Ex vivo and in vivo biological effects of a truncated form of the receptor tyrosine kinase stk when activated by interaction with the friend spleen focus-forming virus envelope glycoprotein or by point mutation.
The erythroleukemia-inducing Friend spleen focus-forming virus (SFFV) encodes a unique envelope protein, gp55, which interacts with the erythropoietin (Epo) receptor complex, causing proliferation and differentiation of erythroid cells in the absence of Epo. Susceptibility to SFFV-induced erythroleukemia is conferred by the Fv-2 gene, which encodes a short form of the receptor tyrosine kinase Stk/Ron (sf-Stk) only in susceptible strains of mice. We recently demonstrated that sf-Stk becomes activated by forming a strong interaction with SFFV gp55. To examine the biological consequences of activated sf-Stk on erythroid cell growth, we prepared retroviral vectors which express sf-Stk, either in conjunction with gp55 or alone in a constitutively activated mutant form, and tested them for their ability to induce Epo-independent erythroid colonies ex vivo and disease in mice. Our data indicate that both gp55-activated sf-Stk and the constitutively activated mutant of sf-Stk induce erythroid cells from Fv-2-susceptible and Fv-2-resistant (sf-Stk null) mice to form Epo-independent colonies. Mutational analysis of sf-Stk indicated that a functional kinase domain and 8 of its 12 tyrosine residues are required for the induction of Epo-independent colonies. Further studies demonstrated that coexpression of SFFV gp55 with sf-Stk significantly extends the half-life of the kinase. When injected into Fv-2-resistant mice, neither the gp55-activated sf-Stk nor the constitutively activated mutant caused erythroleukemia. Surprisingly, both Fv-2-susceptible and -resistant mice injected with the gp55-sf-Stk vector developed clinical signs not previously associated with SFFV-induced disease. We conclude that sf-Stk, activated by either point mutation or interaction with SFFV gp55, is sufficient to induce Epo-independent erythroid colonies from both Fv-2-susceptible and -resistant mice but is unable to cause erythroleukemia in Fv-2-resistant mice.
Rulli
Karen
K
Basic Research Laboratory, National Cancer Institute-Frederick, Frederick, Maryland 21702-1201, USA.
Yugawa
Takashi
T
Hanson
Charlotte
C
Thompson
Delores
D
Ruscetti
Sandra
S
Nishigaki
Kazuo
K
D000818:Animals; D002460:Cell Line; D041905:Erythroid Cells / Q000166:cytology / Q000378:metabolism*; D004921:Erythropoietin / Q000378:metabolism; D005822:Genetic Vectors; D004915:Leukemia, Erythroblastic, Acute / Q000503:physiopathology / Q000821:virology; D051379:Mice; D008810:Mice, Inbred C57BL; D017354:Point Mutation; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D012192:Retroviridae Infections / Q000503:physiopathology / Q000821:virology; D013155:Spleen Focus-Forming Viruses / Q000378:metabolism / Q000472:pathogenicity*; D014412:Tumor Virus Infections / Q000503:physiopathology / Q000821:virology; D014759:Viral Envelope Proteins / Q000378:metabolism*
D014759:Viral Envelope Proteins; C078780:glycoprotein gp55, Friend spleen focus-forming virus; D004921:Erythropoietin; C080835:RON protein; D020794:Receptor Protein-Tyrosine Kinases