Submitted to: Experimental Cell Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2004
Publication Date: January 2, 2005
Citation: Li, C.J., Elsasser, T.H. 2005. Butyrate-induced apoptosis and cell cycle arrest in bovine kidney epithelial cells: involvement of caspase and proteasome pathways. Journal of Animal Science. 83:89-97.
Interpretive Summary: Short chain fatty acids (acetate, propionate, and butyrate,) are produced during bacteria fermentation of dietary fiber in the guts of mammalian species and then directly absorbed at the site of production. They are very important nutrients for cattle. However, one of the short chain fatty acids, butyrate, has another important biological function. It can regulate the function of cells. It can stop cell growing, cause death of cells and so on. Nevertheless, it is unclear how butyrate causes those changes in cells. Cell cycle regulatory and apoptotic effects of butyrate and other SCFA at the cellular and molecular levels in normal bovine cells have not been studied thus far but would serve as a principle launch point to validate the need for further study of these phenomena in cattle. We set up to investigate the effects of butyrate in cattle cells and try to understand how butyrate regulates the cell function. What we found are reported in this paper. Butyrate can cause the programmed cell death and stop growing in cattle cells. After butyrate treatment for 24 hours, two regulatory proteins cdc6 and cdc2/cdk1) in the cells were targeted for destruction, which is very possibly the result of activation of caspase-3 and/or proteasome pathways. We also found two important pathways (caspase and proteasome) that play important roles in butyrate induced cell effects. All of these results suggest that butyrate functions as both a nutrient and signaling molecule regulating the cell growth and proliferation.
Beyond their nutritional impact, Short chain fatty acids (SCFA), especially butyrate, modulate cell differentiation, proliferation, motility, and in particular, they induce cell cycle arrest and apoptosis. We utilized a bovine kidney epithelial cell line (MDBK) to investigate the cell cycle regulatory and apoptotic effects of butyrate. Our results indicated that butyrate not only induced apoptosis, but also induced cell cycle arrest at the G1/S boundary and G2/M in MDBK cells. The cell responses were dose-dependent. In looking into the possible mechanisms for the apoptosis and cell cycle arrest induced by butyrate, we observed that butyrate treatment not only activated caspase-3 activities, induced accumulation of acetylated histone, and up-regulated the expression of p21 protein, but also increased the ubiquitination level of cellular proteins. Moreover, the proteasome inhibitor MG-132 could reverse the cell cycle arrest induced by butyrate, indicating a multiprotein crosstalk wherein the ubiquitination/ proteasome pathway interacted with the caspase signaling pathway. We also found that at least two proteins become targeted for destruction upon butyrate treatment. Cdc6 and cdk1, two important cell cycle checkpoint proteins that regulate the cell cycle progress, are significantly down regulated by proteolytic pathways, which is very possibly the result of activation of caspase-3 and/or proteasome pathways. All of these results suggest that butyrate functions as both a nutrient and signaling molecule regulating the cell growth and proliferation.