Thymidine kinase, DNA synthesis and cancer

Abstract

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.

Transcriptional and posttranscriptional mechanisms regulate murine thymidine kinase gene expression in serum-stimulated cells.

“…Two major versions of the enzyme have been characterized in mammalian cells; one is found in the cytoplasm, and the other is found in the mitochondria (8,27). They are encoded by genes located on different autosomes (15,30,37,63), and although they catalyze the same basic phosphorylation reaction, the biochemical characteristics of each enzyme and of each reaction are unique (27). The cytosolic form of TK is of special interest, since its activity is regulated in association with several cellular metabolic activities and events.…”

Thymidine Kinase Activity in Familial Adenomatous Polyposis.

“…Thymidine kinase (TK) is a key enzyme in the pyrimidine salvage pathway, which catalyzes the phosphorylation of deoxythymidine to form dTMP (Kit 1978). Since rapid replication of DNA requires an adequate supply of deoxyribonucleotides to serve as the substrates for the DNA polymerase reaction, it is not surprising that the activity of this enzyme has been shown to be regulated in response to alterations in DNA replicative activity.…”

“…High TK activity has been consistently observed in rapidly proliferating normal, fetal and neoplastic tissues Sakamoto et al 1984Sakamoto et al , 1985Sakamoto et al , 1986Sakamoto et al , 1987Luccioni et al 1988). Two distinct isozymes of TK have been separated and purified by various methods, including polyacrylamide gel electrophoresis (PAGE), subcellular fraction, affinity column chromatography, and DEAE-cellulose column chromatography (Kit 1978). One of these isozymes is the predominant form seen in terminally differentiated adult tissues and is associated with the mitochondrial cell fraction ; it is often therefore referred to as "TK-A" or "TK-M", and it migrates rapidly during PAGE.…”

“…We have long been using isozymes of thymidine kinase (TK ; EC 2.7.1.21), a DNA-synthesizing enzyme (Kit 1978), to examine such issues in general ; using this tool, we have recently focused on FAP in particular.…”

Transfer of the gene for thymidine kinase to thymidine kinase-deficient human cells by purified herpes simplex viral DNA.

“…Consequently, oncogenic transformation is not a suitable model system for studying the characteristics of gene transfer in general. However, it is well established that herpes simplex viruses (HSV) code for a thymidine kinase (ATP:thymidine 5'-phosphotransferase, EC 2.7.1.75) (TK) (2) and that this enzyme can be transferred to thymidine kinase-deficient (TK-) cells by transformation with UV-inactivated HSV-1 or HSV-2 (3) or with temperaturesensitive mutants of these viruses (4). The viral TK is well characterized and can be easily distinguished from most mammalian cell TKs (2).…”