SMURF1 is associated with CD44 surface expression in sphere-derived cells (SDCs). (A) Flow cytometry analysis of SDCs showing a positive correlation (qualitatively represented by the grey arrow) between CD44 cell surface and intracellular SMURF1 protein expression. Cells were co-stained with fluorescently labeled anti-CD44 (APC) and anti-SMURF1 (Pacific Blue) and the total population is shown. Isotype staining control is shown in B. (B) Gating strategy used to define the CD44high (top ~10%) and CD44low (lower ~10%) SDC populations. (C) Histograms of SMURF1 expression in CD44low and CD44high populations based on the gates drawn in B. The data shown are representative of at least three repeats for each cell line (TR146, left column; SCC-58, middle column; UMSCC-17B, right column).