CD9, a key actor in the dissemination of lymphoblastic leukemia, modulating CXCR4-mediated migration via RAC1 signaling

Abstract

CD9, a member of the tetraspanin family, has been implicated in hematopoietic and leukemic stem cell homing. We investigated the role of CD9 in the dissemination of B acute lymphoblastic leukemia (B-ALL) cells, by stably downregulating CD9 in REH and NALM6 cells. CD9 expression was associated with higher levels of REH cell adhesion to fibronectin and C-X-C motif chemokine receptor 4 (CXCR4)-mediated migration. Death occurred later in NOD/SCID mice receiving REH cells depleted of CD9 for transplantation than in mice receiving control cells. After C-X-C motif chemokine ligand 12 (CXCL12) stimulation, CD9 promoted the formation of long cytoplasmic actin-rich protrusions. We demonstrated that CD9 enhanced RAC1 activation, in both REH cells and blasts from patients. Conversely, the overexpression of a competing CD9 C-terminal tail peptide in REH cytoplasm decreased RAC1 activation and cytoplasmic extension formation in response to CXCL12. Finally, the inhibition of RAC1 activation decreased migration in vitro, and the depletion of RAC1 protein from transplanted REH cells increased mouse survival. Furthermore, a testis-conditioned medium induced the migration of REH and NALM6 cells, and this migration was impeded by an anti-CD9 antibody. The level of CD9 expression also influenced the homing of these cells in mouse testes. These findings demonstrate, for the first time, that CD9 plays a key role in the CXCR4-mediated migration and engraftment of B-ALL cells in the bone marrow or testis, through RAC1 activation.

Proliferation-independent regulation of organ size by Fgf/Notch signaling

“…Celsr1, if reduced, causes otic defects because of loss of apical constrictions due to disturbed actomyosin recruitment to the apical junctional complex (Sai et al, 2014). RNASeq analysis also revealed the induction of cd9b by Notch, a Tetraspanin family member implicated in cell-matrix adhesion and Sdf1 (Cxcl12a) mediated migration (Figure 7L–M’, [Arnaud et al, 2015; Leung et al, 2011]).…”

Tetraspanins Function as Regulators of Cellular Signaling

“…Furthermore, upon EGF stimulation, it was shown that knockdown of CD81 increases Rac activation. A more recent study identified a correlation between CD9 expression and GTP bound Rac1 expression in acute lymphoblastic leukemia patient samples (Arnaud et al, 2015). Moreover, this group also determined that the C-terminal tail of CD9 is important for regulating Rac1 activation.…”

Remodeling our concept of chemokine receptor function: From monomers to oligomers

“…The expression of other proteins might also affect chemokine receptor conformations and thus influence the receptor function. For instance, complexes between CCR5, CXCR4, and CD4 are essential for HIV‐1 infection, and the interaction of CXCR4 with the tetraspanin CD9 modulates CXCL12‐mediated cell migration . The constitutive association of CXCR2 with CCRL2 is essential to fine‐tune CXCR2‐mediated neutrophil recruitment to inflammation sites, and heterodimers between the EBV‐induced receptor 2 (EBI2) and CXCR5 contribute to the plasticity of CXCL13‐mediated B cell responses …”

“…For instance, complexes between CCR5, CXCR4, and CD4 are essential for HIV-1 infection, 50 and the interaction of CXCR4 with the tetraspanin CD9 modulates CXCL12-mediated cell migration. 100 The constitutive association of CXCR2 with CCRL2 is essential to fine-tune CXCR2-mediated neutrophil recruitment to inflammation sites, 70 and heterodimers between the EBV-induced receptor 2 (EBI2) and CXCR5 contribute to the plasticity of CXCL13-mediated B cell responses. 68 Although experimental evidence indicates that the formation of homo-and heterodimers is a general process in the chemokine receptor field, a recent report on class A GPCR members, predicts that this is not always the case, as some receptors exist as monomeric entities.…”