Drebrin is a widespread actin-associating protein enriched at junctional plaques, defining a specific microfilament anchorage system in polar epithelial cells

Using immunoblotting, immunprecipitation with subsequent fragment mass spec trometry, and immunolocalization techniques, we have detected the actin-bin ding ca. 120-kDa protein drebrin, originally identified in - and thought to be specific for - neuronal cells, in diverse kinds of human and bovine non neuronal cells. Drebrin has been found in numerous cell culture lines and i n many tissues of epithelial, endothelial, smooth muscle and neural origin but not in, for example, cardiac, skeletal and certain types of smooth musc le cells, in hepatocytes and in the human epithelium-derived cell culture l ine A-431, By double-label fluorescence microscopy we have found drebrin en riched in actin microfilament bundles associated,vith plaques of cell-cell contact sites representing adhering junctions. These drebrin-positive, adhe ring junction-associated bundles, however, are not identical with the vincu lin-containing, junction-attached bundles, and in the same cell both subtyp es of microfilament-anchoring plaques are readily distinguished by immunolo calization comparing drebrin and vinculin, The intracellular distribution o f the drebrin- and the vinculin-based microfilament systems has been studie d in detail by confocal fluorescence laser scanning microscopy in monolayer s of the polar epithelial cell lines, MCF-7 and PLC, and drebrin has been f ound to be totally and selectively absent in the notoriously vinculin-rich focal adhesions. The occurrence and the possible functions of drebrin in no n-neuronal cells, notably epithelial cells, and the significance of the exi stence of two different actin-anchoring junctional plaques is discussed.