|Reference : Okadaic acid, a protein phosphatase inhibitor, enhances transcription of a receptor gene...|
|Scientific journals : Article|
|Life sciences : Biochemistry, biophysics & molecular biology|
|Okadaic acid, a protein phosphatase inhibitor, enhances transcription of a receptor gene containing sequence A of the human prolactin promoter|
|Wera, S. [> > > >]|
|Belayew, A. [> > > >]|
|Martial, Joseph [Université de Liège - ULg > Département des sciences de la vie > GIGA-R : Biologie et génétique moléculaire >]|
|[en] Calcium/pharmacology/physiology ; Calcium Channels/physiology ; Cyclic AMP/pharmacology/physiology ; Drug Synergism ; Ethers, Cyclic/*pharmacology ; Humans ; Okadaic Acid ; Prolactin/*genetics ; *Promoter Regions, Genetic ; Recombinant Fusion Proteins/*biosynthesis/genetics ; Transcription, Genetic/*genetics|
|[en] Human PRL (hPRL) gene expression is controlled by cAMP and Ca2+. This control is mediated by two cis-elements: a Pit-1 binding site (-62 to -35) and sequence A (-110 to -85), present in the hPRL promoter. We have investigated whether protein phosphatases could be involved in this regulation. GC-type rat pituitary tumor cells were transfected with sequence -138 to -35 of the hPRL gene promoter, upstream from a thymidine kinase promoter and a chloramphenicol acetyltransferase (CAT) reporter gene. Addition of okadaic acid (OA), a specific inhibitor of protein phosphatases 1 and 2A, stimulates transient expression of the CAT gene. The dose-response curve shows a maximal effect at 25 nM OA (2.2-fold stimulation above controls). The OA effect is also observed with a natural 4500-base pair hPRL promoter. A single copy of the hPRL promoter sequence -115 to -85 (sequence A) confers to a thymidine kinase-CAT construct an identical response to OA, whereas a single copy of the proximal Pit-1 binding site does not. Synergism is observed between cAMP and OA in activating PRL gene transcription. This synergism is also observed with a single copy of sequence A. The effect of cAMP is not mediated by an L-type Ca2+ channel, since addition of the Ca2+ channel antagonist verapamil does not decrease it, nor does complexing extracellular Ca2+ significantly reduce it. Furthermore, OA and the Ca2+ channel opener BAY K8644 exert additive effects.|
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