Proux V, Provot S, Felder-Schmittbuhl MP, Laugier D, Calothy G, Marx M. Characterization of a leucine zipper-containing protein identified by retroviral insertion in avian neuroretina cells.
J Biol Chem 1996;
271:30790-7. [PMID:
8940059 DOI:
10.1074/jbc.271.48.30790]
[Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
We reported previously that post-mitotic chicken embryonic neuroretina (NR) cells are induced to proliferate following in vitro infection with RAV-1, a retrovirus that does not carry an oncogene. NR cell multiplication results from the frequent activation and subsequent retroviral transduction of two related serine/threonine protein kinases, the c-mil/c-raf or c-Rmil/B-raf genes. We also showed that a very early event in the activation of these proto-oncogenes is the synthesis of chimeric mRNAs containing viral and cellular sequences joined by a splicing mechanism. In the current study, we have examined the ability of RAV-1 to induce proliferation of quail NR cells. By using the reverse transcription-polymerase chain reaction technique, we identified, in several proliferating quail NR cultures infected with RAV-1, a chimeric mRNA containing cellular sequences joined to the RAV-1 splice donor site. These cellular sequences are derived from a gene designated R10, which is expressed through a 1.9-kilobase (kb) mRNA detected in several embryonic tissues. A second transcript of 2.3 kb is specifically expressed in the NR, where both transcripts are developmentally regulated. The R10 cDNA encodes a 251-amino acid polypeptide that contains a leucine zipper motif. It exhibits significant similarity with the putative D52/N8L protein, encoded by an mRNA reported previously to be overexpressed in human breast and lung carcinomas. By using polyclonal antibodies specific for its amino-terminal and leucine zipper-containing regions, we identified the R10 gene product as a cytoplasmic protein of 23 kDa in cultured avian fibroblasts. A second protein of 30 kDa is detected in post-mitotic NR cells that express the 2.3-kb transcript. We also show, by in vitro transcription/translation and immunoprecipitation, that the R10 protein can readily form homodimers, presumably through its leucine zipper motif.
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