Active Intracellular Domain of Notch Enhances Transcriptional Activation of CCAAT/Enhancer Binding Protein β on a Rat Pregnancy-Specific Glycoprotein Gene

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Abstract
Pregnancy-specific glycoproteins (PSGs) are primarily expressed in the placenta and become the major glycoproteins at term. To understand the regulation of PSG expression, we characterized the promoter elements of a rodent PSG gene, rnCGM3, and delineated three nuclear protein binding sites: FPI, -II, and -III in the 5‘-flanking region of the gene. The FPII-binding factor is shown to be C/EBPβ, which positively regulates rnCGM3 expression [Chen, H., et al. (1995) DNA Cell Biol. 14, 681−688]. In the current study, we used the yeast one-hybrid system to isolate transcription factors binding to the FPIII site and demonstrated that a rodent Jκ recombination signal sequence binding protein, rRBPJκ-2N, bound to the FPIII site. Electrophoretic mobility shift assay with rat placental nuclear proteins revealed a constitutive occupancy of the FPIII site by RBPJκ. By transient expression analyses, we demonstrated that rRBPJκ-2N repressed the expression from an FPIII-driven SV40 promoter. However, this repression effect was counteracted by the active intracellular domain of Notch (NotchIC). Using the native rnCGM3 promoter construct, we demonstrated that the promoter activity stimulated by C/EBPβ was also repressed by rRBPJκ-2N but enhanced by NotchIC. Additionally, we found that NotchIC can stimulate expression through another RBPJκ site within the FPI site. A functional interaction between factors binding to the FPI, FPII, and FPIII sites is proposed.

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