IgH Intronic Enhancer Element HE2 (μB) Functions as a cis‐Activator in Choroid Plexus Cells at the Cellular Level as well as in Transgenic Mice

Abstract

Immunoglobulin heavy-chain (IgH) gene expression is regulated largely by the IgH gene intronic enhancer (ENHiH), which is composed of multiple protein-binding motifs. These motifs are DNA elements that are important for the regulation of IgH gene transcription. It has been reported that the HE2 (mu B) and mu A motifs within the ENHiH affect B cell-specific gene expression. To examine the function of the HE2 and mu A elements in vivo, we established transgenic mouse lines. A deletion mutant of the human ENHiH that contains the HE2 and mu A motifs, but lacks the motifs corresponding to murine E5, E3, and octamer, functioned not only in B lymphocytes but also in choroid plexus cells, which secrete CSF. As a result, we obtained choroid plexus tumor-bearing transgenic mice and could establish choroid plexus carcinoma cell lines. In addition, using the luciferase assay, we confirmed at the cellular level that the HE2 motif shows a fair degree of enhancer activity in cultured choroid plexus carcinoma cells. These results suggest the existence of a trans-acting factor for the HE2 motif in choroid plexus cells. Actually, in this cultured cell line, the existence of a protein binding to the HE2 motif was demonstrated by a gel retardation assay. Due to the sequence homology between the HE2 motif and the Ets-binding sites, an Ets-related protein is a highly probable candidate for being the binding factor.