Activity and enhancer binding factors for JC virus regulatory elements in differentiating embryonal carcinoma cells.

We have studied cell-type-specific expression by JC virus (JCV) DNA regulatory sequences using embryonal carcinoma (EC) cells as a model system. In transient transfection assays, JCV enhancer demonstrated activity in retinoic acid-differentiated neuronal type cells but not in undifferentiated or DMSO-differentiated muscle type cells. To correlate in vivo activity with the binding of transcription factors, we performed DNasel footprinting experiments. Retinoic acid-treated EC cell extracts provided three completely protected regions, each containing sequences with homology to nuclear factor 1 (NF1) binding motifs and the partially protected TATA box. Oligonucleotide competition studies suggest that all three NF1 binding motifs are bound by the same factors but with different affinities and that there are cooperative interactions between NF1 proteins binding to adjacent regions. No protected region other than the partially protected TATA box was detected in undifferentiated and DMSO-differentiated EC cells in which JC regulatory sequences were not expressed.