Tyrosine-phosphorylated plakoglobin is associated with desmogleins but notdesmoplakin after epidermal growth factor receptor activation

Tyrosine phosphorylation of junctional components has been proposed as a me chanism for modulating cell-cell adhesion. Although a correlation exists be tween the tyrosine phosphorylation of the adherens junction protein beta -c atenin and loss of classical cadherin-mediated adhesion, the effects of tyr osine phosphorylation on the function of the adherens junction and desmosom e-associated protein plakoglobin is unknown. In the present study, we inves tigated the effects of epidermal growth factor receptor (EGFR) tyrosine kin ase activation on the subcellular distribution of plakoglobin and its assoc iation with its junctional binding partners. Long term epidermal growth fac tor (EGF) treatment of A431 cells revealed a modest decrease in the cytoske leton-associated pool of plakoglobin (Pg) and a corresponding increase in t he cytosolic pool of Pg. After short term EGF treatment, plakoglobin was ra pidly phosphorylated, and tyrosine-phosphorylated Pg was distributed predom inantly in a membrane-associated Triton X-100-soluble pool, along with a co -precipitating high molecular weight tyrosine-phosphorylated protein identi fied as desmoglein 2, Analysis of deletion and point mutants defined the pr imary EGFR-dependent targets as one or more of three C-terminal tyrosine re sidues. Whereas phosphorylated Pg remained associated with the desmoglein t ail after both short and long term EGFR activation, no phosphorylated Pg wa s found associated with the N-terminal Pg-binding domain (DPNTP) of the int ermediate filament-associated protein, desmoplakin, Together these results are consistent with the possibility that EGF-dependent tyrosine phosphoryla tion of Pg may modulate cell-cell adhesion by compromising the link between desmosomal cadherins and the intermediate filament cytoskeleton.