Butyric acid sensitizes Vero cells to ricin-induced apoptosis via accelerated activation of multiple signal transduction pathways.
We found that the treatment with 1 mM butyric acid for 2 days renders Vero cells highly sensitive to ricin-induced apoptosis reflected by cytolysis concomitant with apoptotic cellular and nuclear morphological changes, DNA fragmentation, and increase in caspase-3 like activity, whereas butyric acid alone had no cytotoxic effect on Vero cells. During the treatment with butyric acid, gradual increase in alkaline phosphatase activity, an indicator for butyric acid-induced differentiation, was observed in Vero cells. Although the potency of ricin-mediated protein synthesis was increased in butyric acid-treated Vero cells as compared to untreated cells, the binding and internalization of ricin to the cells were not much affected. Furthermore, DNA fragmentation caused by other protein synthesis inhibitors such as diphtheria toxin and anisomysin were also highly potentiated in butyric acid-treated Vero cells, whereas the potencies of these toxins to inhibit the protein synthesis were not affected by butyric acid treatment. These results suggest that the apoptosis signaling pathway, which may be triggered by cytotoxic stress response caused by toxins, is sensitized in butyric acid-treated cells, while the pathways leading to the protein synthesis inhibition by these toxins are relatively unchanged. No significant differences in the expression levels of p21, p53, and Bcl-2 proteins were observed between butyric acid-treated and untreated Vero cells. The treatment with ricin resulted in the activation of p38 MAP kinase, and this activation occurred on an accelerated time schedule in butyric acid-treated Vero cells than in untreated cells. The specific inhibitor of p38 MAP kinase SB203580 showed a partial inhibitory effect on ricin-induced apoptosis in control Vero cells, but it was less effective in butyric acid-treated Vero cells. Taken together, our results suggest that butyric acid-treatment may result in sensitization of multiple intracellular signal transduction pathways including apoptotic signaling pathways and p38 MAP kinase pathway.
Tamura
Tadashi
T
Division of Biochemistry, Faculty of Fisheries, Nagasaki University, Bunkyo-machi, Nagasaki 852-8521, Japan.
Tsuruta
Naoko
N
Hirano
Kaori
K
Yamaguchi
Kenichi
K
Oda
Tatsuya
T
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D020148:Butyric Acid / Q000378:metabolism*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D048429:Cell Size; D002522:Chlorocebus aethiops; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D053938:DNA Fragmentation; D004167:Diphtheria Toxin / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism; D006633:Histamine Antagonists / Q000378:metabolism*; D007093:Imidazoles / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011725:Pyridines / Q000378:metabolism; D012276:Ricin / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D014709:Vero Cells; D048051:p38 Mitogen-Activated Protein Kinases
D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004167:Diphtheria Toxin; D004791:Enzyme Inhibitors; D006633:Histamine Antagonists; D007093:Imidazoles; D011500:Protein Synthesis Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D011725:Pyridines; D016159:Tumor Suppressor Protein p53; D020148:Butyric Acid; D012276:Ricin; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D053148:Caspase 3; D020169:Caspases; C093642:SB 203580