Endocrine Abstracts

Human type 2 deiodinase (hD2) regulates T3 production in placenta during trophoblast development. hD2 mRNA and protein levels are elevated only during the first trimester of gestation then becoming barely detectable. These variations are similar to those of chorionic gonadotropin (hCG), a well-known marker of early gestation secreted by the cytotrophoblast. A peculiar promoter architecture of the gene encoding the alpha subunit of hCG allows a CRE-mediated synergism between cAMP and EGF, leading to elevated levels of hCG-mRNA only during early pregnancy. In addition, hCG promoter contains several CCAAT boxes, that are likely to confer tissue specificity to this gene. Similarly, in our previous studies we have demonstrated that Dio2 promoter is synergistically stimulated by cAMP and mitogens. These signals are integrated and converge to the Dio2 CRE, which recruits a transcription factor complex including CREB, c-Jun and c-Fos. Here we show that CCAAT enhancer binding proteins (C/EBPs), are master regulators of Dio2 expression in JEG3 cells, a cell line similar to early trophoblast. RT-PCR studies have demonstrated that C/EBPs significantly increases hD2 mRNA levels. With functional assays of micro-deletion mutant constructs we have shown that C/EBPs robustly enhanced the transcriptional activity of hD2 gene through a highly conserved CCAAT element, located nearby the TATA box. Biochemical evidence confirmed the binding of C/EBPs to this regulatory site. Remarkably, the inducibility was dramatically increased in promoter constructs lacking the CRE or when CREB/CRE interaction was prevented by an acidic dominant negative inhibitor. This latter observation suggested that CREB and C/EBP regulates transcription of Dio2 gene in an antagonistic fashion. In conclusion we have found that αCG and Dio2 genes seem to share a common promoter code, represented by CCAAT, CREs, TATA/TSS units, that imparts tissue specificity and inducibility to both genes in early trophoblast.