Direct Measurements on CD24-Mediated Rolling of Human Breast Cancer MCF-7 Cells on E-Selectin

摘要

ABSTRACT: Tumor cell rolling on the endothelium plays ankey role in the initial steps of cancer metastasis, i.e., extravasa-ntion of circulating tumor cells (CTCs). Identification of thenligands that induce the rolling of cells is thus critical tonunderstanding how cancers metastasize. We have previouslyndemonstrated that MCF-7 cells, human breast cancer cells,nexhibit the rolling response selectively on E-selectin-immobi-nlized surfaces. However, the ligand that induces rolling ofnMCF-7 cells on E-selectin has not yet been identified, as thesencells lack commonly known E-selectin ligands. Here we report,nfor the first time to our knowledge, a set of quantitative andndirect evidence demonstrating that CD24 expressed on MCF-n7 cell membranes is responsible for rolling of the cells onnE-selectin. The binding kinetics betweenCD24 and E-selectin was directlymeasured using surface plasmon resonance (SPR), whichnrevealed that CD24 has a binding affinity against E-selectin (KD = 3.4 ( 0.7 nM). The involvement of CD24 in MCF-7 cell rollingnwas confirmed by the rolling behavior that was completely blocked when cells were treated with anti-CD24. A simulated study bynflowing microspheres coated with CD24 onto E-selectin-immobilized surfaces further revealed that the binding is Can2þ-dependent.nAdditionally, we have found that actin filaments are involved in the CD24-mediated cell rolling, as observed by the decreased rollingnvelocities of the MCF-7 cells upon treatment with cytochalasin D (an inhibitor of actin-filament dynamics) and the stationarynbinding of CD24-coated microspheres (the lack of actins) on the E-selectin-immobilized slides. Given that CD24 is known to bendirectly related to enhanced invasiveness of cancer cells, our results imply that CD24-based cell rolling on E-selectin mediates, atnleast partially, cancer cell extravasation, resulting in metastasis.