Hydroquinone modulates the GM-CSF signaling pathway in TF-1 cells.

Human leukemogens, including alkylating chemotherapeutic agents and benzene, enhance granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent proliferation of human CD34+ bone marrow (BM) cells. The extracellular signal-regulated kinase (ERK) pathway plays an important role in GM-CSF-dependent proliferation and also has been implicated in the pathogenesis of acute myelogenous leukemia. Therefore, we investigated the effects of the benzene metabolite, hydroquinone (HQ), on alterations in the GM-CSF signaling pathway in TF-1 erythroleukemia cells and human CD34+ BM cells. HQ treatment in TF-1 cells results in a strong proliferative response that is dependent on ERK activation and GM-CSF production. HQ also induces ERK-dependent AP-1 activation with concomitant increased transcriptional activity of AP-1 reporter gene. However, the kinetics of ERK activation are different between rhGM-CSF and HQ in TF-1 cells: rhGM-CSF results in immediate activation of ERK, whereas HQ activation of ERK is delayed. Further, HQ and rhGM-CSF together produce an immediate increase in ERK phosphorylation, which is sustained for over 48 h. HQ also stimulates colony formation, AP-1 DNA binding and GM-CSF production in human CD34+ BM cells. These results suggest that HQ stimulates proliferation via activation of ERK/AP-1 and is at least partially mediated via the production of GM-CSF.

Analysis of hydroquinone and catechol in peripheral blood of benzene-exposed workers.

We have developed a gas chromatography-mass spectrometry method for analysis of benzene (BZ) metabolites in human urine and blood. Here we describe peripheral blood concentrations of hydroquinone (HQ(1)) and catechol (CAT(2)) in total, protein-bound, and unbound (free) forms obtained from BZ-exposed factory workers and controls. Total and unbound metabolites were directly measured in independent experiments, while bound forms were calculated as [total]-[unbound]. In this subset of a larger study, breathing zone benzene, toluene, and xylene were measured for the duration of a workshift, and end-shift blood samples taken from 143 subjects and controls. Potential lifestyle and environmental influences were assessed by questionnaire and bioassay, and single nucleotide polymorphisms in xenobiotic metabolizing enzymes NQO1, MPO, CYP2E1, and GSTT1 were also analyzed for potential contribution to differences in blood metabolite concentration. Total CAT, bound CAT, total HQ, and bound HQ correlated well with benzene exposure, while unbound CAT and HQ displayed no correlation. Nearly all of the metabolites found in blood were bound to protein (CAT 96-99+%, HQ 78-92+%), and when the ratio of bound to unbound metabolites were compared in subsets of exposed workers, the increase in blood metabolite concentration was nearly all due to an increase in the protein-bound molecule. These findings suggest that a threshold for conjugation does not exist within the exposure spectrum studied (0.01-78.8 mg/m(3)). This method demonstrates the feasibility of analyzing benzene metabolites in human blood, and should allow for further investigation of the health effects of benzene and its metabolites.

PU.1 phosphorylation correlates with hydroquinone-induced alterations in myeloid differentiation and cytokine-dependent clonogenic response in human CD34(+) hematopoietic progenitor cells.

The transcriptional regulatory factor PU.1 is important for the regulation of a diverse group of hematopoietic and myeloid genes. Posttranslational phosphorylation of PU.1 has been demonstrated in the regulation of a variety of promoters in normal cells. In leukemia cells, differing patterns of PU.1 phosphorylation have been described among acute myelogenous leukemia (AML) subtypes. Therefore, we hypothesized that modulation of PU.1-dependent gene expression might be a molecular mediator of alterations in myeloid cell growth and differentiation that have been demonstrated to be early events in benzene-induced leukemogenesis. We found that freshly isolated human CD34(+) hematopoietic progenitor cells (HPC) exhibit multiple PU.1-DNA binding species that represent PU.1 proteins in varying degrees of phosphorylation states as determined by phosphatase treatment in combination with electrophoretic mobility shift assay (EMSA). Maturation of granulocyte and monocyte lineages is also accompanied by distinct changes in PU.1-DNA binding patterns. Experiments reveal that increasing doses of the benzene metabolite, hydroquinone (HQ) induce a time-and dose-dependent alteration in the pattern of PU.1-DNA binding in cultured human CD34(+) cells, corresponding to hyperphosphorylation of the PU.1 protein. HQ-induced alterations in PU.1-DNA binding are concomitant with a sustained immature CD34(+) phenotype and cytokine-dependent enhanced clonogenic activity in cultured human HPC. These results suggest that HQ induces a dysregulation in the external signals modulating PU.1 protein phosphorylation and this dysregulation may be an early event in the generation of benzene-induced AML.