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

We investigated the localization of receptor-type protein-tyrosine phosphat ase mu (RPTP mu) in tissues by immunofluorescence. RPTP mu immunoreactivity was found almost exclusively within vascular endothelial cells. RPTP mu wa s more abundant in the arterial tree than in the venous circulation. This p attern 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 nonend othelial cell lines, RPTP mu was exclusively at the lateral aspects of endo thelial 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: bronc hial and biliary epithelia and cardiocytes (intercalated discs). Our result s identify RPTP mu as a new marker of endothelial cell heterogeneity and su ggest a possible role in endothelial-specific functions, involving cell-cel l contact. (C) 1999 Academic Press.