Role of phosphatidylinositol 3-OH-kinase activity in the inhibition of apoptosis in haemopoietic cells: phosphatidylinositol 3-OH-kinase inhibitors reveal a difference in signalling between interleukin-3 and granulocyte-macrophage colony stimulating factor.

Apoptosis of haemopoietic cells can be inhibited by various cytokines, but the specific signalling pathways involved are not well defined. Interleukin (IL)-4 has unique actions since it is unable to activate p21ras or mitogen-activated protein kinase, but can activate PtdIns 3-OH-kinase (PtdIns 3-kinase), the latter effect being shared with most other cytokines. In many cases, IL-4 is able to maintain cell viability by inhibiting apoptosis, but is unable to stimulate continuous proliferation of cells. This led us to investigate the role of PtdIns 3-kinase in inhibition of apoptosis. Two potent inhibitors of PtdIns 3-kinase, wortmannin and LY294002, rapidly induced apoptosis in cells incubated in the presence of IL-4, at concentrations consistent with their ability to inhibit PtdIns 3-kinase activity in whole cells. Interestingly, the same effect was seen in cells in the presence of IL-3 and Steel factor, while cells incubated in the presence of granulocyte-macrophage colony stimulating factor, and to a lesser extent, IL-5 could bypass the effect of wortmannin or LY294002. Therefore, this study suggests that PtdIns 3-kinase activity provides an important, although not a unique signal, required to inhibit apoptosis in haemopoietic cells.