Chemokine Unresponsiveness of Chronic Lymphocytic Leukemia Cells Results from Impaired Endosomal Recycling of Rap1 and Is Associated with a Distinctive Type of Immunological Anergy

Abstract

Trafficking of malignant lymphocytes is fundamental to the biology of chronic lymphocytic leukemia (CLL). Transendothelial migration (TEM) of normal lymphocytes into lymph nodes requires the chemokine-induced activation of Rap1 and αLβ2 integrin. However, in most cases of CLL, Rap1 is refractory to chemokine stimulation, resulting in failed αLβ2 activation and TEM unless α4β1 is coexpressed. In this study, we show that the inability of CXCL12 to induce Rap1 GTP loading in CLL cells results from failure of Rap1-containing endosomes to translocate to the plasma membrane. Furthermore, failure of chemokine-induced Rap1 translocation/GTP loading was associated with a specific pattern of cellular IgD distribution resembling that observed in normal B cells anergized by DNA-based Ags. Anergic features and chemokine unresponsiveness could be simultaneously reversed by culturing CLL cells ex vivo, suggesting that these two features are coupled and driven by stimuli present in the in vivo microenvironment. Finally, we show that failure of Rap1 translocation/GTP loading is linked to defective activation of phospholipase D1 and its upstream activator Arf1. Taken together, our findings indicate that chemokine unresponsiveness in CLL lymphocytes results from failure of Arf1/phospholipase D1–mediated translocation of Rap1 to the plasma membrane for GTP loading and may be a specific feature of anergy induced by DNA Ags.

Trisomy 12 chronic lymphocytic leukemia cells exhibit upregulation of integrin signaling that is modulated by NOTCH1 mutations

“…Impaired chemokine responsiveness in CLL cells is likely due to a failure of Rap1-containing endosomes to translocate to the plasma membrane, resulting in defective in Rap1 GTP-loading. 30,31 It is possible that overexpression of CALDAG-GEFI, RAP1B, and RAPL in trisomy 12 CLL cells may compensate for this defect and further improve function, and this will be the focus of future experiments. The mechanisms underlying upregulation of integrin signaling in trisomy 12 remain unclear, although a recent report has implicated altered epigenetic regulation as a cause of increased CD49d expression.…”

The outcome of B-cell receptor signaling in chronic lymphocytic leukemia: proliferation or anergy

“…For CXCR4, it has been proposed that impaired endosomal recycling of Rap1 is important. 61 In addition to these studies which potentially reveal a trans-inhibitory effect of prior antigen engagement in vivo, other modes of BCR crosstalk have been demonstrated following sIgM engagement in vitro with clear effects on the expression and function of the chemokine receptor CXCR4 and the adhesion molecule CD49d. [72][73][74] For CXCR4, sIgM engagement has been shown to reduce expression of CXCR4 but can either enhance or decrease CXCL12-dependent migration.…”

Anatomical Society Summer Meeting in Galway

“…Furthermore, it was reported that defective chemokine-induced Rap1 activation may be linked to impaired motility in a subset of primary CLL cells. 47 Therefore, the fact that we have functionally linked CD38 expression and Rap1 activity is particularly relevant in CLL pathology.…”