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

C-reactive protein (CRP) is an evolutionary highly conserved protein. Like humans, CRP acts as a major acute phase protein in pigs. While regulatory mechanisms have been extensively studied in humans, little is known about the molecular mechanisms that control pig gene expression. The main goal of the present work was to study the regulatory mechanisms and identify functional genetic variants regulating gene expression and CRP blood levels in pigs. The characterization of the porcine proximal promoter region revealed a high level of conservation with both cow and human promoters, sharing binding sites for transcription factors required for 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 . 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 expression in liver, where differences in the enhancer sequences significantly modified activity. The associated polymorphisms disrupted the putative binding sites for HNF4α and FOXA2 transcription factors. The high correlation between and expression levels suggest the participation of HNF4α in the regulatory mechanism of porcine 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 in liver and identify functional polymorphisms that can be included in pig breeding programs to improve immunocompetence.