title: The pattern of deoxycytidine- and deoxyguanosine kinase activity in relation to messenger RNA expression in blood cells from untreated patients with B-cell chronic lymphocytic leukemia.
abstract: Deoxycytidine kinase (dCK) and deoxyguanosine kinase (dGK) catalyze the first step in the intracellular cascade of fludarabine (2-fluoroadenine-beta-D-arabinofuranoside) and cladribine (2-chlorodeoxyadenosine) phosphorylation, which leads to activation of these prodrugs, commonly used for treatment of chronic lymphocytic leukemia (CLL). Thus, resistance to nucleoside analogues may primarily be due to low levels of deoxynucleoside kinase activity. The purpose of this study was to investigate the activity profiles of dCK and dGK and characterize the possible relationship between the levels of dCK enzymatic activities and mRNA levels in B-CLL cells from untreated patient samples in an attempt to determine the best approach for predicting sensitivity to nucleoside analogues and thereby optimizing treatment of CLL. For this purpose, dCK and dGK analyses were done in blood cells from 59 untreated symptomatic patients with CLL. The dGK activity towards 2-chlorodeoxyadenosine was significantly lower than of dCK (median 73 pmol/mg protein/min (85-121, 95% CI) versus 353 pmol/mg protein/min (331-421)). The median dCK mRNA level was 0.107 (0.096-0.120, 95% CI). There was a lack of correlation between the activities of dCK and dGK, which indicates that these proteins are regulated independently. We also found that the dCK and dGK activity measurement towards their endogenous substrates were comparable to the nucleoside analogues tested. Such variations in enzyme activities and mRNA levels may well explain differences in clinical responses to treatment. There was no correlation between the levels of dCK mRNAs and enzymatic activities using a quantitative real-time PCR procedure. Sequencing of dCK mRNA did not reveal alternate splicing or mutations in the coding region. The relation between activity and mRNA levels was studied by short interfering RNA (siRNA) method, which showed that in the siRNA treated cells the down-regulation of dCK expression, and activity followed each other. However, in control cells the mRNA levels remained stable but the protein activity markedly decreased. These data demonstrate that the dCK activity is not reflected by dCK mRNA expression that indicates a post-translational mechanism(s).
authors.affiliation: Department of Medicine and Care, Clinical Pharmacology, Faculty of Health Sciences, Linköping University, Linköping, Sweden. koulo@imv.liu.se
authors.forename: Kourosh
authors.initials: K
authors.lastname: Lotfi
authors.forename: Karin
authors.initials: K
authors.lastname: Karlsson
authors.forename: Anna
authors.initials: A
authors.lastname: Fyrberg
authors.forename: Gunnar
authors.initials: G
authors.lastname: Juliusson
authors.forename: Viggo
authors.initials: V
authors.lastname: Jonsson
authors.forename: Curt
authors.initials: C
authors.lastname: Peterson
authors.forename: Staffan
authors.initials: S
authors.lastname: Eriksson
authors.forename: Freidoun
authors.initials: F
authors.lastname: Albertioni
mesh_terms: D017931:DNA Primers / Q000737:chemistry; D015342:DNA Probes / Q000737:chemistry; D003842:Deoxycytidine Kinase / Q000097:blood*; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000097:blood / Q000201:enzymology*; D007962:Leukocytes / Q000201:enzymology*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000097:blood*; D012333:RNA, Messenger / Q000097:blood*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013937:Thymidine Kinase / Q000378:metabolism
chemical_list: D017931:DNA Primers; D015342:DNA Probes; D012333:RNA, Messenger; D017853:Phosphotransferases (Alcohol Group Acceptor); C019165:deoxyguanosine kinase; D013937:Thymidine Kinase; D003842:Deoxycytidine Kinase