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Mol. Cell. Biol., 10 1995, 5563-5575, Vol 15, No. 10
C Pouponnot, M Nishizawa, G Calothy and A Pierani
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.
Copyright © 1995, American Society for Microbiology
Transcriptional stimulation of the retina-specific QR1 gene upon growth arrest involves a Maf-related protein
Unite Mixte de Recherche 146 du Centre National de la Recherche Scientifique, Institute Curie, Orsay, France.
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