Abstract
PAF complex (PAFc) is an RNA polymerase II associated factor that controls diverse steps of transcription. Although it is generally associated with actively transcribed genes, a repressive PAFc has also been suggested. Here, we report that PAFc regulates the transition from transcription initiation to transcription elongation. PAFc repressed IL-6-induced, but not TNF-α-induced, immediate early gene expression. PAFc constitutively associated with the 5′-coding region of the c-Fos locus, then transiently dissociated upon IL-6 stimulation. When CTR9, a component of PAFc, was depleted, higher levels of serine 5-phosphorylated or serine 2-phosphorylated forms of RNA Polymerase II were associated with the unstimulated c-Fos locus. We also observed an increased association of CDK9, a kinase component of the pTEF-b elongation factor, with the c-Fos locus in the CTR9-depleted condition. Furthermore, association of negative elongation factor, NELF, which is required to proceed to the elongation phase, was significantly reduced by CTR9 depletion, whereas elongation factor SPT5 recruitment was enhanced by CTR9 depletion. Finally, the chromatin association of CTR9 was specifically controlled by IL-6-induced kinase activity, because a JAK2 kinase inhibitor, AG-490, blocked its association. In conclusion, our data suggest that PAFc controls the recruitment of NELF and SPT5 to target loci in a signal- and locus-specific manner.
Highlights
Transcription occurs in three phases: initiation, elongation, and termination
We have previously shown that CTR9, a component of PAF complex (PAFc), aids the transcription of IL-6-inducible acute phase protein (APP) genes, such as fibrinogen (FGG) and haptoglobin (Hp), by stabilizing the binding between STAT3 and chromatin at promoters [26]
We studied an immediate early gene, c-Fos, which is transcriptionally induced by IL-6 in hepatocytes
Summary
General transcription factors recognize promoter sequences and recruit RNA polymerase II (Pol II) to form a preinitiation complex (PIC), the first step of messenger RNA (mRNA) synthesis [1]. Before proceeding to the elongation phase, the functional and structural block created by the pre-initiation complex (PIC), a complex process that is regulated by multiple elongation factors, has to be cleared [2]. TF binding facilitates chromatin remodeling and the recruitment of eukaryotic RNA Pol II to the transcription start site (TSS) to initiate transcription [3]. A genomewide analysis of eukaryotic RNA Pol II revealed that over 30% of human genes are blocked from proceeding to elongation by an RNA Pol II PIC at the promoter-proximal region [4]
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