title: Sf-Stk kinase activity and the Grb2 binding site are required for Epo-independent growth of primary erythroblasts infected with Friend virus.
abstract: During the initial stage of Friend virus-induced erythroleukemia in mice, interaction of the viral protein gp55 with the erythropoietin receptor, and other host factors, drives the expansion of erythroid precursor cells. Recently, we demonstrated that the Friend virus susceptibility locus, Fv2, which is required for the expansion of infected cells, encodes a naturally occurring, N-terminally truncated form of the Stk receptor tyrosine kinase (Sf-Stk). Here we show that in vitro expression of Sf-Stk confers Friend virus sensitivity to erythroid progenitor cells from Fv2(rr) mice. Furthermore, our data reveal that Sf-Stk kinase activity and Y436, but not Y429, are required for Epo-independent colony formation following Friend virus infection. Introduction of a mutation that results in failure to bind Grb2 abrogates the ability of Sf-Stk to induce colonies in response to Friend virus, while the Grb2 binding site from EGFR restores this response. Consistent with the ability of Grb2 to recruit SOS and Gab1, the Ras/MAPK and PI3K pathways are activated by Sf-Stk, and both of these pathways are required for gp55-mediated erythroblast proliferation. These data clearly demonstrate a requirement for signaling through Sf-Stk in the Epo-independent expansion of Friend virus-infected cells, and suggest a pivotal role for Grb2 in this response.
authors.affiliation: Department of Veterinary Science, The Pennsylvania State University, University Park, Pennsylvania, PA 16802, USA.
authors.forename: Lisa D
authors.initials: LD
authors.lastname: Finkelstein
authors.forename: Paul A
authors.initials: PA
authors.lastname: Ney
authors.forename: Qing-Ping
authors.initials: QP
authors.lastname: Liu
authors.forename: Robert F
authors.initials: RF
authors.lastname: Paulson
authors.forename: Pamela H
authors.initials: PH
authors.lastname: Correll
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002455:Cell Division; D002460:Cell Line; D002478:Cells, Cultured; D004900:Erythroblasts / Q000378:metabolism / Q000821:virology*; D004921:Erythropoietin / Q000502:physiology; D005622:Friend murine leukemia virus / Q000472:pathogenicity*; D051380:GRB2 Adaptor Protein; D004915:Leukemia, Erythroblastic, Acute / Q000821:virology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009154:Mutation; D011506:Proteins / Q000378:metabolism*; D020794:Receptor Protein-Tyrosine Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014443:Tyrosine / Q000235:genetics / Q000502:physiology; D014759:Viral Envelope Proteins / Q000235:genetics
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495949:Grb2 protein, mouse; D011506:Proteins; D011956:Receptors, Cell Surface; D014759:Viral Envelope Proteins; C078780:glycoprotein gp55, Friend spleen focus-forming virus; D004921:Erythropoietin; D014443:Tyrosine; C080835:RON protein; D020794:Receptor Protein-Tyrosine Kinases