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Catechol is one of phenolic metabolites of benzene that is a general occupational hazard and a ubiquitous environmental air pollutant. Catechol also occurs naturally in fruits, vegetables and cigarettes. Previous studies have revealed that 72 h exposure to catechol improved hemin-induced erythroid differentiation of K562 cells accompanied with elevated methylation in erythroid specific genes. In present study, K562 cells were treated with 0, 10 or 20 μM catechol for 1–4 weeks, hemin-induced hemoglobin synthesis increased in a concentration- and time-dependent manner and the enhanced hemoglobin synthesis was relatively stable. The mRNA expression of α-, β- and γ-globin genes, erythroid heme synthesis enzymes PBGD and ALAS2, transcription factor GATA-1 and NF-E2 showed a significant increase in K562 cells exposed to 20 μM catechol for 3 w, and catechol enhanced hemin-induced mRNA expression of these genes. Quantitative MassARRAY methylation analysis also confirmed that the exposure to catechol changed DNA methylation levels at several CpG sites in several erythroid-specific genes and their far upstream of regulatory elements. These results demonstrated that long-term exposure to low concentration of catechol enhanced the hemin-induced erythroid differentiation of K562 cells, in which DNA methylation played a role by up-regulating erythroid specific genes. [ABSTRACT FROM AUTHOR]

Abstract: Catechol is widely used in pharmaceutical and chemical industries. Catechol is also one of phenolic metabolites of benzene in vivo. Our previous study showed that catechol improved erythroid differentiation potency of K562 cells, which was associated with decreased DNA methylation in erythroid specific genes. Catechol is a substrate for the catechol-O-methyltransferase (COMT)-mediated methylation. In the present study, the role of COMT in catechol-enhanced erythroid differentiation of K562 cells was investigated. Benzidine staining showed that exposure to catechol enhanced hemin-induced hemoglobin accumulation and induced mRNA expression of erythroid specific genes in K562 cells. Treatment with catechol caused a time- and concentration-dependent increase in guaiacol concentration in the medium of cultured K562 cells. When COMT expression was knocked down by COMT shRNA expression in K562 cells, the production of guaiacol significantly reduced, and the sensitivity of K562 cells to cytotoxicity of catechol significantly increased. Knockdown of COMT expression by COMT shRNA expression also eliminated catechol-enhanced erythroid differentiation of K562 cells. In addition, the pre-treatment with methyl donor S-adenosyl-l-methionine or its demethylated product S-adenosyl-l-homocysteine induced a significant increase in hemin-induced Hb synthesis in K562 cells and the mRNA expression of erythroid specific genes. These findings indicated that O-methylation catalyzed by COMT acted as detoxication of catechol and involved in catechol-enhanced erythroid differentiation of K562 cells, and the production of S-adenosyl-l-homocysteine partly explained catechol-enhanced erythroid differentiation. [Copyright &y& Elsevier]

Abstract: Benzene is a common occupational hazard as well as a widespread pollutant. Its metabolites play important roles in its toxicity to the hematopoietic system, but little is known about how benzene metabolites affect erythropoiesis. Our previous study demonstrated that benzene metabolites, including phenol and hydroquinone, inhibited hemin-induced erythroid differentiation of K562 cells. In present study, to elucidate the role of DNA methylation in benzene metabolites-induced inhibition on erythroid differentiation, it was investigated whether DNA methyltransferase inhibitor, 5-aza-2′-deoxycytidine (5-aza-CdR), was able to prevent benzene metabolites inhibiting hemin-induced erythroid differentiation in K562 cells, and the methylation levels of erythroid-specific genes in benzene metabolites-treated K562 cells were analyzed by Quantitative MassARRAY methylation analysis platform. It was found that treatment of K562 cells with 5-aza-CdR completely prevented phenol and hydroquinone inhibiting hemin-induced hemoglobin synthesis and hemin-induced expression of erythroid specific genes, including α- and β-globin, erythroid porphobilinogen deaminase and GATA binding protein 1 (GATA-1). Consistently, the exposure to benzene metabolites caused an increase in DNA methylation levels at a few CpG sites in some erythroid specific genes, including α-globin gene and α-cluster HS40 element, β-globin gene and HS core sequence in LCR of β-globin gene cluster, erythroid porphobilinogen deaminase gene, and GATA-1 gene. These results indicated that DNA methylation played a role in benzene metabolites inhibiting hemin-induced erythroid differentiation of K562 cells via down-regulating transcription of some erythroid related genes. [Copyright &y& Elsevier]