The mechanisms of TK1 secretion in cancer cells

Abstract: A seventy five percent increase in cancer incidence within 10 years is one of the major human health issues based on the World Health Or-ganization (WHO) evaluation. Prevention of cancer through health screening was suggested by the WHO as a means of early detection of cancer. Thymidine kinase 1 (TK1) is one of the key enzymes for DNA replication and cell division, which could have a role in tumor for-mation and progression. Exosomes are extracellular vesicles which were recently shown to act as messengers of tumor cells to communi-cate with cells in the body. The aim of this study was to evaluate if TK1 was excreted via exosomes in a BJ tumor (BJ-T) cell line as well as BJ normal (BJ-N) cell line. Exosomes were isolated from media superna-tants of BJ-T and BJ-N cells using ultracentrifugation and the final exo-some preparations were resuspended in phosphate buffered saline. TK1 activity and concentration in the supernatants before and after ultracen-trifugation as well as exosome samples were evaluated by [3H]-dThd phosphorylation assay and dot-blot chemiluminescence assay, respec-tively. Specific activity of BJ-T exosome-derived TK1 was 16.9 times more than BJ-N exosome-derived TK1, where there was also two times more TK1 concentration in BJ-T exosomes compared to BJ-N exo-somes. In conclusion, TK1 excretion was via exosomes and exosome-derived TK1 could be a tumor biomarker for BJ-T cells. Furthermore in vitro and in vivo investigations are needed in order to evaluate whether TK1 could be a useful biomarker for tumor tissue and/or in clinical level.