Butyrate Regulates Its Own Metabolic Fate as an HDAC inhibitor in Colorectal Cancer Cells

Abstract

Butyrate is a metabolite derived from the fermentation of dietary fiber by bacteria in the colon, and it has been implicated in protecting against colorectal cancer. Butyrate is the primary energy source for colonic epithelial cells (colonocytes). Butyrate also regulates gene expression by inhibiting histone deacetylases (HDACs). Both of these fates of butyrate (oxidized as an energy source or HDAC inhibition) are not mutually exclusive. Previously, we show that cancerous colonocytes have a reduced capacity to oxidize butyrate compared to non‐cancerous colonocytes, and this metabolic difference impacts butyrate's role as an HDAC inhibitor. Short chain acyl‐CoA dehydrogenase (SCAD) is a mitochondrial enzyme that mediates the oxidation of butyrate, which is diminished in colorectal cancer. Therefore, we hypothesized that decreased SCAD in colorectal cancer cells results in reduced oxidation of butyrate. Here, we report that butyrate itself suppressed SCAD expression in colorectal cancer cells. Butyrate significantly reduced SCAD expression at the gene and protein level (p<0.05). To test whether this decrease in SCAD impacted metabolism in cancerous colonocytes we used the Seahorse XF24 Analyzer to measure butyrate oxidation. The reduction in SCAD was accompanied by lower butyrate oxidation, thus suggesting that butyrate suppresses its own oxidation in the colorectal cancer cell. To determine if HDAC inhibition was involved in regulating SCAD expression we tested whether a structurally unrelated HDAC inhibitor called trichostatin A (TSA) would mimic butyrate's effect on SCAD. TSA decreased the level of SCAD in a manner similar to butyrate, thus suggesting that the mechanism by which butyrate regulates SCAD is through HDAC inhibition. HDAC1 and HDAC3 are the major HDACs targeted by butyrate and were tested for their role in suppressing SCAD. Interestingly, butyrate did not decrease SCAD expression in non‐cancerous colonocytes, showing that this is a selective effect. These data provide a mechanism as to how butyrate oxidation and function is altered in colorectal cancer.