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Mol Cell Biol, August 1998, p. 4698-4706, Vol. 18, No. 8
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

Mazin Khalil Soubt, René Marksitzer, Pierre-Alain Menoud,dagger and Yoshikuni Nagamine*

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/HNF1beta /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.

dagger Present address: Institut d'Histologie et d'Embryologie Générale, Faculté des Sciences, CH-1705 Fribourg, Switzerland.

Mol Cell Biol, August 1998, p. 4698-4706, Vol. 18, No. 8
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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