In vivo transformation of factor-dependent hemopoietic cells: role of intracisternal A-particle transposition for growth factor gene activation.

Cells of the granulocyte-macrophage colony stimulating factor (GM-CSF) or multi-lineage colony stimulating factor (Multi-CSF) dependent line FDC-P1 undergo leukemic transformation after injection into irradiated DBA/2 mice. About one third of factor-independent FDC-P1 variants isolated from leukemic animals express GM-CSF or Multi-CSF, assessed either by bioassay or by sensitive RNA detection using the polymerase chain reaction. All of the GM-CSF-secreting lines studied had a rearrangement in one allele of the GM-CSF gene, three of four Multi-CSF-secreting lines had Multi-CSF gene rearrangements, while factor-independent lines lacking evidence of growth factor production had no demonstrable CSF gene alterations. All rearrangements were characterized by insertions of novel DNA in the 5'-flanking regions of the CSF genes. The inserted segments of DNA varied in size between 0.35 and 6.5 kb and displayed restriction enzyme cleavage maps reminiscent of intracisternal A-particle (IAP) genomes. This was confirmed in two cases by molecular cloning and nucleotide sequence analysis. In these instances, the insertion consisted of solitary IAP long terminal repeats. The transformation system described provides a model for the study of IAP transpositions and their effects on gene activation.