Transcriptional stimulation of the retina-specific QR1 gene upon growth arrest involves a Maf-related protein.
The avian neural retina (NR) is derived from proliferating neuroectodermal precursors which differentiate after terminal mitosis and become organized in cell strata. Proliferation of postmitotic NR cells can be induced by infection with Rous sarcoma virus (RSV) and requires the expression of a functional v-Src protein. QR1 is a retina-specific gene expressed exclusively at the stage of growth arrest and differentiation during retinal development. In NR cells infected with tsPA101, an RSV mutant conditionally defective in pp60v-src mitogenic capacity, QR1 expression is downregulated in proliferating cells at 37 degrees C and is fully restored when the cells become quiescent as a result of pp60v-src inactivation at 41 degrees C. We were able to arrest proliferation of tsPA101-infected quail NR cells expressing an active v-Src protein by serum starvation at 37 degrees C. This allowed us to investigate the role of cell growth in regulating QR1 transcription. We report that QR1 transcription is stimulated in growth-arrested cells at 37 degrees C compared with that in proliferating cells maintained at the same temperature. Growth arrest-dependent stimulation of QR1 transcription requires the integrity of the A box, a previously characterized cis-acting element responsible for QR1 transcriptional stimulation upon v-Src inactivation and during retinal differentiation. We also show that formation of the C1 complex on the A box is increased upon growth arrest by serum starvation in the presence of an active v-Src oncoprotein. Thus, the C1 complex represents an important link between cell cycle and developmental control of QR1 gene transcription during NR differentiation and RSV infection. By using antibodies directed against different Maf proteins of the leucine zipper family and competition with Maf consensus site-containing oligonucleotides in a gel shift assay, we show that the C1 complex is likely to contain a Maf-related protein. We also show that a purified bacterially expressed v-Maf protein is able to bind the A box and that the level of a 43-kDa Maf-related protein is increased upon growth arrest in infected retinal cells. Moreover, ectopic expression of c-mafI, c-mafII, and mafB cDNAs in quiescent tsPA101-infected quail NR cells is able to stimulate transcription of a QR1 reporter gene through the A box. Therefore, QR1 appears to be the first target gene for a Maf-related protein(s) in the NR.
Pouponnot
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Unité Mixte de Recherche 146 du Centre National de la Recherche Scientifique, Institute Curie, Orsay, France.
Nishizawa
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Calothy
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Pierani
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D000595:Amino Acid Sequence; D000818:Animals; D030161:Avian Proteins; D001483:Base Sequence; D002454:Cell Differentiation; D002455:Cell Division; D002478:Cells, Cultured; D003370:Coturnix; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005136:Eye Proteins / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D016350:Leucine Zippers; D050985:MafK Transcription Factor; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D015688:Oncogene Protein pp60(v-src) / Q000502:physiology; D051256:Oncogene Protein v-maf; D015513:Oncogene Proteins / Q000378:metabolism; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D012160:Retina / Q000166:cytology* / Q000196:embryology / Q000254:growth & development; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors; D015533:Transcriptional Activation / Q000502:physiology*; D014764:Viral Proteins
D030161:Avian Proteins; D004268:DNA-Binding Proteins; D005136:Eye Proteins; D050985:MafK Transcription Factor; D009687:Nuclear Proteins; D051256:Oncogene Protein v-maf; D015513:Oncogene Proteins; D009856:Oncogene Proteins, Viral; C091516:QR1 protein, Coturnix japonica; D015534:Trans-Activators; D014157:Transcription Factors; D014764:Viral Proteins; D004247:DNA; D015688:Oncogene Protein pp60(v-src)