Viscum album agglutinin-I (VAA-I) increases cell surface expression of cytoskeletal proteins in apoptotic human neutrophils: moesin and ezrin are two novel targets of VAA-I.

Viscum album agglutinin-I (VAA-I) is a plant lectin, which possesses anti-inflammatory properties, including the ability to induce neutrophil apoptosis by a mechanism that is not completely understood. Among the three actin-binding membrane-anchoring proteins ezrin/radixin/moesin (ERM), neutrophils are known to express ezrin and moesin. The behavior of these proteins in apoptotic neutrophils is not well established. In the present study, the expression and localization of ezrin and moesin by Western blot and immunofluorescence revealed a clear degradation and relocalization of both the proteins during VAA-I-induced apoptosis. Also, flow cytometry analysis revealed that VAA-I markedly and significantly induced the cell surface expression of ezrin and moesin and this was reversed when cells were pretreated with the Syk inhibitor piceatannol. The expression of ezrin and moesin on the cell surface of apoptotic neutrophils may represent a mechanism responsible for the appearance of autoantibodies directed against ERM proteins, which have been found in the serum of patients suffering from autoimmune diseases. Therefore, the ability of VAA-I to increase cell surface expression of cytoskeletal proteins in apoptotic neutrophils provides important insight into a possible toxic mechanism of this plant lectin and this has to be considered for its potential utilization for in vivo treatment.