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

Front Immunol. 2023 Sep 14:14:1250942. doi: 10.3389/fimmu.2023.1250942. eCollection 2023.

Abstract

C-reactive protein (CRP) is an evolutionary highly conserved protein. Like humans, CRP acts as a major acute phase protein in pigs. While CRP regulatory mechanisms have been extensively studied in humans, little is known about the molecular mechanisms that control pig CRP gene expression. The main goal of the present work was to study the regulatory mechanisms and identify functional genetic variants regulating CRP gene expression and CRP blood levels in pigs. The characterization of the porcine CRP proximal promoter region revealed a high level of conservation with both cow and human promoters, sharing binding sites for transcription factors required for CRP expression. Through genome-wide association studies and fine mapping, the most associated variants with both mRNA and protein CRP levels were localized in a genomic region 39.3 kb upstream of CRP. Further study of the region revealed a highly conserved putative enhancer that contains binding sites for several transcriptional regulators such as STAT3, NF-kB or C/EBP-β. Luciferase reporter assays showed the necessity of this enhancer-promoter interaction for the acute phase induction of CRP expression in liver, where differences in the enhancer sequences significantly modified CRP activity. The associated polymorphisms disrupted the putative binding sites for HNF4α and FOXA2 transcription factors. The high correlation between HNF4α and CRP expression levels suggest the participation of HNF4α in the regulatory mechanism of porcine CRP expression through the modification of its binding site in liver. Our findings determine, for the first time, the relevance of a distal regulatory element essential for the acute phase induction of porcine CRP in liver and identify functional polymorphisms that can be included in pig breeding programs to improve immunocompetence.

Keywords: C-reactive protein; RNA-seq; enhancer; fine-mapping; luciferase assays; pig.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • C-Reactive Protein* / genetics
  • C-Reactive Protein* / metabolism
  • CCAAT-Enhancer-Binding Protein-beta / metabolism
  • Cattle
  • Female
  • Genome-Wide Association Study
  • Humans
  • Liver / metabolism
  • Mutation
  • Swine
  • Transcription, Genetic*

Substances

  • C-Reactive Protein
  • CCAAT-Enhancer-Binding Protein-beta

Grants and funding

The authors declare financial support was received for the research, authorship, and/or publication of this article. The study was funded by grants AGL2016-75432-R and PID2020-112677RB-C21 awarded by MCIN/AEI/10.13039/501100011033 and GENE-SWitCH project (https://www.gene-switch.eu), which is funded by the European Union’s Horizon 2020 Research and Innovation Programme under the grant agreement n°817998. T. Jové-Juncà was funded with an IRTA fellowship (CPI1221) and C. Hernández-Banqué was supported by a FPI grant (PRE2021-097825) granted by the Spanish Ministry of Science and Innovation. YR-C was financially supported by a Ramon y Cajal contract (RYC2019-027244-I) from the Spanish Ministry of Science and Innovation. The authors are part to a Consolidated Research Group AGAUR, with the reference 2021-SGR-01552.