The establishment of epithelial cell polarity correlates with the formation of specialized cell-cell junctions and striking changes in the organization of microtubules. A significant fraction of the microtubules in MDCK cells become stabilized, noncentrosomally organized, and arranged in longitudinal bundles in the apical-basal axis. This correlation suggests a functional link between cell-cell junction formation and control of microtubule organization. We have followed the distribution of pp170, a recently described microtubule-binding protein, during establishment of epithelial cell polarity. This protein shows the typical patchy distribution along microtubules in subconfluent fibroblasts and epithelial cells, often associated with the peripheral ends of a subpopulation of microtubules. In contrast to its localization in confluent fibroblasts (A72) and HeLa cells, however, pp170 accumulates in patches delineating the regions of cell-cell contacts in confluent polarizing epithelial cells (MDCK and Caco-2). Double immunolocalization with antibodies specific for cell-cell junction proteins, confocal microscopy, and immunoelectron microscopy on polarized MDCK cells suggest that pp170 accumulates at desmosomal plaques. Furthermore, microtubules and desmosomes are found in close contact. Maintenance of the desmosomal association of pp170 is dependent on intact microtubules in 3-d-old, but not in 1-d-old MDCK cell cultures. This suggests a regulated interaction between microtubules and desmosomes and a role for pp170 in the control of changes in the properties of microtubules induced by epithelial cell-cell junction formation.
Epithelial Cell Polarity From the Outside Looking In