Disruption of the guanylyl cyclase-C gene leads to a paradoxical phenotype of viable but heat-stable enterotoxin-resistant mice.
Heat-stable enterotoxins (STa), which cause an acute secretory diarrhea, have been suggested to mediate their actions through the guanylyl cyclase-C (GC-C) receptor. The GC-C gene was disrupted by insertion of neo into exon 1 and subsequent homologous recombination. GC-C null mice contained no detectable GC-C protein. Intestine mucosal guanylyl cyclase activity was approximately 16-fold higher in wild-type mice than in the GC-C null mice, and STa-stimulable guanylyl cyclase activity was absent in the null animals. Thus, GC-C is the major cyclase activity present in the intestine, and also completely accounts for the STa-induced elevations of cGMP. Gavage with STa resulted in marked fluid accumulation within the intestine of wild-type and heterozygous suckling mice, but GC-C null animals were resistant. In addition, infection with enterotoxigenic bacteria that produce STa led to diarrhea and death in wild-type and heterozygous mice, while the null mice were protected. Cholera toxin, in contrast, continued to cause diarrhea in GC-C null mice, demonstrating that the cAMP signaling pathway remained intact. Markedly different diets (high carbohydrate, fat, or protein) or the inclusion of high salt (K+, Na+) in the drinking water or diet also did not severely affect the null animals. Given that GC-C is a major intestinal receptor in all mammals, the pressure to retain a functional GC-C in the face of diarrhea-inflicted mortality remains unexplained. Therefore, GC-C likely provides a protective effect against stressors not yet tested, possibly pathogens other than noninvasive enterotoxigenic bacteria.
Schulz
S
S
Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75235-9050, USA.
Lopez
M J
MJ
Kuhn
M
M
Garbers
D L
DL
D000818:Animals; D000831:Animals, Newborn; D015139:Blotting, Southern; D015153:Blotting, Western; D001835:Body Weight / Q000187:drug effects; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology; D004768:Enterotoxins / Q000494:pharmacology*; D004926:Escherichia coli / Q000472:pathogenicity; D005526:Food, Formulated; D006162:Guanylate Cyclase / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D007413:Intestinal Mucosa / Q000201:enzymology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled; D018000:Receptors, Peptide / Q000235:genetics* / Q000502:physiology*; D017673:Sodium Chloride, Dietary / Q000494:pharmacology; D015996:Survival Rate
D004768:Enterotoxins; D018000:Receptors, Peptide; D017673:Sodium Chloride, Dietary; D002772:Cholera Toxin; D006162:Guanylate Cyclase; D000074261:Receptors, Enterotoxin; D050705:Receptors, Guanylate Cyclase-Coupled