Moesin becomes linked to the plasma membrane in attached neutrophil granulocytes.

Following 35 min of adhesion to a plastic surface, an 80-kDa F-actin-binding protein was shown to be enriched in the plasma membrane fractions of porcine neutrophils by protein blotting with labeled F-actin. This protein was almost undetectable in membrane fractions of free floating neutrophils, while it was present in total cell samples. The 80-kDa protein appeared to be a major high molecular mass component of the isolated actin-cytoskeleton of both control and attached cells. The studied F-actin-binding protein was recognized by anti-moesin antibodies. Our results suggest that moesin is translocated to the plasma membrane upon adhesion of neutrophils to the extracellular surface.

Major laminin-binding and F-actin-linked glycoproteins of neutrophils.

Two major EHS-laminin-binding membrane glycoproteins--with apparent molecular masses of 50 kD and 18 kD--were shown by protein blotting in membrane fractions of porcine neutrophils. These galectin-like glycoproteins (binding probably via the N-acetyllactosamine sequences to laminin) could also be detected by labelled F-actin in protein blots. Following 35 min adhesion to the plastic surface, the relative amount of the 18 kD protein increased considerably in the light (plasma membrane) and in the dense (intracellular) membrane fractions of the attached cells; the 50 kD polypeptide (identified as a CD14-like protein) seemed to accumulate characteristically in the dense membrane fraction. These observations imply that direct connections could be formed between membrane glycoproteins and microfilaments during cell-substrate adhesion which may be preceded by enhanced cell surface targeting of certain adhesion receptors.