Identification of a putative human mitochondrial thymidine monophosphate kinase associated with monocytic/macrophage terminal differentiation

Abstract

Mitochondrial DNA synthesis requires the supply of thymidine triphosphate (dTTP) independent of nuclear DNA replication. In resting and differentiating cells that withdraw from the cell cycle, mitochondrial thymidine kinase 2 (TK2) mediates thymidine monophosphate (dTMP) formation for the dTTP biosynthesis in mitochondria. However, a thymidine monophosphate kinase (TMPK) that phosphorylates dTMP to form thymidine diphosphate (dTDP) in mitochondria remains undefined. Here, we identified an expressed sequence tag cDNA, which encodes a TMPK with a mitochondrial import sequence at its N‐terminus designated as TMPK2. HeLa cells expressing TMPK2 fused to green fluorescent protein (GFP) displayed green fluorescence in mitochondria. Over‐expression of TMPK2 increased the steady‐state level of cellular dTTP and promoted the conversion of radioactive labeled‐thymidine and ‐dTMP to dTDP and dTTP in mitochondria. TMPK2 RNA was detected in several tissues and erythroblastoma cell lines. We also generated TMPK2 antibody and used it for immunofluorescence staining to demonstrate endogenous expression of TMPK2 in mitochondria of erythroblastoma cells. Finally, we showed that TMPK2 protein expression was upregulated in monocyte/macrophage differentiating cells, suggesting the coordinated regulation of TMPK2 expression with the terminal differentiation program.

Genetic architecture of gene expression underlying variation in host response to porcine reproductive and respiratory syndrome virus infection

“…Among our candidate genes for WG, CMPK2 has been reported to be associated with monocytic/macrophage terminal differentiation27 and CCHCR1 might function in EGFR-STAT3 signaling and innate immunity28. The gene CCHCR1 was significantly down-regulated at 4 DPI compared to day 0 and was expressed at a lower level at all DPI in individuals homozygous for the susceptibility allele.…”

The Human SLC25A33 and SLC25A36 Genes of Solute Carrier Family 25 Encode Two Mitochondrial Pyrimidine Nucleotide Transporters

“…The biochemical properties of recombinant SLC25A33 (that does not transport (d)NMPs) indicate that the main function of this transporter is to catalyze the exchange of cytosolic pyrimidine (d)NTPs for intramitochondrial pyrimidine (d)NDPs. The latter can be produced inside the mitochondria by the intramitochondrial enzymes that convert pyrimidine (d)NMPs to the corresponding (d)NDPs (51,52). According to Floyd et al (11) and Favre et al (12) SLC25A33 is induced by the insulin-like growth factor signaling pathway to mTor, and its expression is higher in transformed fibroblasts, cancer cell lines, and primary prostate cancer than in normal tissues.…”

A Review Comparing Deoxyribonucleoside Triphosphate (dNTP) Concentrations in the Mitochondrial and Cytoplasmic Compartments of Normal and Transformed Cells

“…Additionally, the authors also noted that CMPK2 might be dispensable in dCTP synthesis given that its expression was restricted and was not detected in tissues with high energetic demand such as heart and muscle [23]. Following putative identification, attempts at characterizing the enzyme activity of TMPK2 were unsuccessful both in vitro and in cell extracts [24]. No candidates exist for dGMP phosphorylation activity in the mitochondria.…”