Effects of 5‐azacytidine, sodium butyrate, and phorbol esters on amino acid transport system A in a kidney epithelial cell line, MDCK: Evidence for multiple mechanisms of regulation

Abstract

Neutral amino acid transport by system A was investigated in the epithelial cell lines MDCK and MDCK-T1. The latter line is a chemically induced, oncogenically transformed line derived from MDCK. Inducers of differentiation, sodium butyrate and 5-azacytidine, and a tumor promoter, TPA, were used as probes to delineate pathways of regulation involved in system A response to a variety of physiological conditions and agents. Azacytidine, an inhibitor of DNA methylation, and butyrate, an enhancer of histone acetylation, inhibited expression of system A, had little effect on system ASC, and slightly stimulated system L. Inhibition of system A expression by butyrate and azacytidine occurred under different conditions. Increases in system A activity due to amino acid starvation or transformation were inhibited by butyrate but not by azacytidine. Repressed system A activity, normally observed in the presence of high levels of amino acids, was more sensitive to azacytidine than to butyrate. The tumor promoter, TPA, stimulated system A activity in MDCK cells under normal growth conditions but did not stimulate activity in amino acid-starved MDCK cells or in MDCK-T1 cells. Stimulation of system A activity by TPA was prevented by prior exposure to butyrate but not to azacytidine. These results suggest 1) that system A expression observed in growing amino-acid-repressed MDCK cells is modulated by an azacytidine-sensitive mechanism and 2) that the elevated expression of system A activity induced by amino acid starvation, by chemical transformation to MDCK-T1, and by TPA is modulated by a butyrate-sensitive mechanism.

Use of Sodium Butyrate as an Alternative to Dietary Fiber: Effects on the Embryonic Development and Anti-Oxidative Capacity of Rats

“…In vitro cell culture, SB treatment had no effect on GLUT-1 mRNA expression, but upregulated GLUT2 mRNA expression by activating specific regions within the human GLUT2 promoter [48], [49]. The system A amino acid transporters, Slc38a2 and Slc384, mediate the transport of neutral amino acids, and are modulated by a butyrate-sensitive mechanism [50]. Meanwhile, butyrate increases PepT1 mRNA and protein expression and activity at the transcriptional level in colonic epithelial cells [51].…”

Membrane potential of rat hepatoma cells in culture: Influence of factors affecting amino acid transport

“…This suggests Na+-dependent amino acid uptake is not mediated solely through the membrane potential although under physiological conditions this would have a role as indicated by the results obtained here. There is evidence for the existence of multiple mechanisms of regulation of System A amino acid transport in a kidney epithelial cell line (Boerner and Saier, 1988). Thus, while the results indicate a participation of the membrane potential in active, Na+-dependent, amino acid transport, the incomplete and inconsistent correlation of the potential with aminoisobutyrate uptake under different conditions suggests the involvement of supplementary factors.…”