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Molecular and Cellular Biology, April 2000, p. 2543-2555, Vol. 20, No. 7
Howard Hughes Medical Institute, Department
of Molecular Genetics and Cell Biology, The University of Chicago,
Chicago, Illinois 60637
Received 1 November 1999/Returned for modification 17 December
1999/Accepted 9 January 2000
Keratins K5 and K14 are the hallmarks of mitotically active
keratinocytes of stratified epithelia. They are transcribed at a high
level and in a tissue-specific manner, enabling us to use the K14 gene
to elucidate the regulatory mechanism underlying epidermis-specific
transcription. We have identified four DNase I-hypersensitive sites
(HSs) present in the 5' regulatory sequences of the K14 gene under
specific conditions where the gene is actively expressed. Two of these
sites (HSsII and -III) are conserved in position and sequence within
the human and mouse K14 genes. Using an in vivo transgenic approach and
an in vitro keratinocyte culture approach, we have discovered that most
of K14's transcriptional activity is restricted to a novel 700-bp
regulatory domain encompassing these HSs. This enhancer is sufficient
to confer epidermis-specific activity to a heterologous promoter in
transfection assays in culture and in transgenic mice in vivo. A 125-bp
DNA fragment encompassing HSsII harbors the majority of the
transactivation activity in vitro, and electrophoretic mobility shift
and mutational assays reveal a role for AP-1, ets, and AP-2 family
members in orchestrating the keratinocyte-preferred expression of
HSsII. The HSsII element also confers epidermal expressivity to a
heterologous promoter in transgenic mice, although it is not sufficient
on its own to fully restrict activity to keratinocytes. Within the HSsII element, the ets and AP-2 sites appear to be most critical in
collaborating to regulate epidermal specificity in vivo.
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Defining the Regulatory Factors Required for
Epidermal Gene Expression
*
Corresponding author. Mailing address: Howard Hughes
Medical Institute, Department of Molecular Genetics and Cell Biology, The University of Chicago, 5841 S. Maryland Ave., Room N314, Chicago, IL 60637. Phone: (773) 702-1347. Fax: (773) 702-0141. E-mail: nliptak{at}midway.uchicago.edu.
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