Oct-1 acts as a transcriptional repressor on the C-reactive protein promoter

Abstract

C-reactive protein (CRP), a plasma protein of the innate immune system, is produced by hepatocytes. A critical regulatory region (−42 to −57) on the CRP promoter contains binding site for the IL-6-activated transcription factor C/EBPβ. The IL-1β-activated transcription factor NF-κB binds to a κB site located nearby (−63 to −74). The κB site overlaps an octamer motif (−59 to −66) which is the binding site for the constitutively active transcription factor Oct-1. Oct-1 is known to function both as a transcriptional repressor and as an activator depending upon the promoter context. Also, Oct-1 can regulate gene expression either by binding directly to the promoter or by interacting with other transcription factors bound to the promoter. The aim of this study was to investigate the functions of Oct-1 in regulating CRP expression. In luciferase transactivation assays, overexpressed Oct-1 inhibited (IL-6+IL-1β)-induced CRP expression in Hep3B cells. Deletion of the Oct-1 site from the promoter drastically reduced the cytokine response because the κB site was altered as a consequence of deleting the Oct-1 site. Surprisingly, overexpressed Oct-1 inhibited the residual (IL-6+IL-1β)-induced CRP expression through the promoter lacking the Oct-1 site. Similarly, deletion of the Oct-1 site reduced the induction of CRP expression in response to overexpressed C/EBPβ, and overexpressed Oct-1 inhibited C/EBPβ-induced CRP expression through the promoter lacking the Oct-1 site. We conclude that Oct-1 acts as a transcriptional repressor of CRP expression and it does so by occupying its cognate site on the promoter and also via other transcription factors by an as yet undefined mechanism.

Mutations on a conserved distal enhancer in the porcine C-reactive protein gene impair its expression in liver

“…It is worth noting that the identified OCT-1 binding site conserved in pigs and humans was previously found by Voleti et al. in 2012 ( 22 ) as a modulator of CRP expression in humans by positional competition with other binding sites in the region.…”

“…A more detailed analysis of this region revealed the presence of a putative enhancer element conserved between human and cow species, and containing transcription factor binding sites for STAT3, C/EBP, NF-kB, HNF4α, OCT-1 FOXA1 and FOXA2. These transcription factors have been widely described as being required for the constitutive expression and/or acute phase induction of CRP ( 21 , 22 , 56 – 59 ). Remarkably, a recent study performed in humans identified an enhancer (E1) located 37.7 Kb upstream of the CRP promoter.…”

“…Furthermore, according to several studies, a variety of transcription factors affect the expression of this gene, highlighting the need to further study the interaction and effects of CRP regulatory pathways ( 15 – 19 ). While HNF-1, HNF-3, and OCT-1 transcriptions factors are involved in the regulation of basal CRP expression levels ( 20 – 22 ), the induction of the acute phase expression of CRP is mediated by the effect of cytokines, particularly IL-6, IL-1β and TNF-α, through the activation of STAT3, NF-kB and C/EBP-β transcription factors ( 16 , 19 , 23 – 25 ). In this regard, a recent study in human Hep3B cells identified an enhancer upstream of the CRP promoter enriched in binding sites for STAT3 and C/EBP-β with a major impact on the acute phase induction of CRP expression ( 26 ).…”

Genetic association and functional implications of TLR4 rs1927914 polymorphism on colon cancer risk

“…In gastric cancer cells, Oct1 is recruited to the CDX2 promoter but loses its ability to activate transcription, highlighting its complex regulatory role [ 34 , 35 ]. Additionally, Oct-1 inhibits Slc7a11 and CRP gene expression by binding to their promoters [ 36 , 37 ]. These insights suggest that the protective effect of the TLR4 rs1927914G allele in colon cancer may result from enhanced Oct-1 binding, leading to reduced TLR4 expression and decreased cancer risk.…”

Purification of recombinant C-reactive protein mutants

“…In humans, the concentration of CRP in circulation increases rapidly within hours of an inflammatory stimulus due to its increased hepatic synthesis under transcriptional and post-transcriptional control (Bode et al, 2012;Kim et al, 2015;Singh et al, 2007;Voleti and Agrawal, 2005;Voleti et al, 2012;Zhang et al, 1995). CRP has also been shown to be deposited at localized sites of inflammation such as at atherosclerotic lesions, in the joints of arthritic patients, and surrounding the amyloid plaque deposits in patients with Alzheimer's disease (Gitlin et al, 1977;Hatanaka et al, 1995;Iwamoto et al, 1994).…”