Differential mRNA expression of Ara-C-metabolizing enzymes explains Ara-C sensitivity in MLL gene-rearranged infant acute lymphoblastic leukemia
Infant acute lymphoblastic leukemia (ALL) is characterized by a high incidence of mixed lineage leukemia (MLL) gene rearrangements, a poor outcome, and resistance to chemotherapeutic drugs. One exception is cytosine arabinoside (Ara-C), to which infant ALL cells are highly sensitive. To investigate the mechanism underlying Ara-C sensitivity in infants with ALL, mRNA levels of Ara-C-metabolizing enzymes were measured in infants (n = 18) and older children (noninfants) with ALL (n = 24). In the present study, infant ALL cells were 3.3-fold more sensitive to Ara-C (P =.007) and accumulated 2.3-fold more Ara-CTP (P =.011) upon exposure to Ara-C, compared with older children with ALL. Real-time quantitative reverse trancriptase-polymerase chain reaction (RT-PCR) (TaqMan) revealed that infants express 2-fold less of the Ara-C phosphorylating enzyme deoxycytidine kinase (dCK) mRNA (P =.026) but 2.5-fold more mRNA of the equilibrative nucleoside transporter 1 (hENT1), responsible for Ara-C membrane transport (P =.001). The mRNA expression of pyrimidine nucleotidase I (PN-I), cytidine deaminase (CDA), and deoxycytidylate deaminase (dCMPD) did not differ significantly between both groups. hENT1 mRNA expression inversely correlated with in vitro resistance to Ara-C (r(s) = -0.58, P =.006). The same differences concerning dCK and hENT1 mRNA expression were observed between MLL gene-rearranged (n = 14) and germ line MLL cases (n = 25). An oligonucleotide microarray screen (Affymetrix) comparing patients with MLL gene-rearranged ALL with those with nonrearranged ALL also showed a 1.9-fold lower dCK (P =.001) and a 2.7-fold higher hENT1 (P =.046) mRNA expression in patients with MLL gene-rearranged ALL. We conclude that an elevated expression of hENT1, which transports Ara-C across the cell membrane, contributes to Ara-C sensitivity in MLL gene-rearranged infant ALL.
|Keywords||*Gene Expression, *Proto-Oncogenes, *Transcription Factors, Arabinofuranosylcytosine Triphosphate/metabolism, Cell Survival, Child, Child, Preschool, Cytarabine/*metabolism/*therapeutic use, DCMP Deaminase/genetics, DNA-Binding Proteins/*genetics, Deoxycytidine Kinase/genetics, Drug Resistance, Neoplasm/genetics, Equilibrative Nucleoside Transporter 1/genetics, Female, Gene Rearrangement, Humans, Infant, Leukemia, Lymphocytic, Acute/*drug therapy/*enzymology, Male, Myeloid-Lymphoid Leukemia Protein, Oligonucleotide Array Sequence Analysis, Polymerase Chain Reaction, Pyrimidine Nucleotides/genetics, RNA, Messenger/analysis, Research Support, Non-U.S. Gov't, Tumor Cells, Cultured|
Stam, R.W., den Boer, M.L., Meijerink, J.P.P., Ebus, M.E., Peters, G.J., Noordhuis, P., … Pieters, R.. (2003). Differential mRNA expression of Ara-C-metabolizing enzymes explains Ara-C sensitivity in MLL gene-rearranged infant acute lymphoblastic leukemia. Blood. Retrieved from http://hdl.handle.net/1765/8186