Glial fibrillary acidic protein transcriptional regulation is independent of a TFIID-binding downstream initiator sequence.

Previous studies have shown that the promoter of the glial fibrillary acidic protein (GFAP) gene contains a transcriptional initiator located downstream from the transcription initiation (cap) site. This initiator was shown to be essential for efficient in vitro TATA box binding and function of TATA box-binding factor (TFIID); its deletion significantly reduced in vitro template transcription by the GFAP promoter and inhibited almost completely expression of a reporter gene under control of human GFAP promoter and upstream sequences in glial cells. However, although activity of initiator-containing GFAP promoter in human and murine GFAP-reporter constructs in transfected cells was shown to increase sharply when upstream cis-acting elements are added, initiator-lacking murine constructs have shown a small GFAP promoter region to have high activity in glioma cells, with no increase in activity when regulatory sequences are extended further upstream. These findings suggested a possible difference between the in vitro and in vivo effects of the downstream initiator on the promoter region itself, as well as an in vivo interplay between the initiator and regulatory sequences upstream from the promoter region. Here we have analyzed the effect of the downstream initiator on gene expression in cells using matched (pairs of otherwise identical initiator-containing and initiator-deleted plasmids) constructs extending to different upstream positions. We show that matched initiator-containing and initiator-deleted counterparts direct similar expression levels, and that, with or without the downstream initiator, expression levels increase sharply when upstream sequences are added to the GFAP promoter. Our results show that the downstream initiator is not required for GFAP transcriptional activity in cultured cells.(ABSTRACT TRUNCATED AT 250 WORDS)