The stimulation of gastric acid secretion from parietal cells involves both intracellular calcium and cAMP signaling. To understand the effect of increased cAMP on parietal cell function, we engineered transgenic mice expressing cholera toxin (Ctox), an irreversible stimulator of adenylate cyclase. The parietal cell-specific H(+),K(+)-ATPase beta-subunit promoter was used to drive expression of the cholera toxin A1 subunit (CtoxA1). Transgenic lines were established and tested for Ctox expression, acid content, plasma gastrin, tissue morphology, and cellular composition of the gastric mucosa. Four lines were generated, with Ctox-7 expressing approximately 50-fold higher Ctox than the other lines. Enhanced cAMP signaling in parietal cells was confirmed by observation of hyperphosphorylation of the protein kinase A-regulated proteins LASP-1 and CREB. Basal acid content was elevated and circulating gastrin was reduced in Ctox transgenic lines. Analysis of gastric morphology revealed a progressive cellular transformation in Ctox-7. Expanded patches of mucous neck cells were observed as early as 3 mo of age, and by 15 mo, extensive mucous cell metaplasia was observed in parallel with almost complete loss of parietal and chief cells. Detection of anti-parietal cell antibodies, inflammatory cell infiltrates, and increased expression of the Th1 cytokine IFN-gamma in Ctox-7 mice suggested that autoimmune destruction of the tissue caused atrophic gastritis. Thus constitutively high parietal cell cAMP results in high acid secretion and a compensatory reduction in circulating gastrin. High Ctox in parietal cells can also induce progressive changes in the cellular architecture of the gastric glands, corresponding to the development of anti-parietal cell antibodies and autoimmune gastritis.

The regulation of acid secretion in the stomach involves a complex network of factors that stimulate secretion in response to the ingestion of a meal and maintain homeostasis of gastric pH. Genetically engineered mouse models have provided a new opportunity to investigate the importance and function of specific molecules and pathways involved in the regulation of acid secretion. Mouse mutants with disruptions in the three major stimulatory pathways for acid secretion in parietal cells, gastrin, histamine, and acetylcholine, have been generated. Disruption of the gastrin pathway results in a major impairment in both basal and induced acid secretion. Histamine and acetylcholine pathway mutants also have significant alterations in acid secretion, although the impairment does not appear to be as severe as in gastrin pathway mutants, perhaps due in part to the hypergastrinemia that occurs. Mice with a disruption in the somatostatin pathway have increased gastric acid secretion, which confirms an important negative regulatory role for this factor. This review discusses these genetically engineered mouse models, as well as others, that provide insight into the complex regulation of in vivo gastric acid secretion. The regulation of growth and cellular morphology of the stomach in these mouse models is also presented. In addition, transgene promoters that are expressed in the gastric epithelium are discussed because these promoters will be important tools to alter cellular physiology in new mouse models in the future.

A quantitative proteomics screen to identify substrates of the Src family of tyrosine kinases (SFKs) whose phosphorylation promotes CrkL-SH2 binding identified the known Crk-associated substrate (Cas) of Src as well as the orphan receptor ESDN. Mutagenesis analysis of ESDN’s seven intracellular tyrosines in YxxP motifs found several contribute to the binding of ESDN to the SH2 domains of both CrkL and a representative SFK Fyn. Quantitative mass spectrometry showed that at least three of these (Y565, Y621 and Y750), as well as non-YxxP Y715, are reversibly phosphorylated. SFK activity was shown to be sufficient, but not required for the interaction between ESDN and the CrkL-SH2 domain. Finally, antibody-mediated ESDN clustering induces ESDN tyrosine phosphorylation and CrkL-SH2 binding.

Gastrin-deficient mice have impaired basal and agonist-stimulated gastric acid secretion. To analyze whether an intrinsic parietal cell defect contributed to the reduced acid secretion, we analyzed parietal cell calcium responses and acid secretory function in vitro. Parietal cells were purified by light-scatter cell sorting and calcium responses to gastrin, histamine, and carbachol were measured in gastrin-deficient and wild-type mice cell preparations. Surprisingly, basal and histamine-induced calcium concentrations were higher in the mutant cell preparations. [14C]aminopyrine uptake analysis in acutely isolated gastric glands revealed that basal acid accumulation was enhanced in gastrin-deficient cell preparations as well as on treatment with carbachol or histamine. These results suggested that an intrinsic parietal cell defect was not responsible for the reduced acid secretion in gastrin-deficient mice. Flow cytometric analysis of dispersed, H+-K+-ATPase-immunostained gastric mucosal preparations revealed a marked increase in parietal cell number in gastrin-deficient mice, which may have accounted for the enhanced in vitro acid secretion detected in this study. Parietal cells were found to be significantly smaller in the mutant cell preparations, suggesting that gastrin stimulation modulates parietal cell morphology.