American Journal of Clinical Nutrition, Vol 32, 268-268, Copyright © 1979 by The American Society for Nutrition

In vitro inhibition of DNA, RNA, and protein syntheses by Shigella dysenteriae type 1 enterotoxin

¹ From the Department of Microbiology, School of Medicine, University of Missouri-Columbia, Columbia, Missouri 65201

A protein exotoxin isolated from culture filtrates of Shigella dysenteriae type 1 was examined to determine its molecular basis of action. After Sephadex G-100 fractionation, dialysis, and subsequent inoculation into rabbit ileal loops, positive samples were further studied to determine their effects upon DNA, RNA, and protein syntheses. Partially confluent monolayers (60 to 70%) of human intestinal epitheial cells were pretreated with enterotoxin for a 2-hr period and then exposed to H³-labeled precursors. In all experiments appropriate positive controls (daunomycin, 10 µg/ml; actinomycin D, 1 µg/ml; cyclohexamide, 10 µg/ml), negative controls (normal untreated), and heat-inactivated (100 C for 20 min) enterotoxin preparations were included as samples. Cell monolayers treated with the enterotoxin preparations demonstrated a marked decrease in their capacity to incorporate the labeled precursors into DNA, RNA, and proteins as compared to the normal untreated controls. Similarly, all positive controls depressed the incorporation of labeled precursors into cellular constituents, but to a much greater extent. Heat-inactivated enterotoxin depressed the incorporation of labeled precursors in all of the systems examined but to only a minimal extent. This may be attributed to the presence of residual endotoxic lipopolysaccharide in the samples (1 µg/ml concentrations). The results indicate that, on a temporal basis, both protein and RNA syntheses are the systems affected earliest by the enterotoxin treatment followed later by an inhibition of cellular DNA synthesis.