title: Growth factor-independent proliferation of erythroid cells infected with Friend spleen focus-forming virus is protein kinase C dependent but does not require Ras-GTP.
abstract: Interaction of erythropoietin (Epo) with its cell surface receptor activates signal transduction pathways which result in the proliferation and differentiation of erythroid cells. Infection of erythroid cells with the Friend spleen focus-forming virus (SFFV) leads to the interaction of the viral envelope glycoprotein with the Epo receptor and renders these cells Epo independent. We previously reported that SFFV induces Epo independence by constitutively activating components of several Epo signal transduction pathways, including the Jak-Stat and the Raf-1/mitogen-activated protein kinase (MAPK) pathways. To further evaluate the mechanism by which SFFV activates the Raf-1/MAPK pathway, we investigated the effects of SFFV on upstream components of this pathway, and our results indicate that SFFV activates Shc and Grb2 and that this leads to Ras activation. While studies with a dominant-negative Ras indicated that Ras was required for Epo-induced proliferation of normal erythroid cells, the Epo-independent growth of SFFV-infected cells can still occur in the absence of Ras, although at reduced levels. In contrast, protein kinase C (PKC) was shown to be required for the Epo-independent proliferation of SFFV-infected cells. Further studies indicated that PKC, which is thought to be involved in the activation of both Raf-1 and MAPK, was required only for the activation of MAPK, not Raf-1, in SFFV-infected cells. Our results indicate that Ras and PKC define two distinct signals converging on MAPK in both Epo-stimulated and SFFV-infected erythroid cells and that activation of only PKC is sufficient for the Epo-independent proliferation of SFFV-infected cells.
authors.affiliation: SAIC-Frederick, National Cancer Institute, Frederick Cancer Research and Development Center, Frederick, Maryland 21702-1201, USA.
authors.forename: K W
authors.initials: KW
authors.lastname: Muszynski
authors.forename: D
authors.initials: D
authors.lastname: Thompson
authors.forename: C
authors.initials: C
authors.lastname: Hanson
authors.forename: R
authors.initials: R
authors.lastname: Lyons
authors.forename: A
authors.initials: A
authors.lastname: Spadaccini
authors.forename: S K
authors.initials: SK
authors.lastname: Ruscetti
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D015153:Blotting, Western; D002455:Cell Division; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism; D004900:Erythroblasts / Q000378:metabolism* / Q000821:virology; D004921:Erythropoietin / Q000378:metabolism*; D051380:GRB2 Adaptor Protein; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology; D008301:Maleimides / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D055765:Shc Signaling Adaptor Proteins; D015398:Signal Transduction; D013155:Spleen Focus-Forming Viruses / Q000378:metabolism*; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D019311:Staurosporine / Q000494:pharmacology; D013449:Sulfonamides; D014162:Transfection; D014407:Tumor Cells, Cultured; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D004791:Enzyme Inhibitors; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; D007211:Indoles; D007546:Isoquinolines; D008301:Maleimides; D011506:Proteins; C528024:SHC1 protein, human; D055765:Shc Signaling Adaptor Proteins; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D013449:Sulfonamides; D004921:Erythropoietin; D006160:Guanosine Triphosphate; C043204:N-(2-guanidinoethyl)-5-isoquinolinesulfonamide; D066246:ErbB Receptors; D019908:Proto-Oncogene Proteins c-raf; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins; D019311:Staurosporine; C088060:bisindolylmaleimide