Molecular and Cellular Biology, December 2001, p. 8461-8470, Vol. 21, No. 24
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.24.8461-8470.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Molecular Oncogenesis Laboratory, Regina Elena Cancer Institute, 00158 Rome, Italy,1 and Institute for Molecular and Cellular Biology, Osaka University, Osaka 565-0871, Japan2
Received 27 July 2001/Returned for modification 4 September 2001/Accepted 25 September 2001
The newly discovered p73 gene encodes a nuclear protein that has
high homology with p53. Furthermore, ectopic expression of p73 in
p53+/+ and p53
/
cancer cells recapitulates
some of the biological activities of p53 such as growth arrest,
apoptosis, and differentiation. p73
/
-deficient mice
exhibit severe defects in proper development of the central nervous
system and pheromone sensory pathway. They also suffer from
inflammation and infections. Here we studied the transcriptional
regulation of p73 at the crossroad between proliferation and
differentiation. p73 mRNA is undetectable in proliferating C2C12 cells
and is expressed at very low levels in undifferentiated P19 and
HL60 cells. Conversely, it is upregulated during muscle and
neuronal differentiation as well as in response to tetradecanoyl
phorbol acetate-induced monocytic differentiation of HL60 cells. We
identified a 1-kb regulatory fragment located within the first intron
of p73, which is positioned immediately upstream to the ATG codon
of the second exon. This fragment exerts silencer activity on p73 as
well as on heterologous promoters. The p73 intronic fragment contains
six consensus binding sites for transcriptional repressor ZEB, which
binds these sites in vitro and in vivo. Ectopic expression of
dominant-negative ZEB (ZEB-DB) restores p73 expression in proliferating
C2C12 and P19 cells. Thus, transcriptional repression of p73 expression
by ZEB binding may contribute to the modulation of p73 expression
during differentiation.
This work is dedicated to the memory of F. Tatò.
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