Tyrosine-phosphorylated plakoglobin is associated with desmogleins but not desmoplakin after epidermal growth factor receptor activation.

Tyrosine phosphorylation of junctional components has been proposed as a mechanism for modulating cell-cell adhesion. Although a correlation exists between the tyrosine phosphorylation of the adherens junction protein beta-catenin and loss of classical cadherin-mediated adhesion, the effects of tyrosine phosphorylation on the function of the adherens junction and desmosome-associated protein plakoglobin is unknown. In the present study, we investigated the effects of epidermal growth factor receptor (EGFR) tyrosine kinase activation on the subcellular distribution of plakoglobin and its association with its junctional binding partners. Long term epidermal growth factor (EGF) treatment of A431 cells revealed a modest decrease in the cytoskeleton-associated pool of plakoglobin (Pg) and a corresponding increase in the cytosolic pool of Pg. After short term EGF treatment, plakoglobin was rapidly phosphorylated, and tyrosine-phosphorylated Pg was distributed predominantly in a membrane-associated Triton X-100-soluble pool, along with a co-precipitating high molecular weight tyrosine-phosphorylated protein identified as desmoglein 2. Analysis of deletion and point mutants defined the primary EGFR-dependent targets as one or more of three C-terminal tyrosine residues. Whereas phosphorylated Pg remained associated with the desmoglein tail after both short and long term EGFR activation, no phosphorylated Pg was found associated with the N-terminal Pg-binding domain (DPNTP) of the intermediate filament-associated protein, desmoplakin. Together these results are consistent with the possibility that EGF-dependent tyrosine phosphorylation of Pg may modulate cell-cell adhesion by compromising the link between desmosomal cadherins and the intermediate filament cytoskeleton.

Immediate hemodynamic effects of thrombolytic therapy on the ischemic myocardium.

Thrombolytic agents are used to restore coronary artery perfusion and limit the size of a myocardial infarction. The systemic effects of these drugs, streptokinase (SK), urokinase (UK), and recombinant tissue plasminogen activator (rtPA), have been studied extensively. Although their effects on rheology and late myocardial performance have been well-documented to date, there have not been any studies evaluating the acute hemodynamic consequences of thrombolytics immediately after administration. In this report we use an isolated Langendorf rodent heart preparation to evaluate the acute hemodynamic effects of thrombolytic therapy on both the normal and the ischemic myocardium. We quantified performance by documenting cardiac output, coronary blood flow, and blood pressure. Although each thrombolytic agent significantly transiently impairs cardiac performance, differences in effect between the agents were statistically insignificant. This was also the case with both the normal as well as the ischemic myocardium. The results of this study would not support favoring the use of one of these agents over the other with regards to primary myocardial performance.