Aminopeptidase N: A Constitutive Cell-Surface Protein on Human Dermal Fibroblasts

Monoclonal antibodies were developed against human dermal fibroblast cell-surface membranes. Our goal was to find evidence of differential expression of antigens on fibroblast clones derived by limiting dilution. Antibodies were then used to isolate and identify membrane proteins. By sequence analysis of membrane immunoprecipitates, one monoclonal antibody, BR2, was subsequently shown to recognize the enzyme aminopeptidase N (hAPN; EC 3.4.11.2), originally described as a marker for certain hematopoetic cells. We have used biochemical techniques, electron microscopy, flow cytometry, and ELISA to characterize aminopeptidase N expression by human dermal fibroblasts. The presence of abundant aminopeptidase N confers enzymatic properties to human dermal fibroblasts which heretofore have been largely unexplored and suggest that the cellular distribution of aminopeptidase N is wider than originally appreciated.