Role of erythropoietin receptor signaling in Friend virus-induced erythroblastosis and polycythemia

Department of Biochemistry, St Jude Children's Research Hospital, 332 North Lauderdale St, Memphis, TN 38105-2794, USA.
Blood (Impact Factor: 10.45). 02/2006; 107(1):73-8. DOI: 10.1182/blood-2005-05-1784
Source: PubMed


Friend virus is an acutely oncogenic retrovirus that causes erythroblastosis and polycythemia in mice. Previous studies suggested that the Friend virus oncoprotein, gp55, constitutively activates the erythropoietin receptor (EPOR), causing uncontrolled erythroid proliferation. Those studies showed that gp55 confers growth factor independence on an interleukin-3 (IL-3)-dependent cell line (Ba/F3) when the EPOR is coexpressed. Subsequently, we showed that a truncated form of the stem-cell kinase receptor (sf-STK) is required for susceptibility to Friend disease. Given the requirement for sf-STK, we sought to establish the in vivo significance of gp55-mediated activation of the EPOR. We found that the cytoplasmic tyrosine residues of the EPOR, and signal transducer and activator of transcription-5 (STAT5), which acts through these sites, are not required for Friend virus-induced erythroblastosis. The EPOR itself was required for the development of erythroblastosis but not for gp55-mediated erythroid proliferation. Interestingly, the murine EPOR, which is required for gp55-mediated Ba/F3-cell proliferation, was dispensable for erythroblastosis in vivo. Finally, gp55-mediated activation of the EPOR and STAT5 are required for Friend virus-induced polycythemia. These results suggest that Friend virus activates both sf-STK and the EPOR to cause deregulated erythroid proliferation and differentiation.

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Available from: Paul Ney, May 22, 2014
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    • "Several studies have investigated the ability of Epo to affect inflammatory responses. In a mouse model of autoimmune encephalomyelitis, Epo treatment upon onset of paresis was reported to significantly improve neurological functional recovery associated with a significant reduction in inflammatory infiltrates and demyelination [24] [44]. Epo was found to reduce astrocyte activation and recruitment of leukocytes and microglia in the ischemic brain associated with reduction of levels of inflammatory cytokines including monocyte chemoattractant protein-1 (MCP-1), TNF and IL6 in the ischemic brain in the rat stroke model. "
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    • "Stat transcription factors, particularly Stats 1 and 5, are thought to play a role in Epo-induced erythroid cell differentiation [52,81]. In the first stage of SFFV-P-induced disease, both Stats 1 and 5 are constitutively phosphorylated and bind DNA [52,82]. In contrast, Stat1 DNA binding is blocked in SFFV-transformed cells from the second stage of the disease, even in the presence of Epo [82]. "
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    • "Alternatively, although activation of the EpoR by gp55 is not required for the erythroblastosis induced by FV, it is required for the development of polycythemia (Zhang et al., 2006). "
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