Abstract
B-cell acute lymphoblastic leukemia (B-ALL) is immune to the chemotherapy-induced apoptosis as a result of the protection of bone marrow mesenchymal stromal cells (BMSCs). However, the precise underlying mechanism of such protection remains unclear so far. In this experiment, protein tyrosine phosphatase 2 (Shp2), which was encoded by the PTPN11 gene, was highly expressed in BMSCs of the newly diagnosed and the recurrent B-ALL patients. The plasmid-induced (including Shp2 E76K) Shp2 activation in BMSCs (Shp2-activated BMSCs) markedly increased the BMSCs-mediated resistance of leukemia cells both in vitro and in vivo. Additionally, studies in vitro suggested that, the expression of vascular cell adhesion molecule 1 (VCAM-1) was markedly up-regulated in Shp2-activated BMSCs, and VCAM-1 expression in BMSCs of B-ALL patients was negatively correlated with Shp2 expression. Down-regulation of VCAM-1 in BMSCs using siRNA reversed the resistance of CCRF-SB cells mediated by the Shp2-activated BMSCs. As for the molecular mechanism, the PI3K/AKT pathway mediated the regulation of VCAM-1 by Shp2. Blocking the very late antigen-4 (VLA-4) by antibodies in CCRF-SB cells dramatically reversed the resistance of CCRF-SB cells mediated by the Shp2-activated BMSCs, and decreased the adhesion effects of both CCRF-SB cells and BMSCs. In conclusion, Shp2 activation in BMSCs up-regulates VCAM-1 expression through increasing the PI3K/AKT phosphorylation level, and targeting the VCAM-1/VLA-4 signaling may serve as a clinically relevant mechanism to overcome the BMSCs-mediated chemoresistance of B-ALL cells.