Tumor Cell Adhesion to Endothelial Cells Is Increased by Endotoxin via an Upregulation of β-1 Integrin Expression

Abstract

Background. Recent studies have demonstrated that metastatic disease develops from tumor cells that adhere to endothelial cells and proliferate intravascularly. The β-1 integrin family and its ligand laminin have been shown to be important in tumor-to-endothelial cell adhesion. Lipopolysaccharide (LPS) has been implicated in the increased metastatic tumor growth that is seen postoperatively. We postulated that LPS increases tumor cell expression of β-1 integrins and that this leads to increased adhesion.Methods. The human metastatic colon cancer cell line LS174T was labeled with an enhanced green fluorescent protein (eGFP) using retroviral transfection. Cell cultures were treated with LPS for 1, 2, and 4 h (n = 6 each) and were subsequently cocultured for 30 or 120 min with confluent human umbilical vein endothelial cells (HUVECs), to allow adherence. Adherent tumor cells were counted using fluorescence microscopy. These experiments were carried out in the presence or absence of a functional blocking β-1 integrin monoclonal antibody (4B4). Expression of β-1 integrin and laminin on tumor and HUVECs was assessed using flow cytometric analysis. Tumor cell NF-κB activation after incubation with LPS was measured.Results. Tumor cell and HUVEC β-1 integrin expression and HUVEC expression of laminin were significantly (P < 0.05) enhanced after incubation with LPS. Tumor cell adhesion to HUVECs was significantly increased. Addition of the β-1 integrin blocking antibody reduced tumor cell adhesion to control levels. LPS increased tumor cell NF-κB activation.Conclusions. Exposure to LPS increases tumor cell adhesion to the endothelium through a β-1 integrin-mediated pathway that is NF-κB dependent. This may provide a target for immunotherapy directed at reducingpostoperative metastatic tumor growth.