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Mol Cell Biol, August 1998, p. 4698-4706, Vol. 18, No. 8
Friedrich Miescher Institute, Basel,
Switzerland
Received 15 January 1998/Returned for modification 7 March
1998/Accepted 21 May 1998
A cyclic AMP (cAMP)-inducible enhancer in the pig urokinase-type
plasminogen activator gene located 3.4 kb upstream of the transcription
initiation site is composed of three protein-binding domains, A, B, and
C. Domains A and B each contain a CRE (cAMP response element)-like
sequence but require the adjoining C domain for full cAMP
responsiveness. A tissue-specific transcription factor,
LFB3/HNF1
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Role of Tissue-Specific Transcription Factor LFB3
in a Cyclic AMP-Responsive Enhancer of the Urokinase-Type
Plasminogen Activator Gene in LLC-PK1 Cells
and
/vHNF1, binds to the C domain. Mutation analyses suggest
that the imperfect CRE and LFB3-binding sequences are required for
tight coupling of hormonal and tissue-specific regulation. CREB and
ATF1 bind to domains A and B, and this binding is enhanced upon
phosphorylation by cAMP-dependent protein kinase (protein kinase A
[PKA]). Analysis in a mammalian two-hybrid system revealed that
CREB/ATF1 and LFB3 interact and that transactivation potential is
enhanced by PKA activation. Interestingly, however, phosphorylation of
CREB at Ser-133 does not contribute to its interaction with LFB3. The
region of LFB3 involved in its interaction with CREB/ATF1 lies, at
least partly, between amino acids 400 and 450. Deletion of this region
removed the ability of LFB3 to mediate cAMP induction of the ABC
enhancer but did not impair its basal transactivation activity on the
albumin promoter. Thus, the two activities are distinct functions of
LFB3.
*
Corresponding author. Mailing address: Friedrich
Miescher Institute, P.O. Box 2543, CH-4002 Basel, Switzerland. Phone:
41-61-697-6669 or -697-4499. Fax: 41-61-697-3976. E-mail:
nagamine{at}fmi.ch.
Present address: Institut d'Histologie et d'Embryologie
Générale, Faculté des Sciences, CH-1705 Fribourg,
Switzerland.
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