| Friend virus-mediated erythroleukemia is a well-established model of murine oncogenesis. Key molecular events include constitutive activation of the EPO-R as well as expression and kinase activity of Sf-STK. While both receptors are essential in Friend disease, it is unknown whether Sf-STK modulates EPO-R-mediated signalling.; In this study we show constitutive co-immunoprecipitation of EPO-R with both Sf-STK and STK. Furthermore, we demonstrate that EPO-R and STK participate in bi-directional cross-talk and co-stimulation, resulting in enhanced tyrosine phosphorylation of both receptors. Unlike EPO-R, STK ligand-independent tyrosine phosphorylation was dependent on its kinase activity. STK was shown to co-regulate specific EPO-dependent signalling pathways. Co-operative phosphorylation was observed for ERK 1/2 and PKB, but not JAK2, STAT1, STAT5, SAPK and p38, in a GAB2-dependent manner. Additionally, STK expression enhanced EPO-regulated expression of cis and socs-3. This work suggests that Sf-STK contributes to Friend disease by enhancing proliferative and survival signals downstream of the EPO-R. |
