Transcriptional Regulator CTR9 Inhibits Th17 Differentiation via Repression of IL-17 Expression

Abstract

PAF complex is an evolutionarily conserved transcriptional complex that associates with RNA polymerase II in the coding region of actively transcribing genes. Although its transcriptional activity is closely related to diverse cellular processes, such as cell-cycle progression or development in mammals, its role in immune responses has not been addressed yet. In this study, we show that CTR9, a component of PAF complex, functions as a repressor of Th17 differentiation. Both mRNA and protein levels of CTR9 were significantly decreased during the differentiation processes of naive T into Th17 effector cells. When CTR9 was depleted, IL-17 expression was induced and differentiation into Th17 cells enhanced. In naive T cells, CTR9 occupied the coding region of Il17a, but dissociated under Th17 in vitro-polarizing conditions. In contrast, both CDC73 and PAF1 were recruited to the Il17a locus under Th17-differentiation conditions. In the IL-6–stimulated splenocytes, expression of CTR9 was decreased, and chromatin-bound CTR9 disappeared in the coding region of Il17a. IL-6 also directly repressed expression of CTR9 gene, as promoter activity of CTR9 was similarly repressed by IL-6 treatment. Moreover, in mice with collagen-induced arthritis, lentivirus-mediated CTR9 overexpression in the joints ameliorated arthritis severity, decreasing the frequency of CD4+IL-17+ T cells in lymph nodes. In conclusion, our data propose a novel feed-forward loop of IL-17 transcriptional regulatory circuit, via IL-6–mediated repression of CTR9 which is a transcriptional repressor of IL-17.

Cln 3-requiring 9 is a negative regulator of Th17 pathway-driven inflammation in anti-glomerular basement membrane glomerulonephritis

“…Although the low efficiency of delivery and off-target effects of siRNAs prevented us from trying to inject Ctr9-siRNAs or Ctr9 overexpression vectors into mice with anti-GBM GN, in vitro differentiation experiments with splenocytes and intrarenal lymphocytes illustrated that Ctr9 represses Th17 differentiation in the context of autoimmune inflammation. This finding is consistent with a previous report that Ctr9 inhibition enhances Th17 differentiation and worsens inflammation in collagen-induced arthritis, a model of autoimmune joint inflammation (35). Disruption of Ctr9 in intrarenal lymphocytes increased the proportion of Th17 cells and the mRNA abundances for Th17-related transcription factors STAT3 and ROR␥t.…”

“…2E). Since IL-6 initiates Th17 differentiation and directly represses Ctr9 expression (35), it is more likely that low IL-6 production in STAT3␤ Ϫ/Ϫ mice led to a decrease in repression of Ctr9. IL-17 knockout essentially reproduced the protective effect of STAT3␤ knockout, consistent with prior knowledge on the role of IL-17 in organ-specific autoimmune disorders (1,12).…”

“…STAT3 phosphorylated by JAK2 forms homo-or heterodimers with STAT3 or STAT1 and migrates into the nucleus and binds to its target promoters. STAT3 dimers interact with DNA or histone proteins at the promoter of their target genes, and this interaction is mediated by the RNA polymerase-associated factor complex (PAFc) (35,36,38). PAFc is an evolutionarily conserved mediator of general transcriptional processes including transcription initiation, elongation, RNA processing, and histone modification (10).…”

“…In mice injected with lipopolysaccharide, Ctr9 in hepatocytes regulates the transcription of IL-6responsive genes by modulating STAT3-DNA interaction (38). In T cells, Ctr9 inhibits Th17 differentiation by repressing IL-17 transcription: without IL-6, Ctr9 proteins are normally bound to the gene body of Il17a and thereby repress its transcription; with IL-6, Ctr9 is released from the gene body of Il17a, allowing transcription to proceed (35). Another study on Ctr9 in the regulation of IL-6-responsive genes has shown that depletion of Ctr9 decreased the association of a negative elongation factor and increased the association of cyclindependent kinase 9, a kinase component of the positive transcription elongation factor at the elongation checkpoint (36).…”

Drosophila CG2469 Encodes a Homolog of Human CTR9 and Is Essential for Development

“…In addition to its role in regulating transcriptional elongation, the Paf1 complex has also been implicated in telomeric silencing (Ng et al 2003), 3′ end formation of mRNA (Krogan et al 2003; Li et al 2003; Schaft et al 2003), and 3′ end formation of snoRNAs (Tomson et al 2013). Other studies suggest that the Paf1 complex may also participate in transcriptional repression in certain contexts (Crisucci and Arndt 2011, 2012; Yoo et al 2014). …”