Molecular and functional relations and intracellular polarized movement of the functional molecules in stomach and intestine.

点击翻译按钮获取中文摘要

We investigated vectorial-transporting mechanisms of gastric acid secretion and intestinal ion-secretion.1. We established the stable cell lines expressing the gastric proton a-and/or B-subunits. The a-subunit was retained in intracellular compartment and was unstable in the absence of β-subunit, but it was stabilized and reached the cell surface in the presence of β-subunit. We found that the extracellular three disulfide bonds of β-subunit are essential for assembly with a-subunit and expression of the pump activity as well as for cell surface delivery of a-subunit. The ubiquitin/proteasome system was involved in degradation of unassembled α-subunits in ER.2. We found that Glu-345 in the fourth transmembrane (M4) segment of the proton pump is involved in cation-induced conformational change in the pump. We also found that Leu-819 and Glu-822 in the M6 segment are involved in K+-dependent dephosphorylation, and that Asp-826, Ile-827 and Leu-833 in the M6 are involved in phosphorylation of the pump.3. We clarified that the binding site of SCH 28080, an acid pump antagonist, is a cavity in the E2 form of the proton pump a-subunit, and Tyr-801 faces the cavity.4. We found that the phospholipid flippase activity is part of the proton pump reaction.5. We confirmed that ClC-2 Cl^-channel is not a Cl^-transporting protein for gastric acid secretion in parietal cells.6. We established new gastric epithelial cell lines expressing proton a-subunit mRNA from mice transgenic for temperature-sensitive simian virus 40 large T antigen.7. We found that thromboxane A2 is involved in the mechanism of secretory diarrhea in colon, and that thromboxane A2 is released only in pathophysiological condition.8. We found that a decrease in Na^+,K^+-ATPase al-isoform expression and an increase in Na^+,K^+-ATPase a3-isoform expression are associated with human colorectal cancer.