Molecular Characterization of a Transforming Retrovirus Involved in Pre-B Cell Lymphomas

Abstract

Cas-Br-M is a biologically cloned ecotropic murine leukemia virus [MuLV] originally isolated from wild mice of the Lake Casitas region of California. Inoculation of Cas-Br-M into newborn NFS/N mice induces hematopoietic neoplasms. The tumors are evident at 18–30 weeks and include T- and B-cell lymphomas, myeloid leukemias and erythroleukemias [Fredrickson et al, 1984]. it is unclear how Cas-Br-M is able to generate such a wide spectrum of hematopoietic neoplasms, although envelope-recombinant mink cell focus-forming [MCF] MuLVs are involved in some of these tumors [Holmes et al, 1986]. This was determined by preparing cell-free extracts from a range of tumors and injecting the extracts into newborn NFS/N mice. It was reasoned that if Cas-Br-M was the etiological agent then the mice should develop a range of tumor phenotypes with long latencies. If, however, MCF viruses were involved, the mice should develop tumors with the same phenotype as the extracted tumor and with reduced latency. Of 12 extracts examined, three appeared to support the latter hypothesis [Holmes et al, 1986]. On further examination one of these extracts, called Cas NS-1, was found to contain a virus capable of transforming mouse fibroblasts.