IGF-I and IL-4 prevent apoptosis and increase expression of bcl-2 in myeloid progenitor cells

We have shown that IGF-I increases survival by preventing apoptosis in the myeloid progenitor cell line FDCP-l/Mac-1 via a PI 3-kinase dependent pathway (J. Immunol. 156:939,1996). To better define the intracellular signaling mechanisms involved in regulating apoptosis, we determined that IGF-I and IL-4 increase inducible PI 3-kinase activity in FDCP cells by six- and four-fold above control, respectively. CSF-deprived FDCP cells were double stained with PI and HO 33342 and analyzed by flow cytometry to determine the apoptotic population. Recombinant IGF-I (100 ng/ml) and IL-4 (10 U/ml) reduced the early apoptotic population at 24 h from 39±4% to 16±3% and 21+3%, respectively (n=4, p<0.01). Cells treated with the combination of IGF-I and IL-4 showed a decrease in apoptotic cells as compared to cells treated with either agent alone (11 ±2%; n= 3, p<0.01). The expression of bcl-2, a 26 kD protein known to inhibit apoptotic cell death, was measured by Western blot and densitometric quantitation. Both IGF-I and IL-4 increased expression of bcl-2 by four(410±24%) and about two-fold (186±18%, n=2), respectively, over controls after 24 h. These results were verified by intracellular flow cytometric analysis of the bcl-2 protein. These data demonstrate that IL-4, like IGF-I, inhibits apoptosis in CSF-deprived FDCP cells and that IGF-I and IL-4 may suppress apoptosis by upregulating bcl-2 expression via a PI 3-kinase-dependent pathway. (NIH Grant AG 06246).