Inhibition of ‘y-Glutamyl Transpeptidase Activity at the Surface of Human Myeloid Cells Is Correlated with Macrophage Maturation and Transforming Growth Factor 3 Production’

The protease ‘y-glutamyl transpeptidase (7-CT) activity was detected at the surface of human blood granulocytes and monocytes and myeloblastic HL-60 and monoblastic U937 leukemia cell lines using an enzymatic assay (cleavage of ‘y-glu-p-nitroanilide and inhibition by the specific irreversible inhibitor of 7-CT, i.e., acivicin). Flow cytome ric analysis of 7-GT expression and detection of a 2.4-kb 7-CT mRNA species by Northern blot analysis confirmed the presence of 7-CT in cells of the monocytic-granulocytic lineage. Differentiation of HL-60, U937 cells, and blood monocytes along the macrophage pathway or granulocytic maturation of HL-60 cells was accompanied by an increase in 7-CT mRNA levels without modulation of cell surface 7-CT activity and protein. When added to leukemic cell cultures, acivicin produced a doseand time-dependent inhibitory growth effect associated with the induction of morphological features characteristic of macrophage maturation and enhanced surface expression of phenotypic markers CD1 1 b and CD71 characteristic of monocyte development. When cultured in the presence of acivicin, freshly isolated monocytes also underwent characteristic changes in morphology and antigenic phenotype (increase in CD71 and HLA-DR class II) consistent with their differentiation into macrophages. In parallel, a marked production of latent transforming growth factor (TCF)-j3 was observed in supernatants of cells cultured with acivicin, although TCF1 mRNA species were expressed in these cells at a level almost similar to that in unstimulated cell cultures. Moreover, acivicin-treated cells still differentiated into macrophages in the presence of a neutralizing antibody to TCF31/ 2. Together, these data indicate that human myeloid precursor cells express a functional 7-CT; inhibition of proteolytic activity is associated with induction of macrophage maturation and TCF-131 production.