Protein kinase D-dependent CXCR4 down-regulation upon BCR triggering is linked to lymphadenopathy in chronic lymphocytic leukaemia.

Stéphane Saint-Georges,Lionel Guittat,Vanessa Laurienté,Florence Ajchenbaum-Cymbalista,Stéphanie Le Coquil,Marouane Bouyaba,Vincent Lévy,Maude Quettier,Christine Le Roy,Dominique Ledoux,Nadine Varin-Blank

doi:10.18632/oncotarget.9031

Abstract

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.

Highlights

Chronic Lymphocytic Leukaemia (CLL) presents with a very heterogeneous clinical course from indolent to aggressive disease [1,2,3,4,5]
We have previously demonstrated that the capacity for CLL B cells to down-regulate CXCR4 upon Binding of antigen to their receptor (BCR) engagement was correlated to shorter PFS [10]
As CLL major proliferation sites, are an important clinical indicator of progression, we investigated BCR-mediated CXCR4 downregulation capacity in patients presenting or not with lymphadenopathy (Table 1)

Summary

Introduction

Chronic Lymphocytic Leukaemia (CLL) presents with a very heterogeneous clinical course from indolent to aggressive disease [1,2,3,4,5]. In spite of promising clinical results with recent signaling inhibitors, CLL remains incurable with standard therapy. Antigen-driven signals are involved in the progression of CLL [7,8,9,10,11], notably within the lymph node microenvironment [12, 13]. CLL cases (n = 72) were divided based on their cellular percentage of CXCR4 down-regulation in response to BCR trigering: Low capacity = CXCR4 decrease ≤ 5% and High capacity = CXCR4 decrease > 5%. Statistical analysis of the absence or presence of lymph nodes in both groups demonstrated that high BCR-mediated CXCR4 down-regulation was strongly linked to lymphadenopathy in CLL patients (‘Yates’ continuity corrected Chi test, p < 0.001)

Methods

Results

Conclusion