Role of ICAM-1 polymorphisms (G241R, K469E) in mediating its single-molecule binding ability: atomic force microscopy measurements on living cells.

Atherosclerosis (As) is characterized by chronic inflammation and is a major cause of human mortality. ICAM-1-mediated adhesion of leukocytes in vessel walls plays an important role in the pathogenesis of atherosclerosis. Two single nucleotide polymorphisms (SNPs) of human intercellular adhesion molecule-1 (ICAM-1), G241R and K469E, are associated with a number of inflammatory diseases. SNP induced changes in ICAM-1 function rely not only on the expression level but also on the single-molecule binding ability which may be affected by single molecule conformation variations such as protein splicing and folding. Previous studies have shown associations between G241R/K469E polymorphisms and ICAM-1 gene expression. Nevertheless, few studies have been done that focus on the single-molecule forces of the above SNPs and their ligands. In the current study, we evaluated both single molecule binding ability and expression level of 4 ICAM-1 mutations - GK (G241/K469), GE (G241/E469), RK (R241/K469) and RE (R241/E469). No difference in adhesion ability was observed via cell adhesion assay or atomic force microscopy (AFM) measurement when comparing the GK, GE, RK, or RE genotypes of ICAM-1 to each other. On the other hand, flow cytometry suggested that there was significantly higher expression of GE genotype of ICAM-1 on transfected CHO cells. Thus, we concluded that genetic susceptibility to diseases related to ICAM-1 polymorphisms, G241R or K469E, might be due to the different expressions of ICAM-1 variants rather than to the single-molecule binding ability of ICAM-1.