Muszynski K W, Ohashi T, Hanson C, Ruscetti S K
Intramural Research Support Program, SAIC Frederick, National Cancer Institute-Frederick Cancer Research and Development Center, Maryland 21702-1201, USA.
J Virol. 1998 Feb;72(2):919-25. doi: 10.1128/JVI.72.2.919-925.1998.
The erythroleukemia-inducing Friend spleen focus-forming virus (SFFV) encodes a unique envelope glycoprotein which allows erythroid cells to proliferate and differentiate in the absence of erythropoietin (Epo). In an attempt to understand how the virus causes Epo independence, we have been studying signal transduction pathways activated by Epo to determine if SFFV exerts its biological effects by constitutively activating any of these pathways in the absence of Epo. We previously demonstrated that Stat proteins, the downstream components of the Epo-induced Jak-Stat pathway, are constitutively activated in SFFV-infected cells. In this study, we demonstrate that SFFV also activates Raf-1, MEK and mitogen-activated protein (MAP) kinase, the downstream components of the Raf-1/MAP kinase pathway. This pathway was activated in cells infected with the polycythemia-inducing strain of SFFV, which induces both proliferation and differentiation of erythroid cells in the absence of Epo, as well as in cells infected with the anemia-inducing strain of the virus, which still require Epo for differentiation. Inhibition of Raf-1 by using antisense oligonucleotides led to a partial inhibition of the Epo-independent proliferation of SFFV-infected cells. Expression of the transcription factors c-Jun and JunB, but not c-Fos, was induced in SFFV-infected cells in the absence of Epo, suggesting that constitutive activation of the Raf-1/MAP kinase pathway by the virus may result in deregulation of AP-1 activity. We conclude from our studies that infection of erythroid cells with SFFV leads to the constitutive activation of signal transduction molecules in both the Jak-Stat and Raf-1/MAP kinase pathways and that both of these pathways must be activated to achieve maximum proliferation and differentiation of erythroid cells in the absence of Epo.
诱发红白血病的弗氏脾集落形成病毒（SFFV）编码一种独特的包膜糖蛋白，该蛋白可使红系细胞在无促红细胞生成素（Epo）的情况下增殖和分化。为了弄清楚该病毒如何导致对Epo的非依赖性，我们一直在研究由Epo激活的信号转导途径，以确定SFFV是否通过在无Epo的情况下组成性激活这些途径中的任何一条来发挥其生物学效应。我们先前证明，Epo诱导的Jak-Stat途径的下游成分Stat蛋白在SFFV感染的细胞中被组成性激活。在本研究中，我们证明SFFV还激活Raf-1、MEK和丝裂原活化蛋白（MAP）激酶，它们是Raf-1/MAP激酶途径的下游成分。在感染了诱导红细胞增多的SFFV毒株的细胞中，该途径被激活，这种毒株在无Epo的情况下可诱导红系细胞的增殖和分化，在感染了诱导贫血的病毒毒株的细胞中该途径也被激活，这种毒株在分化时仍需要Epo。使用反义寡核苷酸抑制Raf-1会导致SFFV感染细胞的Epo非依赖性增殖受到部分抑制。在无Epo的情况下，SFFV感染的细胞中诱导了转录因子c-Jun和JunB的表达，但未诱导c-Fos的表达，这表明病毒对Raf-1/MAP激酶途径的组成性激活可能导致AP-1活性失调。我们从研究中得出结论，SFFV感染红系细胞会导致Jak-Stat和Raf-1/MAP激酶途径中的信号转导分子组成性激活，并且在无Epo的情况下，这两条途径都必须被激活才能实现红系细胞的最大增殖和分化。
