Abstract 1070: Differential response dynamic of leukemia cells to GM-CSF and IL-3 stimulation in signal transduction pathways

Abstract

Abstract GM-CSF and IL-3 regulate the survival, proliferation, differentiation, and functional activation of hematopoietic cells. GM-CSF also contributes to controlling the function of dendritic cells and T-cells. Aberrant function of GM-CSF has been linked to multiple diseases including juvenile myelomonocytic leukemia (JMML), chronic myelomonocytic leukemia, rheumatoid arthritis, and alveolar proteinosis. GM-CSF and IL-3 share a common βc subunit on their receptor. Many studies have revealed that dys-regulation of Ras/PI3K/Akt and Ras/Raf/Mek/Erk pathways are responsible for hypersensitivities of GM-CSF and IL-3 in various diseases. However, few data have distinguished the difference of signal transduction pathways between the two cytokines. We previously reported that JMML cells are selectively hypersensitive to GM-CSF in vitro, while they show normal sensitivity to IL-3. Others documented that there was a time gap between CREB responded to GM-CSF and IL-3 stimulation. In the present study, we hypothesized that the signal transduction pathway of GM-CSF has differential response dynamic from that of IL-3. We first tested the CFU-GM growth pattern of a leukemia cell line, TF-1, in response to GM-CSF and IL-3 stimulation. We found that the GM-CSF dose-response curve was markedly shifted leftward, indicating that TF-1 cells were more sensitive to GM-CSF than to IL-3. This pattern is very similar to that observed in primary JMML cells. We next investigated the activities of the elements downstream in Ras pathway. After serum starving in medium with 0.5% BSA for 16 hours, TF-1 cells were stimulated with GM-CSF or IL-3 at a concentration range of 0.01-500pM. We found that the total protein levels of CREB were consistently unchanged. On the other hand, significant phosphorylation of CREB on serine 133 began to occur at concentrations of GM-CSF at 10pM. Significant phosphorylation of Erk was observed even at a concentration as low as 1 pM of GM-CSF. However, this phosphorylation pattern was not seen until 100pM of IL-3, and the level of phosphorylation was lower. The same dynamic, GM-CSF vs. IL-3, was also found in pAkt and pSTAT5. In conclusion, our data demonstrate that leukemia cells respond to GM-CSF and IL-3 stimulation in different dynamic patterns in signal transduction pathways. This indicates that the selective hypersensitivity to GM-CSF in some leukemia cells may be caused by aberrant elements in signal transduction pathways that are responsive to the low concentrations of GM-CSF stimulation. We raise a concern that any study related to responsiveness of GM-CSF or IL-3 stimulation should be interpreted cautiously; with specific attention paid to the concentration levels and the length of stimulation, in order to precisely characterize the function of GM-CSF and IL-3. This observed differential response dynamic might apply to a broader phenomenon in other cytokines or hormones in other tissues. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1070. doi:1538-7445.AM2012-1070