Functional identification of secondary mutations inducing autonomous growth in synergy with a truncated interleukin-3 receptor: implications for multi-step oncogenesis.
OBJECTIVE
A truncated common beta chain (Deltabeta(C)) of the interleukin-3 (IL-3) receptor complex was previously identified as a key factor in inducing autonomous growth of IL-3-independent mutants. Expression of Deltabeta(C) in IL-3-dependent hematopoietic cells does not result in immediate factor-independent growth, but increases the frequency of obtaining autonomous mutants by three to four orders of magnitude. This study was designed to delineate the mechanisms by which Deltabeta(C) increases the frequency to autonomous growth.


METHODS
Retroviral vectors were used to express Deltabeta(C) into IL-3-dependent myeloid cells, which were then tested for factor-independent growth. To determine if secondary genetic events were required for conversion to autonomous growth, elements of the Cre-loxP recombinant system were used to excise Deltabeta(C) in factor-independent clones.


RESULTS
Excision of Deltabeta(C) in factor-independent clones revealed two types of phenotypes: reversion to factor-dependent growth (1/8) or continued IL-3-dependent growth (7/8). Analysis of cells that remained factor independent revealed constitutive activation of STAT5, not observed in factor-dependent revertants. Analysis of revertant cells demonstrated the presence of interacting secondary mutations that synergize with Deltabeta(C)-induced proliferation. A cysteine residue within the truncated extracellular domain of Deltabeta(C) was also found to be required for its oncogenic potential, supporting a model of dimerization for receptor activation.


CONCLUSIONS
The high incidence of obtaining factor-independent mutants from cells expressing Deltabeta(C) results from the selection of mutations that either complement Deltabeta(C) expression to promote proliferation or that singly or in synergy with other secondary mutations negate the requirement of Deltabeta(C) expression for proliferation.
Prassolov
V
V
Department of Cell and Virus Genetics, Heinrich-Pette-Institut für Experimentelle Immunologie und Virologie an der Universität Hamburg, Hamburg, Germany.
Meyer
J
J
Brandenburg
G
G
Hannemann
J
J
Bergemann
J
J
Ostertag
W
W
Stocking
C
C
D000818:Animals; D002455:Cell Division / Q000187:drug effects / Q000276:immunology*; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D003545:Cysteine; D004268:DNA-Binding Proteins / Q000378:metabolism; D019281:Dimerization; D005822:Genetic Vectors; D007377:Interleukin-3 / Q000494:pharmacology*; D051379:Mice; D008894:Milk Proteins; D016297:Mutagenesis, Site-Directed; D010954:Plasmacytoma; D016185:Receptors, Interleukin-3 / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D011994:Recombinant Proteins / Q000378:metabolism; D012190:Retroviridae; D050799:STAT5 Transcription Factor; D017384:Sequence Deletion; D015534:Trans-Activators / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; D007377:Interleukin-3; D008894:Milk Proteins; D016185:Receptors, Interleukin-3; D011994:Recombinant Proteins; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D003545:Cysteine