MOLECULAR ENVIRONMENT OF ZO-1 IN EPITHELIAL AND NONEPITHELIAL CELLS

We previously reported the expression of ZO-1 in cell types that do no t form tight junctions. Here we compare the molecular environments of ZO-1 in epithelial cells, primary cultures of astrocytes and in the no n-epithelial S180 sarcoma cell line. ZO-1 co-localizes with a subset o f actin filaments in all cell types. In astrocytes, ZO-1 is found conc entrated in discrete bands at points of cell-cell contact. Indirect im munofluorescent microscopy shows that these bands of ZO-1 co-localize with the adherens junction proteins vinculin and alpha-actinin, and wi th the antigen recognized by a pan-cadherin antibody. In contrast, ZO- 1 in S180 cells, which exhibit limited cell-cell interactions, is diff usely distributed over the plasma membrane, with concentrations in lam ellipodia where actin filaments accumulate. ZO-1 does not co-localize with vinculin at focal adhesions in this cell type. Analysis of ZO-1 i mmunoprecipitation profiles from different cell types, performed under conditions previously demonstrated to maintain interactions between Z O-1, ZO-2 and p130 from the MDCK epithelial cell line, show that the p roteins which co-precipitate with ZO-1 vary with cell type. Precipitat ion of polypeptides at 165 kDa, potentially ZO-2, and 65 kDa occurs in both a mouse kidney tubule epithelial cell line and the non-epithelia l S180 cells. No proteins specifically associate with ZO-1 immunopreci pitated from astrocytes. Spectrin, alpha-actinin, vinculin and cadheri n are not detected in immunoblots of ZO-1 immunoprecipitates from any cell type. (C) 1995 Wiley-Liss, Inc.