SURFACE AMINOPEPTIDASE ACTIVITY OF RAT NATURAL-KILLER-CELLS .1. BIOCHEMICAL AND BIOLOGICAL PROPERTIES

Aminopeptidase (AP) activity on rat natural killer (NK) cells was foun d to have the following characteristics: (1) the activity was surface associated and not secreted, as determined by extracellular location o f product and by the cessation of hydrolysis of substrate upon removal of the cells from the medium. (2) The activity was linear with respec t to time and cell number. (3) The enzymatic activity on splenocytes a nd on the NK leukemia cell line CRNK-16, but not on IL-2 activated NK (A-NK) cells, was sensitive to trypsin treatment. (4) The AP activity on intact cells had a broad pH dependency with optimal activity at sli ghtly alkaline pH but lower activity at acidic pH. (5) There was a pre ference for neutral substrates and essentially no activity towards aci dic substrates. (6) Enzymatic activity was inhibited in the presence o f the AP inhibitors bestatin and amastatin, and in the presence of the chelator, 1,10 phenanthroline, indicating the involvement of a metall oprotease. (7) Culture of A-NK cells with bestatin resulted in a decre ase in cytotoxicity against YAC-1 and P815 targets. Amastatin treatmen t caused only a slight decrease in cytotoxicity against YAC-1 targets, but a significant decrease in cytotoxicity against P815 targets. (8) Treatment of A-NK cultures with specific inhibitors of APases caused a n increase in expression of CD2 (an increase from 20-80% with bestatin and an increase from 25-35% in the presence of amastatin). These resu lts provide the first evidence for the existence of APases on the surf ace of NK cells and suggest a role for these enzymes in the regulation of cytotoxic activity and of CD2 surface expression.