Kidney proximal tubule cells: Epithelial cells without EGTA-extractable annexins?

The expression and the subcellular localizations of annexins I, II, IV, VI, and XIII in renal epithelial cells were investigated, using immunological techniques with specific monoclonal antibodies. Upon performing Western blo tting experiments, no annexins VI and XIII were detected in kidney, whereas annexins I, II, and IV were. Immunofluorescence labelling procedure perfor med on thin frozen renal sections showed the presence of these three annexi ns along the plasma membrane of the collection duct cells with a restricted expression of annexin I at principal cells. Annexin I was also found prese nt in some glomerular cells. None of these annexins, however, were detected in the proximal tubular cells upon performing immunofluorescence labelling and electrophoretic analysis on an EGTA (ethylenebis(oxyethylenenitrilo)te traacetic acid)-extractable annexin fraction prepared from freshly isolated cells. This is the first time a mammalian epithelial cell has been found t o express non-typical annexin (at least partly solubilized with EGTA). Howe ver, when these cells were grown in primary culture, they were found to exp ress annexins I, II, IV, and V. As well as being located along the basolate ral membrane, annexins I and II are also present on vesicles, which suggest s that these annexins may be involved in vesicular traffic under cell cultu re conditions.