Tumorigenesis of a v-Ha-ras-expressing pre-B cell line selects for c-myc activation.

Seven tumors independently derived from a v-Ha-ras-expressing pre-B cell line were examined to determine the oncogene activations cooperating with v-Ha-ras in in vivo tumor progression. The pre-B cell line was generated by infection with Moloney murine leukemia virus (MoMuLV) and a MoMuLV-derived recombinant expressing v-Ha-ras. Two of seven tumors possessed a MoMuLV integration immediately upstream and in reverse transcriptional orientation to c-myc. This correlated with a 3-fold increased level of c-myc mRNA. Two other tumors displayed elevated c-myc mRNA levels, although the mechanism of enhanced expression was unclear. Thus the tumor progression of a v-Ha-ras-expressing murine pre-B cell line selects for the activation of c-myc.