Butyrate mediated regulation of RNA binding proteins in the post-transcriptional regulation of inflammatory gene expression

Abstract

Short chain fatty acids (SCFAs) are produced by commensal bacteria in the gut and are known to reduce inflammation through transcriptional inhibition of cytokines and inflammatory proteins such as cyclooxygenase-2 (COX-2). Butyrate is a SCFA that was reported to alter the mRNA stability of inflammatory genes by increasiing the expression of the RNA binding protein (RBP) Tristetraprolin (TTP). We have hypothesized that butyrate may regulate gene expression post-transcriptionally through global effects on the expression or cytoplasmic translocation of RBPs. Using bioinformatics analyses of publicly available microarray data as well as colon cancer cell lines treated with sodium butyrate, we have observed that butyrate treatment led to a general reduction in expression of several (but not all) RBPs and inhibition in the cytosolic translocation of HuR, a well-known stabilizing RBP. This was reflected in reduced NanoLuc reporter activity of several different AU-rich element (ARE) sequences in the presence of butyrate; this suppression was retained even when HuR was overexpressed. Mechanistically, we have shown that reduced activity of HuR was related to decreased phosphorylation of p38 and MK2 and enhanced phosphorylation of Chk2. As a proof of concept, we show butyrate-mediated inhibition in binding of HuR to the 3’UTR of COX-2 mRNA resulting in reduced mRNA and protein levels of the inflammatory gene. Overall, our data suggest that butyrate can reduce the expression of inflammatory genes not only by transcriptional regulation, but also by post-transcriptional regulation via inhibition of mRNA stabilizing proteins.