Enhanced Sensitivity to Cholera Toxin in ADP-Ribosylarginine Hydrolase-Deficient Mice

Cholera toxin (CT) produced byVibrio cholerae causes the devastating diarrhea of cholera by catalyzing the ADP-ribosylation of the α subunit of the intestinal Gs protein (Gsα ), 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 Gsα . 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 Gsα modification. Similarly, intestinal loops in the ADPRH−/− mouse were more sensitive than their wild-type counterparts to toxin effects on fluid accumulation, Gsα 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.