Intragenic transcriptional interference regulates the human immune ligand MICA.

Abstract

Abstract Regulation of MICA expression is incompletely understood, but human MICA can be upregulated in cancer cells, virus-infected cells and rapidly proliferating cells. Binding of MICA to the activating NKG2D receptor on cytotoxic immune cells promotes elimination of the cell expressing MICA. We noted that MICA has tandem promoters that drive overlapping forward transcription. We show that the MICA gene contains a conserved upstream promoter that expresses a non coding transcript. Transcription from the upstream promoter represses transcription from the standard downstream MICA promoter in cis through transcriptional interference. The effect of transcriptional interference depends on the strength of transcription from the upstream promoter and quantitative studies show that it is described by a simple reciprocal repressor function. The time course of transcriptional interference coincides with recruitment at the standard downstream promoter of factors involved in nucleosomal remodeling during transcription. Transcriptional interference is demonstrated in the regulation of MICA expression by the physiological inputs interferon-γ and interleukin-4, that both act through regulatory DNA elements in the upstream promoter. These findings have significant implications for the understanding of MICA expression. Transcription factors activating the downstream promoter will upregulate MICA expression, whereas transcription factors activating the upstream promoter will downregulated MICA expression. A genome-wide analysis indicates that transcriptional interference between tandem intragenic promoters may be involved in regulating the expression of multiple other human genes.