Polarized localizations of annexins I, II, VI and XIII in epithelial cells of intestinal, hepatic and pancreatic tissues.

The cellular and subcellular localizations of annexins I, II, VI and XIII in the rabbit intestine, liver and pancreas were studied by performing immunofluorescence labeling on thin frozen tissue sections using specific monoclonal antibodies. The expression of annexins was found to be finely regulated. Annexins XIII and I were expressed exclusively in the small intestine and the colon, respectively, whereas annexin II was present in all the tissues tested and annexin VI specifically in the liver and pancreas. These different annexins were concentrated in the basolateral domain of polarized cells, and some of them had an extra-apical localization: annexin XIII was concentrated in the lower 3/4 of enterocyte brush border microvilli; annexin II was present in the upper part of the terminal web in intestinal absorbent cells as well as in the bile canalicular area in hepatocytes, whereas annexin VI was detected on some apical vesicles concentrated around the bile canaliculi. In pancreatic acinar cells, the presence of annexin II on some zymogen granules provides further evidence that annexin II may be involved in exocytic events. In conclusion, this study shows that the basolateral domain of polarized cells appears to be the main site where annexins are located, and they may therefore be involved in the important cellular events occurring at this level.