The coupling of TEL/PDGFbetaR to distinct functional responses is modulated by the presence of cytokine: involvement of mitogen-activated protein kinases

Abstract

The TEL/PDGFbetaR oncogenic fusion protein is the product of the t(5;12)(q33; p13) translocation recurrently found in patients with chronic myelomonocytic leukemia (CMML). To investigate the coupling of molecular signaling events activated by TEL/PDGFbetaR to functional responses, we expressed TEL/PDGFbetaR in interleukin 3 (IL-3)-dependent BaF/3 cells using the tetracycline-regulated expression system. Induction of TEL/PDGFbetaR expression led to increased cell survival following IL-3 withdrawal and constitutive activation of protein kinase B (PKB), signal transducer and activator of transcription 5 (STAT5), extracellular signal-regulated kinases 1/2 (ERK1/2), Jun N-terminal kinases 1/2 (JNK1/2), and p38 mitogen-activated protein kinase (MAPK) pathways. However, inducible expression of TEL/PDGFbetaR failed to generate factor-independent cells, whereas constitutive expression of TEL/PDGFbetaR did, albeit at low frequency, suggesting the duration of TEL/PDGFbetaR expression is important for transformation. Surprisingly, in cells induced to express TEL/PDGFbetaR, IL-3-dependent growth was dramatically reduced as a result of increased apoptosis of cells receiving combined IL-3 and TEL/PDGFbetaR signals. We demonstrate that TEL/PDGFbetaR expression augmented IL-3-induced activation of PKB, STAT5, ERK1/2, p38, and JNK1/2. Inhibition of neither phosphoinositide-3 kinases nor p38 MAPKs reduced the inhibition of IL-3-driven proliferation observed when TEL/PDGFbetaR was expressed. However, inhibition of MEKs or JNKs partially reversed the combined inhibitory effects of TEL/PDGFbetaR and IL-3 on proliferation and survival. These results suggest that the combination of TEL/PDGFbetaR and IL-3-induced signals activate apoptosis through ERK and JNK MAPK-dependent pathways. Given that in vivo hematopoietic cells are in contact with a variety of cytokines, our results have important implications for cellular responses in the pathogenesis of CMML.