INDUCTION OF APOPTOSIS IN B-LINEAGE CELLS BY ACTIVIN-A DERIVED FROM MACROPHAGES

A factor produced by P388D(1) cell line murine macrophages showed a pr ofound suppressive effect on the in vitro proliferation of B lineage c ells, It was purified to homogeneity from conditioned media of P388D(1 ) cells stimulated with phorbol 12-myristate 13-acetate far 48 h by a three-step procedure. The purified factor gave a single band of protei n with a molecular mass of 16 kD on SDS-polyacrylamide gel electrophor esis, We show here that exposure of B lineage cells to this factor res ults in the induction of a cytotoxic effect and a significant increase in the proportion of fragmented DNA, DNA fragmentation was detected i n B lineage cells after 3 h culture with the factor in the quantitativ e colorimetric determination, The mechanism of cell death was characte rized by a ladder-like electrophoretic pattern of degraded chromosomal DNA, indicating that the factor induces apoptosis. The NH2-terminal a mino acid sequence of this factor was identical with that of activin A over the 26 amino acid residues identified, We sought to determine wh ether apoptosis could be modulated by two kinds of inhibitor of protei n kinases, H7 and HA1004, in concentrations that are below their toxic ity limits, Apoptosis induced by the factor was suppressed by H7 but w as relatively unaffected by HA1004. These findings suggest that the si gnals by protein kinases may regulate apoptotic B cell death by the fa ctor activin A, derived from macrophages.