Nucleic acid sequence and oncogenic properties of the HZ2 feline sarcoma virus v-abl insert

Hardy-Zuckerman 2 feline sarcoma virus (HZ2-FeSV), isolated from multicentric feline fibrosarcoma is a replication-defective acute transforming feline retrovirus which originated by transduction of feline c-abl sequences with feline leukemia virus (FeLV) and is known to encode a 110-kilodalton gag-abl fusion protein with tyrosine-specific protein kinase activity. The nucleotide sequence of the abl segment in the HZ2-FeSV genome was determined and compared with the murine and human v-abl and c-abl sequences. The predicted transforming protein consists of 344 amino acids (aa) of FeLV gag origin, 439 aa of abl origin, and at least 200 aa of FeLV pol origin (p110(gag-abl-pol)). The 1,317-base-pair HZ2-FeSV v-abl segment (fv-abl) corresponds to 5' abl sequences which include the region known to specify the protein kinase domain. The 5' 189 base pairs of fv-abl correspond to 5' c-abl sequences not contained in Abelson murine leukemia virus (MuLV) v-abl. The mouse c-abl exon which contains these segments was identified, and its nucleotide sequence was determined. Comparison of the predicted amino acid sequence of fv-abl with those of Abelson MuLV v-abl and c-abl revealed five aa differences. The 5' junction between FeLV and abl was found to involve a preferred region in FeLV gag p30. A six-base homology exists at the recombination site between the parental FeLV and the c-abl sequences. The 3' junction between fv-abl and FeLV pol predicts an in-frame fusion of fv-abl and FeLV pol. A transformed cell line containing a truncated gag-abl-pol protein, p85, that lacks most of the FeLV pol sequences was obtained by transfection of NIH 3T3 mouse cells. This result implies that the pol sequences of the p110(gag-abl-pol) protein are dispensable for fibroblast transformation. To assess whether the fv-abl segment specifies the unique biological properties of HZ2-FeSV, we constructed a Moloney MuLV-based version of HZ2-FeSV, Mo-MuLV(fv-abl), in which the fv-abl sequences were contained in a genetic context similar to that in HZ2-FeSV. When injected into neonatal NSF/N mice, MoMuLV(fv-abl) amphotropic pseudotype virus induced lymphosarcoma of B-cell origin with kinetics similar to those of the disease caused by Abelson MuLV variants which, like HZ2-FeSV, lack 3' c-abl sequences. These results suggest that the fv-abl segment does not specify an altered oncogenic potential.