LCK Is an Important Mediator of B-Cell Receptor Signaling in Chronic Lymphocytic Leukemia Cells

Abstract

B-cell receptor (BCR) signals promote survival of chronic lymphocytic leukemia (CLL) cells, and it is believed that overexpressed and constitutively active Lyn mediates this signaling. Here, we show that CLL cells express lymphocyte-specific protein tyrosine kinase (LCK) and that inhibition of this Src family tyrosine kinase with the specific inhibitor [4-amino-5-(4-phenoxyphenyl)-7H-pyrrolo[3,2-d]pyrimidin-7-yl-cyclopentane (Lck-i)], or reduction of its expression with siRNA, blocks the induction of CD79a, Syk, inhibitor of IkB kinase (IKK), Akt, and extracellular signal-regulated kinase (ERK) phosphorylation by BCR cross-linking in these cells. Furthermore, we show that CLL cells with high levels of LCK expression have higher levels of BCR-mediated IKK, Akt, and ERK phosphorylation as well as cell survival than CLL cells with low levels of LCK expression. We also show that treatment of CLL cells with Lck-i inhibits BCR cross-linking-induced cell survival. Taken together, these data show a major role for LCK in proximal and distal BCR-mediated signaling in CLL cells and suggest that LCK expression is important in the pathogenesis of this disease. On a clinical level, these studies advocate the use of specific LCK inhibitors in the treatment of progressive CLL. Mol Cancer Res; 11(5); 541-54. Ó2013 AACR.

SLP76 integrates into the B-cell receptor signaling cascade in chronic lymphocytic leukemia cells and is associated with an aggressive disease course

“…Due to the critical role of LCK in TCR upstream signaling, and its ectopic expression in CLL cells, we also determined its role in the activation of SLP76 after BCR triggering. LCKi, a highly selective inhibitor of LCK that does not affect LYN activity, 32 reduced SLP76 phosphorylation in response to BCR engagement to baseline level ( Figure 3C). The clinicallyused SYK inhibitor R406 completely abolished SLP76 phosphorylation ( Figure 3D), in a manner similar to the activity of SYKII ( Figure 3A).…”

“…For inhibition assays, cells were incubated prior to IgM stimulation in the absence or presence of the following: 10 mM PP2 for 15 min, 10 mM SYK inhibitor II for 15 min, 0.5 mM ibrutinib for 1 h, 20 mM cytochalasin B for 30 min, 10 mM MβCD for 30 min, 40, 200, and 1000 nM LCK inhibitor for 2 h, and 0.2, 1, and 5 mM R406 for 30 min. These concentrations were chosen on the basis of previous publications, 32,[34][35][36][37] and in this study were titrated to obtain a maximal effect without killing the cells. Inhibitors were dissolved in dimethylsulfoxide, while controls were treated accordingly with dimethylsulfoxide.…”

“…However, both LCK and SYK participate in the upstream signaling of SLP76 in CLL cells, as evident from the inhibition of SLP76 tyrosine phosphorylation using inhibitors directed to LCK or Syk. 30,32 In addition, SYK but not LCK, appears to maintain a basal level of SLP76 phosphorylation independently of BCR engagement. Our findings are compatible with previous reports which show that SLP76 is phosphorylated in a SYK-dependent manner in several non-T-cell subtypes.…”

“…30 Formation of the SLP76-LAT multimolecular complex allows proximity between the signaling molecules and facilitates an efficient propagation of various TCR signaling processes. 30 Since CLL cells express ZAP-70 and LCK, 15,16,31,32 we examined whether they also express additional TCR-associated molecules. Here we report, for the first time, the aberrant expression of SLP76 in CLL cells, which plays a role in the BCR signaling pathway and correlates with an aggressive clinical course.…”

SAP Facilitates Recruitment and Activation of LCK at NTB-A Receptors during Restimulation-Induced Cell Death

“…FYN is the major Src-family kinase shown to mediate signal transduction of SLAM-Rs (including NTB-A) in thymocytes and NK cells (13)(14)(15)(16)(17)(18)(19)(20). To examine the role of both FYN and LCK in RICD, we first used highly selective inhibitors for FYN (SU6656) (21) or LCK [LCK inhibitor I (LCKi)] (22). Surprisingly, inhibition of FYN did not affect RICD (Fig.…”