Insertional activation of myb by F-MuLV in SCID mice induces myeloid leukemia.

Identification of retrovirus integration sites is a powerful method to identify cancer-related genes. This approach led to the discovery of the Friend murine leukemia virus (F-MuLV) integration site-1 (fli-1). Viral insertion at the fli-1 locus induces erythroleukemia in susceptible strains of mice. Our recent data demonstrated that, F-MuLV-infected SCID mice, in contrast to wt CB17 controls, developed a non‑erythroleukemic leukemia without viral integration at the fli-1 locus. Using ligation-mediated polymerase chain reaction (LM-PCR) approach we identified a total of 15 viral integration sites in F-MuLV-infected SCID mice. One of the identified insertion sites was located about 62 kb upstream of the myeloblastosis (myb) gene. While integration within or surrounding the myb gene has been reported before for murine leukemia viruses, the location of the viral integration site identified in F-MuLV‑infected SCID mice is novel and has never been reported. Using PCR analysis we showed that viral integration at the myb locus occurs with a frequency of 35% and therefore is considered as a common integration site. Integration of F-MuLV in this locus resulted in upregulation of the MYB protein. Flow cytometry analysis and methylcellulose culture of leukemic cells isolated from tumors with viral integration close to the myb indicated tumors of myeloid origin. Our findings indicate that, in contrast to wt CB17 mice, F-MuLV-infected SCID mice display viral integration within myeloid specific gene loci that result in the development of myelogenous leukemia.