RESUMEN
Vav1 exhibits two signal transducing properties as an adaptor protein and a regulator of cytoskeleton organization through its Guanine nucleotide Exchange Factor module. Although the expression of Vav1 is restricted to the hematopoietic lineage, its ectopic expression has been unraveled in a number of solid tumors. In this study, we show that in lung cancer cells, as such in hematopoietic cells, Vav1 interacts with the Spleen Tyrosine Kinase, Syk. Likewise, Syk interacts with ß-catenin and, together with Vav1, regulates the phosphorylation status of ß-catenin. Depletion of Vav1, Syk or ß-catenin inhibits Rac1 activity and decreases cell migration suggesting the interplay of the three effectors to a common signaling pathway. This model is further supported by the finding that in turn, ß-catenin regulates the transcription of Syk gene expression. This study highlights the elaborated connection between Vav1, Syk and ß-catenin and the contribution of the trio to cell migration.
Asunto(s)
Neoplasias Pulmonares , beta Catenina/metabolismo , Proteínas Adaptadoras Transductoras de Señales/metabolismo , Humanos , Fosforilación , Proteínas Proto-Oncogénicas c-vav/genética , Transducción de Señal , Quinasa Syk/metabolismoRESUMEN
In Chronic Lymphocytic Leukemia (CLL), infiltration of lymph nodes by leukemic cells is observed in patients with progressive disease and adverse outcome. We have previously demonstrated that B-cell receptor (BCR) engagement resulted in CXCR4 down-regulation in CLL cells, correlating with a shorter progression-free survival in patients. In this study, we show a simultaneous down-regulation of CXCR4, CXCR5 and CD62L upon BCR triggering. While concomitant CXCR4 and CXCR5 down-regulation involves PKDs, CD62L release relies on PKC activation. BCR engagement induces PI3K-δ-dependent phosphorylation of PKD2 and 3, which in turn phosphorylate CXCR4 Ser324/325. Moreover, upon BCR triggering, PKD phosphorylation levels correlate with the extent of membrane CXCR4 decrease. Inhibition of PKD activity restores membrane expression of CXCR4 and migration towards CXCL12 in BCR-responsive cells in vitro. In terms of pathophysiology, BCR-dependent CXCR4 down-regulation is observed in leukemic cells from patients with enlarged lymph nodes, irrespective of their IGHV mutational status. Taken together, our results demonstrate that PKD-mediated CXCR4 internalization induced by BCR engagement in B-CLL is associated with lymph node enlargement and suggest PKD as a potential druggable target for CLL therapeutics.
Asunto(s)
Leucemia Linfocítica Crónica de Células B/genética , Linfadenopatía/genética , Proteína Quinasa C/fisiología , Proteínas Proto-Oncogénicas c-bcr/genética , Receptores CXCR4/genética , Receptores CXCR4/metabolismo , Linfocitos B/metabolismo , Regulación hacia Abajo/genética , Regulación Leucémica de la Expresión Génica , Humanos , Leucemia Linfocítica Crónica de Células B/complicaciones , Leucemia Linfocítica Crónica de Células B/metabolismo , Leucemia Linfocítica Crónica de Células B/patología , Linfadenopatía/complicaciones , Linfadenopatía/metabolismo , Linfadenopatía/patología , Fosforilación , Proteínas Proto-Oncogénicas c-bcr/metabolismo , Transducción de Señal/fisiología , Células Tumorales CultivadasRESUMEN
Vav family members function as remarkable scaffold proteins that exhibit both GDP/GTP exchange activity for Rho/Rac GTPases and numerous protein-protein interactions via three adaptor Src-homology domains. The exchange activity is under the unique regulation by phosphorylation of tyrosine residues hidden by intra-molecular interactions. Deletion of the autoinhibitory N-terminal region results in an oncogenic protein, onco-Vav, leading to a potent activation of Rac GTPases whereas the proto-oncogene barely leads to transformation. Substitution of conserved residues of the SH2-SH3 adaptor region in onco-Vav reverses oncogenicity. While a unique substitution D797N did not affect transformation induced by onco-Vav, we demonstrate that this single substitution leads to transformation in the Vav1 proto-oncogene highlighting the pivotal role of the adaptor region. Moreover, we identified the cell junction protein ß-catenin as a new Vav1 interacting partner. We show that the oncogenicity of activated Vav1 proto-oncogene is associated with a non-degradative phosphorylation of ß-catenin at residues important for its functions and its redistribution along the cell membrane in fibroblasts. In addition, a similar interaction is evidenced in epithelial lung cancer cells expressing ectopically Vav1. In these cells, Vav1 is also involved in the modulation of ß-catenin phosphorylation. Altogether, our data highlight that only a single mutation in the proto-oncogene Vav1 enhances tumorigenicity.