As an approach to facilitating the understanding of proteinases associated with monocytes we have studied U-937 monocytelike cells. Elastase activity was identified in U-937 cell extracts and compared to monocyte elastase activity, neutrophil elastase, and the elastase activity from a continuous line of murine macrophagelike cells (P388D1). Serine proteinase activity which solubilized 14C-labeled elastin accounted for >90% of the neutral proteinase activity of both U-937 cells and monocyte extracts. U-937 cell and monocyte elastase activities were similar catalytically, resembling neutrophil elastase. U-937 cells and monocytes showed other similarities: (a) both had activities reacting with [3H]diisopropylfluorophosphate that migrated in sodium dodecyl sulfate (SDS) polyacrylamide gels at ∼30,000 and 60,000 daltons and (b) both contained material that cross-reacted with antiserum raised to neutrophil elastase. Preliminary characterization of U-937 cell elastase activity by affinity chromatography and ion-exchange chromatography suggested the presence of at least two distinct elastases. Minimal elastase activity was found in U-937 cell-conditioned medium, indicating that the activity is not spontaneously released by the cells. In contrast to the elastase activity associated with U-937 cells and monocytes, the elastase activity associated with P388D1 cells was a metalloproteinase and was found principally in the culture medium. These results indicate (a) U-937 cells will be useful for further investigation of proteinases associated with normal monocytes; (b) monocytes and U-937 cells contain material with catalytic and immunologic similarities to neutrophil elastase; (c) monocyte elastase activity differs from elastase activity secreted by murine macrophages and murine macrophagelike cells of the P388D1 line.
Robert M. Senior, Edward J. Campbell, Jill A. Landis, Fraya R. Cox, Charles Kuhn, Hillel S. Koren