Cooperation between STAT5 and phosphatidylinositol 3-kinase in the IL-3-dependent survival of a bone marrow derived cell line

Abstract

Cytokine-dependent activation of distinct signaling pathways is a common scheme thought to be required for the subsequent programmation into cell proliferation and survival. The PI 3-kinase/Akt, Ras/MAP kinase, Ras/ NFIL3 and JAK/STAT pathways have been shown to participate in cytokine mediated suppression of apoptosis in various cell types. However the relative importance of these signaling pathways seems to depend on the cellular context. In several cases, individual inhibition of each pathway is not su cient to completely abrogate cytokine mediated cell survival suggesting that cooperation between these pathways is required. Here we showed that individual inhibition of STAT5, PI 3-kinase or MEK activities did not or weakly a ected the IL-3 dependent survival of the bone marrow derived Ba/F3 cell line. However, the simultaneous inhibition of STAT5 and PI 3-kinase activities but not that of STAT5 and MEK reduced the IL-3 dependent survival of Ba/F3. Analysis of the expression of the Bcl-2 members indicated that phosphorylation of Bad and Bcl-x expression which are respectively regulated by the PI 3-kinase/Akt pathway and STAT5 probably explain this cooperation. Furthermore, we showed by co-immunoprecipitation studies and pull down experiments with fusion proteins encoding the GST-SH2 domains of p85 that STAT5 in its phosphorylated form interacts with the p85 subunit of the PI 3-kinase. These results indicate that the activations of STAT5 and the PI 3-kinase by IL-3 in Ba/F3 cells are tightly connected and cooperate to mediate IL-3-dependent suppression of apoptosis by modulating Bad phosphorylation and Bcl-x expression.

Overexpression of Sp1 transcription factor induces apoptosis

“…bcl-x gene has Sp1-binding sites in its promoter (Grillot et al, 1997) and has been shown to be tightly regulated in Baf-3 cells (Leverrier et al, 1999;Rosa Santos et al, 2000). Although the decrease of Bcl-X might sensitize the cells to apoptosis, this decrease is unlikely to be the cause of Baf-3 cell death as it has been previously shown that they can remain viable with minimal Bcl-X expression levels (Low et al, 2001).…”

Naturally occurring dominant-negative Stat5 suppresses transcriptional activity of estrogen receptors and induces apoptosis in T47D breast cancer cells

“…For instance, inhibition of either Stat5 or PI3 kinase alone did not affect IL-3-mediated survival or proliferation of BaF3 cells, but blockade of both Stat5 and PI3 kinase effectively induced apoptosis in these cells (Rosa Santos et al, 2000). It was also reported that functional cooperation among Ras, Stat5, and P13 kinase was required for full oncogenic activities of Bcr-Abl in K562 cells (Sonoyama et al, 2002).…”

The Src tyrosine kinase Hck is required for Tel-Abl- but not for Tel-Jak2-induced cell transformation

“…Immunoprecipitation studies using NP40 cell lysates were performed as previously described (Rosa Santos et al, 2000). …”