In vivo adhesion of malignant B cells to bone marrow microvasculature is regulated by α4β1 cytoplasmic-binding proteins

40 p.-7 fig. Martínez-Moreno, Mónica et al.Multiple myeloma (MM) and chronic lymphocytic leukemia (CLL) cells must attach to the bone marrow (BM) microvasculature before lodging in the BM microenvironment. Using intravital microscopy (IVM) of the BM calvariae we demonstrate that the α4β1 integrin is required for MM and CLL cell firm arrest onto the BM microvasculature, while endothelial P-selectin and E-selectin mediate cell rolling. Talin, kindlin-3 and ICAP-1 are β1-integrin-binding partners that regulate β1-mediated cell adhesion. We show that talin and kindlin-3 cooperatively stimulate high affinity and strength of α4β1-dependent MM and CLL cell attachment, whereas ICAP-1 negatively regulates this adhesion. A functional connection between talin/kindlin-3 and Rac1 was found to be required for MM cell attachment mediated by α4β1. Importantly, IVM analyses with talin- and kindlin-3-silenced MM cells indicate that these proteins are needed for cell arrest on the BM microvasculature. Instead, MM cell arrest is repressed by ICAP-1. Moreover, MM cells silenced for talin and kindlin-3, and cultured on α4β1 ligands showed higher susceptibility to bortezomib-mediated cell apoptosis. Our results highlight the requirement of α4β1 and selectins for the in vivo attachment of MM and CLL cells to the BM microvasculature, and indicate that talin, kindlin-3 and ICAP-1 differentially control physiological adhesion by regulating α4β1 activity.This work was supported by the following grants from the Ministerio de Economía y Competitividad (Spain): SAF2011-24022 to J.T; SAF2012-31613 to A.G-P; SAF2012-31142 and SAF2013-49662-EXP to A.H; PI13/01454 to P.S-M; RD12/0036/0061 to J.T. and A.G-P; RD12/0036/0058 to N.C.G. The work was also funded by grant P2010/BMD-2314 from the Comunidad de Madrid to A.G-P., J.T., P. S-M and A.H., and partially supported by a CRIS foundation grant to fight cancer to J.M-L. N.C.G. is also funded by a grant from the Asociación Española Contra el Cáncer (GCB120981SAN), and from the Gerencia Regional de Salud, Junta de Castilla y León (GRS-702/A/11).Peer reviewe