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Unchanged thymidine triphosphate pools and thymidine metabolism in two lines of thymidine kinase 2‐mutated fibroblasts
Author(s) -
Frangini Miriam,
Rampazzo Chiara,
Franzolin Elisa,
Lara MariCarmen,
Vilà Maya R.,
Martí Ramon,
Bianchi Vera
Publication year - 2009
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2008.06853.x
Subject(s) - thymidine kinase , thymidine , ribonucleotide reductase , biochemistry , nucleotide salvage , cytosol , chemistry , deoxycytidine kinase , thymidine phosphorylase , kinase , microbiology and biotechnology , biology , enzyme , dna , deoxycytidine , gene , protein subunit , genetics , nucleotide , cancer , virus , herpes simplex virus , gemcitabine
Mitochondrial thymidine kinase (TK2) catalyzes the phosphorylation of thymidine in mitochondria. Its function becomes essential for dTTP synthesis in noncycling cells, where cytosolic dTTP synthesis via R1/R2 ribonucleotide reductase and thymidine kinase 1 is turned down. Mutations in the nuclear gene for TK2 cause a fatal mtDNA depletion syndrome. Only selected cell types are affected, suggesting that the other cells compensate for the TK2 deficiency by adapting the enzyme network that regulates dTTP synthesis outside S‐phase. Here we looked for such metabolic adaptation in quiescent cultures of fibroblasts from two TK2‐deficient patients with a slow‐progressing syndrome. In cell extracts, we measured the activities of TK2, deoxycytidine kinase, thymidine phosphorylase, deoxynucleotidases and the amounts of the three ribonucleotide reductase subunits. Patient cells contained 40% or 5% TK2 activity and unchanged activities of the other enzymes. However, their mitochondrial and cytosolic dTTP pools were unchanged, and also the overall composition of the dNTP pools was normal. TK2‐dependent phosphorylation of [ 3 H]thymidine in intact cells and the turnover of the dTTP pool showed that even the fibroblasts with 5% residual TK2 activity synthesized dTTP at an almost normal rate. Normal fibroblasts apparently contain more TK2 than needed to maintain dTTP during quiescence, which would explain why TK2‐mutated fibroblasts do not manifest mtDNA depletion despite their reduced TK2 activity.