Membrane-associated CD19-LYN complex is an endogenous p53-independent and Bc1-2-independent regulator of apoptosis in human B-lineage lymphoma cells.

Abstract

CD19 receptor is expressed at high levels on human B-lineage lymphoid cells and is physically associated with the Src protooncogene family protein-tyrosine kinase Lyn. Recent studies indicate that the membrane-associated CD19-Lyn receptor-enzyme complex plays a pivotal role for survival and clonogenicity of immature B-cell precursors from acute lymphoblastic leukemia patients, but its significance for mature B-lineage lymphoid cells (e.g., B-lineage lymphoma cells) is unknown. CD19-associated Lyn kinase can be selectively targeted and inhibited with B43-Gen, a CD19 receptor-specific immunoconjugate containing the naturally occurring protein-tyrosine kinase inhibitor genistein (Gen). We now present experimental evidence that targeting the membrane-associated CD19-Lyn complex in vitro with B43-Gen triggers rapid apoptotic cell death in highly radiation-resistant p53-Bax- Ramos-BT B-lineage lymphoma cells expressing high levels of Bcl-2 protein without affecting the Bcl-2 expression level. The therapeutic potential of this membrane-directed apoptosis induction strategy was examined in a scid mouse xenograft model of radiation-resistant high-grade human B-lineage lymphoma. Remarkably, in vivo treatment of scid mice challenged with an invariably fatal number of Ramos-BT cells with B43-Gen at a dose level < 1/10 the maximum tolerated dose resulted in 70% long-term event-free survival. Taken together, these results provide unprecedented evidence that the membrane-associated anti-apoptotic CD19-Lyn complex may be at least as important as Bcl-2/Bax ratio for survival of lymphoma cells.

Distinctive Functions of Syk and Lyn in Mediating Osmotic Stress- and Ultraviolet C Irradiation-induced Apoptosis in Chicken B Cells

“…Lyn is physically and functionally associated with CD19 (29), and inhibition of Lyn activity by an anti-CD19-genistein immunoconjugate triggers rapid apoptotic cell death in Ramos Burkitt lymphoma cells, suggesting that Lyn in association with CD19 is an important regulator of apoptosis (30). To investigate the specificity or the functional redundancy of PTKs in mediating osmotic stress-induced apoptotic process in DT40 cells, the roles of Lyn in cell apoptosis were examined using established Lyn-deficient (DT40/Lyn Ϫ ) cells.…”

“…Lyn is expressed predominantly in B-lineage cells (28,29), and Lyn in association with CD19 is an important mediator of apoptosis in Ramos Burkitt lymphoma cells (30). These findings led us to examine whether Lyn was involved in mediating the apoptotic response induced by osmotic stress.…”

The SH2 Domain Containing Tyrosine Phosphatase-1 Down-regulates Activation of Lyn and Lyn-induced Tyrosine Phosphorylation of the CD19 Receptor in B Cells

“…-Although the precise profile of effectors that mediate induction of CD19 tyrosine phosphorylation following BCR ligation is unclear, an important role for the Lyn PTK has been suggested by the detection of Lyn kinase activity in anti-CD19 immunoprecipitates and by data implicating the CD19-Lyn complex in regulation of B cell survival (25,26,34). In view of these observations, the kinase activity contained in immunoprecipitates from me/me and me v /me v B cells was next investigated using an in vitro assay of kinase activity.…”

“…The results of these studies confirm that BCR-induced tyrosine phosphorylation of CD19 is enhanced in SHP-1-deficient mice but also suggest that the contribution of SHP-1 to the direct dephosphorylation of CD19 is small. Because of these observations, as well as data revealing CD19 to be associated with the Lyn protein-tyrosine kinase following BCR engagement (25,26) and identifying a central role for Lyn in modifying CD19 effects on B cell survival (33,34), we next investigated the possibility that SHP-1 influence on CD19 tyrosine phosphorylation is mediated via the regulation of Lyn activity. The results of this analysis indicate both BCR-induced tyrosine phosphorylation and activation of the Lyn protein-tyrosine kinase to be markedly augmented in me/me and me v /me v compared with wild-type B cells.…”

Role of Tyrosine Kinases in Induction of the c-junProto-oncogene in Irradiated B-lineage Lymphoid Cells

“…sc-294-G, affinity-purified goat polyclonal IgG, 0.2 mg/ml, Santa Cruz Biotechnology; and anti-JAK-3: C-21, catalog no. sc-513, affinity-purified rabbit polyclonal IgG, 0.2 mg/ml, Santa Cruz Biotechnology); and kinase assays were performed following a 1-h exposure of the immunoprecipitated JAK proteins to the quinazoline compounds, as described in detail elsewhere (20,(22)(23)(24). As shown in Fig.…”