Pathogenicity of retroviruses containing either the normal human c-Ha-ras1 gene or its mutated form derived from the bladder carcinoma EJ/T24 cell line.

Cellular ras oncogenes transduced by retroviruses carry mutations in amino acids 12, 59 and 122. Similar mutations have been observed in ras oncogenes activated during induction of neoplasia in both humans and experimental animals. The unmutated normal rat or human c-Ha-ras-1 genes have the ability to transform NIH 3T3 cells in culture when activated by a RNA synthesis promoter. These findings raise the question of whether the mutations are necessary for the ras oncogenes to induce the neoplastic phenotype in vivo. To address this question, we inserted the normal human c-Ha-ras-1 or its mutated counterpart EJ/T24 bladder carcinoma oncogene independently into a retrovirus vector derived from the M1 strain of Moloney murine sarcoma virus (MoMuSV). Both recombinant clones induced foci of transformed cells in an NIH 3T3 cell transfection assay. Infectious virus particles were rescued from cloned transformants carrying a single copy of the integrated provirus using the nonpathogenic amphotrophic wild mouse leukemia virus (WMLV) as helper. The pseudotypes rescued from the EJ/T24-containing transformants had higher titers than the normal c-Ha-ras-1 pseudotypes as determined by a focus assay and gave rise to larger and earlier detected foci upon infection of NIH 3T3 cells. The two pseudotypes were tested for in vivo pathogenicity by inoculation into newborn NFS mice and were compared to the pseudotype WMLV/Harvey murine sarcoma virus (HaMuSV) (positive control) and WMLV (negative control). While the WMLV/EJ/T24 and the WMLV/HaMuSV pseudotypes induced erythroleukemias and sarcomas with a latency period of 6-9 weeks, the WMLV/c-Ha-ras-1 pseudotype induced only mild splenomegaly. As expected the WMLV negative control induced no pathology. Tumor-bearing animals that were not euthanized at 6-9 weeks died within 2-3 months following virus inoculation.