Biol. Pharm. Bull. 30(10) 1954—1957 (2007)

polar, hydrophilic compounds is an important prerequisite for the detoxification and eventual elimination of xenobiotics from the body. This mechanism also provides the first line of intracellular defense and is mediated by a number of enzyme superfamilies, including cytochrome P450 (CYP) and several conjugation enzymes including the sulfotransferases, UDPglucuronosyl transferases and glutathione S-transferases. These enzymes also catalyze the bioactivation and inactivation of a wide variety of endogenous compounds, including steroid hormones and eicosanoids. Most of these enzymes are localized in the liver but many are also expressed in extrahepatic tissues such as the small intestine, the lungs and the kidneys. Among the extrahepatic tissues, little is known about the expression of drug metabolizing enzymes in peripheral blood cells. CYP1A1 enzymes in human peripheral blood lymphocytes might be responsible for aryl hydrocarbon hydroxylation, which is reported to correlate positively with the susceptibility to lung cancer from tobacco smoke exposure. It has also been reported that CYP3A enzymes are expressed in human polymorphic neutrophiles (PMNs). Previously, we have reported that CYP genes are expressed in the human myeloblastic and lymphoid cell lines, and reported the induction of the CYP3A4 and GSTP1 genes by oxidative stress in the human erythroleukemia cell line, K562. However, only limited data is currently available concerning the lineage specific expression of drug metabolizing enzymes and a more detailed understanding of this will potentially clarify the role of these enzymes during hematogenesis and in the etiology of human hematopoietic malignancy and bone marrow chemotherapeutic drug resistance. The human leukemia K562 cell line is a well-established model system for the study of both spontaneous and induced differentiation to erythrocytic, granulocytic and monocytic lineages. K562 cells are precursors that proceed toward erythroid differentiation upon treatment with agents such as hemin. When induced to differentiate with hemin, K562 cells produce the embryonic and fetal hemoglobin, a property associated with the more mature erythroid cells. Our present study describes the changes in the expression of CYP genes in differentiated K562 cells induced by hemin.