A phosphatidylcholine phospholipase C inhibitor, D609, blocks interleukin-3 (IL-3)-induced bcl-2 expression but not...

Activation of the interleukin-3 (IL-3) receptor is required for the induction of cell proliferation and suppression of apoptosis in primitive hematopoietic progenitor cells. A rapid activation of tyrosine kinases and a phosphatidylcholine-specific phospholipase C has been observed in these cells in response to IL-3. The signal transduction cascades regulating cell proliferation and the suppression of apoptosis are poorly understood. Using human IL-3-dependent TF-1 cells, we have found that the tyrosine kinase inhibitor genistein blocks both the IL-3 suppression of apoptosis and the expression of the cell survival gene bcl-2. In addition, we have found that D609, a specific inhibitor of phosphatidylcholine-specific phospholipase C, also inhibits IL-3-induced expression of the bcl-2 gene without affecting IL-3-induced tyrosine phosphorylation. D609 also drove these cells into apoptosis even in the presence of IL-3. Significantly, genistein inhibited the IL-3 induction of both bcl-2 and c-myc gene. The latter gene is related to the induction of cell proliferation. D609, however, blocked the induction only of the cell survival gene bcl-2. Thus, phosphatidylcholine hydrolysis appears linked to the induction of genes related to cell survival. These data fit with the hypothesis that there is a bifurcation in the signaling pathways downstream of IL-3 receptor-induced tyrosine phosphorylation.