Identification of DNMT3B2 as the Predominant Isoform of DNMT3B in Porcine Alveolar Macrophages and Its Involvement in LPS-Stimulated TNF-α Expression

DNA methyltransferase 3B (DNMT3B) as one member of the DNMT family functions as a de novo methyltransferase, characterized as more than 30 splice variants in humans and mice. However, the expression patterns of DNMT3B in pig as well as the biological function of porcine DNMT3B remain to be determined. In this study, we first examined the expression patterns of DNMT3B in porcine alveolar macrophages (PAM). We demonstrated that only DNMT3B2 and DNMT3B3 were the detectable isoforms in PAM. Furthermore, we revealed that DNTM3B2 was the predominant isoform in PAM. Next, in the model of LPS (lipopolysaccharide)-activated PAM, we showed that in comparison to the unstimulated PAM, (1) expression of DNTM3B is reduced; (2) the methylation level of TNF-α gene promoter is decreased. We further establish that DNMT3B2-mediated methylation of TNF-α gene promoter restricts induction of TNF-α in the LPS-stimulated PAM. In summary, these findings reveal that DNMT3B2 is the predominant isoform in PAM and its downregulation contributes to expression of TNF-α via hypomethylation of TNF-α gene promoter in the LPS-stimulated PAM.