ZAP70 and acute lymphoblastic leukemia: Specifically, zeta-chain-associated protein kinase 70 (ZAP70) up-regulated CXCR4 expression through ERK1/2 signaling and guided CXCR4 migration to ligand, thus resulting in more severe CNS involvement in T-ALL patients with high ZAP70 and CXCR4 expression 92.