Disease relevance of DCK

• Deoxycytidine kinase (dCK) phosphorylates 2'-deoxycytidine, as well as the purine deoxyribonucleosides and a number of nucleoside analogues that are important in the chemotherapy of leukemias [1].
• HepG2 hepatocellular carcinoma cells were used to study the transcriptional regulation of dCK [2].
• Deoxycytidine kinase and deoxyguanosine kinase of Lactobacillus acidophilus R-26 are colinear products of a single gene [3].
• Gemcitabine (2'-2'-difluorodeoxycytidine; dFdC) is a deoxycytidine analogue which is effective against solid tumours, including lung cancer and ovarian cancer. dFdC requires phosphorylation by deoxycytidine kinase (dCK) for activation [4].
• 2-Chlorodeoxyadenosine (CdA), an antileukemic agent used in treatment of hairy cell leukemia and chronic lymphocytic leukemias (B-CLL), is phosphorylated by dCK which was used as the selective substrate for this enzyme [5].

High impact information on DCK

• DCK expression in cultured lymphoblast cell lines is not solely a function of the T or B lineage derivation [1].
• To characterize the dCK promoter region and to determine whether it mediates higher levels of gene expression in T lymphoblasts, we have analyzed a 700-bp genomic fragment encompassing 548 bp of 5' flanking region for functional activity and for transcription factor binding using T and B lymphoblast cell lines and nuclear extracts [1].
• The comparative order of PHA-induced increase in cellular enzyme activities examined was: thymidine kinase > uridine kinase > deoxycytidine kinase > adenosine kinase > 5'-nucleotidase [6].
• Activities of deoxycytidine kinase, deoxycytidylate deaminase, and pyrimidine nucleoside monophosphate kinase were not different between any of the leukemic cell types [7].
• Consequently, the specific activity of enzymes that peak during S-phase increases, and deoxycytidine kinase increases 3.6-fold over untreated controls [8].

Chemical compound and disease context of DCK

• Three of the four deoxynucleoside kinases required for growth of Lactobacillus acidophilus R-26 exist as heterodimeric pairs specific for deoxyadenosine (dAK) and deoxycytidine (dCK) or dAK and deoxyguanosine (dGK) [3].
• Single high dose rate irradiation of 4 Gy in SW-1573 cells, derived from non-small cell lung cancer, led to increased activities of deoxycytidine kinase (dCK) and thymidine kinase 1 and 2 (TK1 and 2) [9].
• The HL60/CdA cells showed cross-resistance to 2-chloro-2'-arabino-fluoro-2'-deoxyadenosine, Fara-A, arabinofuranosyl cytosine, difluorodeoxyguanosine, and difluorodeoxycytidine toxicity, most likely because of the decreased phosphorylation of these analogues by dCK [10].
• Deoxycytidine kinase (dCK) is essential for the phosphorylation of cytarabine (ara-C), a deoxycytidine analog active against acute leukemias [11].
• A troxacitabine-resistant prostate cancer subline (DU145(R); 6300-fold) that exhibited reduced uptake of troxacitabine was cross-resistant to both gemcitabine (350-fold) and cytarabine (300-fold). dCK activity toward deoxycytidine in DU145(R) cell lysates was <20% of that in DU145 cell lysates, and no activity was detected toward troxacitabine [12].

Biological context of DCK

• The expression of dCK, an activation enzyme, and of CDA, an inactivation enzyme, was decreased and increased in the late phase, respectively [13].
• The longest open reading frame encoded a protein that was 48% identical to dCK at the amino acid level [14].
• A human cDNA sequence homologous to human deoxycytidine kinase (dCK; EC 2.7.1.74) was identified in the GenBank sequence data base [14].
• In this work, we used a CEM mutant cell line containing low endogenous levels of dGK and deficient in dCK (dCK-) to assess the role of these kinases in ara-G phosphorylation [15].
• To elucidate dCK, dGK and 5'-NT gene expressions in cell lines and in samples from patients with leukemia, we have established a real-time quantitative PCR (RQ-PCR) method [16].

Anatomical context of DCK

• Northern blot analysis determined the length of dGK mRNA to 1.3 kbp with no cross-hybridization to the 2.8-kbp dCK mRNA. dGK mRNA was detected in all tissues investigated with the highest expression levels in muscle, brain, liver, and lymphoid tissues [14].
• When ara-G was used as a substrate in a cell-free system, the maximum accumulation of phosphorylated product was observed in dGK+ extracts at low ara-G levels (10 microM) and in dCK+ extracts at high concentrations of ara-G (100 microM) [15].
• For this purpose, dCK and dGK analyses were done in blood cells from 59 untreated symptomatic patients with CLL [17].
• We confirm that dCK is expressed constitutively and predominantly in lymphoid cells, but conclude that a significant expression may be found in non-lymphoid tissues as well, with increased levels in the corresponding tumor tissue [5].
• High levels of dCK were found in normal mononuclear leukocytes (91-145 ng dCK/mg protein) and in B-cell chronic lymphocytic leukemia (80 +/- 30 ng/mg, n = 23) [5].

Associations of DCK with chemical compounds

• Deoxycytidine kinase (EC 2.7.1.74, dCK) is central to drug activity of anticancer and antiviral agents such as cytosine arabinoside (araC) and gemcitabine [2].
• CONCLUSIONS: Decreased hENT-1 expression and function is causatively responsible for the acquisition of Ara-C resistance and alterations in dCK and CDA contribute to the higher concentration range [13].
• The dCK homodimer strongly resembles human dCK, with a low K(m) for deoxycytidine, the ability to phosphorylate deoxyadenosine and deoxyguanosine at much higher K(m) values, and end-product inhibition by dCTP [3].
• Our findings suggest that dCK and dGK are evolutionarily related, as well as related to the family of herpes virus thymidine kinases [14].
• Only the dCK+ cell line phosphorylated 1-beta-D-arabinofuranosylcytosine (used as a substrate for dCK) in a cell-free system; phosphorylation of this compound by dGK+ was below the limit of detection [15].

Enzymatic interactions of DCK

• Direct enzymatic phosphorylation does not seem to be essential to the mechanism of action of the nucleoside insofar as competitive inhibition of deoxycytidine kinase (an enzyme that directly phosphorylates purines as well as pyrimidines) or of deoxyguanosine kinase fails to inhibit 8BrGuo stimulation selectively [18].
• 5'-Nucleotidase (5'-NT) dephosphorylates cladribine-MP and the accumulation of cladribine-TP depends on the ratio of dCK and 5'-NT in the cells [19].

Other interactions of DCK

• The decline to normal levels of dCK concurred with a further increase in the activity of TK1, 8 h after irradiation [9].
• From the available dCK, dGK and 5'-NT cDNA sequences we designed specific primers and fluorogenic probes for the respective genes [16].
• Role of USF1 in the differential expression of the human deoxycytidine kinase gene in acute myeloid leukemia [20].
• Several 5'-substituted analogues of dC were good non-substrate inhibitors of dCK and, to a lesser extent, of TK2 [21].
• We assume that dCK activation elicited by cellular damage might be a proapoptotic factor in terms of generating dATP well before the release of cytochrome c and deoxyguanosine kinase from mitochondria [22].

Analytical, diagnostic and therapeutic context of DCK

• 5'-Deletion and site-directed mutagenesis of the dCK upstream region (positions -464 to -27) confirmed the importance of two GC-boxes (positions -317 to -309 and -213 to -206) and two E-boxes (positions -302 to -297 and -278 to -273) [2].
• Real-time quantitative PCR assays for deoxycytidine kinase, deoxyguanosine kinase and 5'-nucleotidase mRNA measurement in cell lines and in patients with leukemia [16].
• These results show that the quantitative evaluation by RQ-PCR is a valuable tool in the determination of dCK, dGK and 5'-NT mRNA levels in cell lines and in clinical samples which were expressed at various levels [16].
• Western blot analysis using a polyclonal antibody showed no detectable deoxycytidine kinase (dCK) protein in CdA-resistant cells, whereas in Fara-A-resistant cells, it was at the same level as in the parental cells [10].
• Three major activities were resolved by ion exchange and affinity chromatography: deoxyguanosine-deoxycytidine kinase, deoxycytidine-deoxyadenosine kinase, and adenosine-deoxyadenosine kinase [23].

References