Characterization of a leucine zipper-containing protein identified by retroviral insertion in avian neuroretina cells.
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.
Proux
V
V
Unité Mixte de Recherche 146 du CNRS, Institut Curie, Laboratoire 110, Centre Universitaire, 91405 Orsay Cédex, France. marx@curie.u-psud.fr
Provot
S
S
Felder-Schmittbuhl
M P
MP
Laugier
D
D
Calothy
G
G
Marx
M
M
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics*; D002451:Cell Compartmentation; D003370:Coturnix; D003593:Cytoplasm / Q000737:chemistry; D018076:DNA, Complementary / Q000235:genetics; D005136:Eye Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D016350:Leucine Zippers; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D015183:Restriction Mapping; D012160:Retina / Q000737:chemistry; D016415:Sequence Alignment
D002352:Carrier Proteins; D018076:DNA, Complementary; D005136:Eye Proteins; C102534:Gag R10 protein, Coturnix coturnix; D009363:Neoplasm Proteins; D012097:Repressor Proteins; C114751:TPD52 protein, human