Sialylation and PECAM‐1‐Dependent Ligand Binding

PECAM‐1, a sialylated cell surface molecule expressed on endothelial cells (ECs), has been implicated in both EC motility and angiogenesis. Neuraminidase 1 (NEU1) sialidase inhibits wound‐induced EC migration and disrupts in vitro tube formation though PECAM‐1‐desialylation. The mechanisms by which desialylation of PECAM‐1 disrupts its activity are undefined. The effects of PECAM‐1 on cell function are mediated by the binding of PECAM‐1 to other PECAM‐1 molecules (homophilic) or to non‐PECAM‐1 molecules (heterophilic), such as heparin/heparan sulfate glycosaminoglycan (GAG)‐containing proteoglycans. We hypothesized that desialylation of PECAM‐1 disrupts PECAM‐1‐dependent ligand binding. For these studies, we employed REN cells (an EC surrogate) expressing mouse PECAM‐1 in mixed aggregation studies in which PECAM‐1‐expressing REN cells are mixed with control REN cells. In this assay, homophilic interactions result in aggregates that are enriched for PECAM‐1‐expressing cells, while heterophilic binding generates aggregates composed of both PECAM‐1 and non‐PECAM‐1 cell types. Analysis of 5‐cell aggregates in mixed aggregation studies for the PECAM‐1‐expressing REN cells resulted in comparable proportions of homophilic (46%) versus heterophilic (34%) aggregates. However, the formation of both homophilic and heterophilic aggregates was suppressed by adenoviral‐mediated overexpression of NEU1 in the PECAM‐1‐expressing REN cells compared to those that were transduced with adenovirus‐expressing GFP alone or when a catalytically‐inactive mutant of NEU1 was overexpressed. These data suggest that NEU1‐mediated inhibition of in vitro EC activity involves the disruption of PECAM‐1‐dependent ligand interactions. Support or Funding Information Veterans Administration Merit Award