Receptor-type protein-tyrosine phosphatase mu is expressed in specific vascular endothelial beds in vivo

We investigated the localization of receptor-type protein-tyrosine phosphatase mu (RPTP mu) in tissues by immunofluorescence. RPTP mu immunoreactivity was found almost exclusively within vascular endothelial cells. RPTP mu was more abundant in the arterial tree than in the venous circulation. This pattern of expression was opposite to that of the von Willebrand factor and demonstrated a lack of difference in expression of VE-cadherin. RPTP mu was undetectable in the endocardium, In agreement with previous work on nonendothelial cell lines, RPTP mu was exclusively at the lateral aspects of endothelial cells in vivo and at cell-cell contacts as well as ex vivo in two- or three-dimensional endothelial cell cultures, and expression levels were upregulated by cell density. RPTP mu was detected in few other cells: bronchial and biliary epithelia and cardiocytes (intercalated discs). Our results identify RPTP mu as a new marker of endothelial cell heterogeneity and suggest a possible role in endothelial-specific functions, involving cell-cell contact. (C) 1999 Academic Press