Fourth, in WC5 cells transformed by temperature-sensitive v-Src and expressing E-cadherin ectopically, immunoprecipitates of PTP from lysates of cells cultured in the nonpermissive temperature contained coprecipitating cadherin, whereas in the permissive temperature the levels of connected cadherin were reduced substantially (Fig. were associated with dissociation of PTP from your complex. Furthermore, we have demonstrated the COOH-terminal 38 residues of the cytoplasmic section of E-cadherin was required for association with PTP in WC5 cells. Zondag et al. (Zondag, G., W. Moolenaar, and M. Gebbink. 1996. 134: 1513C1517) have asserted the association we observed between PTP and the cadherinCcatenin complex in immunoprecipitates of the phosphatase arises from nonspecific cross-reactivity between BK2, our antibody to PTP, and cadherins. With this study we have confirmed our initial observation and shown the presence of cadherin in immunoprecipitates of PTP acquired with three antibodies that recognize unique epitopes in the phosphatase. In addition, we have shown directly the anti-PTP antibody BK2 that we used initially did not cross-react with cadherin. Our data reinforce the observation of an connection between PTP and E-cadherin in vitro and in vivo, further emphasizing the potential importance of reversible tyrosine phosphorylation in regulating cadherin function. The cadherins are a major family of calcium-dependent, homophilic cell adhesion molecules that are concentrated at specialized contact points in the cell termed adherens junctions (for review observe Gumbiner, 1996). The cadherins are transmembrane proteins that possess an extracellular section, characterized by the presence of calcium-binding motifs, and an intracellular section that is highly conserved between members of the family (for shikonofuran A review observe Takeichi, 1995). The intracellular section serves as the site of connection with proteins termed catenins (-, -, and -catenin) (for review observe Gumbiner, 1995). It appears that -catenin and -catenin/ plakoglobin, which are related to the product of the section polarity gene for 5 min and processed for immunoprecipitation and immunoblotting as explained below. Antibodies Hybridoma cells expressing a rat monoclonal antibody against the extracellular website of E-cadherin, ECCD-2 (Shiroyashi et al., 1986), were generously provided by Masatoshi Takeichi. Conditioned medium from these cells was used in our experiments. A mouse monoclonal antibody to E-cadherin, antibodies to -catenin, and antiphosphotyrosine antibody (PY20) were purchased from Transduction Labs (Lexington, KY). In the course of our experiments involving antibody acknowledgement of E-cadherin fusion proteins, we identified the antiCE-cadherin antibody from Transduction Labs identified the juxtamembrane half of the intracellular section. Pan-cadherin antibodies (monoclonal and polyclonal), which react with the conserved COOH-terminal 24 amino acids of the cadherin cytoplasmic section, were purchased from (St. Louis, MO). The cadherin-4 antibody (120A) was generously provided by ICOS Corp. (Seattle, WA). Antibody to N-cadherin (BD7873) was generously provided by Dr. J. Hemperly at Labs (Res. Triangle Park, NC) and has been explained previously (Payne et al., 1996). Monoclonal antibodies to the intracellular section of PTP (SK series) and monoclonal antibody BK-2, generated against a peptide derived from the extracellular section of PTP, have been explained previously (Brady-Kalnay et al., 1993; Brady-Kalnay and Tonks 1994). Polyclonal antibodies to glutathione S transferase (GST) (Brady-Kalnay et al., 1995) and the FG6 monoclonal antibody to PTP1B (Flint et al., 1993) have been explained previously. Binding Assays In Vitro The GST fusion protein of the extracellular section of PTP (EXTRA-PTP) has been explained previously (Brady-Kalnay et al., 1993). Two GST/E-cadherin fusion proteins were generated that contain either amino shikonofuran A acids 572C631 (the juxtamembrane-half of the cytoplasmic section, JM E-cad) or amino acids 648C729 (the COOH-terminal, catenin-binding portion of the intracellular section, CB E-cad). Proteins were indicated in and purified using glutathione Sepharose (Brady-Kalnay et al., 1995). In slot blot analyses, purified protein samples were adsorbed to nitrocellulose mounted in a slot blot apparatus (Bio-Rad Laboratories, Hercules, CA). The nitrocellulose strip was clogged in 5% nonfat dry milk in TTBS (20 mM Tris-Cl, pH 7.5, 660 mM NaCl, 0.05% Tween-20) and then incubated with primary antibody for 16 h at 4C. The blot was washed in TTBS and then developed using horseradish peroxidaseCconjugated secondary antibodies and TNFSF4 Enhanced Chemiluminescence reagents (and illustrate a series of immunoprecipitates that have been blotted with the ECCD-2 shikonofuran A antibody to the extracellular section of E-cadherin. (and pan-cadherin), ( em D /em ) antibody to the intracellular section of PTP (SK15), or ( em E /em ) the BK2 antibody the extracellular section of PTP. The data illustrate the BK2 antibody does not cross-react with the intracellular section of E-cadherin, which is the portion of E-cadherin required for association with PTP. Conversation Components of adherens junctions are subjected to quick, reversible tyrosine phosphorylation inside a cellular context (Volberg et al., 1991). Tyrosine phosphorylation of the cadherinCcatenin complex has been observed under a variety of conditions, including in response to oncoprotein PTKs, such as Src (Matsuyoshi et al., 1992; Behrens et al., 1993), or to oncogenic forms of.