Enhanced sensitivity to cholera toxin in ADP-ribosylarginine hydrolase-deficient mice

Cholera toxin (CT) produced by Vibrio cholerae causes the devastating diarrhea of cholera by catalyzing the ADP-ribosylation of the alpha subunit of the intestinal G(s) protein (G(s alpha)), leading to characteristic water and electrolyte losses. Mammalian cells contain ADP-ribosyltransferases similar to CT and an ADP-ribosyl(arginine)protein hydrolase (ADPRH), which cleaves the ADP-ribose-(arginine) protein bond, regenerating native protein and completing an ADP-ribosylation cycle. We hypothesized that ADPRH might counteract intoxication by reversing the ADP-ribosylation of G(s alpha). Effects of intoxication on murine ADPRH(-/-) cells were greater than those on wild-type cells and were significantly reduced by overexpression of wild-type ADPRH in ADPRH(-/-) cells, as evidenced by both ADP-ribose-arginine content and G(s alpha) modification. Similarly, intestinal loops in the ADPRH(-/-) mouse were more sensitive than their wild-type counterparts to toxin effects on fluid accumulation, G(s alpha) modification, and ADP-ribosylarginine content. Thus, CT-catalyzed ADP-ribosylation of cell proteins can be counteracted by ADPRH, which could function as a modifier gene in disease. Further, our study demonstrates that enzymatic cross talk exists between bacterial toxin ADP-ribosyltransferases and host ADP-ribosylation cycles. In disease, toxin-catalyzed ADP-ribosylation overwhelms this potential host defense system, resulting in persistence of ADP-ribosylation and intoxication of the cell.