Dkk1 targets β-catenin in MDSCs and correlates with CD15 myeloid marker. (A and B) LRP5 and LRP6 mRNA expression in MDSCs isolated from LLC tumor-bearing mice 14 d after tumor injection (A), or in Gr1⁺/CD11b⁺ naive cells incubated in vitro in the presence or absence of 10% serum from tumor-bearing mice (B). Mean ± SD (n = 3 mice/group) *, P < 0.05; **, P < 0.01. (C) Western blot analysis of β-catenin in Gr1⁺/CD11b⁺ naive cells cultured for 6 h in medium containing 10% serum from tumor-bearing mice in the presence of rDkk1 (100 ng/ml) or anti-Dkk1 (100 ng/ml). One representative experiment of three is shown. (D) LEF1, TCF4, and Axin2 mRNA levels were measured in cells as in B. Mean ± SD from three independent experiments. *, P < 0.05. (E–H) LEF1 and TCF4 mRNA levels were measured in CD33⁺ PBMCs isolated from healthy donors, cultured in the presence of 10% serum from cancer patients and stimulated in vitro with rDkk1 (100 ng/ml; E and F) or incubated with anti-Dkk1 (100 ng/ml; G and H). Representative graphs from seven different donors are shown. Experiment was repeated more than three times. (I) Representative IHC from pancreatic cancer tissues with high or low Dkk1 expression is shown. CD15 staining, as a marker of granulocytic MDSCs, is also shown. (J) Correlation between CD15⁺ cell numbers and Dkk1 pixel density from 55 pancreatic cancer tissues is shown (Spearman’s r = 0.27; P = 0.04).