LACK OF ASSOCIATION BETWEEN RECEPTOR PROTEIN-TYROSINE-PHOSPHATASE RPTP-MU AND CADHERINS

RPTP mu is a receptor-like protein tyrosine phosphatase that mediates hemophilic cell-cell interactions. Surface expression of RPTP mu is re stricted to cell-cell contacts and is upregulated with increasing cell density, suggesting a role for RPTP mu in contact-mediated signaling. It was recently reported (Brady-Kalnay, S.M., D.L. Rimm, and N.K. Ton ks. 1995. J. Cell Biol. 130:977-986) that RPTP mu binds directly to ca dherin/catenin complexes, and thus may regulate the tyrosine phosphory lation of such complexes. Here we report that this concept needs revis ion. Through reciprocal precipitations using a variety of antibodies a gainst RPTP mu, cadherins, and catenins, we show that RPTP mu does not interact with cadherin/catenin complexes, even when assayed under ver y mild lysis conditions. We find that the anti-RPTP mu, antiserum used by others precipitates cadherins in a nonspecific manner independent of RPTP mu. We conclude that, contrary to previous claims, RPTP mu doe s not interact with cadherin complexes and thus is unlikely to directl y regulate cadherin/catenin function.