Identification of nucleolin as a lipid-raft-dependent β1-integrin-interacting protein in A375 cell migration

Lipid rafts are related to cell surface receptor function. Integrin is a major surface receptor protein in cell adhesion and migration on the extracellular matrix (ECM). Here, we showed that lipid rafts played a critical role in human melanoma A375 cell spreading and migration on fibronectin; an important component of the ECM that interacts with beta 1 integrin. We found that the disruption of lipid rafts did not markedly inhibit the expression and activation of beta 1 integrin. By coimmunoprecipitation and mass spectrometry, we investigated the influence of lipid rafts on the beta 1 integrin complex and identified nucleolin as a potential lipid-raft-dependent beta 1-integrin-interacting protein. Upon confirmation of the interaction between beta 1 integrin and nucleolin, further studies revealed that nucleolin colocalized with beta 1 integrin in lipid rafts and raft disruption interrupted their association. In addition, knockdown of nucleolin markedly attenuated A375 cell spreading and migration on fibronectin. Taken together, we demonstrated that nucleolin is a critical lipid-raft-dependent beta 1-integrin-interacting protein in A375 cell spreading and migration on fibronectin.