| Abstract
| - Pregnancy-specific glycoproteins (PSGs) are primarily expressed in the placenta and becomethe major glycoproteins at term. To understand the regulation of PSG expression, we characterized thepromoter 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]. Inthe current study, we used the yeast one-hybrid system to isolate transcription factors binding to the FPIIIsite and demonstrated that a rodent Jκ recombination signal sequence binding protein, rRBPJκ-2N, boundto the FPIII site. Electrophoretic mobility shift assay with rat placental nuclear proteins revealed aconstitutive occupancy of the FPIII site by RBPJκ. By transient expression analyses, we demonstratedthat rRBPJκ-2N repressed the expression from an FPIII-driven SV40 promoter. However, this repressioneffect was counteracted by the active intracellular domain of Notch (NotchIC). Using the native rnCGM3promoter construct, we demonstrated that the promoter activity stimulated by C/EBPβ was also repressedby rRBPJκ-2N but enhanced by NotchIC. Additionally, we found that NotchIC can stimulate expressionthrough another RBPJκ site within the FPI site. A functional interaction between factors binding to theFPI, FPII, and FPIII sites is proposed.
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