GPR30 Expression On Pre-B Acute Lymphocytic Leukemia Cells Results in Modulation of CXCR4 Activity by CCL18.

CCL18, together with CXCL12, two homeostatic chemokines, are present at high concentration in the serum of B Acute Lymphocytic Leukemia (ALL). Chemokines are involved of the recruitment and localization of cells and particularly of immune cells in homeostasis and pathological conditions. CXCL12 (formerly called SDF-1) is centrally involved in the localization of B-cells at different stages of their differentiation, however expression of its receptor CXCR4 does not always correlate with the ability of CXCL12 to induce its response. CCL18 has been reported to induce the classical chemokine responses like chemotaxis in different cell types, including B lymphocytes. However, despite the extensive work carried out on CCL18, the identification of its agonistic receptor is still lacking. We have investigated CCL18 regulation of CXCL12/CXCR4 cellular activation in the context of pre-B ALL primary cells and cell lines and identified GPR-30, a chemokine like receptor, to be involved in these regulation processes.

Primary cells from pre-B ALL and common ALL patients as well as the pre-B ALL Nalm-6 model cell line were used to characterize CCL18 activities. CCL18 alone activation was first characterized (chemotaxis, calcium release). Then the influence of CCL18 on CXCL12 induced pre-B cell activation was done (chemotaxis, calcium release). Three receptors, candidates to mediate this effect, were investigated among which GPR30 was identified to be involved. Expression of GPR30 at the surface of the cellular models was evidenced and neutralization of the observed effects by antibodies against receptors expressed at the surface of these cells were used to confirm the involvement of GPR30 in this mechanism.

In this study we showed that CCL18, a poorly characterized homeostatic chemokine, could bind to GPR30 expressing cells and that this binding could be competed by antibodies against GPR30, suggesting interactions of CCL18 with this receptor. In addition, we have demonstrated that GPR30 was expressed at the surface of pre-B ALL cells but not at the surface of common ALL primary cells. Furthermore, we demonstrated GPR30 to be one of the receptors mediating CCL18 induced down-regulation of CXCR4 activation in the context of pre-B ALL cells from cell lines and patients. GPR30 has been recently identified as a modulator of the estrogen receptor but we have evidenced that CCL18 binding to GPR30 can modify the responses of another chemokine receptor: CXCR4, the CXCL12 receptor. Activation of CXCR4 by CXCL12 was reduced in presence of CCL18 when tested in chemotaxis as well as calcium release assays.

Regulation of CXCR4 activation throughout B cells differentiation has been shown to be finely controlled by other receptors and proteins. We have shown that CCL18 could regulate CXCL12 receptor CXCR4 via chemokine like receptor GPR30 in pre-B ALL primary cells and cell lines, and that this could account for specific pre-B leukemic cell controlled of CXCR4 activation. Pre-B cells present a very high level of expression of CXCR4 which is not in agreement with observed reduced migration toward CXCL12, we suggest CCL18 to be involved in this regulation. This is to be related to CCL18 and CXCL12 high level concentration in serum of ALL patients. Therefore, we suggest CCL18 to be involved in the localization and maturation of pre-B ALL with some impact in the pathophysiology of pre-B ALL. Expression of GPR30 at the surface of B cells at different stages of differentiation will be further investigated to assess GPR30 as a potential bio-marker of pre-B ALL condition.

No relevant conflicts of interest to declare.