Control of growth, morphology, and alkaline phosphatase activity by butyrate and related short-chain fatty acids in the retinoid-responsive 9-1C rat prostatic adenocarcinoma cell

The actions of butyrate and related short-chain fatty acids were analyzed on the 9-1C retinoid-responsive rat prostatic adenocarcinoma cell. The 9-1C cells, which are inducible for alkaline phosphatase (AP) by retinoic acid, were also inducible for the enzyme by three- to six-carbon fatty acids. The most effective inducer was the four-carbon acid, butyrate, which caused an essentially linear increase in AP activity in the concentration range of 2 to 10 mM. A comparison of AP induction by butyrate and retinoic acid showed the retinoid to be a more potent inducer of the enzyme by several orders of magnitude. Butyrate and related short-chain fatty acids also suppressed 9-1C cell growth, an effect which is not mediated by retinoic acid in these cells. Total growth suppression was achieved at butyrate concentrations of 5 mM and above; 1.5 mM caused 50% inhibition. As in the case of AP induction, all three- to six-carbon fatty acids suppressed growth to some extent, although butyrate was the most effective. The order of carbon chain length effectiveness for both AP induction and growth suppression by the fatty acids was 4 greater than 5 greater than 3 greater than 6. Butyrate appeared to be unique among the various fatty acids in causing an increase in cell protein. The protein content of 9-1C cells cultured in the presence of 4 mM butyrate for 72 h was more than 4-fold greater than that of control cells. This observation paralleled observations on cell volumes analyzed by forward-angle light-scatter flow cytometry, which showed a concentration-related increase in the cross-sectional areas of 9-1C cells following butyrate treatment. This effect has also been shown, in a recent study, to be mediated by retinoids. One of the most striking effects of butyrate treatment was on cellular morphology. The fatty acid caused 9-1C cells, which normally grow in a disorganized array with no apparent affinity for each other, to spread out and become organized into parallel tracts through the monolayer.