Abstract
The microenvironment provides essential growth and survival signals to chronic lymphocytic leukemia (CLL) cells and contributes to their resistance to cytotoxic agents. Pharmacologic inhibition of spleen tyrosine kinase (SYK), a key mediator of B-cell receptor (BCR) signaling, induces apoptosis in primary CLL cells and prevents stroma contact-mediated cell survival. This report demonstrates a role of SYK in molecularly defined pathways that mediate the CLL-microenvironmental crosstalk independent from the BCR. Chemokine and integrin stimulation induced SYK phosphorylation, SYK-dependent Akt phosphorylation, and F-actin formation in primary CLL cells. Inhibition of SYK by 2 pharmacologic inhibitors and siRNA-knockdown abrogated downstream SYK signaling and morphologic changes induced by these stimuli. CLL cell migration toward CXCL12, the major homing attractor, and CLL cell adhesion to VCAM-1, a major integrin ligand expressed on stromal cells, were markedly reduced by SYK inhibition. In combination with fludarabine, the SYK inhibitor R406 abrogated stroma-mediated drug resistance by preventing up-regulation of the antiapoptotic factor Mcl-1 in CLL cells. SYK blockade in CLL is a promising therapeutic principle not only for its inhibition of the BCR signaling pathway, but also by inhibiting protective stroma signals in a manner entirely independent of BCR signaling.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Actins / metabolism
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Aged
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Animals
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Apoptosis / drug effects
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Chemokine CXCL12 / metabolism
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Chemokines / metabolism
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Chemotaxis
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Coculture Techniques
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Female
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Fibronectins / metabolism
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Humans
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Integrin alpha4 / metabolism
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Integrins / metabolism
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Intracellular Signaling Peptides and Proteins / antagonists & inhibitors*
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Intracellular Signaling Peptides and Proteins / genetics
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Intracellular Signaling Peptides and Proteins / metabolism
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Leukemia, Lymphocytic, Chronic, B-Cell / drug therapy*
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Leukemia, Lymphocytic, Chronic, B-Cell / metabolism*
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Leukemia, Lymphocytic, Chronic, B-Cell / pathology
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Male
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Mice
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Middle Aged
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Myeloid Cell Leukemia Sequence 1 Protein
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Oxazines / pharmacology*
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Prognosis
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Protein Kinase Inhibitors / pharmacology*
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Protein-Tyrosine Kinases / antagonists & inhibitors*
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Protein-Tyrosine Kinases / genetics
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Protein-Tyrosine Kinases / metabolism
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Proto-Oncogene Proteins c-akt / metabolism
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Proto-Oncogene Proteins c-bcl-2 / metabolism
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Pyridines / pharmacology*
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RNA, Small Interfering / genetics
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Receptors, Antigen, B-Cell / metabolism
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Signal Transduction / drug effects
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Stromal Cells / drug effects
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Stromal Cells / metabolism
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Syk Kinase
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Tumor Cells, Cultured
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Vascular Cell Adhesion Molecule-1 / metabolism
Substances
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Actins
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CXCL12 protein, human
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Chemokine CXCL12
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Chemokines
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Fibronectins
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Integrins
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Intracellular Signaling Peptides and Proteins
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Mcl1 protein, mouse
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Myeloid Cell Leukemia Sequence 1 Protein
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N4-(2,2-dimethyl-3-oxo-4H-pyrid(1,4)oxazin-6-yl)-5-fluoro-N2-(3,4,5-trimethoxyphenyl)-2,4-pyrimidinediamine
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Oxazines
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Protein Kinase Inhibitors
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Proto-Oncogene Proteins c-bcl-2
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Pyridines
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RNA, Small Interfering
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Receptors, Antigen, B-Cell
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Vascular Cell Adhesion Molecule-1
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Integrin alpha4
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Protein-Tyrosine Kinases
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SYK protein, human
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Syk Kinase
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Syk protein, mouse
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Proto-Oncogene Proteins c-akt