Lack of the leukocyte-associated Ig-like receptor-1 expression in high-risk chronic lymphocytic leukaemia results in the absence of a negative signal regulating kinase activation and cell division

In this study, we analysed 30 patients with B-cell chronic lymphocytic leukaemia (CLL), compared with 10 healthy donors, for the expression and function of the leukocyte-associated Ig-like receptor-1 (LAIR-1). LAIR-1 is an inhibitory receptor containing a cytoplasmic tyrosine-based inhibitory motif (ITIM) that binds to the SH2 domain of phosphatases, leading to dephosphorylation of different kinases. Constitutive activation of c-Jun aminoterminal kinase (JNK), p38 mitogen-activated protein kinase and extracellular signal-regulated kinase, has been reported in CLL. We show that LAIR-1 is absent in high-risk (HR) CLL and differently expressed on intermediate-and low-risk CLL and the intensity of expression, which is always significantly lower than in healthy donors, correlates with disease stage and progression. Interestingly, both constitutive and sIgM-induced phosphorylation of p38 and JNK is inhibited by LAIR-1 through an ITIM-dependent signal, as demonstrated by the use of specific ITIM-binding peptides; importantly, this inhibitory signal is missing when LAIR-1 is not expressed as occurs in HR CLL. Moreover, engagement of LAIR-1 blocks constitutive and sIgM-induced Akt phosphorylation, besides nuclear factor kappa-B nuclear translocation, and prevents CLL division. These results suggest that CLL lacking LAIR-1 may miss one of the molecular mechanisms controlling B-cell activation and proliferation.