Expression of v-rel in a replication competent virus: transformation and biochemical characterization

The avian reticuloendotheliosis virus strain T (REV-T) transforms bone marrow cells and may cause phenotypic changes in fibroblasts. Both events are thought to result from expression of the v-rel oncoprotein, a member of the NF-kappa B family of transcription factors. Most REV stocks contain a cytopathic and immunosuppressive helper virus (REV-A) unrelated to standard avian retroviruses, and thus the degree to which v-rel expression alone contributes to the transformed phenotype in bone marrow cells and fibroblasts is complicated by helper virus expression. To gain a more accurate picture of how v-rel contributes to transformation, we have cloned the v-rel gene into a replication-competent avian retrovirus vector (RCAS) and have expressed it in both chick embryo fibroblasts (CEF) and bone marrow cells. Transfection of RCAS-rel into CEF readily produced a partially transformed phenotype, demonstrating that expression of the v-rel protein is sufficient for fibroblast transformation. The RCAS-rel virus also transformed bone marrow cells in vitro, but required culture conditions different from those normally required for transformation by REV-T. The v-rel protein expressed in transformed CEF was biochemically indistinguishable from that expressed in transformed bone marrow cells, being localized to the cytoplasm and the nucleus, and forming a complex with cellular proteins. We also demonstrate that the RCAS-rel-transformed hematopoietic cells exhibited a distinct differentiation phenotype.