MicroRNAs Mediated Regulation of Expression of Nucleoside Analog Pathway Genes in Acute Myeloid Leukemia.

Bhise Bhise,Cao Cao,Lamba Lamba,Elsayed Elsayed,Pounds Pounds

doi:10.3390/genes10040319

Abstract

Nucleoside analog, cytarabine (ara-C) is the mainstay of acute myeloid leukemia (AML) chemotherapy. Cytarabine and other nucleoside analogs require activation to the triphosphate form (ara-CTP). Intracellular ara-CTP levels demonstrate significant inter-patient variation and have been related to therapeutic response in AML patients. Inter-patient variation in expression levels of drug transporters or enzymes involved in the activation or inactivation of cytarabine and other analogs is a prime mechanism contributing to development of drug resistance. Since microRNAs (miRNAs) are known to regulate gene-expression, the aim of this study was to identify miRNAs involved in regulation of messenger RNA expression levels of cytarabine pathway genes. We evaluated miRNA and gene-expression levels of cytarabine metabolic pathway genes in 8 AML cell lines and The Cancer Genome Atlas (TCGA) data base. Using correlation analysis and functional validation experiments, our data demonstrates that miR-34a-5p and miR-24-3p regulate DCK, an enzyme involved in activation of cytarabine and DCTD, an enzyme involved in metabolic inactivation of cytarabine expression, respectively. Further our results from gel shift assays confirmed binding of these mRNA-miRNA pairs. Our results show miRNA mediated regulation of gene expression levels of nucleoside metabolic pathway genes can impact interindividual variation in expression levels which in turn may influence treatment outcomes.

Highlights

Nucleoside analogs (NA) are a class of chemotherapeutic agents that structurally resemble the endogenous purine or pyrimidine nucleosides
In order to validate the significant correlations between miRNAs and messenger RNA (mRNA) identified in acute myeloid leukemia (AML) cell lines, we evaluated the correlation between miRNA expression and nucleoside analog pathway gene expression in AML patient samples from The Cancer Genome Atlas (TCGA) database (n = 186)
Cytarabine, a pyrimidine nucleoside analog is the backbone of AML chemotherapy, while clofarabine is a second-generation purine nucleoside analog that is currently being investigated for treatment of AML in various clinical trials

Summary

Introduction

Nucleoside analogs (NA) are a class of chemotherapeutic agents that structurally resemble the endogenous purine or pyrimidine nucleosides. Some of the nucleoside analogs inhibit or block the enzymes that are required for the synthesis of purine or pyrimidine nucleotides and RNA synthesis, leading to the activation of the caspase cascade and cell death. One of the primary mechanisms of resistance to nucleoside analogs is insufficient intracellular concentration of the active triphosphate metabolite. This insufficient triphosphate levels could be due to inefficient cellular uptake of the drug, reduced levels of the activating enzyme, increased levels of inactivating enzymes and/or due to increased levels of endogenous deoxynucleotide (dNTP) pools [1,2,3,4]. Since the expression and activity of drug transporters and metabolizing enzymes in the activation pathway of nucleoside analogs plays an important role in development of resistance to the NAs, it is essential to understand the factors influencing the expression and activity of these proteins

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