Bovine lactoferrin is a transcription factor stimulating IL‐1 beta gene expression in the small intestine

Abstract

Lactoferrin (Lf) is an iron‐binding glycoprotein present in high concentration in human milk. It is a pleiotropic protein and involved in diverse bioactivities. Since Lf is partly resistant to proteolysis in the gastrointestinal tract, Lf may play important roles in intestinal development. Human Lf (hLf) is internalized by human intestinal epithelial cells (Caco‐2) and translocates to the nucleus where it functions as a transcription factor to up‐regulate expression of genes, such as IL‐1 beta. Bovine Lf (bLf) shares 69% amino acid identity with hLf and has been shown to have similar physiological functions as hLf. Therefore, we hypothesized that bLf is able to enter the nucleus of Caco‐2 and transactivate gene transcription. Confocal microscopy and immunoblotting using nuclear fractions showed that bLf was internalized and localized to the nucleus of Caco‐2. After Caco‐2 cells were treated with bLf, IL‐1 beta transcription was two fold up‐regulated as revealed by RT‐PCR. To determine if bLf binds to the promoter of IL‐1 gene, an IL‐1 beta promoter fragment containing a hLf potential DNA binding site were then inserted to a luciferase promoter‐less vector and luciferase assays were conducted. The results show that bLf binds to the IL‐1 beta promoter and activates IL‐1 beta transcription. Results from chromatin immunoprecipitation (ChIp) assays also demonstrated that bLf interacts with the potential hLf DNA binding site in the promoter of the IL‐1 beta gene in vivo. In conclusion, bLf is able to enter the nucleus of human intestinal epithelial cells, bind to the promoter of IL‐1 gene and functionally regulate gene transcription. It is therefore possible that bLf may insert some of the biological activities of Lf in human milk. Supported by Mead Johnson Nutrition.