Figure 6. PTN promotes OS resistance to DOX by upregulating MDR1/P-gp through the ALK/GSK3β/β-catenin signaling pathway.

(A) The protein levels of ALK, β-catenin, MDR1/P-gp and p-GSK3β were higher in DOX-resistant MG63/DOX cells than in parental MG63 cells (left). PTN knockdown reduced the expression of these molecules in MG63 (middle) and MG63/DOX (right) cells, while PTN overexpression enhanced their expression in MG63 cells (middle) (β-actin was used as the reference protein). (B) β-catenin and MDR1/P-gp levels were reduced in MG63 (left panel) and MG63/DOX (right panel) cells treated with the β-catenin inhibitor XAV939, and supplementation with rhPTN could not reverse these effects (β-actin was used as the reference protein). (C, D) XAV939 impaired the chemoresistance to DOX in MG63 (C) and MG63/DOX (D) cells, and supplementation with rhPTN could not reverse this effect. (E) In rhPTN-treated MG63 (left) and MG63/DOX (right) cells, XAV939 reduced the expression of β-catenin and MDR1/P-gp, while the MDR1/P-gp inhibitor Verapamil only reduced the expression of MDR1/P-gp (β-actin was used as the reference protein). (F, G) rhPTN enhanced the resistance to DOX in MG63 (F) and MG63/DOX (G) cells, while XAV939 and Verapamil could equally reverse this effect. *, p<0.05. PTN: pleiotrophin; ALK: anaplastic lymphoma kinase; MDR1/P-gp: multidrug resistance protein 1/P-glycoprotein; OS: osteosarcoma; DOX: doxorubicin; rhPTN: recombinant human pleiotrophin; sh: short hairpin; oe: overexpression; NS: not significant.