Identification of common variant alleles of the human guanosine monophosphate reductase gene

Cloning and functional characterization of GMPR2, a novel human guanosine monophosphate reductase, which promotes the monocytic differentiation of HL-60 leukemia cells

PURPOSE

To identify the biological function of a novel molecule which shows high homology with human guanosine monophosphate reductase (GMPR) and is named GMPR2.

METHODS

GMPR2 cDNA was cloned from the cDNA library of human dendritic cells and was characterized by Bioinformatics. The expression pattern of GMPR2 was analyzed by Northern blotting. The enzymatic activity of the purified recombinant GMPR2 protein was determined using a spectrophotometric assay. HL-60 leukemia cells were transfected with GMPR2 and the expression of CD14 and myeloperoxidase (MPO) in HL-60 cells with and without 12- o-tetra-decanoyl-phorbol-13-acetate (TPA) induction was monitored by FACS analysis.

RESULTS

The novel gene contained ten exons and nine introns and was mapped to 14q11-21. Northern blotting indicated a ubiquitous expression of GMPR2 mRNA in most of the human tissues and cancer cell lines investigated. The recombinant GMPR2 protein was able to reduce GMP. The expression of CD14 and MPO in HL-60 leukemia cells overexpressing GMPR2 clearly increased after induction by TPA.

CONCLUSIONS

GMPR2 is a novel human GMP reductase, and overexpression of GMPR2 can promote the monocytic differentiation of HL-60 leukemia cells.

NADPH-dependent GMP reductase isoenzyme of human (GMPR2). Expression, purification, and kinetic properties

GMP reductase (EC 1.6.6.8) is the only known metabolic step by which guanine nucleotides can be converted to the pivotal precursor of both adenine and guanine nucleotides. Human GMP reductase has been previously partially purified from erythrocytes and a chromosome 6-linked cDNA has been identified to correspond for encoding human GMP reductase. Here, we reported a distinct cDNA for human GMP reductase isoenzyme isolated from a human fetal brain library, and the GenBank accession number is AF419346. The deduced protein shows 90% identity with human GMP reductase reported (named GMPR1 compared with GMPR2 of this paper) and 69% with E. coli GMP reductase. Comparison of GMPR2 cDNA sequence with human genome indicates the corresponding gene spans about 6.6kb on chromosome 14, which encodes 348 amino acid residues. Northern hybridization analysis indicates a differential and disproportionate expression of mRNAs for GMPR1 and GMPR2, suggesting the existence of distinct molecular species of GMP reductase in human. The apparent Km of GMPR2 for NADPH and GMP are 26.6 and 17.4 microM, respectively. This is the first report suggesting the existence of two distinct types of human GMP reductase molecular species, which can be used to explain the bimodal saturation curve noted with the purified human erythrocyte GMP reductase.