VLA-4 Induces Chemoresistance of T Cell Acute Lymphoblastic Leukemia Cells via PYK2-Mediated Drug Efflux.

Cell adhesion plays a critical role in the development of chemoresistance, which is a major issue in anti-cancer therapies. In this study, we have examined the role of the VLA-4 integrin, a major adhesion molecule of the immune system, in the chemoresistance of T-ALL cells. We found that attachment of Jurkat and HSB-2 T-ALL cells to VCAM-1, a VLA-4 ligand, inhibits doxorubicin-induced apoptosis. However, their adhesion to fibronectin, which is mainly mediated via VLA-5, had no effect. Even the presence of the chemoattractant SDF1α (Stromal cell-derived factor-1α), which enhances the adhesion of T-ALL cells to fibronectin, did not modify the sensitivity of the cells attached on fibronectin towards doxorubicin-induced apoptosis. Mechanistically, we found that VLA-4 promoted T-ALL chemoresistance by inducing doxorubicin efflux. Our results showed that cell adhesion to both fibronectin and VCAM-1-induced Focal adhesion kinase (FAK) phosphorylation in T-ALL cells. However, only cell adhesion to VCAM-1 led to PYK2 phosphorylation. Inhibition studies indicated that FAK is not involved in doxorubicin efflux and chemoresistance, whereas PYK2 inhibition abrogated both VLA-4-induced doxorubicin efflux and chemoresistance. Together, these results indicate that the VLA-4/PYK2 pathway could participate in T-ALL chemoresistance and its targeting could be beneficial to limit/avoid chemoresistance and patient relapse.