A novel oncogene, v-ryk, encoding a truncated receptor tyrosine kinase is transduced into the RPL30 virus without loss of viral sequences

Abstract

The RPL viruses are acute oncogenic avian retroviruses isolated from chicken tumors. We carried out a genetic analysis of three of the viruses, RPL25, RPL28, and RPL30. While RPL25 and RPL28 were shown to contain the erbB oncogene, RPL30 appeared to contain a novel protein tyrosine kinase oncogene. This gene, v-ryk, was cloned and sequenced. The v-ryk oncogene contains a 1.39-kb nonretroviral sequence that includes a tyrosine kinase domain which was inserted into the viral envelope protein gp37-coding region and fused in frame with upstream gp37 to generate a P69gp37-ryk fusion oncoprotein. Unlike that of other acutely transforming retroviruses, transduction of the v-ryk gene into RPL30 did not result in deletion of viral sequences. Sequence analysis suggested that v-Ryk is more homologous to receptor-type tyrosine kinases than to nonreceptor-type kinases. By reconstitution of a virus from its cDNA, the v-ryk oncogene has been shown to be fully responsible for the transforming activity of the RPL30 virus. Antibodies specific to v-Ryk immunoprecipitated the v-Ryk oncoprotein from cells transformed by the RPL30 virus. The v-Ryk protein was shown to be first synthesized as a 150-kDa precursor and then cleaved into the mature 69-kDa gp37-Ryk fusion protein, both parts of which were found to be localized to the membrane fraction. As expected from the sequence of v-Ryk, immunoprecipitates of v-Ryk from RPL30-transformed cells were found to display a protein tyrosine kinase activity in vitro, and the levels of tyrosine-phosphorylated proteins are elevated in v-ryk-transformed cells.