Advanced prostate cancer commonly metastasizes to bone, but transit of malignant cells across the bone marrow endothelium (BMEC) remains a poorly understood step in metastasis. Prostate cancer cells roll on E-selectin(+) BMEC through E-selectin ligand-binding interactions under shear flow, and prostate cancer cells exhibit firm adhesion to BMEC via ?1, ?4, and ?V?3 integrins in static assays. However, whether these discrete prostate cancer cell-BMEC adhesive contacts culminate in cooperative, step-wise transendothelial migration into bone is not known. Here, we describe how metastatic prostate cancer cells breach BMEC monolayers in a step-wise fashion under physiologic hemodynamic flow. Prostate cancer cells tethered and rolled on BMEC and then firmly adhered to and traversed BMEC via sequential dependence on E-selectin ligands and ?1 and ?V?3 integrins. Expression analysis in human metastatic prostate cancer tissue revealed that ?1 was markedly upregulated compared with expression of other ? subunits. Prostate cancer cell breaching was regulated by Rac1 and Rap1 GTPases and, notably, did not require exogenous chemokines as ?1, ?V?3, Rac1, and Rap1 were constitutively active. In homing studies, prostate cancer cell trafficking to murine femurs was dependent on E-selectin ligand, ?1 integrin, and Rac1. Moreover, eliminating E-selectin ligand-synthesizing ?1,3 fucosyltransferases in transgenic adenoma of mouse prostate mice dramatically reduced prostate cancer incidence. These results unify the requirement for E-selectin ligands, ?1,3 fucosyltransferases, ?1 and ?V?3 integrins, and Rac/Rap1 GTPases in mediating prostate cancer cell homing and entry into bone and offer new insight into the role of ?1,3 fucosylation in prostate cancer development.
