A key event in the progression of systemic inflammation resulting from severe trauma or shock involves microvascular hyperpermeability, which leads to excessive plasma fluid and proteins accumulating in extravascular space resulting in tissue edema. The precise molecular mechanism of the hyperpermeability response is not completely understood. Protein tyrosine kinase 6 (PTK6, also known as breast tumor kinase BRK) is a non-receptor tyrosine kinase related to Src-family proteins. Although it has also been shown that PTK6 participates in regulating epithelial barrier function, the role of PTK6 in endothelial barrier function has not been reported. In this study, we hypothesized that PTK6 is (1) expressed in vascular endothelial cells, and (2) contributes to vascular endothelial hyperpermeability in response to TNF alpha. Results showed that PTK6 was detected in mouse endothelial cells at the level of protein and mRNA. In addition, PTK6 knockdown attenuated TNF alpha induced decrease in endothelial barrier function as measured by electric cell-substrate impedance sensing (ECIS) and in vitro transwell albumin-flux assays. Furthermore, we showed that TNF alpha treatment of endothelial cells increased active PTK6 association with p120-catenin at endothelial cell-cell junctions. Further analysis using immunocytochemistry and immunoprecipitation demonstrated that PTK6 knockdown attenuated TNF alpha induced VE-cadherin internalization as well as promoting its association with p120-catenin. Our study demonstrates a novel role of PTK6 in mediating endothelial barrier dysfunction. (C) 2014 Elsevier Inc. All rights reserved.