Induction of Differentiation in Human Myeloid Leukemic Cells by Proteolytic Enzymes

Eitan Fibach, Aliza Treves, Miriam Kidron, and Michael Mayer

Departments of Hematology (EF, AT) and Biochemistry (MK, MM), Hadassah University Hospital, Ein-Kerem
91120 Jerusalem, Israel
Tel: 972-2-6776751; Fax: 972-2-6423067; e-mail: Fibach@yahoo.com

Exogenous serine proteases were found to induce differentiation in human myeloid leukemic cells from either in vitro established long-term cell lines or in primary cultures of cells derived directly from patients with acute myeloid leukemia.  Exposure of the human promyelocytic cell line HL-60 to trypsin, chymotrypsin, or elastase induced the appearance, within 3-6 days, of neutrophilic granulocytes defined by their morphology, their ability to reduce nitro blue tetrazolium, and their efficient phagocytosis of latex particles.  Upon further incubation monocyte-like cells appeared.  While these cells developed into fully mature macrophage population.  The inducing effect could be observed when the enzyme was presented alone, whereas a synergistic effect was noted when the protease was added in the presence of subthreshold concentrations of chemicals known to induce differentiation in this cell line such as dimethylsulfoxide, retinoic acid, butyric acid, or hexamethylene bisacetamide.  Optimal induction of differentiation by trypsin required a 48 hr continuous exposure to the enzyme.  When the protease was removed earlier no appreciable differentiation was noticed.  The protease induced differentiation involve a direct interaction with the cells and was not due to a proteolytic cleavage of a serum component because it could be obtained in serum-free cultures.  The enzymatic activity of the protease was needed for its effect on cell maturation: Addition of protease inhibitors such as soybean-trypsin inhibitor or trasylol completely blocked differentiation induced by the proteases but had no effect on differentiation induced by the other inducers.  It is still to be determined whether a proteolytic process is a general molecular event in cell differentiation or induction by chemicals involves mechanisms different from that initiated by exogenous proteases.

Copyright 1985 ALAN R. LISS, INC.