SOX7 inhibited Wnt/β-catenin activity in K562 cells. (A) DNA (upper) and protein alignment (lower) of SOX7 and SOX7-deleted β-catenin binding site (SOX7Δ). (B) K562 cells nucleofected with β-catenin and either GFP, GFP-SOX7, or GFP-SOX7Δ. Immunoprecipitation (IP) was performed using anti-β-catenin antibody, and both the input lysate and the pull-downs were subjected to western blot analysis using anti-SOX7 antibody. Whole cell lysates of the K562 were also subjected to western blot analysis using anti-β-catenin and SOX7 antibodies, with β-actin as a loading control. GFP-SOX7Δ showed diminished binding to β-catenin as compared to SOX7. SOX7 expression downregulated Wnt/β-catenin activity in K562 (C), THP-1 (D), and MV4-11 cells (E), as enumerated by TOPFlash, normalized with respect to GFP-transduced cells. Deletion of β-catenin binding site in SOX7Δ significantly reduced the inhibitory effects of SOX7 on β-catenin activity. TOPFlash activity in GFP-transduced cells was arbitrarily set as 1 (K562, n = 3; THP-1, n = 4; MV4-11, n = 3 separate experiments). (F) SOX7 overexpression in K562 significantly reduced the active form (nonphosphorylated) of β-catenin, whereas SOX7Δ overexpression had no effect. (G) SOX7 overexpression in THP-1 cells significantly reduced the cellular proliferation, and the effect could be reversed by β-catenin expression. SOX7Δ expression with or without β-catenin had no significant effect.