Lack of association between receptor protein tyrosine phosphatase RPTPμ and cadherins

Abstract

RPTPμ is a receptor-like protein tyrosine phosphatase that mediates homophilic cell-cell interactions. Surface expression of RPTPμ is restricted to cell-cell contacts and is upregulated with increasing cell density, suggesting a role for RPTPμ in contact-mediated signaling. It was recently reported (Brady-Kalnay, S.M., D.L. Rimm, and N.K. Tonks. 1995. J. Cell Biol. 130:977-986) that RPTPμ binds directly to cadherin/catenin complexes, and thus may regulate the tyrosine phosphorylation of such complexes. Here we report that this concept needs revision. Through reciprocal precipitations using a variety of antibodies against RPTPμ, cadherins, and catenins, we show that RPTPμ does not interact with cadherin/catenin complexes, even when assayed under very mild lysis conditions. We find that the anti-RPTPμ antiserum used by others precipitates cadherins in a nonspecific manner independent of RPTPμ. We conclude that, contrary to previous claims, RPTPμ does not interact with cadherin complexes and thus is unlikely to directly regulate cadherin/catenin function.