RGS-5 is specifically up-regulated in perivascular cells of RIP1-Tag5 tumors. Endothelial cells (CD31⁺, ME-9F1⁺) and PDGFR-β⁺ cells were separated from end-stage RIP1-Tag5 tumors by flow cytometry. (A) Total RNA from isolated cells was analyzed for marker gene expression to confirm endothelial cell or pericyte phenotypes. αSMA expression in the endothelial cell fraction most likely indicates the presence of some perivascular cells, which remain attached to endothelial cells during purification. (B) Relative RGS-5 expression was quantified for each cell population and compared to RGS-5 expression in total RNA prepared from whole tumors (–RT indicates minus reverse transcriptase control). Expression levels in panels A and B were normalized to HPRT as an internal standard. In situ hybridization, followed by immunohistochemistry shows colocalization of the pericyte marker desmin (green) with RGS-5 transcripts (red) in panel C, but in panel D no perfect match was seen with RGS-5 (red) and the endothelial cell marker CD31 (green) in RIP1-Tag5 tumor vessels (original magnification × 16).