Distribution of Hepatocyte Growth Factor Activator Inhibitor Type 1 (HAI-1) in Human Tissues: Cellular Surface Localization of HAI-1 in Simple Columnar Epithelium and Its Modulated Expression in Injured and Regenerative Tissues

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Abstract
We used a specific monoclonal antibody to human hepatocyte growth factor activator inhibitor type 1 (HAI-1) in immunohistochemical procedures to determine the distribution and localization of HAI-1 in human tissues. In normal adult tissues, HAI-1 was predominantly expressed in the simple columnar epithelium of the ducts, tubules, and mucosal surface of various organs. In all cases, HAI-1 was localized predominantly on the cellular lateral (or basolateral) surface. By contrast, hepatocytes, acinar cells, endocrine cells, stromal mesenchymal cells, and inflammatory cells were hardly stainable with the antibody, and stratified squamous epithelium showed only faint immunoreactivity on the surface of cells of the basal layer. In the gastrointestinal tract, the surface epithelium was strongly stained. RNA blot analysis confirmed the presence of specific mRNA transcript in the gastrointestinal mucosa, and in situ hybridization revealed that HAI-1 mRNA showed a similar cellular distribution pattern. Although HAI-1 was not expressed in normal hepatocytes, strong immunoreactivity was observed on the epithelium of pseudo-bile ducts and on the surface of scattered hepatocytes in fulminant hepatitis. The enhanced expression was also noted in regenerating tubule epithelial cells of the kidney after infarction. We conclude that HAI-1 is preferentially expressed in the simple columnar epithelium of the mucosal surface and duct, that the predominant localization of HAI-1 is the cell surface, and that the expression of HAI-1 can be modulated by tissue injury and regeneration.

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