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Molecular and Cellular Biology, January 2000, p. 661-671, Vol. 20, No. 2
Center for Advanced Biotechnology and
Medicine1 and Departments of
Pediatrics2 and Neuroscience and Cell
Biology,3 UMDNJ-Robert Wood Johnson Medical
School, Piscataway, New Jersey 08854
Received 12 July 1999/Returned for modification 19 August
1999/Accepted 27 September 1999
Despite their significance for mammalian embryogenesis, the
molecular mechanisms that regulate placental growth and development have not been well defined. The Esx1 homeobox gene is of
particular interest because it is among the few regulatory genes that
have specific expression and function in the placenta during murine development. In addition, the ESX1 protein contains several notable features that are not often associated with homeoproteins, including an
atypical homeodomain of the paired-like class, a
proline-rich region that contains an SH3 binding motif, and a novel
repeat region consisting of prolines alternating with phenylalanines or
asparagines that we term the PF/PN motif. We have found that the ESX1
protein is expressed in the labyrinth layer of the placenta in vivo,
where its subcellular localization is primarily cytoplasmic. Our
results suggest that this unexpected subcellular localization is
conferred by the PF/PN motif, which inhibits nuclear localization of
ESX1 in cell culture, as well as its DNA binding activity in vitro.
Finally, we show that the proline-rich region of ESX1 mediates interactions in vitro with the c-abl SH3 domain as well as
with certain WW domains. We propose that the PF/PN motif provides a novel mechanism for regulating nuclear entry and that the essential function of ESX1 during placental development is mediated by its ability to couple cytoplasmic signal transduction events with transcriptional regulation in the nucleus.
0270-7306/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
A Novel PF/PN Motif Inhibits Nuclear Localization
and DNA Binding Activity of the ESX1 Homeoprotein
*
Corresponding author. Mailing address for M.M.S.: CABM,
679 Hoes Ln., Piscataway, NJ 08854. Phone: (732) 235-5645. Fax: (732) 235-5318. E-mail: mshen{at}cabm.rutgers.edu. Mailing
address for C.A.-S.: CABM, 679 Hoes Ln., Piscataway,
NJ 08854. Phone: (732) 235-5161. Fax: (732) 235-4850. E-mail:
abate{at}cabm.rutgers.edu.
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