High molecular weight kininogen (HK) is a plasma glycoprotein with multiple functions, including the regulation of coagulation. We previously demonstrated that domain 5 (D5(H)), a functional domain of HK, and its derived peptides played an important role in the vitronectin-mediated suppression of cancer cell adhesion and invasion. However, the underlying mechanisms of the D5(H)-mediated suppressive effects remain to be elucidated. Here, we showed that D5(H) and its derivatives inhibited the collagen-mediated cell adhesion and invasion of human osteosarcoma MG63 cells. Using purified D5(H) fused to glutathione-S-transferase (GST) and D5(H)-derived peptides for column chromatography, an actin-binding protein, α-actinin-4, was identified as a binding protein of D5(H) with high-affinity for P-5m, a core octapeptide of D5(H). Immunofluorescence microscopy demonstrated that D5(H) co-localized with α-actinin-4 inside MG63 cells. In addition, exogenous GST-D5(H) added to the culture media was transported into MG63 cells, although GST alone as a control was not. As α-actinin-4 regulates actin polymerization necessary for cell adhesion and is related to the integrin-dependent attachment of cells to the extracellular matrix, our results suggest that D5(H) may modulate cell adhesion and invasion together with actinin-4.
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