MOMULV PROVIRAL INTEGRATIONS IDENTIFIED BY SUP-F SELECTION IN TUMORS FROM INFECTED MYC PIM BITRANSGENIC MICE CORRELATE WITH ACTIVATION OF THE GFI-1 GENE/

Infecting mice with a mutant Moloney murine leukemia virus which conta ins the bacterial suppressor tRNA supF in its LTR allows rapid cloning of proviral integration sites from genomic tumour DNA. In a previous study E mu pim-1/E mu L-myc bitransgenic mice had been inoculated neon atally with MoMuLV supF virus, The retroviral infection led to acceler ation of lymphomagenesis indicating the proviral activation of further oncogenes cooperating with myc and pim-1 in tumour development. Using a functional supF screen for analysis of genomic mouse tumour DNA lib raries which had been constructed in the phage vector EMBL3A, a common proviral integration site on mouse chromosome 5 was cloned and found to be identical to the proviral integration site evi-5 which has recen tly been identified in an AKXD T-cell lymphoma and which is located 18 kb upstream of the gfi-1 gene, Tumours bearing evi-5 integrations sho wed an enhanced gfi-1 expression level suggesting that gfi-1 is the ta rget gene for insertions at the evi-5 locus. Together with three other previously described Moloney integration clusters all responsible for enhanced gfi-1 expression the number of tumours from infected double transgenic E mu L-myc/E mu pim-1 transgenic mice with retrovirally act ivated gfi-1 added up to 53% underscoring the role of GFI-1 as an effe ctive collaborator for MYC and PIM-1 in the process of lymphomagenesis .