The LPS-Induced Transcriptional Upregulation of the Chicken Lysozyme Locus Involves CTCF Eviction and Noncoding RNA Transcription

Transcription of the lysozyme gene is rapidly induced by proinflammatory stimuli such as treatment with bacterial lipopolysaccharide (LPS). Here we show that this induction involves both the relief of repression mediated by the enhancer-blocking protein CTCF that binds to a negative regulatory element at -2.4 kb, and the activation of two flanking enhancer elements. The downstream enhancer has promoter activity, and LPS stimulation initiates the transient synthesis of a noncoding RNA (LINoCR) transcribed through the -2.4 kb element. Expression of LINoCR is correlated with IKK alpha recruitment, histone H3 phosphoacetylation in the transcribed region, the repositioning of a nucleosome over the CTCF binding site, and, eventually, CTCF eviction. Each of these events requires transcription elongation. Our data reveal a transcription-dependent mechanism of chromatin remodeling that switches a cis-regulatory region from a repressive to an active conformation.