to 8, 150%. Activities of glucose-6-phosphate dehydrogenase and transaldolase did not increase, but that of pyruvate kinase was elevated to 154%. Similar enzymic programs were observed in a transplantable adenocarcinoma of the colon in the rat. The alterations in gene expression in colon tumor manifested in an integrated pattern of enzymic imbalance indicate the display of a program, a segment of which is shared with rat and human liver and kidney tumors. These alterations in gene expression should confer selective advantages to colon tumor cells. The striking increases in the activities of CTP synthetase, OMP decarboxylase, glutamine PRPP amidotransferase and thymidine kinase mark out these enzymes as potentially sensitive targets for combination chemotherapy by specific inhibitors of these enzyme activities.     

The sex difference in the regulation of liver regeneration after partial hepatectomy in the rat

The increases in the activity of hepatic thymidylate synthetase and thymidine kinase, which catalyzes the formation of thymidylate via the de novo and salvage pathways, respectively, were significantly suppressed 24 h after 70% partial hepatectomy in female rats administered either alpha- or beta-adrenoreceptor antagonists. The injection of beta-antagonist to male or ovariectomized female rats had no effect on the activities of these enzymes. Only alpha-adrenoceptor antagonist depressed these enzymatic activities of 24-h-regenerating liver in male and ovariectomized female rats. The decrease of the activities of thymidylate synthetase and thymidine kinase was accompanied by a concomitant reduction of DNA content in 24-h-regenerating liver. It is concluded that catecholamine regulates the female rat liver regeneration through both alpha- and beta-adrenergic pathways by the inductions of thymidylate synthase and thymidine kinase, while in adult male and ovariectomized female rats, only the alpha-mediated pathway is involved.     

Association of thymidylate kinase activity with pyrimidine deoxyribonucleoside kinase induced by herpes simplex virus.

Thymidine kinase derived from LMTK+ does not exhibit thymidylate kinase activity. However, protein isolated by affinity column chromatography from thymidine kinase-deficient mouse cells (LMTK-) infected by herpes simplex virus type 1 shows thymidylate kinase activity in addition to thymidine kinase and deoxycytidine kinase activities. The virus-induced multifunctional enzyme has a molecular weight of 85,000, whereas the molecular weight of thymidylate kinase from uninfected LMTK- mouse cells is 71,000. The virus-induced enzyme has a Km for thymidine of 0.8 micromolar, and for thymidylate of 25 micromolar, and for thymidylate of 25 micromolar; the ratio of Vmax for thymidylate kinase to thymidine kinase is 1.7. When subjected to isoelectric focusing, thymidylate kinase activity is not separated from thymidine kinase activity, and even though four peaks of activity are observed they have a constant ratio of thymidylate kinase to thymidine kinase activity. The isoelectric points (pI) of these four peaks are 4.8, 5.8, 6.2, and 6.6, respectively. Thymidylate kinase, derived from uninfected cells when subjected to isoelectric focusing, separates into a major component with an isoelectric point at pH 8.2 and a minor component at pH 7.7. Although thymidine and thymidylate kinase activities derived from the virus-infected cells cannot be separated either by affinity column chromatography, glycerol density gradient centrifugation, or isoelectric focusing, there is a differential rate of inactivation when the enzyme is subjected to incubation at 37 degrees, with thymidylate kinase activity being more labile than thymidine kinase activity.     

Thymidylate synthetase during synchronous nuclear division cycle and differentiation of Physarum polycephalum

Thymidylate synthetase and thymidine kinase activities in wild type strain M₃b and in thymidine kinase-deficient mutant TU63 of Physarum polycephalum are studied. Whenever nuclear division occurs in macroplasmodia of wild type, thymidine kinase and thymidylate synthetase activities sharply increase, although the increase of thymidylate synthetase activity is less pronounced than thymidine kinase activity. This is also true for other investigated nuclear divisions during the life cycle of P. polycephalum. It is shown for the first time that thymidylate synthetase is a periodically fluctuating enzyme during the naturally synchronous nuclear division cycle of P. polycephalum with a peak of specific activity in the S phase. In macroplasmodia, as well as after germination of microsclerotia of M₃b, thymidine kinase is the dominant enzyme, whereas at the time of the precleavage mitosis in sporulating macroplasmodia thymidylate synthetase is the predominant enzyme. This study describes and compares both dTMP-synthesizing enzymes during proliferation and differentiation of the same organism.     

Enxymology of human colon tumors

The biochemical strategy of human colon adenocarcinoma was studied by elucidating the enzymic programs of pyrimidine biosynthesis and degradation, glycolysis, pentose phosphate production, and galactose metabolism in normal colon mucosa and in 9 cases of primary colon adenocarcinoma. Enzymic activities were determined in the 100,000 X $\text{g}$ supernatant fluid with spectrophotometric or isotopic assays under optimum conditions yielding linear kinetics. In the human colon tumors the activities of enzymes of the $\text{de}$$\text{novo}$ pyrimidine biosynthesis, CTP synthetase, OMP decarboxylase, and orotate phosphoribosyltransferase, were increased to 348, 183, and 201% of those of normal human colon mucosa. The activities of the salvage pathway enzymes, thymidine kinase, uracil phosphoribosyltransferase and uridine kinase, were increased to 331, 254 and 281%. By contrast, the activity of the catabolic enzyme, uridine phosphorylase, was decreased to 69%. The ratio of activities of uridine kinase/ uridine phosphorylase was elevated to 564%. The activities of the key glycolytic enzymes, hexokinase and pyruvate kinase, and those of pentose phosphate production, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and transaldolase, increased to 348, 209, 262, 156, and 180% respectively. The activity of the first committed enzyme of galactose utilization, galactokinase, was increased to 315%. The enzymic program of human primary colonic adenocarcinoma was similar in most respects to that which we observed in chemically-induced, transplantable adenocarcinomas of the colon in mouse and in rat (4). The reprogramming of gene expression in human colon tumor provides an increased capacity for biosynthesis of pyrimidines and ribose 5-phosphate, and for utilization of the glycolytic pathway and of galactose. These alterations in gene expression should confer selective advantages to the human colon tumor cells. The marked elevations in the activities of the salvage enzymes, uridine-cytidine kinase and thymidine kinase, explain in part the failure to obtain good therapeutic results with inhibitors of the $\text{de}$$\text{novo}$ pathway and account, in part at least, for the clinical difficulties encountered in the treatment of colon tumors. The elevated activities of CTP synthetase, OMP decarboxylase, uridine-cytidine kinase and thymidine kinase mark out these enzymes as targets for combination chemotherapy. Through such enzyme-pattern-targeted chemotherapy the drug treatment of human colon tumors should be improved.     

CORRELATION OF DNA ACCUMULATION RATE WITH THYMIDYLATE SYNTHETASE AND THYMIDINE KINASE ACTIVITIES IN DEVELOPING RAT CEREBELLUM: EFFECT OF THYROXINE1

Abstract— Using the method of least squares, a logistic curve was fitted to the data points for DNA content in neonatal rat cerebellum versus postnatal age (day 0 is the day of birth). The resultant equation was differentiated to give an expression for the rate of cerebellar DNA accumulation in units of ng/h per mg wet cerebellum. The DNA accumulation rate in control rats increased from 77.0 at 2 days of age to a maximum of 108 at 7 days of age and declined thereafter to a minimum of 16.3 on day 15. Thyroxine treatment significantly (P < 0.05) increased the rate to 89.8 (117% of control) at 2 days of age, and a significant elevation was maintained to 6 days of age at which time a maximum rate of 115 (114% of control) was attained. The rate was significantly decreased below control at 9 and 12 days of age, and reached a minimum of 9.22 on day 15. The developmental pattern for the activity of cerebellar thymidylate synthetase (EC 2.1.1.6), in units of pmol/h per mg wet cerebellum, closely paralleled the pattern for DNA accumulation rate in both control and thyroxine-treated animals. In controls, thymidylate synthetase activity increased from 98.6 at 2 days of age to a maximum of 125 at 7 days of age and declined thereafter to a minimum of 30.0 at 15 days of age. In thyroxine-treated animals, the activity was significantly increased to 118 (122% of control) at 4 days of age and remained significantly elevated through 6 days of age at which time a maximum activity of 154 (115% of control) was attained; thereafter, the activity was significantly decreased below control and reached a minimum of 16.9 (56.3% of control) on day 15. The developmental pattern for the activity of cerebellar thymidine kinase (EC 2.7.1.21) did not parallel the DNA accumulation rate quite so closely, in neither treated nor control animals, as did the pattern for thymidylate synthetase activity. These data suggest that thymidylate synthetase activity in the developing rat cerebellum may be more important for maintenance of replicative DNA synthesis than is thymidine kinase activity. In addition, the thyroxine-induced acceleration of the increase and subsequent decline in rate of DNA accumulation and in the activities of thymidylate synthetase and thymidine kinase in developing rat cerebella is probably the result of alterations in the number of external granular cells undergoing replicative DNA synthesis.     

Thymidine phosphorylase, thymidine kinase and thymidylate synthetase activities in cerebral hemispheres of developing chick embryos

The changes in activities of thymidine phosphorylase (EC 2.4.2.4), thymidine kinase (EC 2.7.1.75) and thymidylate synthetase (methylenetetrahydrofolate:dUrd-5′-P C-methyltransferase, EC 2.1.1.-) in the cerebral hemispheres of developing chick embryos were determined and compared with the course of DNA synthesis and of natural cell death in this organ. Thymidine phosphorylase activity reaches a broad maximum at the 12th to 14th day of incubation, followed by a rapid decrease. Thymidine kinase and thymidylate synthetase activities are highest at the earliest time studied (day 10) and decrease until day 14, followed by an increase from day 14 to 16 and a further decrease from day 16 through 1 day post-hatching. The rate of DNA synthesis essentially follows these activities, but the increase at day 16 is not discernible. Our previous study revealed high DNA synthesis at day 10, with natural cell death concurring on days 12-14, followed by another peak after day 16 (glial proliferation) and a decrease after day 16. It appears that thymidine phosphorylase activity reaches a maximum (days 12-14) at the time of maximum cell death, which may be correlated with the degradative function of this enzyme. This was also the time for minimum activities of thymidine kinase and thymidylate synthetase; on the other hand, these activities reach a first (day 10) and second (day 16) maximum at the time of maximum DNA synthesis; this may be correlated with the synthetic functions of these enzymes.     

Biochemical Aspects of Chick Embryo Retina Development: The Effects of Glucocorticoids

In chick embryo retina during development, DNA synthesis and the activities of DNA polymerase, thymidine kinase, thymidylate synthetase, and ornithine decarboxylase (ODC) declined in parallel from day 7 to 12. The administration in ovo of hydrocortisone reduced significantly, particularly at 8-10 days of incubation, both DNA synthesis and the four enzyme activities tested. The effect was dose dependent, reaching the maximum with 50-100 nmol of hydrocortisone, 8-16 h after treatment. The highest inhibition was found for ODC activity (70%), followed by thymidine kinase activity (62%) and DNA synthesis (45%), whereas activities of DNA polymerase and thymidylate synthetase were reduced only by 30%. The inhibitory effect was exerted by all the glucocorticoids tested, with dexamethasone and hydrocortisone being the most efficacious. The results support the view that glucocorticoids reduce the proliferative events in chick embryo retina, particularly at 8-10 days of embryonic life.     

Effect of colchicine and vincristine on DNA synthesis in regenerating rat liver

The increases in the activities of hepatic thymidylate synthetase and thymidine kinase were significantly suppressed at 24 h after 70% partial hepatectomy in rats which had been administered a microtubule disrupter, colchicine or vincristine. The decrease of these enzymic activities was accompanied by a reduction of DNA content in 24 h regenerating liver. The immunoblotting assay showed that the depression of the thymidylate synthetase activity by the injection of colchicine or vincristine was due to the decrease of the enzyme protein. These results indicate that colchicine and vincristine inhibit the DNA synthesis during liver regeneration by inhibiting the induction of the key enzyme in DNA synthesis.     

Epithelial cell kinetics in the descending colon of the rat

Epithelial cell kinetics were investigated in the descending colon of the rat. The number of cells per crypt was found to be approximately 625, with 33 cells per cell column and 19 cell columns per crypt circumference. The growth fraction of the colonic crypt was 0.42, and proliferating cells were situated largely in the lower half of the crypt. The cell cycle time was 50.5 h, with values for the G1, S and G2 phases of 40.0, 7.6 and 2.9 h respectively. Cell migration studies showed that it took 60-72 h for a cell to migrate from the upper border of the proliferative cell compartment in the crypt to the luminal surface of the colon. Data were also obtained from continuous labelling with tritiated thymidine and from studying the circadian rhythm of proliferative activity, which suggest that the cells in the bottom of the crypt may constitute a separate, more slowly cycling (stem)cell compartment.     

Thymidine 5′-Monophosphate-Requiring Mutants of Saccharomyces cerevisiae Are Deficient in Thymidylate Synthetase

Thymidylate synthetase activity was measured in crude extracts of the yeast Saccharomyces cerevisiae by a sensitive radiochemical assay. Spontaneous non-conditional mutants auxotrophic for thymidine 5'-monophosphate (tmp1) lacked detectable thymidylate synthetase activity in cell-free extracts. In contrast, the parent strains (tup1, -2, or -4), which were permeable to thymidine 5'-monophosphate, contained levels of activity similar to those found in wild-type cells. Specific activity of thymidylate synthetase in crude extracts of normal cells or of cells carrying tup mutations was essentially unaffected by the ploidy or mating type of the cells, by the medium used for growth, by the respiratory capacity of the cells, by concentrations of exogenous thymidine 5'-monophosphate as high as 50 mug/ml, or by subsequent removal of thymidine 5'-monophosphate from the medium. Extracts of a strain bearing the temperature-sensitive cell division cycle mutation cdc21 lacked detectable thymidylate synthetase activity under all conditions tested. Its parent and another mutant (cdc8), which arrests with the same terminal phenotype under restrictive conditions, had normal levels of the enzyme. Cells of a temperature-sensitive thymidine 5'-monophosphate auxotroph arrested with a morphology identical to the cdc21 strain at the nonpermissive temperature and contained demonstrably thermolabile thymidylate synthetase activity. Tetrad analysis and the properties of revertants showed that the thymidylate synthetase defects were a consequence of the same mutation causing, in the auxotrophs, a requirement for thymidine 5'-monophosphate and, in the conditional mutants, temperature sensitivity. Complementation tests indicated that tmp1 and cdc21 are the same locus. These results identify tmp1 as the structural gene for yeast thymidylate synthetase.     

Levels of true thymidine kinase and nucleoside phosphotransferase in two strains of Tetrahymena pyriformis under different growth conditions.

Activities of typical thymidine kinase and nucleoside phosphotransferase are both present in logarithmically growing tetrahymena pyriformis, GL-1 and ST strains, contrary to previous reports. 2. Activities of thymidine kinase and nucleoside phosphotransferase are also found in both GL-1 and ST strains grown in the defined medium, PPL medium and Neff's medium. 3. The specific activities of both enzymes are very much influenced by the growth state. Both the specific activities of thymidine kinase and nucleoside phosphotransferase decrease steadily from the start of the experiments when the cell numbers were about 2-3 x 10(4) cells/ml in the PPL medium, while in the Neff's medium, the specific activities of thymidine kinase increase up to when the cell numbers reached 3-5 x 10(5) cells/ml and then decreased, but the specific activities of nucleoside phosphotransferase continuously decreased when the cell concentrations were 2-6 x 10(4) cells/ml. 4. In the PPL medium, the final cell numbers reached are about 6.5 x 10(5) cells/ml, while in the Neff's medium, the cell numbers increase further (to about 2 x 10(6) cells/ml). 5. No striking difference in activities of thymidine kinase and nucleoside phosphotransferase was observed when the cells were transferred from the defined medium to the Neff's medium, contrary to that reported by others for the activity of thymidylate synthetase.     

Thymidine salvage in Pseudomonas stutzeri and Pseudomonas aeruginosa provided by heterologous expression of Escherichia coli thymidine kinase gene.

Unlike enteric bacteria, Pseudomonas spp. generally lack thymidine phosphorylase and thymidine kinase activities, thus preventing their utilization of exogenous thymine or thymidine and precluding specific radioactive labeling of their DNA in vivo. To overcome this limitation, a DNA fragment encoding thymidine kinase (EC 2.7.1.21) from Escherichia coli was cloned into pKT230, a small, broad-host-range plasmid derived from plasmid RSF1010. From transformed E. coli colonies, the recombinant plasmid bearing the thymidine kinase gene was conjugally transferred to Pseudomonas stutzeri, Pseudomonas aeruginosa, Pseudomonas mendocina, Pseudomonas alcaligenes, and Pseudomonas pseudoalcaligenes. Thymidine kinase activity was expressed in all of these species, and all gained the ability to incorporate exogenous [2-14C]thymidine into their DNA. Thymidine incorporation into P. stutzeri was enhanced 12-fold more in mutants lacking thymidylate synthetase activity. These mutants produced higher levels of thymidine kinase and were thymidine auxotrophs; thymineless death resulted from removal of thymidine from a growing culture.     

Assay of intracellular thymidylate synthetase activity and inhibition by 5-fluoro-2'-deoxyuridine in lymphocytes.

Thymidylate synthetase catalyses the formation of thymidine monophosphate from deoxyuridine monophosphate. Purified thymidylate synthetase can be assayed radiochemically using labelled deoxyuridine monophosphate as substrate, but cells are impervious to deoxyuridine monophosphate and so intracellular thymidylate synthetase activity cannot be assayed in this way. In this paper we describe the assay of intracellular thymidylate synthetase activity in intact cells using labelled 2'-deoxyuridine. The assay showed linear kinetics with respect to time, concentration of 2'-deoxyuridine, and cell concentration. 5-fluoro-2'-deoxyuridine inhibited intracellular thymidylate synthetase activity measured with this assay by 50% at 5 nM. Cell growth was inhibited by 50% at 6 nM 5-fluoro-2'-deoxyuridine. The assay was specific for thymidylate synthetase and enabled measurement of thymidylate synthetase activity in situ in intact cells.     

Association of diamine oxidase and ornithine decarboxylase with maturing cells in rapidly proliferating epithelium

Diamine oxidase and ornithine decarboxylase activities are shown to have a parallel distribution across rat small intestine mucosa; levels of both enzyme activities are sharply higher in mature cells in the villus tip region than in proliferating cells in the crypt areas. Histidine decarboxylase levels were not measurable in the same cell preparations and aromatic-L-amino-acid decarboxylase activity was distributed in an opposite pattern to diamine oxidase and ornithine decarboxylase. The results suggest that intestinal diamine oxidase could be involved with polyamine metabolism. The new findings for ornithine decarboxylase suggest an in vivo role for polyamines in non-proliferative cells; rat small intestinal mucosa may be an excellent model for investigating the function of polyamines in regenerating cells.     

Association of diamine oxidase and ornithine decarboxylase with maturing cells in rapidly proliferating epithelium.

Diamine oxidase and ornithine decarboxylase activities are shown to have a parallel distribution across rat small intestine mucosa; levels of both enzyme activities are sharply higher in mature cells in the villus tip region than in proliferating cells in the crypt areas. Histidine decarboxylase levels were not measurable in the same cell preparations and aromatic-L-amino-acid decarboxylase activity was distributed in an opposite pattern to diamine oxidase and ornithine decarboxylase. The results suggest that intestinal diamine oxidase could be involved with polyamine metabolism. The new findings for ornithine decarboxylase suggest an in vivo role for polyamines in non-proliferative cells; rat small intestinal mucosa may be an excellent model for investigating the function of polyamines in regenerating cells.     

Human Thymidine Kinase Can Functionally Replace Herpes Simplex Virus Type 1 Thymidine Kinase for Viral Replication in Mouse Sensory Ganglia and Reactivation from Latency upon Explant

Herpes simplex virus type 1 thymidine kinase exhibits a strikingly broad substrate specificity. It is capable of phosphorylating deoxythymidine and deoxyuridine as does human thymidine kinase, deoxycytidine as does human deoxycytidine kinase, the cytosolic kinase whose amino acid sequence it most closely resembles, and thymidylate as does human thymidylate kinase. Following peripheral inoculation of mice, viral thymidine kinase is ordinarily required for viral replication in ganglia and for reactivation from latency following ganglionic explant. To determine which activity of the viral kinase is important for replication and reactivation in mouse ganglia, recombinant viruses lacking viral thymidine kinase but expressing individual human kinases were constructed. Each recombinant virus expressed the appropriate kinase activity with early kinetics following infection of cultured cells. The virus expressing human thymidine kinase exhibited thymidine phosphorylation activity equivalent to ~5% of that of wild-type virus in a quantitative plaque autoradiography assay. Nevertheless, it was competent for ganglionic replication and reactivation following corneal inoculation of mice. The virus expressing human thymidylate kinase was partially competent for these activities despite failing to express detectable thymidine kinase activity. The virus expressing human deoxycytidine kinase failed to replicate acutely in neurons or to reactivate from latency. Therefore, it appears that low levels of thymidine phosphorylation suffice to fulfill the role of the viral enzyme in ganglia and that this role can be partially fulfilled by thymidylate kinase activity alone.     

Thymidine kinase, thymidylate synthase, and endothelial cell growth under hyperoxia

To determine the respective role of thymidine kinase and thymidylate synthase activities in the hyperoxia-induced decrease in DNA synthesis and their relationship with cell replication, we measured these two enzyme activities in primary cultures of porcine aortic endothelial cells under different O2 concentrations for various durations. In confluent cells, exposure to 95% O2 for 5 days reduced thymidine kinase activity to 15% of control values; thymidylate synthase activity was unaffected. In preconfluent cells exposed to 95% O2 for 2 days, similar results were obtained, together with evidence for arrest in cell proliferation. Thymidylate synthase activity could therefore not be related to decreased cell proliferation under hyperoxia. [3H]thymidine incorporation into DNA, thymidine kinase activity, and cell proliferation were all similarly affected under exposure to graded O2 concentration for 2 days. Thymidine kinase appears to be a key enzyme in the modulation of DNA synthesis from thymidine and in its replication in endothelial cells.     

Inhibition of Thymidine Kinase Activity and Deoxyribonucleic Acid Synthesis in L Cells Infected with the Meningopneumonitis Agent

The activities of enzymes related to deoxyribonucleic acid (DNA) synthesis were studied in uninfected L cells and in L cells infected with Chlamydia psittaci (strain meningopneumonitis). The meningopneumonitis agent multiplied normally but failed to induce the synthesis of thymidine kinase in LM (TK(-)) cells which contain no thymidine kinase in the uninfected state. It was concluded that this microorganism has no thymidine kinase of its own and that it does not depend on the functioning of the host enzyme for synthesizing its DNA. Exposure of clone 5b L cells to the meningopneumonitis agent was followed by a decline in their thymidine kinase activity to nearly zero levels, whereas the levels of uridine kinase and thymidylate synthetase remained unchanged. Inhibition of thymidine kinase activity in L cells occurred soon after infection and required new protein synthesis by the meningopneumonitis agent. This inhibition occurred before inhibition of host DNA synthesis, but it was not an essential prelude to the latter inhibition. On the basis of this and previous investigations and in light of present knowledge of the mammalian cell cycle, it was postulated that the meningopneumonitis agent inhibits macromolecular synthesis in L cells by preventing the initiation of a new cell cycle.