In Vitro Effects of γ-Glutamyltranspeptidase Inhibitor Acivicin on Human Myeloid and B Lineage Cells

Abstract

Gamma-glutamyltranspeptidase (γ-GT, EC 2.3.2.2) (Figure 1) is a widely distributed enzyme that acts as a transferase in the transfer of the γ-glutamyl group from a wide variety of peptide donors to other amino acids and peptide acceptors, and as a hydrolase in removing the γ-glutamyl residue from such peptides [1]. γ-GT activity was initially detected at the surface of human monocytes [2]. Using a spectrophotometric method, we showed it to be a sensitive assay of γ-GT activity detected on the surface of intact cells, as well as in highly purified cell membrane fractions. Cell-surface γ-GT (assayed with γ—Glu-para-nitroanilide as substrate and Gly-Gly as acceptor and abolished by the specific inhibitor of γ-GT i.e. acivicin) was confirmed in the myeloblastic (HL-60) and monoblastic (U937) cell lines [3]. Peripheral blood monocytes, granulocytes as well as macrophages developed in vitro from monocytes. were also found to exhibit γ-GT activity [3]. Another line of evidence that human myeloid cells express γ-GT was obtained from Northern blot analysis. In humans, there are at least four potential genes for γ-GT located on chromosome 22 [4]. Using a liver γ-GT probe, we have detected an mRNA species of 2.4 kb, corresponding to that previously described for the HepG2 cell line [5] in both cell lines and in granulocytes and macrophages [3]. Resting human B cells purified from blood as well as plasma cell lines (U266, RPMI 8226, Eskol) expressed γ-GT activity. However, no γ-GT transcripts were detected in any cells of the B lineage.