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Smad3 and Pitx2 cooperate in stimulation of FSHbeta gene transcription.
Mol Cell Endocrinol. 2008 Jan 16;281(1-2):27-36
Authors: Suszko MI, Antenos M, Balkin DM, Woodruff TK
Abstract
Activin is a member of the TGFbeta superfamily of growth and differentiation factors that control a variety of cellular and physiological functions. The canonical intracellular pathway of this ligand is well established and involves Smad signaling molecules. The tissue- and cell-specificity of activin action is achieved by Smad interaction with various transcriptional co-factors in the nucleus. In the reproductive axis, activin induces biosynthesis and secretion of follicle stimulating hormone (FSH) through transcriptional control of FSHbeta-subunit. Whereas it has been well demonstrated that this regulation is mediated by Smad pathway, the molecular mechanisms underlying gonadotrope-specific expression of the FSHbeta gene are not fully understood. Previously, we have identified Pitx2 as a pituitary-expressed transcription factor involved in activin-dependent induction of the FSHbeta promoter. Present data demonstrate that Pitx2 is not only sufficient, but also necessary for FSHbeta gene transcription, as a siRNA-mediated downregulation of Pitx2 protein expression abrogates both Smad3- and activin-mediated stimulation of the FSHbeta promoter. In addition, downregulation of Smad3 protein expression has a significant effect on Pitx2-dependent stimulation of the FSHbeta promoter, suggesting that cooperation between these factors is necessary for full transcriptional activation of the FSHbeta promoter. Furthermore, we show that Pitx2/Smad protein complexes assemble and can be co-immunoprecipitated. This interaction is mediated through the homeodomain of Pitx2 and is important for stimulation of FSHbeta gene transcription. Overall, these data contribute to the emerging molecular mechanism underlying both basal and activin-dependent FSHbeta gene regulation.
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PMID: 18022758 [PubMed - indexed for MEDLINE]