Transcriptional regulation of the XXXX chorionic gonadotropin beta gene during villous trophoblast differentiation.

@entity1 @entity268 @entity7807 @entity5962 @entity3419 @entity28549 @entity18720 @entity1928
Expression of the trophoblast-specific subunit of @entity1 chorionic gonadotropin, @entity7807 , is associated with fusion of cytotrophoblasts into a multinuclear syncytium. Here, we studied regulation of the CGbeta5 gene in trophoblasts undergoing in vitro syncytialization. Transfection of luciferase reporters harboring different lengths of the CGbeta5 upstream sequence revealed that the proximal promoter region (-345 to +114) is sufficient to govern differentiation-dependent induction. Mutational analyses suggested that two selective promoter factor (Sp) and three activating protein 2 ( @entity18720 ) recognition sequences are necessary for full activity of the promoter. During syncytialization these elements interacted with increasing amounts of the transcription factors @entity3419 , @entity28549 , and @entity18720 in electrophoretic mobility shift assay, but only @entity18720 binding rose upon elevation of @entity268 levels with @entity1928 . Increasing expression of different isoforms of @entity3419 and @entity28549 could also be detected by Western blot analyses. @entity3419 / @entity28549 localized to syncytial nuclei both in differentiated cultures and in term placental tissue, suggesting assembly of functional transcriptional complexes. Costaining of the transcription factors with @entity5962 on term placental sections revealed that 47 and 33% of cytotrophoblast nuclei were negative for @entity3419 and @entity28549 , respectively. In contrast, immunohistochemistry of early tissue demonstrated expression of @entity3419 in the majority of cyto- and syncytiotrophoblasts, whereas @entity28549 was absent from the syncytium. @entity3419 and @entity28549 induced wild-type/mutant promoter constructs upon transfection in Sp-deficient SL-2 cells, indicating that the Sp elements function as activating sequences. The data suggest that increasing concentrations of @entity3419 , @entity28549 , and @entity18720 enhance transcription of @entity7807 in differentiating term trophoblasts, whereas a different combination of factors may control expression in early placentas.
