ATRA decreases cell surface S100A10 levels. NB4 cells were treated with 1μM ATRA or a vehicle control for the indicated times. Cell lysates were prepared, and total levels of S100A10, annexin A2, or α-enolase were examined by Western blotting with the use of actin as a loading control (A). Flow cytometric analysis of cell surface S100A10 (B) and annexin A2 (C) in ATRA-treated NB4 cells. Cells were incubated with anti-S100A10 and anti–annexin A2 antibodies. Quantification of flow cytometric analysis of cell surface S100A10 and annexin A2 in NB4 cells was calculated with WinMDI software (**P < .01 and ***P < .001). NB4 cells treated with ATRA for 5 days were incubated with Sulfo-NHS-SS-biotin and lysed, and the biotinylated (cell surface) proteins were collected with streptavidin beads and subjected to SDS-PAGE and Western blotting for S100A10, annexin A2 (D).