Non-identical patterns of proviral insertions around host transcription units in lymphomas induced by different strains of murine leukemia virus.

In a small sample of 57 retrovirus integration sites (RISs) isolated from 23 end-stage lymphomas induced in NMRI mice by the B-lymphotropic Akv wt or an enhancer mutant hereof, Akv1-99, we identified 14 novel RISs and defined 9 novel CISs (common insertion sites). Moreover, when comparing with RISs from tumors induced by the T-lymphomagenic SL3-3, we observed that SL3-3 targets RefSeq promoter regions with a significantly higher frequency than Akv/Akv1-99 and in an orientation-dependent way. Altogether, our results strongly emphasize the importance of host genetic background and virus type for retroviral insertion mutagenesis screens and suggest that different types of MLV may favor specific genomic regions and orientations in order exert optimal effect on target gene expression during lymphoma induction and development.