A SMALL MOLECULAR-MASS INHIBITOR OF GROWTH OF 3T3 CELLS AND PORCINE AORTIC SMOOTH-MUSCLE CELLS RELEASED FROM THE MACROPHAGE CELL-LINE P388D1

Murine peritoneal macrophages and the macrophage-like cell line, P388D 1, were found to release both mitogenic and inhibitory modulators of g rowth of cells in culture. These growth factors were effective against both murine Swiss 3T3 fibroblasts and porcine aortic smooth muscle ce lls as assessed by [H-3]thymidine incorporation into DNA and by measur ement of cell number. Partial characterisation of the inhibitory activ ity demonstrated it to be lost on dialysis using a membrane with a 10 kDa cut-off, trypsin sensitive, heat stable, and slightly sensitive to freeze-thawing. The inhibitory activity not only affected cell growth but was found to change the morphology of porcine aortic smooth muscl e cells. Gel permeation studies showed an estimated molecular mass in the range 2.5 to 6.5 kDa. The inhibitory activity could be partially p urified using ion-exchange chromatography. Experiments with a neutrali sing antibody against transforming growth factor beta (TGF-beta) showe d that TGF-beta is not responsible for the activity observed. Indometh acin had no effect on the production of inhibitor suggesting that it i s not an inhibitory prostanoid. The inhibitory activity was not due to a nonspecific toxic mechanism as confirmed by a [H-3]adenine release assay. Incubation of P388D1 cells with cycloheximide prevented the rel ease of inhibitory activity.