Glutathione S-transferase enzyme expression in hematopoietic cell lines implies a differential protective role for T1 and A1 isoenzymes in erythroid and for M1 in lymphoid lineages

Department of Molecular and Cellular Pathology, University of Dundee Medical School, Dundee, UK. BACKGROUND AND OBJECTIVES: Glutathione S-transferases (GSTs) are phase II metabolizing enzymes which catalyze the conjugation of glutathione (GSH) to electrophilic substrates and possess selenium-independent glutathione peroxidase activity. The GST enzyme family includes the cytosolic isoforms GST-alpha, mu (GSTM), pi (GSTP), theta (GSTT) and sigma (GSTS). GSTT1, P1 and M1 are polymorphic and altered polymorphic frequency of genes encoding these proteins has been suggested as a potential risk factor for the development of hematopoietic malignancies. Overexpression of GSTs has also been implicated in chemotherapeutic drug resistance. This study was undertaken to elucidate the potential functional relevance of these genetic polymorphisms in hematopoiesis. DESIGN AND METHODS: GST genotype of 14 hematopoietic cell lines was determined by polymerase- chain-reaction (PCR). Gene expression of GSTs in a cell line was detected by real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) on TaqMan 7700 and by semi-quantitative RT-PCR. Cytosolic GST protein expression was detected by Western blot. GST conjugation activity was assayed using 1-chloro-2,4-dinitrobenzene (CDNB) as substrate. RESULTS: GSTP1 expression was higher than other GSTs in 13/14 cell lines and paralleled CDNB conjugation activity. GSTP1 and GSTM1 predominated in lymphoid lines whilst T1 expression was relatively greatest in erythroid lines but was absent in 7/12 non-null lines. GSTT2 was expressed in only 3/4 lines. The 3 cell lines which expressed GSTA1 were all erythroid. INTERPRETATION AND CONCLUSIONS: Glutathione S-transerases showed differential lineage expression in hematopoietic cell lines. This implies a greater cytoprotective role for GSTT1 and GSTA1 in erythroid cells and GSTM1 in lymphoid cells. We postulate that inherited gene deletion of GSTT1 and M1 may produce increased genotoxic susceptibility for erythroid and lymphoid cell respectively, following exposure to xenobiotics that are substrates for these enzymes.