Opposing effects of low and high molecular weight kininogens on cell adhesion

High molecular weight kininogen (HK) blocks cell spreading but not cell attachment to surfaces coated with vitronectin and other ligands of beta 3 integrins, We sought to learn the structural basis of this phenomenon. Monoclonal antibodies against the histidine-rich D5 domain in the light chain of a-chain HK abolished the inhibitory effect of a-chain HK on spreading of MG-63 osteosarcoma cells on vitronectin-coated tissue-culture plastic. The antibodies were effective only if incubated with a-chain HK in solution and did not abolish the anti-cell-spreading effect of a-chain HK that was pre-adsorbed to tissue-culture plastic. Exposure of an epitope in the histidine-rich domain was less when HK was adsorbed to tissue-culture plastic (oxidized polystyrene) than when it was adsorbed to ELISA plastic (untreated polystyrene), Loss of the epitope correlated with increased anti-cell-spreading activity of HK on tissue-culture plastic. The light chain of 2-chain HK containing D5 and that containing recombinant D5 both had anti-cell-spreading activity, but only when present in solution during adhesion assays. Pre-adsorption of recombinant D5 to tissue-culture plastic resulted in a surface on which adsorbed a-chain HK had little anti-cell-spreading activity. Binding study revealed that HKa bound to immobilized vitronectin, The histidine-rich D5 domain of light chain of HK was identified as one of the binding sites of vitronectin, suggesting that the masking of the RGD cell-binding site of immobilized vitronectin is the molecular mechanism of anti-cell-spreading effect of HKa. In contrast, low molecular weight kininogen (LK), which lacks D5, augmented cell spreading on vitronectin-coated tissue-culture plastic, Thus, HK and LK have opposing effects on VN-dependent cell adhesion. The augmenting effect of LK was greater if LK was preincubated with cells or adsorbed to the surface at pH>7.0. Analysis of fragments of LK and antibody inhibition studies localized the cell-adhesion activity to the D3 domain that is common to LK and HK, These findings indicate that the D5 domain mediates the adsorption of HK or 2-chain HK to vitronectin substratum in anti-adhesive conformations, i.e., masking of the RGD cell-binding site of vitronectin. Such conformers inhibit cell spreading on vitronectin even though a cell-adhesion site is present in D3.