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

Abstract

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.

Role of LFA-1 and ICAM-1 in Cancer

“…In addition to chemokines, migration of CLL cells requires the participation of the two lymphocyte integrins: VLA-4 (CD49d/CD29) and LFA-1, which show varied levels of expression in CLL cells [ 60 ]. VLA-4 contributes to the homing in of CLL cells on bone marrow [ 61 ]. However, the regulation of LFA-1 adhesion is impaired in CLL cells, due to defective signaling by Rap1 GTPase, a major signaling element of the inside-out signaling cascade, which impedes proper clustering of LFA-1 [ 62 ].…”

Inside the Cell: Integrins as New Governors of Nuclear Alterations?

“…In breast cancer cells, integrin signaling via PI3K (Phosphoinositide 3-kinase) and FAK controls the translocation of Bax to the mitochondrial membrane, thereby repressing apoptosis [ 30 ]. A similar cytoprotective effect is observed in hematological cancers when cells are retained in microenvironmental niches [ 31 , 32 ]. Several groups have described how integrins and their focal adhesion (FA) partners also regulate apoptosis by modulating the oncogene p 53.…”

VLA-4 Expression and Activation in B Cell Malignancies: Functional and Clinical Aspects

“…This, in turn, enables the linkage of the integrin to the actin cytoskeleton, thus enabling force-induced adhesion strengthening. In experiments using CLL and multiple myeloma cell lines, both tumor entities shared a dependence on kindlin-3 and talin, and both adaptors cooperatively stimulated a high-affinity and strength of VLA-4-dependent attachment to bone marrow endothelium [62]. Integrin Cytoplasmic domain-Associated Protein-1 (ICAP-1), a specific adaptor of the β1 integrin subunit cytoplasmic domain, was described as a negative regulator of adhesion in this study.…”