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Mol. Cell. Biol., Oct 1996, 5846-5856, Vol 16, No. 10
A Sandmoller, H Meents and HH Arnold
The adenovirus E1A oncoprotein completely blocks muscle differentiation and
specifically inhibits the transactivating function of myogenic basic
helix-loop-helix (bHLH) transcription factors. This inhibition is dependent
on the conserved region CR1 of E1A, which also constitutes part of the
binding sites for the pocket proteins pRB, p107, and p130 and the
transcriptional coactivators p300 and CBP. Here we report a detailed
mutational analysis of E1A and the identification of a muscle inhibition
motif within CR1. This motif encompasses amino acids 38 to 62 and inhibits
Myf-5- or MyoD-mediated activation of myogenin and the muscle creatine
kinase gene. Overexpression of this E1A region also inhibits the conversion
of 10T1/2 fibroblasts to the myogenic lineage. The sequence motif EPDNEE
(amino acids 55 to 60) within CR1 appears to be particularly important,
because point mutations of this sequence diminish the E1A inhibitory
activity. Interactions of E1A with pRB and with p300 do not seem to be
necessary for the muscle-specific enhancer repression, because E1A mutants
which lack these interactions still inhibit Myf-5- and MyoD-mediated
transactivation. Moreover, overexpression of p300 fails to overcome
muscle-specific inhibition by wild-type E1A and mutant E1A protein which
lacks pRB binding. Since we have no evidence for direct E1A interaction
with bHLH proteins, we propose that E1A may target a necessary cofactor of
the muscle-specific bHLH transcription complex.
Copyright © 1996, American Society for Microbiology
A novel E1A domain mediates skeletal-muscle-specific enhancer repression independently of pRB and p300 binding
Department of Cell and Molecular Biology, University of Braunschweig, Germany. A.Sandmoeller@tu-bs.de
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