INHIBITION OF GAMMA-GLUTAMYL-TRANSPEPTIDASE ACTIVITY AT THE SURFACE OF HUMAN MYELOID CELLS IS CORRELATED WITH MACROPHAGE MATURATION AND TRANSFORMING GROWTH-FACTOR-BETA PRODUCTION

The protease gamma-glutamyl transpeptidase (gamma-GT) activity was det ected at the surface of human blood granulocytes and monocytes and mye loblastic HL-60 and monoblastic U937 leukemia cell lines using an enzy matic assay (cleavage of gamma-glu-p-nitroanilide and inhibition by th e specific irreversible inhibitor of gamma-GT, i.e., acivicin). Flow c ytometric analysis of gamma-GT expression and detection of a 2.4-kb ga mma-GT mRNA species by Northern blot analysis confirmed the presence o f gamma-GT in cells of the monocytic-granulocytic lineage. Differentia tion of HL-60, U937 cells, and blood monocytes along the macrophage:pa thway or granulocytic maturation of HL-60 cells was accompanied by an increase in gamma-GT mRNA levels without modulation of cell surface ga mma-GT activity and protein. When added to leukemic cell cultures, aci vicin produced a dose- and time-dependent inhibitory growth effect ass ociated with the induction of morphological features characteristic of macrophage maturation and enhanced surface expression of phenotypic m arkers CD11b and CD71 characteristic of monocyte development. When cul tured in the presence of acivicin, freshly isolated monocytes also und erwent characteristic charges in morphology and antigenic phenotype (i ncrease in CD71 and HLA-DR class II) consistent with their differentia tion into macrophages. In parallel, a marked production of latent tran sforming growth factor (TGF)-beta was observed in supernatants of cell s cultured with acivicin, although TGF-beta 1 mRNA species were expres sed in these cells at a level almost similar to that in unstimulated c ell cultures. Moreover, acivicin-treated cells still differentiated in to macrophages in the presence of a neutralizing antibody to TGF-beta 1/beta 2. Together, these data indicate that human myeloid precursor c ells express a functional gamma-GT; inhibition of proteolytic activity is associated with induction of macrophage maturation and TGF-beta 1 production.