Chronic lymphocytic leukemia B cells contain anomalous Lyn tyrosine kinase, a putative contribution to defective apoptosis
Antonella Contri, … , Gianpietro Semenzato, Arianna Donella-Deana
Antonella Contri, … , Gianpietro Semenzato, Arianna Donella-Deana
Published February 1, 2005
Citation Information: J Clin Invest. 2005;115(2):369-378. https://doi.org/10.1172/JCI22094.
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Article Hematology

Chronic lymphocytic leukemia B cells contain anomalous Lyn tyrosine kinase, a putative contribution to defective apoptosis

Abstract

B cell chronic lymphocytic leukemia (B-CLL) is a neoplastic disorder characterized by accumulation of B lymphocytes due to uncontrolled growth and resistance to apoptosis. Analysis of B cells freshly isolated from 40 patients with chronic lymphocytic leukemia demonstrated that the Src kinase Lyn, the switch molecule that couples the B cell receptor to downstream signaling, displays anomalous properties. Lyn is remarkably overexpressed at the protein level in leukemic cells as compared with normal B lymphocytes, with a substantial aliquot of the kinase anomalously present in the cytosol. Whereas in normal B lymphocytes Lyn activation is dependent on B cell–receptor stimulation, in resting malignant cells, the constitutive activity of the kinase accounts for high basal protein tyrosine phosphorylation and low responsiveness to IgM ligation. Addition of the Lyn inhibitors PP2 and SU6656 to leukemic cell cultures restores cell apoptosis, and treatment of malignant cells with drugs that induce cell apoptosis decreases both activity and amount of the tyrosine kinase. These findings suggest a direct correlation between high basal Lyn activity and defects in the induction of apoptosis in leukemic cells. They also support a critical role for Lyn in B-CLL pathogenesis and identify this tyrosine kinase as a potential therapeutic target.

Authors

Antonella Contri, Anna Maria Brunati, Livio Trentin, Anna Cabrelle, Marta Miorin, Luca Cesaro, Lorenzo A. Pinna, Renato Zambello, Gianpietro Semenzato, Arianna Donella-Deana

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Figure 5

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Subcellular localization of Lyn in normal and CLL B cells. (A) Analysis ...
Subcellular localization of Lyn in normal and CLL B cells. (A) Analysis by differential ultracentrifugation. B cells were sonicated in isotonic buffer and cytosol, and microsomes (II particulate fraction, II-P) were separated from the cell debris and the other cellular particles (I particulate fraction, I-P) by ultracentrifugation. Comparable aliquots of the different fractions were loaded on SDS/PAGE and the separated proteins were immunostained with either anti-Lyn antibody or the antibodies specific for the indicated distribution control markers: complex II (I particulate, mitochondria), SERCA2 (II particulate, endoplasmic reticulum), and CD79b (II particulate, plasma membrane). Other aliquots were immunoprecipitated with anti-Lyn antibody, and the kinase activity of the immunocomplexes was detected in vitro. The data are representative of experiments performed with 3 different normal and 14 B-CLL samples. (B) Confocal microscopic analysis of the ganglioside GM1 labeled with cholera toxin B subunit (Texas Red) and Lyn (FITC) in normal and leukemic B lymphocytes. The data are representative of experiments performed with 5 normal and 10 different leukemic samples. Original magnification, ×60.