Lee Y, Broxmeyer H E
Department of Microbiology/Immunology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
Biochem Biophys Res Commun. 2001 Mar 9;281(4):897-901. doi: 10.1006/bbrc.2001.4430.
Steel factor (SLF) plus GM-CSF induces proliferative synergy in factor-dependent cell line MO7e and hematopoietic progenitor cells. We previously reported ERK1/2 involvement in this synergy, but its downstream signaling molecules are not defined. Here, we investigated activation of the 90-kDa ribosomal S6 kinase (RSK) proteins by measuring the phosphorylation status and in vitro kinase activity in MO7e cells. Both GM-CSF and SLF induced activation of RSK, and the combined stimulation with these two cytokines induced synergistic and persistent activation of RSK. RSK activity was reduced by PI3 kinase inhibitor LY294002 or MEK1 inhibitor PD98059, suggesting that the ERK as well as the PI3 kinase pathways are involved in regulation of RSK activity. Sensitivities of RSK activity to inhibitory drugs correlated well with those of c-fos gene induction. Taken together, synergistic activation of RSK may contribute, at least in part, to the synergistic induction of c-fos after combined stimulation with GM-CSF plus SLF.
钢因子（SLF）加粒细胞-巨噬细胞集落刺激因子（GM-CSF）可在因子依赖性细胞系MO7e和造血祖细胞中诱导增殖协同作用。我们之前报道过细胞外信号调节激酶1/2（ERK1/2）参与这种协同作用，但其下游信号分子尚未明确。在此，我们通过检测MO7e细胞中的磷酸化状态和体外激酶活性，研究了90 kDa核糖体S6激酶（RSK）蛋白的激活情况。GM-CSF和SLF均可诱导RSK激活，这两种细胞因子的联合刺激可诱导RSK的协同和持续激活。RSK活性可被磷脂酰肌醇-3激酶（PI3激酶）抑制剂LY294002或丝裂原活化蛋白激酶激酶1（MEK1）抑制剂PD98059降低，提示ERK以及PI3激酶途径均参与RSK活性的调节。RSK活性对抑制药物的敏感性与原癌基因c-fos诱导的敏感性密切相关。综上所述，RSK的协同激活可能至少部分促成了GM-CSF加SLF联合刺激后c-fos的协同诱导。
