Abstract
Butyric acid and sphingomyelin (SM) affect colonic tumorigenesis. We examined the potential link between butyrate stimulation and SM metabolism in colonic and hepatic cancer cell lines. After incubating HT29 and HepG2 cells with butyrate and other short-chain fatty acids, we found that butyrate increased acid but not neutral or alkaline sphingomyelinase (SMase) activity by 10- to 20-fold. The effects occurred after 16 h of incubation and were associated with reduced SM and phosphatidylcholine contents and increased ceramide levels. Northern blotting showed increased acid SMase mRNA levels in these cells after butyrate stimulation. Propionate was less potent, and acetate had no effect. No similar changes of acid phosphatase could be identified. At concentrations that increased acid SMase expression, butyrate inhibited cell proliferation, activated caspase 3, and induced apoptosis. However, the antiproliferative and apoptotic effects of butyrate preceded the changes of acid SMase and were not affected by knocking down acid SMase expression by small, interfering RNA. In addition, butyrate-induced acid SMase expression was not affected by blocking the caspase pathway. In conclusion, butyrate regulates SM metabolism by stimulating acid SMase expression in colon and liver cancer cells, but the increased acid SMase is not a critical mechanism for initiating the anticancer effects of butyrate.
Highlights
Butyric acid and sphingomyelin (SM) affect colonic tumorigenesis
When cell proliferation and apoptosis were determined, we found that butyrate at concentrations that stimulated acid SMase expression significantly inhibited cell proliferation (Fig. 7, top panel), induced apoptosis, and increased caspase 3 activity dose-dependently
The present study demonstrates that butyrate increases acid SMase, but not neutral or alkaline SMase, activity in human colon cancer HT29 cells and liver cancer HepG2 cells
Summary
Butyric acid and sphingomyelin (SM) affect colonic tumorigenesis. We examined the potential link between butyrate stimulation and SM metabolism in colonic and hepatic cancer cell lines. At concentrations that increased acid SMase expression, butyrate inhibited cell proliferation, activated caspase 3, and induced apoptosis. Butyrate regulates SM metabolism by stimulating acid SMase expression in colon and liver cancer cells, but the increased acid SMase is not a critical mechanism for initiating the anticancer effects of butyrate.—Wu, J., Y. In a recent study in human hepatoma HuH6 and HepG2 cells [10], butyrate was found to induce apoptosis by reducing mitochondrial membrane potential, releasing cytochrome c, and activating the caspase 9 and 3 pathways, which causes a secondary decrease in antiapoptotic factors such as -catenin, pRb, cyclins and Bcl-Xl. Sphingomyelin (SM) hydrolysis triggered by sphingomyelinase (SMase) generates both antiproliferative molecules such as ceramide and sphingosine and proliferative molecules such as sphingosine-1-phosphate [11, 12]. For the first time, links the effects of butyrate to SM metabolism via acid SMase, but the increased acid SMase is not involved directly in mediating the antiproliferative and apoptotic effects of butyrate in these cells
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