Molecular cloning and functional characterization of porcine nucleotide-binding oligomerization domain-2 (NOD2)

The nucleotide-oligomerization domain (NOD) 2 is an important molecule involved in host defense. In this study, we report the cloning and characterization of porcine NOD2 (poNOD2) cDNA. The open reading frame of poNOD2 contains 3042 bp which encode 1013 amino acid residues. The putative poNOD2 protein shares higher level of homology with human counterpart (81.6% amino acid identity) than the mouse protein (76.6% amino acid identity). In order to determine the function of poNOD2, we established human embryonic kidney (HEK) 293 cells transfected to express poNOD2 cDNA. We found that poNOD2 was expressed not only in the cytoplasm but also in the inner side of the plasma membrane of HEK293 cells. HEK293 cells expressing poNOD2 responded to muramyl dipeptide (MDP) by activation of the nuclear factor kappa B (NF-κB). Quantitative real-time PCR revealed that poNOD2 mRNA was expressed by a number of tissues isolated from adult and newborn swine such as esophagus, duodenum, jejunum, ileum, ileal Peyer's patches (Pps), colon, spleen, and mesenteric lymph nodes (MLNs). In the newborn swine, the expression of poNOD2 mRNA was detected at higher levels in MLNs and spleen as compared to other tissues. In the adult swine, the highest expression was observed in ileal Pps. Furthermore, Toll-like receptor (TLR) and NOD2 ligands as well as immunobiotic lactic acid bacteria (LAB) enhanced the expression of NOD2 in gut-associated lymphoid tissues (GALT) in adult and newborn swine. Our results implicate NOD2 as an important immunoregulator in the swine intestinal immunity.