ZAP-70 Expression in Chronic Lymphocytic Leukemia Is Associated with Altered Signal Transduction.

Abstract B-cell chronic lymphocytic leukemia (CLL) is a malignancy of mature B-cells with a variable clinical course. Given the heterogeneity of disease course, identification of prognostic factors is imperative. One recently identified negative prognostic indicator in CLL is the T-cell tyrosine kinase ZAP70. ZAP70 is analogous to, and can functionally substitute for, the B-cell tyrosine kinase Syk and is activated following B cell receptor (BCR) crosslinking in CLL cells. However, the role of ZAP70 expression in CLL remains elusive. Utilizing flow cytometric analyses of signal transduction molecules, this study examined if ZAP70 expression affects signal transduction in CLL. Peripheral blood samples from ZAP70+ and ZAP70− CLL patients were analyzed. The levels of phosphorylated ERK, STAT5, and S6 (p-ERK, p-STAT5, p-S6) were measured by flow cytometry with and without BCR stimulation. Kinase inhibitors were used to verify the measured phosphorlyated protein levels. Increased constitutive levels of p-ERK, p-STAT5, and p-S6 were seen in ZAP70+ CLL cells as compared to ZAP70− CLL cells. BCR crosslinking gave variable responses in both ZAP70+ and ZAP70− CLL. The majority of ZAP70− cases showed no significant activation or a predominant activation of ERK with rare p-S6 activation. ZAP70+ cells showed activation of either, or both, ERK and S6 pathways and fewer showing no activation. In summary, though the role of ZAP70 in B cell signaling is poorly understood, expression of ZAP70 in CLL correlates with a constitutively active phenotype. Additionally, differential response in ZAP70+ versus ZAP70− cases following BCR crosslinking suggests a possible modulatory role of the BCR pathway. Current studies are underway to determine if these measures carry prognostic information and if the varying signal responses to BCR stimulation correlate with reported differences in apoptotic versus proliferative response.